APPENDIX II-S: Communities Reject Adulticiding.






H.R. 1749








SEPTEMBER 29, 2005



􀂄 In 2003 the city of Boulder, CO did not use adulticides to combat the presence of

West Nile virus (WNV) and showed an 80% reduction in mosquito populations

reporting as many as 94 million mosquitoes killed prior to becoming biting adults.

The city also reported lower attack rates (or rates of serious illness) per population

than surrounding cities where adulticiding took place.1

􀂄 Despite high mosquito counts and large percentages of infected birds, Shaker

Heights, Ohio refused to adulticide, like its neighboring cities in Cuyahoga County,

due to concerns of health hazards and efficacy. 2002 results showed that Shaker

Heights had only 2 human WNV cases out of the county’s 219 cases.2

􀂄 The counties of Goshen and Plate, WY rely heavily on adulticides and in 2003

counted 80 WNv cases, 8 fatalities and 77 cases, 3 fatalities, respectively. The

neighboring county of Cheyenne, with 2 times the population and 3 times the

landmass, used only larvicides and had 20 cases of WNv and 1 fatality.3

􀂄 Lyndhurst, Ohio, passed a landmark ordinance in 2003 prohibiting the spraying of

pesticides for WNv. During a Task Force sponsored forum, a panel of experts

discussed the hazards and low efficacy of adulticides. The Council stated, “[T]here is

substantial belief that the more effective way of controlling the mosquito populations

is by larvacide treatment and thorough education...” Concluding that, “[T]he dangers

of WNV are minimal and affect a very small segment of the population and that the

long-term health and environmental risks of spraying with synthetic pesticides poses

a much greater risk.”4

􀂄 Washington, DC health officials continue their no-spray policy stating that pesticide

spraying is inappropriate in a heavily populated area with asthmatics. Instead,

officials focus on larval control and pubic education, with education materials

distributed in four languages. The Department of Health is also implementing a Tire

Round-Up program for residents to discard old tires, a major breeding site for


􀂄 In York County, Virginia, officials distribute the mosquito eating fish, Gambusia

holbrooki, to residents in order to decrease pesticide use for mosquito control. Several

thousand of the fish have been bred by the county's fishery as part of its mosquito

prevention program.5

1 City of Boulder WNV Surveillance and Control Plan, 2003 Season.

2 Lynch, Joe. Cuyahoga County Board of Health, and Ryan Sullivan, Shaker Heights WNV Task Force.

Personal Communications, June/July 2004, Beyond Pesticides.

3 Lee, Robert A. Director Environmental Management, City of Cheyenne and Larimer County. Personal

Communication, April 2004, Beyond Pesticides.

4 Beyond Pesticides. 2003. “Ohio City Adopts Landmark Law to Stop Pesticide Spraying for West Nile

Virus.” Daily News. Washington, DC. July 14.

5 York County Environment and Development Services. Div. Drainage and Mosquito Control.

H (July 2, 2004)


􀂄 In Dallas, Texas, the City Council's Health, Environment and Human Services

Committee adopted a mosquito control plan in 2003 that calls for more public

education and allows the use of pesticide sprays only as a last resort and upon

approval of the pertinent council member.6

􀂄 Ft. Worth, Texas has not sprayed for mosquitoes since 1991. In 2003, Ft. Worth had

3 WNV cases and no deaths. Brian Boerner, Director of Environmental Management,

states, “the spraying of chemicals also has the potential of contaminating our

waterways, killing the beneficial fish and organisms that feed on mosquito larva,

adding harmful volatile organic chemicals to the atmosphere-a precursor chemical to

ozone formation-and providing a potential inhalation or ingestion hazard to

residents.” 7

􀂄 Nassau County, New York joins others in using predacious fish in hard to reach saltwater


􀂄 Marblehead, MA has a WNV Response Plan that requires a town hall meeting

before the use of adulticides (and only after a locally-acquired human death).9

􀂄 In 2003, Boulder, Colorado focused on larviciding, surveillance and public

education without the use of adulticides and offered free WNv information

workshops for neighborhood groups and distributes free samples of Mosquito Dunks,

a least-toxic larvacide product, for use in stagnant water.14

􀂄 In preparation for WNv, Lane county, OR have an easy to read public educational

flyer that is put in local newspapers and distributed with utility bills early in the


􀂄 In 2003, Seattle, Washington adopted an Integrated Pest Management Plan for

Mosquito Control, which identifies public education, personal protection, and

breeding source reduction on public property as, “…the most effective and

appropriate techniques for the City to use.”11

6 Beyond Pesticides. 2003. “Virginia and Texas Towns Find Alternatives for West Nile Virus Control.”

Daily News. June 12, 2003.

7 Ft. Worth Public Health Department, Mosquito Prevention and Control.

H (viewed July 6, 2004)

8 Turrillion, G. 2002. Director of Mosquito Control Program in Nassau County, NY. Personal

Communication. March.

9 Town of Marblehead, MA West Nile Virus Protocol and Response Plan. 2002.

H (July 6, 2004)

10 Northwest Coalition for Alternatives to Pesticides. July 2004. Personal Communication.

11 City of Seattle. Office of Sustainability and Environment. February 20, 2002. Integrated Pest

Management Plan for Mosquito Control.

H (July 2, 2004)



West Nile Virus and Mosquito Control

David Pimentel

Cornell University, Ithaca, New York, U.S.A.


The West Nile virus, which causes serious encephalitis in

Americans, was introduced from Africa into northeastern

United States in 1999. No one knows exactly how the

virus was transported here, but with rapid air travel and

large numbers of people and goods being moved

throughout the world, the West Nile virus could have

been carried to the United States by an infected bird,

person, or even by a mosquito.

By the year 2003, the Centers for Disease Control

(CDC) reported there were 8900 reported human infections

of the West Nile disease with 218 deaths, with many

of the infections and deaths occurring in Ohio. The rate

of infections and deaths is running significantly ahead of

last year, with most of the infections and deaths occurring

in Colorado where the incidence has increased from only

14 infections in 2002 to 635 West Nile infections by

August 2003.


The prime reservoir of West Nile is the bird population. At

least 125 species of birds have been reported infected with

West Nile,[1] with crows, blue jays, sparrows, hawks,

eagles, and others identified as reservoirs. Birds appear to

be especially susceptible to the virus and are more likely

to die of an infection than are humans. In some localities

crows and blue jays have all but disappeared. Estimates

are that 20,000 birds were killed last year from West Nile

in the United States. Because birds travel long distances in

their seasonal migrations, infected birds spread the disease

to humans, horses, and other animals. Mosquitoes obtain

the virus mostly from infected birds and in turn infect

humans by biting them.


In the Northeast, the prime mosquito vector between birds

and humans is Culex pipens, the house mosquito. In New

York and New Jersey, when 32,000 mosquitoes were

examined by the CDC,[2] the great majority associated

with West Nile were Culex pipens.[3] In Colorado, the

prime mosquito vectors are Culex tarsalis and Culex

pipens. Other mosquito species capable of transmitting the

West Nile virus include other Culex species, Anopheles sp,

Coquilletidia sp., Ochlerotatus spp., and Psorophora sp.

Male mosquitoes feed primarily on nectar and do not

bite humans. The female mosquito requires a blood meal

and when she bites an infected bird she then transmits the

West Nile virus to humans by biting them.

The life cycle of Culex mosquito is about 14 days at

temperatures of about 21_C (70_F). The female obtains

her blood meal from birds, humans, and other animals.

She mates either before or after her blood meal. Then she

lays about 250 eggs in pools of water, including bird

baths, flower pots, tin cans, old tires, as well as other pools

of collected water. The egg stage lasts 1 to 2 days and the

emerging larvae feed on algae, bacteria, and other organic

matter in the water. The larval stage lasts 7 days followed

by the pupal stage that lasts 2 to 3 days. Adult mosquitoes

emerge from the pupae and the life cycle begins again.

The adult mosquitoes normally live a week or two, but

also hibernate in protected locations during the winter

(Fig. 1).

Adult mosquitoes are not strong fliers and usually

travel only a few hundred feet from the place of

emergence. They may be carried by the wind several

miles. In general, when the wind is blowing above 5 mph

they will not fly. Female mosquitoes feed most often

during the evening and morning.


The CDC advises that mosquito control should focus

primarily on mosquito larval control and secondarily on

the less efficient adulticiding.[4] Effective larval control

curtails the supply of adult mosquitoes.

In aquatic habitats, mosquito larvae have many

predators, but few parasites. The predators include

damselfly larvae, back swimmers, dragonfly larvae, water

boatman, dytiscid beetles, frogs, fishes, and salamanders.

However, none of these predators is effective because they

usually inhabit permanent water bodies, whereas most

mosquito larvae live in temporary pools of water.

Encyclopedia of Pest Management 1

DOI: 10.1081/E-EPM 120009995

Copyright D 2004 by Marcel Dekker, Inc. All rights reserved.


Although mosquito larvae can be killed by bacteria,

protozoans, nematodes, and fungi, none of these provides

control for large mosquito populations. One exception, a

strain of Baccilus thringiensis isrraeliensis or BT has

proven effective. Various commercial formulations of this

bacterium are available for application to ponds and pools

where larvae are found.

In addition to eliminating all mosquito breeding sites,

such as bird baths, flower pots, tires, ponds, and pools of

water, such breeding habitats may also be treated,

provided some water remains in them. BT is an effective

larvacide that is safe for humans and pests, but it may kill

some beneficial insects in water bodies.

In some small bodies of water, a thin layer of light oil

can be spread over the surface. This will kill both

mosquito larvae and pupae in the water. However, the oil

also may have negative impacts on small fish and

arthropods in the water.

Most insecticides are banned from water bodies

because they are highly toxic to most aquatic organisms,

such as fish, frogs, salamanders, and arthropods.


Instead of focusing control efforts on larval mosquitoes as

suggested by CDC, most homeowners and municipalities

focus on adult mosquito control.

Adult Mosquito Control with Predators

Adult mosquitoes have relatively few predators because

they are so small and not a large meal for a predator.

Dragonflies, bats, and small birds such as purple martins

feed on a few adult mosquitoes, but none of these animals

can be counted on to control large populations of

adult mosquitoes.


Before municipalities spray for mosquitoes, the mosquito

population should be measured for 5 days before spraying

and 5 days after spraying using various mosquito traps.

Such data will assist the government officials to determine

whether the several thousand or millions of dollars spent

in spraying was effective.

Homeowners should require warning 72 hr in advance

of community spraying. During spraying, the windows

and doors should be closed and the people should stay

inside away from the insecticide spray.

When many West Nile infected birds are found and the

mosquito population is relatively abundant, municipalities

are often pressured into spraying pyrethroid insecticides

for mosquito control. This spraying is carried out using

trucks mounted with ultralow volume (ULV) sprayers.

The insecticide spray produced from these units is like a

smoke or fine mist and is carried downwind. Even

assuming that the spraying is carried out in the evening

when wind is minimal, the spray is carried downwind in

an open area, for instance, on a golf course. Downwind,

from 150 to 300 ft and at 3 ft height, the mosquito kill will

range from 25% to 75%.[5] However, ZERO mosquitoes

will be killed upwind by the insecticide spray. Thus the

average upwind and downwind kill is only 21% to 45%.

Note, the insecticide spray does not penetrate buildings,

and mosquitoes behind buildings are not killed. Further,

dense vegetation hinders spray treatment and desired

mosquito control. For example, downwind in a dense

stand of trees, mosquito kill is reported to be only 34% to


For effective mosquito control, at least 90% of the

adults must be killed. Only a few scientific studies of the

effectiveness of spraying for mosquito control have been

reported. These results are relatively discouraging. For

Fig. 1 Culex mosquito eggs, larva, pupa, and adult female.

2 West Nile Virus and Mosquito Control


example, in Greenwich, CT, only a 34% mosquito

population reduction was reported after ground spraying,

and in Houston, TX, only a 30% reduction occurred after

spraying.[6] Then in Cicero Swamp, FL, populations of

disease-carrying mosquito populations increased 15-fold

after spraying,[6] when the mosquito population was

measured 11 days after spraying. However, it is doubtful

that the insecticide spray caused the increase in the

mosquito population, but clearly the insecticide provided

insufficient adult mosquito control.

Aerial ULV Spraying

The aerial application of insecticides for adult mosquito

control has some advantages over ground applications.

Reports on the effectiveness of aerial ULV spraying range

from 42% to 93%.[7,8] However, using ULV aerial

equipment results in only 10% to 25% of the insecticide

reaching the target area, whereas up to 90% drifts away

from the target into the environment at large.[9,10] Aerial

application covers a larger area faster than the ground

application equipment, but it is more expensive than

ground application, costing from $250 to $1000 per hour

(truck spraying costs from $150 to $250 per hour). Also to

be considered are the serious public health and environmental

problems associated with the application of

insecticides from aircraft.[11]

Insecticide Effectiveness in Reaching

Target Mosquitoes

With ULV spraying, the spray particles are minute and

measure from 7 to 22 mm. The lethal dose of a pyrethroid

insecticide is one particle 18 to 20 mm. Based on the fact

that many billions of spray droplets are produced per

kilogram of insecticide for both ground and aerial

spraying, less than 0.0001% of the insecticide applied is

reaching the target mosquitoes.[12] Thus by both ground

and aerial application 99.999% of the insecticide spreads

into the environment, when it can cause public health and

other environmental problems.

Because many adult mosquitoes remain after spraying

and more adult mosquitoes will emerge, if the mosquito

larvae are not controlled, then insecticide spraying is

required every 7 days. Costs of spraying every 7 days

are prohibitive.


Homeowners should drain standing water in pools,

gutters, and flower pots in the yard. Water in bird baths

and wading pools should be changed every 3 days. If

outdoors during dawn or dusk when mosquitoes are most

abundant and the wind is not blowing, then long pants and

a long-sleeve shirt made of heavy material, such as denim,

should be worn. Adult mosquitoes easily bite through a

light T-shirt.

Various adult mosquito traps and zappers are sold to

homeowners for control, but rarely do these units provide

continuous satisfactory control of mosquitoes.[13] While

outside, homeowners may use an insecticide fogger or can

of insecticide spray for temporary control of mosquitoes.

However, if the wind is blowing sufficiently strong

(5 mph or stronger), the mosquitoes will not be a problem

because the mosquitoes will not fly in the wind.

Of the numerous chemical repellants, the most popular

is the pesticide, DEET. DEET should be applied only to

the outer layer of heavy clothes. The chemical should

only be used, if there is a serious West Nile threat. DEET

has been known to cause rashes, restlessness, lethargy,

confusion, slurred speech, clumsiness, seizures, and in a

few cases death.[14] For some individuals, the DEET

pesticide is reported to cause allergic reactions and may

interfere with the immune and endocrine systems for

some people.

Located on a patio or other small area, a large fan

blowing air about 5 mph or higher will discourage the

presence of mosquitoes.


West Nile virus is a health hazard to humans, birds,

horses, and other animals. Culex mosquitoes are important

vectors in the United States. The prime method of control

is the elimination of the breeding habitats for larval

mosquitoes, such as water accumulating in bird baths,

flower pots, old tires, and other containers.

Widespread ULV spraying from ground equipment or

aircraft for control of mosquitoes and West Nile virus is

relatively ineffective, costly, and has been associated with

environmental and public health risks.

During the evening and early morning, repellants can

protect humans from mosquito bites. However, the

pesticide DEET and related chemicals should not be

applied directly to the skin of children or adults, because

they pose serious public health risks.


1. Environmental Defense. West Nile Virus on the Rise, Threatening

Humans and Wildlife; Environmental Defense:

New York, 2003.

article.cfm?ContentID=2871 (8/14/03).

West Nile Virus and Mosquito Control 3


2. CDC. West Nile Virus: Statistics, Surveillance, and

Control; Centers for Disease Control: Atlanta, 2002.

CaseCount02.htm (8/17/03).

3. Nasci, R.S.; White, D.J.; Stirling, H.; Oliver, J.O.; Daniels,

T.J.; Falco, R.C.; Campbell, S.; Crans, W.J.; Savage, H.M.;

Lanciotti, R.S.; Moore, C.G.; Godsey, M.S.; Gottried,

K.L.; Mitchell, C.J. Emerging Infectious Diseases; Communicable

Disease Center: Atlanta, 2001; Vol. 7. Past

Issue. No. 4, Jul–Aug 2001. 10 pp.

4. West Nile Control. West Nile Virus and Mosquito Control

Practices; 2002.

mosquito/mosquito2/Mosquito2.htm (8/16/03).

5. Mount, G.A. A critical review of ultralow-volume aerosols

of insecticide applied with vehicle-mounted generators for

adult mosquito control. J. Am. Mosq. Control Assoc. 1998,

14 (3), 305–334.

6. Outcome. Outcome Studies: Control Efforts for West Nile

Virus and Mosquito Population; 2003. http://www.ccheinfo.

com/pdf/cche-wnv_outcome_studies.pdf (8/13/03).

7. Andis, M.D.; Sackett, S.R.; Carrol, M.K.; Bordes, E.S.

Strategies for the emergency control of arboviral epidemics

in New Orleans. J. Am. Mosq. Control Assoc. 1987, 3 (2),


8. Williams, R.E.; Knapp, F.W.; Clarke, J.L. Aerial insecticide

applications for control of adult mosquitoes in the Ohio

River Basin USA. Mosq. News 1979, 39 (3), 622–626.

9. Bird, S.L.; Esterly, D.M.; Perry, S.G. Atmospheric pollutants

and trace gases. J. Environ. Qual. 1996, 25, 1095–


10. Pimentel, D.; McLaughlin, L.; Zepp, A.; Lakitan, B.; Kraus,

T.; Kleinman, P.; Vancini, F.; Roach, W.J.; Graap, E.;

Keeton, W.S.; Selig, G. Environmental and Economic

Impacts of Reducing Agricultural Pesticide Use. In

Pesticide Question: Environment, Economics and Ethics;

Pimentel, D., Ed.; Chapman and Hall: New York, 1993;


11. Pimentel, D. Environmental and Economic Costs of the

Application of Pesticides in the U.S. In Environment,

Development and Sustainability; in press.

12. Pimentel, D. Amounts of pesticides reaching target pests:

Environmental impacts and ethics. J. Agric. Environ.

Ethics 1995, 8 (1), 17–29.

13. Mosquito Buzz. Mosquito Magnet: Competitive Comparison

Chart; 2003.

comparisonchart2.html (8/16/03).

14. Marshall, L. Physicians urge caution with DEET. Daily

Camera 2003, 4A.

4 West Nile Virus and Mosquito Control


There is mounting scientific evidence that synthetic pyrethroids, increasingly the

most popular mosquito pesticide, are capable of disrupting the endocrine

(hormonal) system in wildlife and humans at extremely low doses (ppb).

The following are a sample of studies to illustrate this point.

Aziz MH, Agrawal AK, Adhami VM, Shukla V, Seth PK. 2001. Neurodevelopmental

consequences of gestational exposure (GD14-GD20) to low dose deltamethrin in

rats. Neurosci Lett 300(3):161-165.

Abstract: Effect of low level in utero exposure to deltamethrin (DT) (1 mg/kg wt.)

during gestation day 14-20 was studied on selected neurobehavioral,

neurochemical, immunohistochemical parameters in rats at 6 and 12 weeks

postnatal period. The significant increase in acetylcholinesterase activity and

decrease in H-3-quinuclidinyl benzilate binding in the hippocampal region of DT

exposed animals, suggesting impairment in cholinergic (muscarinic) receptors. A

significant decrease in the learning and memory performances was also observed

both at 6 and 12 weeks, which is directly correlated with decrease in muscarinic

receptor binding. Immunohistochemistry and image analysis of growth associated

protein-43, a neuron specific protein present in axonal growth cone and a marker

for neuronal differentiation and synaptogenesis, exhibit aberrant increase in its

expression in the hippocampus in DT exposed rats at both time periods. The data

suggests that low level exposure to DT in utero during brain growth spurt period

adversely affects the developing brain and the changes persist even upto 12 weeks

postnatal period in rats. Although there is no significant recovery at 12 weeks

assessment but still significant impairment persist on biochemical and

behavioural parameters.

[Deltamethrin = Pyrethroid insecticide]

Berrill M, Bertram S, Wilson A, Louis S, Brigham D, Stromberg C. 1993. Lethal and

sublethal impacts of pyrethroid insecticides on amphibian embryos and tadpoles.

Environmental Toxicology & Chemistry 12:525-539.

Abstract: Amphibian populations are potentially sensitive to aquatic contaminants

such as pesticides. We exposed embryos and larvae of five amphibians (the frogs

Rana sylvatica, Rana pipiens, Rana clamitans; the toal Bufo americanus; the

salamander Ambystoma maculatum) to one or both of the pyrethroid pesticides

permethrin and fenvalerate. Concentrations ranged from 0.01 ppm to 2 ppm, and

exposures lasted 22 or 96 h. No significant mortality of embryos, anuran

tadpoles, or salamander larvae occurred during or following exposure to

pyrethroids. However, tadpole growth was delayed following exposure, and

tadpoles and salamander larvae responded to prodding not by darting away but by

twisting abnormally. Both effects may result in greater vulnerability to predation.

Recovery of normal avoidance behavior occurred more rapidly at 20 than at 15şC

and following exposure to lower concentrations of the pesticides, indicating both

temperature and dose effects. Tadpoles exposed later in development did not feed

for a period of days following exposure but were still capable of metamorphosis.


Of the five tested species, Ambystoma maculatum, a tadpole predator, was

particularly sensitive. An amphibian community is therefore likely to be sensitive

to low-level contamination events.

Chen AW, Fink JM, Letinski DJ. 1996. Analytical methods to determine residual

cypermethrin and its major acid metabolites in bovine milk and tissues. Journal

of Agricultural & Food Chemistry 44(11):3534-3539.

Abstract: Several analytical methods were developed to determine cypermethrin

and its acid metabolite residues in bovine milk, cream, kidney, liver, muscle, and

fat samples. These methods used solvent extraction or acid reflux, liquid-liquid

and/or solid phase extraction, with or without chemical derivatization, and

quantitation by gas chromatograph with electron capture or mass selective

detector. The LOQ and LOD for milk were set at 10 and 2 ppb, respectively. The

average method recoveries for cypermethrin, cis-DCVA, trans-DCVA, and m-

PBA in cow milk were 81% (n=39), 96% (n=22), 99% (n=22), and 106% (n=22),

respectively. For bovine tissues and cream samples, the LOQ and LOD were 50

and 10 ppb, respectively. The overall average method recoveries for

cypermethrin, cis-DCVA, trans-DCVA, and m-PBA in cream and tissue samples

were 92% (n=27), 97% (n=25), 103% (n=25), and 98% (n=25), respectively.

Satisfactory recoveries were also obtained with higher fortification levels for milk

and fat samples.

[Cypermethrin = Pyrethroid insecticide]

Eriksson P. 1997. Developmental neurotoxicity of environmental agents in the neonate.

Neurotoxicology 18(3):719-726.

Abstract: The development of an organism includes periods that can be critical for

its normal maturation. One such appears to occur during perinatal development of

the brain, the so-called 'brain growth spurt'. This period in the development of the

mammalian brain is associated with numerous biochemical changes that

transform the feto-neonatal brain into that of the mature adult. We have observed

that low-dose exposure to environmental agents such as DDT; pyrethroids,

organophosphates, nicotine paraquat and polychlorinated biphenyls (PCBs)

during the 'brain growth spurt' can lead to irreversible changes in adult brain

function in the mouse. The induction of behavioural and cholinergic disturbances

in the adult animal appears to be limited to a short period during neonatal

development, around postnatal day 10, and following doses that apparently have

no permanent effects when administered to the adult animal. Furthermore,

neonatal exposure to a low dose of a neurotoxic agent can lead to an increased

susceptibility in adults to an agent having a similar neurotoxic action, resulting in

additional behavioural disturbances and learning disabilities.

Eriksson P, Fredriksson A. 1991. Neurotoxic effects of two different pyrethroids,

bioallethrin and deltamethrin, on immature and adult mice: changes in behavioral

and muscarinic receptor variables. Toxicol Appl Pharmacol 108(1):78-85.

Abstract: We have recently shown that two pyrethroids, bioallethrin and

deltamethrin, affect muscarinic cholinergic receptors (MAChR) in the neonatal


mouse brain when given to suckling mice during the period of rapid brain growth.

Such early exposure to these pyrethroids can also lead to permanent changes in

the MAChR and behavior in the mice as adults. In the present study, male NMRI

mice were given bioallethrin (0.7 mg), deltamethrin (0.7 mg), or a 20% fat

emulsion vehicle (10 ml) per kilogram of body weight per os once daily between

the 10th and 16th postnatal day. The mice were subjected to behavioral tests upon

reaching the age of 17 days and at 4 months. Within 1-2 weeks after the

behavioral tests the mice were killed by decapitation and crude synaptosomal

fractions (P2) were prepared from the cerebral cortex, hippocampus, and striatum.

The densities of MAChR were assayed by measuring the amounts of

quinuclidinyl benzilate ([3H]QNB) specifically bound in the P2 fraction. The

proportions of high-affinity (HA) and low- affinity (LA) binding sites of MAChR

were assayed in a displacement study using [3H]QNB/carbachol. The behavioral

tests at an adult age of 4 months indicated a significant increase in spontaneous

motor behavior in both bioallethrin- and deltamethrin-treated mice. There was

also a significant decrease and a tendency toward a decrease in the density of

MAChR in the cerebral cortex in mice receiving bioallethrin and deltamethrin,

respectively. The proportions of HA- and LA-binding sites of MAChR were not

changed. This study further supports that disturbances of the cholinergic system

during rapid development in the neonatal mouse can lead to permanent changes in

cholinergic and behavioral variables in the animals as adults.

Eriksson P, Talts U. 2000. Neonatal exposure to neurotoxic pesticides increases adult

susceptibility: a review of current findings. Neurotoxicology 21(1-2):37-47.

Abstract: An environmental mischance commonly occuring in nature is the

combination of neonatal exposure and later adult exposure to various toxic

substances. During neonatal life, offspring can be affected by toxic agents either

by transfer via mother's milk or by direct exposure. In many mammalian species

the perinatal period is characterized by a rapid development of the brain--'the

brain growth spurt' (BGS). We have observed that exposure to pesticides, such as

DDT and bioallethrin, during the BGS in mice can potentiate susceptibility to

bioallethrin or paraoxon in adult life. This combined neonatal and adult exposure

caused spontaneous behavioural aberrations and changes in muscarinic

cholinergic receptors and led to impairment of the faculties of learning and

memory. Our studies indicate that neonatal exposure to pesticides--even in low

doses--can potentiate and/or modify the reaction to adult exposure to xenobiotics,

and thereby accelerate dysfunctional processes.

[Bioallethrin = Pyrethroid insecticide]

Go, V, Garey J, Wolff MS, Pogo BGT. 1999. Estrogenic Potential of Certain Pyrethroid

Compounds in the MCF-7 Human Breast Carcinoma Cell Line. Environ Health

Perspect 107(3):173-177.

Abstract: Estrogens, whether natural or synthetic, clearly influence reproductive

development, senescence, and carcinogenesis. Pyrethroid insecticides are now the

most widely used agents for indoor pest control, providing potential for human

exposure. Using the MCF-7 human breast carcinoma cell line, we studied the

estrogenic potential of several synthetic pyrethroid compounds in vitro using pS2


mRNA levels as the end point. We tested sumithrin, fenvalerate, d-trans allethrin,

and permethrin. Nanomolar concentrations of either sumithrin or fenvalerate were

sufficient to increase pS2 expression slightly above basal levels. At micromolar

concentrations, these two pyrethroid compounds induced pS2 expression to levels

comparable to those elicited by 10 nM 17ß-estradiol (fivefold). The estrogenic

activity of sumithrin was abolished with co-treatment with an antiestrogen (ICI

164,384), whereas estrogenic activity of fenvalerate was not significantly

diminished with antiestrogen co-treatment. In addition, both sumithrin and

fenvalerate were able to induce cell proliferation of MCF-7 cells in a doseresponse

fashion. Neither permethrin nor d-trans allethrin affected pS2

expression. Permethrin had a noticeable effect on cell proliferation at 100 µM,

whereas d-trans allethrin slightly induced MCF-7 cell proliferation at 10 µM, but

was toxic at higher concentrations. Overall, our studies imply that each pyrethroid

compound is unique in its ability to influence several cellular pathways. These

findings suggest that pyrethroids should be considered to be hormone disruptors,

and their potential to affect endocrine function in humans and wildlife should be


Greenlee AR, Ellis TM, Berg RL. 2004. Low-dose agrochemicals and lawn-care

pesticides induce developmental toxicity in murine preimplantation embryos.

Environ Health Perspect 112(6):703-709.

Abstract: Occupational exposures to pesticides may increase parental risk of

infertility and adverse pregnancy outcomes such as spontaneous abortion, preterm

delivery, and congenital anomalies. Less is known about residential use of

pesticides and the risks they pose to reproduction and development. In the present

study we evaluate environmentally relevant, low-dose exposures to agrochemicals

and lawn-care pesticides for their direct effects on mouse preimplantation embryo

development, a period corresponding to the first 5-7 days after human conception.

Agents tested were those commonly used in the upper midwestern United States,

including six herbicides [atrazine, dicamba, metolachlor, 2,4-

dichlorophenoxyacetic acid (2,4-D)], pendimethalin, and mecoprop), three

insecticides (chlorpyrifos, terbufos, and permethrin), two fungicides

(chlorothalonil and mancozeb), a desiccant (diquat), and a fertilizer (ammonium

nitrate). Groups of 20-25 embryos were incubated 96 hr in vitro with either

individual chemicals or mixtures of chemicals simulating exposures encountered

by handling pesticides, inhaling drift, or ingesting contaminated groundwater.

Incubating embryos with individual pesticides increased the percentage of

apoptosis (cell death) for 11 of 13 chemicals (p less than or equal to 0.05) and

reduced development to blastocyst and mean cell number per embryo for 3 of 13

agents (p less than or equal to 0.05). Mixtures simulating preemergent herbicides,

postemergent herbicides, and fungicides increased the percentage of apoptosis in

exposed embryos (p less than or equal to 0.05). Mixtures simulating groundwater

contaminants, insecticide formulation, and lawn-care herbicides reduced

development to blastocyst and mean cell number per embryo (p less than or equal

to 0.05). Our data demonstrate that pesticide-induced injury can occur very early

in development, with a variety of agents, and at concentrations assumed to be


without adverse health consequences for humans.

Lazarini CA, Florio JC, Lemonica IP, Bernardi MM. 2001. Effects of prenatal exposure

to deltamethrin on forced swimming behavior, motor activity, and striatal

dopamine levels in male and female rats. Neurotoxicol Teratol 23(6):665-673.

Abstract: The effects of prenatal exposure of rat pups to 0.08 mg/kg deltamethrin

(DTM) on physical, reflex and behavioral developmental parameters, on forced

swimming and open-field behaviors, and on striatal monoamine levels at 60 days

of age were observed. Maternal and offspring body weight, physical and reflex

development were unaffected by the exposure to the pesticide. At 21 days of age,

open-field locomotion frequency and immobility duration of male and female

offspring were not different between control and exposed animals. However, male

rearing frequency was increased in experimental animals. A decreased immobility

latency to float and in general activity after the swimming test in male offspring

was observed at adult age; no interference was detected in the float duration

during the swimming test. In addition, these animals presented higher striatal 3,4-

dihydroxyphenylacetic acid (DOPAC) levels without modification in dopamine

(DA) levels and an increased DOPAC/DA ratio. These data indicate a higher

activity of the dopaminergic system in these animals. Noradrenaline (NA) levels

were increased, while MHPG levels were not detectable in the system studied.

Serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) levels, as well as the

homovanillic acid (HVA)/DA ratio, were not modified by the exposure to the

pesticide. No changes were observed in swimming and open-field behaviors nor

were there any changes in striatal monoamines or their metabolites in the female

experimental group. In relation to the pesticide formula, the present data showing

that prenatal exposure to DTM alters latency to float and the activity of striatal

dopaminergic system might reflect a persistent effect of the pesticide on animal

motor activity, mainly in males. On the other hand, the decrease in general

activity observed in experimental male rats suggests higher levels of emotionality

induced by previous exposure to the swimming behavior test in relation to control

animals. Data gathered in the present study may be important for the assessment

of the safety of pyrethroid insecticides.

[Deltamethrin = Pyrethroid insecticide]

Leng G, Gries W. 2005. Simultaneous determination of pyrethroid and pyrethrin

metabolites in human urine by gas chromatography-high resolution mass

spectrometry. Journal of Chromatography B-Analytical Technologies in the

Biomedical & Life Sciences 814(2):285-294.

Abstract: A new developed gas chromatographic-high resolution mass

spectrometric method for the sensitive simultaneous determination of transchrysanthemumdicarboxylic

acid, cis- and trans-3-(2,2-dichlorovinyl)-2,2-

dimethylcyclopropane carboxylic acid, cis-3-(2,2-dibromovinyl)2,2-

dimethylcyclopropane carboxylic acid, 3-phenoxybenzoic acid and 4-fluoro-3-

phenoxybenzoic acid in human urine is presented. These metabolites are

biomarkers for an exposure to pyrethrum, allethrin, resmethrin, phenothrin,

tetramethrin, cyfluthrin, cypermethrin, deltamethrin or permethrin. Therefore,

with the help of this method for the first time a complete assessment of exposure


to pyrethroid and pyrethrin insecticides is possible. After acid hydrolysis and

extraction with tert-butyl-methyl-ether the residue is derivatized with 1,1,1,3,3,3-

hexafluoroisopropanol and analyzed by GC/HRMS in electron impact mode

(detection limits <0.1 mug/l) as well as in negative chemical ionization mode

(detection limit <0.05 mug/l urine).

Monteiro-Riviere NA, Baynes RE, Riviere JE. 2003 Feb 1. Pyridostigmine bromide

modulates topical irritant-induced cytokine release from human epidermal

keratinocytes and isolated perfused porcine skin. Toxicology 183(1-3):15-28.

Abstract: Gulf War personnel were given pyridostigmine bromide (PB) as a

prophylactic treatment against organophosphate nerve agent exposure, and were

exposed to the insecticide permethrin and the insect repellent N,N-diethyl-mtoluamide

(DEET). The purpose of this study was to assess the effects of PB to

modulate release of inflammatory biomarkers after topical chemical exposure to

chemical mixtures containing permethrin and DEET applied in ethanol or water

vehicles. Treatments were topically applied to isolated perfused porcine skin flaps

(IPPSFs). Concentrations of interleukin-8 (IL-8), tumor necrosis factor-alpha

(TNF-alpha) and prostaglandin E-2 (PGE(2)) were assayed in perfusate to probe

for potential inflammatory effects after complex mixture application. IPPSFs (n =

4/treatment) were topically dosed with mixtures of permethrin, DEET, and

permethrin/DEET, in ethanol. Each treatment was repeated with perfusate spiked

with 50 ng/ ml of PB. Perfusate was also spiked with 30 ng/ml

diisopropylfluorophosphate to simulate low level organophosphate nerve agent

exposure. Timed IPPSF venous effluent samples (0.5,1,2,4, and 8 h) were assayed

by ELISA for IL-8 and TNF-alpha and by EIA for PGE(2). Overall, PB infusion

caused a decrease or IL-8 and PGE(2) release. Effects on TNF-alpha were vehicle

dependent. To probe the potential mechanism of this PB effect, human epidermal

keratinocyte HEK cell cultures were exposed to permethrin DEET

permethrin/DEET, with and without PB in DMSO. IL-8 was assayed at 1, 2, 4, 8,

12 and 24 h. PB suppressed IL-8 in permethrin and ethanol treatment from 4 to 24

h confirming the IPPSF results. In conclusion, these studies suggest that systemic

exposure to PB suppressed IL-8 release at multiple time points in two skin model

systems. This interaction merits further study.

Nassif M, Brooke JP, Hutchinson DBA, Kamel OM, Savage EA. 1980. Studies with

permethrin against bodylice in Egypt. Pesticide Science 11:679-684.

Abstract: Approximately 350 people, the inhabitants of two villages in the Fayum

district of Egypt, were individually dusted with 50 g of powder containing 2.5 or

5.0 g permethrin kg(-1). The inhabitants of a third village were left untreated as a

control. Before treatment, approximately two-thirds of the population of all three

villages were infested with bodylice. Fourteen days after treatment, the

permethrin dust at the lower strength reduced the infestation by 98.8% and at the

highest strength of residual control for at least 91 days. The other gave a lower

level of control at this time. Urine samples, taken from subjects in each of the

treated villages before and after dusting, were analyses for permethrin

metabolites. Results indicated that the maximum amount of permethrin absorbed,

orally, through the skin, or by inhalation, was 39 ug/kg(-1) body weight, 24 h


after treatment. No residue was found 30 days and 60 days after treatment. It was

concluded that there was a very substantial safety margin when permethrin dusts

were used on man for bodylice control.

Sheets LP, Doherty JD, Law MW, Reiter LW, Crofton KM. 1994. Age-dependent

differences in the susceptibility of rats to deltamethrin. Toxicol Appl Pharmacol


Abstract: Separate groups of weanling and adult rats were exposed to both

behaviorally active and lethal doses of deltamethrin to examine age-dependent

toxicity of a pyrethroid over a wide dose range. The acoustic startle response

(ASR) was selected for comparison at low doses since it is a sensitive,

quantifiable biological indicator of pyrethroid effects in rats. Acute mortality was

included for comparison at the upper limit of the dose-response. Deltamethrin

was administered by gavage as a single dose in corn oil for all tests. Effects on

the ASR were comparable in 21- and 72-day-old rats, with a 4-mg/kg dose

decreasing ASR amplitude by approximately 50% (ED50) at both ages. By

comparison, LD50 values in 11-, 21-, and 72- day old rats were 5.1, 11 and 81

mg/kg, respectively. Thus, 11- and 21- day-old male rats were 16 and 7 times,

respectively, more sensitive than adults to acute lethality. The concentration of

deltamethrin was measured in whole-brain tissue from weanling and adult males

treated with ED50 and LD50 doses. The brain concentration of deltamethrin at

the ED50 dose of 4 mg/kg was higher in weanling rats than adults. This suggests

a possible functional difference, with weanling rats being less susceptible than

adults to a low dose. By comparison, there was an equivalent concentration of

deltamethrin in brain tissue following an LD50 dose of 12 mg/kg in weanling rats

and 80 mg/kg in adults. These results support age-related differences in

pharmacokinetics as the basis for the markedly greater sensitivity of young rats to

a lethal dose of deltamethrin.

van Haaren F, Haworth SC, Bennett SM, Cody BA, Hoy JB, Karlix JL, Tebbett IR. 2001

May-2001 Jun 30. The effects of pyridostigmine bromide, permethrin and deet

alone, or in combination, on fixed-ratio and fixed-interval behavior in male and

female rats. Pharmacol Biochem Behav 69(1-2):23-33.

Abstract: Concurrent exposure to pyridostigmine bromide (PB), permethrin

(PERM) and/or N,N-diethyl-m-toluamide (DEET) may have contributed to the

development of a syndrome that appears to have afflicted military personnel who

served during the Gulf War. The present experiment sought to evaluate the

behavioral effects of these compounds alone, or in various combinations, in male

and female rats. Subjects were exposed to a multiple fixed-ratio (FR) 50, fixedinterval

(FI) 2-min schedule of reinforcement. PB dose-dependently decreased FR

and FI response rates. FR responding was disrupted by lower doses and there

were no differences between the sexes. PERM vehicle administration decreased

response rates maintained by both schedules of reinforcement; this was offset by

an increase in response rate after the administration of the intermediate dose of

PERM. The highest dose of PERM decreased both FR and FI response rates. FR

rates in male rats were more disrupted than those in female rats. Only the highest

dose of DEET decreased FR and FI response rates in male and female rats. FR


rates were more disrupted in female rats than in male rats. Synergistic effects

were only observed when FI response rates decreased in male rats upon exposure

to half the low dose of PB with half the low dose of PERM or half the low dose of

PB with half the low dose of DEET. The results of this experiment thus show that

small doses of PB, PERM and DEET disrupt well-established, schedulecontrolled

behavior in male and female rats in a schedule- and gender-dependent

manner; schedule-dependent and gender-dependent synergistic effects were also

observed. The mechanism by which the compounds exert these behavioral effects

remains to be determined.

Walker AN, Bush P, Puritz J, Wilson T, Chang ES, Miller T, Holloway K, Horst MN.

2005. Bioaccumulation and metabolic effects of the endocrine disruptor

methoprene in the lobster, Homarus americanus. Integrative & Comparative

Biology 45(1):118-126.

Abstract: Methoprene is a pesticide that acts as a juvenile hormone agonist.

Although developed initially against insects, it has since been shown to have toxic

effects on larval and adult crustaceans. Methoprene was one of several pesticides

applied to the Western Long Island Sound (WLIS) watershed area during the

summer of 1999; the other pesticides were malathion, resmethrin, and sumethrin.

These pesticides were applied as part of a county-by-county effort to control the

mosquito vector of West Nile Virus. Subsequently, the seasonal lobster catches

from the WLIS have decreased dramatically. The lethality of the pesticides to

lobsters had been unknown. We studied the effects of methoprene while other

investigators studied effects of the other pesticides. We questioned whether

methoprene, through its effects on larvae, adults or both, could have contributed

to this decline. We found that low levels of methoprene had adverse effects on

lobster larvae. It was toxic to stage II larvae at 1 ppb. Stage IV larvae were more

resistant, but did exhibit significant increases in molt frequency beginning at

exposures of 5 ppb. Juvenile lobsters exhibited variations in tissue susceptibility

to methoprene: hepatopancreas appeared to be the most vulnerable, reflected by

environmental concentrations of methoprene inhibiting almost all protein

synthesis in this organ. Our results indicated that methoprene concentrates in the

hepatopancreas, nervous tissue and epidermal cells of the adult lobster.

Methoprene altered the synthesis and incorporation of chitoproteins (cuticle

proteins) into adult postmolt lobster explant shells. SDS PAGE analyses of adult

post-molt shell extracts revealed changes in the synthesis of chitoproteins in the

methoprene-treated specimens, suggesting that methoprene affects the normal

pathway of lobster cuticle synthesis and the quality of the post-molt shell.

Although it is likely that a combination of factors led to the reduced lobster

population in WLIS, methoprene may have contributed both by direct toxic

effects and by disrupting homeostatic events under endocrine control.



Provided below is an overview of the study to follow on page 5, Appendix D.

Toxic Synthetic Pyrethroid Pesticide Levels Found in Stream Sediments

(Beyond Pesticides, May 10, 2004) A family of pesticides, synthetic pyrethroids, used

increasingly nationwide in place of more heavily restricted organophosphate pesticides

has accumulated in many creek sediments to levels that are toxic to freshwater bottom

dwellers, according to a new study. The study, "Distribution and Toxicity of Sediment-

Associated Pesticides in Agriculture-Dominated Water Bodies of California's Central

Valley," Weston, D. P.; You, J. C.; Lydy, M. J.; Environ. Sci. Technol. (April, 2004), is

available on line to members/subscribers of the American Chemical Society.

This study is believed to be the first to evaluate the effect of synthetic pyrethroids on

sediment-dwelling organisms, such as midge larvae or shrimp-like amphipods, according

to University of California, Berkeley, biologist Donald P. Weston, adjunct associate

professor of integrative biology and lead author. Ironically, the two organisms studied,

are used by the U.S. Environmental Protection Agency (EPA) as indicators of the health

of fresh water sediment, according to the author.

Dr. Weston and colleague Michael J. Lydy of Southern Illinois University (SIU) in

Carbondale collected sediment samples from 42 rivers, creeks, sloughs and drainage

ditches in California's Central Valley and exposed amphipods and midge larvae to the

sediments for 10 days. Twenty-eight percent of the sediment samples (20 of 71) killed

amphipods at an elevated rate, and in 68 percent of these sediments, the pyrethroids were

at levels high enough to account for the deaths. Thus, while other pesticides may well

have contributed to the amphipod deaths in some sediment samples, pyrethroids alone

explain the toxicity in the vast majority of the sediment samples, Dr. Weston said.

"About one-fifth of our Central Valley sediment samples are toxic to a standard testing

species due to a class of pesticides no one has tested for before, for which there are little

data on their toxicology when sediment-bound, and which are being promoted as an

alternative to the increasingly restricted organophosphate insecticides," Dr. Weston said.

In the tests, the midge larvae died at higher rates when exposed to sediment from 13

percent of 39 collection sites, and 40 percent of these sediment samples contained enough

pyrethroids to account for the deaths. Weston notes that these midges (Chironomus

tentans) are known to be about three times less sensitive to pyrethroids than are the

amphipods (Hyalella azteca), which explains the difference between the species results.

"Since the levels are high enough to be toxic to the standard 'lab rat' species, the next

question is: What's happening with the resident species?" Dr. Weston said. "The concern

is that invertebrates, particularly crustaceans, could have reduced populations, and these

organisms are an important food for a variety of bottom-feeding fish."


Alternatively, the amphipods and midge larvae from areas of intensive agricultural or

urban pesticide use may have adapted to live with normally toxic levels of the pesticide.

Dr. Weston and his colleagues now are sampling these organisms from the rivers, creeks,

sloughs and ditches to determine if they respond the same way as lab-raised organisms.

Pyrethroids are a class of compounds represented by permethrin, first marketed in 1973,

and various other chemicals usually ending in the suffix -thrin. Permethrin is found in

home and garden pesticides ranging from RAID to flea killers and head lice creams, but

permethrin and it's kin find broad use in agriculture, such as on cotton, fruit and nut

orchards, and on lettuce and rice. California's Central Valley produces more than half the

nation's fruits, vegetables and nuts.

Though pyrethroids are used far less than organophosphates like diazinon and

chlorpyrifos, their use in California has risen rapidly in recent years because of increased

regulation of the spraying of organophosphates, due to health threats to farm workers and

increased toxic runoff from fields. According to Weston, pyrethroid use in California

increased 58 percent from 2001 to 2002, if account is taken of the increased potency of

newer pyrethroids such as cypermethrin. Over a quarter of a million pounds of

pyrethroids were spread on California farm fields in 2002, while about 500,000 pounds

were used for structural and pest control and landscape maintenance.

Despite this increased use, environmental monitoring still concentrates on

organophosphates, he said. Monitoring also tends to focus on concentrations in the water

column, under the assumption that sediment-bound chemicals like pyrethroids are

unavailable. The current study shows that to be untrue.

"It's amazing that, after 20 years of use, there is not one published study on pyrethroids in

sediments in areas of intensive agriculture," Dr. Weston said.

Part of the reason for a lack of data is that analytical methods to detect pyrethroids in

sediment have not been broadly available or standardized. Lydy, an environmental

toxicologist with SIU-Carbondale's Illinois Fisheries and Aquaculture Center, developed

such a method.

"Prior to our study, scientists in area water-monitoring programs were seeing that if they

placed aquatic invertebrates in their sediment samples, the animals would die, but they

didn't know why - they'd attribute it to organophosphates or organochlorines (two

pesticide ingredients being phased out because of environmental concerns), or they'd put

it down to 'unknown causes,'" Dr. Lydy said.

He continued: "Where our study is unique is that we looked at the toxicity and tried to

figure out what was actually causing it. We detected organochlorines, such as DDT and

chlordane, in the sediments, but at concentrations not high enough to cause the toxicity

we noted, whereas concentrations of pyrethroids were high enough to account for that



The samples, over 70 in all, were obtained from two major rivers - the San Joaquin and

the Feather - and 19 creeks or sloughs, 17 irrigation ditches and two tailwater ponds in 10

Central Valley counties, including the ones with the greatest pyrethroid use: Fresno,

Madera, Stanislaus and Sutter. Each sample was placed in a jar and left with 10 test

organisms for 10 days, and the death rate compared with similar organisms raised with

pristine sediment. The levels of pesticides in each sediment sample also were measured,

and 75 percent contained pyrethroids.

Weston, who focuses on freshwater and marine pollution and how it gets from sediments

into creatures living on the bottom, noted that another chemical sometimes applied with

pyrethroids may be making the situation worse.

Piperonyl butoxide, or PBO, is a synergist that shuts down the enzymes that detoxify

pyrethroids, making them last longer in an organism and increasing their killing potential.

He and his colleagues are now trying to measure the level of pyrethroid that kills

amphipods, which is around 3 parts per billion in sediments, and whether levels of PBO

need to be considered in order to estimate the true toxicity of pyrethroid pesticides. UC

Berkeley post-doctoral researcher Erin Amweg is conducting the latter study.

"I don't want to give the impression that pyrethroids are destroying the streams, since that

has not yet been shown, but if we are serious about maintaining stream health, we have to

consider the sediments and not limit our sampling just to the water above," said Dr.

Weston. "While pyrethroids may be preferable to the organophosphates that preceded

them, our work shows that the environmental effects of pyrethroids can not be ignored

and have had too little study for too long. We need to know more about pyrethroids,

because if we don't, how can we regulate them?"

Dr. Lydy said, "Best management practices,' such as introducing buffer strips and

wetlands, may reduce pesticide loads in aquatic systems, which would reduce the risk to

non-target species."

The study by Drs. Weston, Lydy and post-doctoral researcher Jing You in the

Department of Zoology at SIU appeared in the April 8 online version of the American

Chemical Society's journal Environmental Science & Technology and will be published

later in hard copy.

For more information, contact Robert Sanders,, 510-643-6998,

University of California – Berkeley, or find the study under:

Weston, D. P., J.C. You, M.J. Lydy. 2004. Distribution and Toxicity of Sediment-

Associated Pesticides in Agriculture-Dominated Water Bodies of California's Central

Valley. Environ. Sci. Technol. 38(10): 2752-2759.


Distribution and Toxicity of

Sediment-Associated Pesticides in

Agriculture-Dominated Water Bodies

of California’s Central Valley

D . P . W E S T O N , * , † J . C . Y O U , A N D

M . J . L Y D Y

Department of Integrative Biology,

University of California, 3060 Valley Life Sciences Building,

Berkeley, California 94720-3140, and

Fisheries and Illinois Aquaculture Center & Department of

Zoology, Southern Illinois University, 171 Life Sciences II,

Carbondale, Illinois 62901

The agricultural industry and urban pesticide users are

increasingly relying upon pyrethroid insecticides and shifting

to more potent members of the class, yet little information

is available on residues of these substances in aquatic

systems under conditions of actual use. Seventy sediment

samples were collected over a 10-county area in the

agriculture-dominated Central Valley of California, with

most sites located in irrigation canals and small creeks

dominated by agricultural effluent. The sediments were

analyzed for 26 pesticides including five pyrethroids, 20

organochlorines, and one organophosphate. Ten-day sediment

toxicity tests were conducted using the amphipod

Hyalella azteca and, for some samples, the midge

Chironomus tentans. Forty-two percent of the locations

sampled caused significant mortality to one test species

on at least one occasion. Fourteen percent of the sites (two

creeks and four irrigation canals) showed extreme

toxicity (>80% mortality) on at least one occasion. Pyrethroid

pesticides were detected in 75% of the sediment samples,

with permethrin detected most frequently, followed by

esfenvalerate > bifenthrin >lambda-cyhalothrin. Based

on a toxicity unit analysis, measured pyrethroid concentrations

were sufficiently high to have contributed to the toxicity

in 40% of samples toxic to C. tentans and nearly 70% of

samples toxic to H. azteca. Organochlorine compounds

(endrin, endosulfan) may have contributed to the toxicity

at a few other sites. This study provides one of the first

geographically broad assessments of pyrethroids in

areas highly affected by agriculture, and it suggests there

is a greater need to examine sediment-associated

pesticide residues and their potential for uptake by and

toxicity to benthic organisms.


The dominance of organophosphates (OPs) among agricultural

insecticides over the past several decades has led

environmental monitoring programs in California to focus

on dissolved phase pesticides and their toxicity (1, 2). The

emphasis on OPs has diverted attention from more hydrophobic

pesticides associated with soils and sediments. Legacy

pesticides such as some organochlorines and some currently

used pesticides such as the pyrethroids are strongly hydrophobic,

and monitoring suspended or bedded sediments

would bemoreappropriate. First generation pyrethroids (e.g.,

permethrin) have been available since the 1970s, and many

second generation pyrethroids (e.g., bifenthrin, cyfluthrin,

lambda-cyhalothrin) became available in the 1980s, yet there

are little data on their concentrations in aquatic sediments.

There have been several mesocosm studies (e.g., refs 3 and

4), but published field data from agricultural areas are

minimal. Given recent federal restrictions on residential and

some agricultural applications of OPs, and a shift to pyrethroids

as replacements, data are needed on realistic

environmental concentrations of these compounds.

After gradual decline throughout the 1990s, agricultural

use of pyrethroids in California increased 25% from 105 171

kg in 1999 to 131 422 kg in 2002 (data from California’s

Pesticide Use Reporting database; In

addition, the diversity of pyrethroids used is increasing, and

the newer compounds have far greater toxicity to aquatic

life. About half of agricultural pyrethroid use in California

occurs in the Central Valley, a region lying within the

watersheds of the Sacramento and San Joaquin Rivers (Figure

1) that produces more than half of the fruits, vegetables, and

nuts grown in the United States. Our goal was to determine

the concentrations of pyrethroids and other hydrophobic

pesticides in sediments of agriculture-dominated water

bodies of the Central Valley and to determine whether toxicity

to aquatic life was associated with these residues.

* Corresponding author phone: (510)231-5626; fax: (510)231-9504;

e-mail: dweston@

University of California.

Southern Illinois University.

FIGURE 1. Location of California’s Central Valley (shaded area) and

the counties in which sampling sites were located. The counties

shown are as follows: BU ) Butte, YU ) Yuba, SU ) Sutter, CO

) Colusa, YO ) Yolo, SO ) Solano, SJ ) San Joaquin, ST )

Stanislaus, MA ) Madera, and FR ) Fresno.

10.1021/es0352193 CCC: $27.50 ã xxxx American Chemical Society VOL. xx, NO. xx, xxxx / ENVIRON. SCI. & TECHNOL. 9 A

PAGE EST: 7.2 Published on Web 00/00/0000

Materials and Methods

Site Selection. We combined data from two studies with

different site selection approaches. The first study used the

California Department of Pesticide Regulation’s Pesticide Use

Reporting (PUR) database to identify Central Valley counties

with the greatest agricultural use of pyrethroids. Three of the

four counties with the greatest pyrethroid use in the San

Joaquin River watershed (Fresno, Madera, Stanislaus) and

the leading county in the Sacramento River watershed (Sutter)

were selected for sampling. For ease of access to some water

bodies, a few samples were taken across county lines into

neighboring Butte, San Joaquin, and Yuba counties. We also

used the PUR database to identify crops in each county on

which the majority of pyrethroids were used, months of

greatest pyrethroid use, and thecompoundsemployed (Table

1). Sampling sites were located within the regions of each

county where these crops were grown. A few additional sites

were added in water bodies with anecdotal evidence of

sediment toxicity. Sampling sites were located in two major

rivers, 11 creeks or sloughs, eight irrigation canals, and two

tailwater ponds.

Most stations were sampled twice, termed “peak use”

and “winter”. The peak use sampling occurred in the month

immediately after the peak use of pyrethroids on the target

crop(s) within each county. The time of peak use sampling

ranged from July 2002 to November 2002, depending on the

specific crop. We sampled all sites again in March 2003

following heavy rains (“winter” sampling).

In the second study, samples were obtained from an

investigation of irrigation return flows. Farms in the region

typically receive irrigation water through a network of canals,

and excess irrigation water that flows off the soil surface

(tailwater) is returned to the canal system. Sampling stations

were located within these canals, termed “agricultural drains”,

or in creeks to which the canal systems discharged. The

principal criteria for site selection was flow dominated by

irrigation return water, with only minimal consideration of

local pesticide use. Sites were sampled at the beginning

(March/April 2003) and toward the end of the irrigation

season (August 2003).

In total, the two studies sampled 42 locations, most twice,

yielding 70 samples, or 81 including replicates (see Table S1

in Supporting Information).

Sampling Procedures. All sites were sampled from the

bank, using a steel trowel to skim the upper 1 cm of the

sediment column. In the PUR-guided study, two replicate

samples were collected on each sampling occasion, with the

second sample processed only if substantial toxicity was seen

in the first replicate. In the irrigation return study, a second

replicate was collected at only a few sites. All sediments were

homogenized by hand mixing, then held at 4 °C (toxicity

samples) or -20 °C (chemistry samples).

Analytical Procedures. Sediment samples were analyzed

following the methods of You et al. (5) for five pyrethroids:

cis- and trans-permethrin(summedin data presented), esfenvalerate,

bifenthrin,andlambda-cyhalothrin. Organochlorine

pesticides analyzed included alpha-, beta-, delta-, and

gamma-BHC, heptachlor, heptachlor epoxide, alpha- and

gamma-chlordane, alpha- and beta-endosulfan, endosulfan

sulfate, p,p¢- DDE, p,p¢- DDD, p,p¢- DDT, aldrin, dieldrin,

endrin, endrin aldehyde, endrin ketone, and methoxychlor.

Chlorpyrifos was the only organophosphate insecticide

quantified. Briefly, analysis was performed on an Agilent 6890

series gas chromatograph with an Agilent 7683 autosampler

and an electron capture detector (Agilent Technologies, Palo

Alto, CA).Twocolumns from Agilent, aHP-5MS,anda DB-608

were used. Qualitative identity was established using a retention

window of 1% with confirmation on a second column.

Grain size distribution was determined by wet sieving.

Total organic carbon was determined on a CE-440 Elemental

Analyzer from Exeter Analytical (Chelmsford, MA), following

acid vapor treatment to remove inorganic carbon.

Toxicity Testing. In the PUR-guided study, bulk sediments

were tested with 7-10-d old Hyalella azteca and 10-d old

larvae of Chironomus tentans, generally following the protocols

of the U.S. Environmental Protection Agency (6). The

irrigation return study samples were tested with only H.

azteca. Testing was done in 400 mL beakers containing 50-

75 mL of sediment and 250 mL of overlying water, with

continuous aeration at 23 °C and a 16 h light:8 h dark cycle.

Water was 80% replaced every 48 h using Milli-Q purified

water (Millipore Corp., Billerica, MA) made moderately hard

by addition of salts (7). Temperature, dissolved oxygen, pH,

alkalinity, hardness, and ammonia were measured at days

2 and 10 prior to water replacement. Both species were fed

by adding a slurry of 10 mg of Tetrafin Goldfish Flakes to

TABLE 1. Patterns of Pyrethroid Use in Those Counties Selected for Sampling in the PUR-Guided Studyc


annual agricultural

pyrethroid use

(kg in 2001)

crops on which most

pyrethroids used

(% of total pyrethroid

use in county)

primary pyrethroids used

on specified crop (% of

total annual pyrethroid

use on crop)

months of greatest

pyrethroid use on specified

crop (% of total annual

pyrethroid use on crop)

Fresno 14927 lettuce (32%) a permethrin (87%) Mar (31%)

cypermethrin (6%) Oct (37%)

cotton (12%) b cyfluthrin (77%) July (51%)

bifenthrin (8%) Aug (38%)

(s)-cypermethrin (7%)

lambda-cyhalothrin (5%)

alfalfa (7%) lambda-cyhalothrin (44%) Mar (32%)

bifenthrin (38%) July (33%)

permethrin (16%)

Madera 5224 pistachios (55%) permethrin (100%) May (38%)

June (28%)

July (22%)

Stanislaus 4809 almonds (46%) permethrin (79%) July (59%)

esfenvalerate (21%)

Sutter 3305 peaches (51%) permethrin (89%) May (41%)

esfenvalerate (11%) June (43%)

aHead and leaf lettuce data combined. Use of pyrethroids on head lettuce comprises 88% of total use on lettuce. b Sampling site selection was

based on pesticide use data from the year 2000, the most recent data available at the time. In that year, lettuce and alfalfa were the primary crops

in Fresno County on which pyrethroids were used, and sample sites in the vicinity of these crops were selected. A 7-fold increase in cyfluthrin

usage on cotton between 2000 and 2001 resulted in cotton moving to the second ranked crop in Fresno County in this table, based on 2001 data.

c Data from the California Department of Pesticide Regulation’s pesticide use reporting database, year 2001.

B 9 ENVIRON. SCI. & TECHNOL. / VOL. xx, NO. xx, xxxx

each beaker daily. Survival was determined after a 10-d

exposure period. Five to eight replicates per sample were

tested. Sediment from San PabloDamReservoir, El Sobrante,

CA was used as a control. Control survival averaged 91% for

H. azteca and 82% for C. tentans. Due to difficulties with H.

azteca culturing, there was a significant delay in testingmany

of the PUR peak use sample set (18% of total samples) with

this species. Testing could not be done for 5 months, with

the sediment samples maintained in the dark at 4 °C during

this time. This delay is noted below where it affects

interpretation of results.

Spiked sediment tests were done with H. azteca and/or

C. tentans to determine 10-d LC50 values for methoxychlor,

endrin, and endosulfan. Control sediment containing 1%

organic carbon was spiked with each pesticide and stored at

10 °C for 7 days before testing.

Data were analyzed using ToxCalc Version 5.0 (Tidepool

Scientific Software, McKinleyville, CA). Dunnett’s Multiple

Comparison test was used to identify stations with significantly

greater mortality than the control. Arcsin squareroot

transformation was used when necessary to meet assumptions

of normality and homogeneity of variance. Maximum

likelihood regression using probit transformation was used

when determining LC50 by dilution of test sediments.


Sediment Chemistry. The tailwater ponds (stations FL and

LL; Table 2) were the most contaminated of all sites, with

sediments containing a wide variety of pesticides. These

sediments had the highest observed concentrations of

bifenthrin (28.8 ng/g), lambda-cyhalothrin (16.8 ng/g),

permethrin (459 ng/g), and total endosulfan (571 ng/g), and

the second highest concentrations of total BHC (11.4 ng/g)

and totalDDT(384 ng/g). The ponds received tailwater from

adjacent lettuce fields, and their contents were recycled back

onto the fields with no discharge to public waters. Many

farms do not have tailwater ponds, and irrigation return flow

reaches public waters either directly or indirectly via canals.

TABLE 2. Physical Properties and Pesticide Residues in the Sediments Sampleda

station sampling time

% silt

and clay

% organic

carbon Bif Esf Lam Per


BHC total DDT Diel




Endo Met

AD2 Apr 2003 33.1 0.53 U U 1.0 7.2 U 9.2 U U U U

AD2, rep. 1 Aug 2003 67.2 2.35 U 9.7 U 15.1 2.2 20.1 U U U U

AD2, rep. 2 Aug 2003 75.7 2.38 U 12.2 U 18.7 3.1 23.6 U U U 1.1

AD5 Aug 2003 68.0 1.65 U 10.9 U 129 1.3 14.3 1.1 U U U

AD6 Apr 2003 87.6 1.80 U 5.1 U 20.7 U 15.4 1.2 962 U 2.0

AD6 Aug 2003 91.2 1.49 U 27.5 U U 1.3 13.5 1.2 U U U

AD8 Aug 2003 32.3 1.06 U 30.0 U U U 34.9 1.8 1.2 1.3 U

AD10 Mar 2003 14.0 0.47 U U U 1.3 U 1.4 U 345 U U

AD11 Mar 2003 78.7 1.25 U U U 1.4 U 17.5 U 9.2 U 1.4

AD13 Aug 2003 56.0 1.81 U U U U 8.5 2.1 U U U 1.1

AD16 Aug 2003 81.5 2.20 U U U 1.1 3.4 5.9 U U U U

AD18 Apr 2003 69.1 0.85 U U U U U 13.8 374 U U 190

AD19 Apr 2003 56.8 1.67 U U U 13.8 U 8.8 U 399 U U

AD19 Aug 2003 66.3 0.86 U U U U U 16.2 U U 1.1 9.0

AD21 Apr 2003 52.8 0.44 U U U U U 3.8 U 1.9 U U

AD24 Apr 2003 69.6 0.97 U U U U U 23.6 U 1.0 U 117

AD24 Aug 2003 54.4 1.30 U U U U U 20.1 1.3 U 2.3 8.1

DC July 2002 17.2 3.16 1.1 1.4 U 7.3 2.3 3.1 U 2.5 U 1.6

DP Aug 2002 83.7 1.09 21.0 17.9 2.6 46.9 15.8 78.5 2.6 10.1 17.7 22.7

DP, rep. 1 Mar 2003 58.9 1.40 2.8 1.9 1.0 7.4 U 48.4 1.4 U U U

DP, rep. 2 Mar 2003 35.0 0.50 U 1.4 U 3.7 U 33.2 1.3 1.4 U 1.1

FA Aug 2002 48.4 1.01 U U U 1.5 4.3 5.8 U U U U

FL, rep.1 Nov 2002 54.7 0.48 U U U 224 1.1 85.6 1.9 9.8 22.3 1.7

FL, rep. 2 Nov 2002 56.5 0.65 2.6 1.3 U 133 1.3 97.4 1.7 10.3 23.2 4.3

FL Mar 2003 72.6 0.88 U U U 14.1 U 76.1 1.2 1.2 12.6 U

FR, rep 2 July 2002 16.0 0.61 U U U 4.0 U U U U U 4.6

FS, rep. 1 Aug 2002 58.1 0.59 3.6 U 2.6 10.1 1.1 408 11.3 9.3 11.6 2.2

FS, rep. 2 Aug 2002 55.8 0.55 2.0 U 2.3 5.8 U 60.0 5.7 6.3 10.7 1.6

GS Mar 2003 36.9 1.72 U U U 5.3 U 8.0 U U U U

IC, rep.1 Mar 2003 77.9 0.80 1.4 2.2 1.6 6.8 U 228 2.7 3.5 1.7 U

IC, rep. 2 Mar 2003 49.8 1.25 U 7.3 1.5 14.1 U 155 5.3 9.2 2.3 U

JS Mar 2003 55.8 2.05 U U U 3.2 U 4.8 4.7 U 2.7 U

LL, rep 1 Nov 2002 70.2 1.00 6.5 7.0 16.8 459 11.4 371 2.9 27.7 81.5 16.4

LL, rep. 2 Nov 2002 75.1 0.76 28.8 11.6 8.3 290 7.1 257 2.3 18.1 62.5 14.7

LL Mar 2003 56.0 0.32 7.2 U 1.0 70.5 U 384 3.3 24.4 571 1.6

MA Mar 2003 60.8 1.30 8.8 U 7.8 6.0 U 61.2 1.9 U 11.3 U

MS July 2002 34.3 1.26 U 1.3 U 5.9 6.9 61.4 U U U U

MS Mar 2003 41.6 1.84 U 10.7 U 7.8 U 67.4 U U U U

RC July 2002 45.4 1.05 U 1.1 U 55.4 U U U U U 2.8

RC Mar 2003 64.8 1.40 7.7 U U 120 U 4.8 U U U U

SJ, rep. 1 July 2002 57.4 0.78 1.2 2.7 1 U U 54.5 U 2.2 2.2 6.3

SJ, rep. 2 July 2002 55.3 U 1.8 U U U 35.2 U 1.0 1.2 U

SS, rep. 2 July 2002 21.2 0.48 U U U U 1.4 3.1 U U U 1.2

TL, rep. 1 Mar 20 03 57.6 1.36 10.4 U U U U 7.5 U U 1.0 U

a Pesticide concentrations as ng/g, dry weight basis, with <1 ng/g indicated by “U”. The samples listed were in the highest 10th percentile for

the concentrations of one or more analytes and/or were found to show toxicity to one or both test species. Analytical chemistry data for all samples

is available in Table S2 of the Supporting Information. Bif ) bifenthrin, Esf ) esfenvalerate, Lam ) lambda-cyhalothrin, Per ) permethrin, Diel

) dieldrin, Endr ) endrin, Endo ) endosulfan, and Met ) methoxychlor. Total BHC ) sum of alpha-, beta-, delta-, and gamma-BHC. Total DDT

) sum of p,p¢-DDT, p,p¢-DDE, and p,p¢-DDD. Total endrin ) sum of endrin, endrin aldehyde, and endrin ketone. Total endosulfan ) sum of alphaand

beta-endosulfan, and endosulfan sulfate.

VOL. xx, NO. xx, xxxx / ENVIRON. SCI. & TECHNOL. 9 C

Nevertheless, since the lettuce tailwater ponds do not

discharge to public waters and since sediment quality in the

ponds was not typical of Central Valley surface waters in

general, their data are excluded from the remainder of these

sediment chemistry results.

At a detection limit of 1 ng/g, pyrethroids were detected

in 75% of the samples. Permethrin was the most frequently

reported pyrethroid, found in66%of the samples.Themedian

concentration was 1.5 ng/g, with highs of 129 ng/g in an

irrigation canal (AD5); 55.4 and 120 ng/g in Root Creek

adjacent to pistachio groves; and 46.9 ng/g in Del Puerto

Creek, a small creek passing through orchards and diverse

row crops. Bifenthrin was detectable in 18% of the samples,

with a maximum of 21.0 ng/g in Del Puerto Creek. Two

irrigation canals, sitesMAand TL, also contained substantial

amounts of bifenthrin (8.8 and 10.4 ng/g, respectively).

Esfenvalerate was detectable in 32% of the samples. Highest

concentrations were found in Little John Creek (30.0 ng/g),

three irrigation canals (AD2, AD5, AD6; 9.7-27.5 ng/g), Del

Puerto Creek (17.9 ng/g), and in Morisson Slough (10.7 ng/g)

in an area of peach and plum orchards. Lambda-cyhalothrin

was detectable in 12% of the samples. Maximum concentration

was 7.8 ng/g in irrigation canal sediments from an alfalfagrowing


TotalDDTwas quantifiable in almost all samples. Median

concentration was 6.9 ng/g and reached a maximum of 408

ng/g in an irrigation canal.DDEwas the principal degradation

product found, typically comprising about two-thirds of the

total DDT. Dieldrin was rarely found at concentrations more

than a few ng/g but reached 374 ng/g in one creek used for

irrigation return. Endrin also had several atypically high concentrations

(345-962 ng/g) in water bodies dominated by

irrigation return flow. TotalBHCreached 15.8 ng/g. Concentrations

of the most toxicgammaisomer ofBHCnever exceeded

2 ng/g.

Endosulfan and methoxychlor are currently used organochlorines.

Peak endosulfan concentrations were largely limited

to the ponds adjacent to lettuce fields, but 17.7 ng/g was

found in Del Puerto Creek. The most toxic form, alpha-endosulfan,

typically comprised about 10% of the total endosulfan

but reached 50% in some tailwater pond samples. Methoxychlor

concentrations were usually low but reached 117 and

190 ng/g in two water bodies with high inputs of irrigation

return flow.

Data are not presented for aldrin, alpha- and gammachlordane,

chlorpyrifos, heptachlor, and heptachlor epoxide

as they were rarely detected and were at low concentrations

when measurable (<7 ng/g).

Toxicity Testing. Sediments of the tailwater ponds not

only had the highest concentrations of many pesticides but

also proved to be highly toxic. They were the only samples

that caused statistically significant mortality in both C. tentans

and H. azteca, with total or near total mortality in both species.

A dilution series using sediments from LL (replicate 2, Nov

2002) and varying amounts of control sediments indicated

a 10-d LC50 to C. tentans of 13% LL sediment (95% confidence

interval ) 10-16%). Dilution series with sediments from FL

(replicate 2, Nov. 2002) indicated a C. tentans 10-d LC50 of

92% (c.i. ) 89-94%) and a H. azteca 10-d LC50 of 69% (c.i.

) 60-80%).

Excluding the tailwater ponds, toxicity to one of the test

species was seen in 32% of the 77 samples tested (see Table

S3 in Supporting Information). Five of the 39 samples tested

with C. tentans showed toxicity, and 20 of 71 samples were

toxic to H. azteca. No stations other than tailwater ponds

were toxic to both species. Sites with particularly high or

persistent mortality to H. azteca included Del Puerto and

Ingram Creeks and 4 irrigation canals (AD2, AD6, MA, TL).

A dilution series with the August AD6 sample provided a

10-d LC50 to H. azteca of 36% (c.i.)25-49%), and the March

MA sample indicated a 10-d LC50 of 26% (c.i. ) 18-34%).

Investigating Causes of Sediment Toxicity.Atoxicity unit

(TU) approach was used to identify pesticides potentially

responsible for observed toxicity. TU was calculated as the

actual concentration divided by the LC50, both on an organic

carbon (oc) normalized basis. Sediment LC50 values (Tables

3 and 4) for both species were estimated as follows:

Pyrethroids. Cypermethrin 10-d LC50 values average 1.3

íg/g oc (range)0.48-2.20) and 0.38 íg/g oc (range)0.18-

0.60) for C. tentans and H. azteca, respectively (8). Cypermethrin

is not one of the major pyrethroids used in our study area

and thus not among our analytes, but it is possible to use

these data to estimate sediment LC50s for other pyrethroids.

Solomon et al. (9) plotted all water toxicity data for a wide

variety of pyrethroids and noted that the 10th percentile of

the toxicity distributions is a convenient criterion for characterizing

relative toxicity. The 10th percentile LC50s for cypermethin)

10 ng/L, lambda-cyhalothrin)10 ng/L, bifenthrin

)15 ng/L, esfenvalerate/fenvalerate)37 ng/L, and permethrin

) 180 ng/L. Given the sediment toxicity of cypermethrin

and the relative toxicity of other pyrethroids, sediment LC50

values for the other pyrethroids were estimated. This

approach assumes that the other pyrethroids are comparable

to cypermethrin in the bioavailability of particle-adsorbed

residues. This assumption is reasonable, since the toxicity of

pyrethroids to benthic organisms is predictable by the

equilibrium partitioning-derived pore water concentration

(8), and the pyrethroids in this study have Koc’s comparable

to cypermethrin (10).

Two published LC50s are available as an independent

check on the estimated LC50 values. The permethrin 10-d

sediment LC50 for C. riparius is 21.9 íg/g oc (11), a value very

close to our estimated permethrin 10-d LC50 for C. tentans

(23 íg/g oc).Thelambda-cyhalothrin 28-dEC50 for emergence

of C. riparius is 6.8 íg/g oc ((12) given an oc content of the

test sediment of 3.7% provided by J. Warinton (personal

communication)), a value five times greater than our estimate

of 1.3 íg/g oc.

DDE, DDD, DDT. 10-d LC50s of DDT to H. azteca range

from 100 to 470 íg/g oc and average 260 íg/g oc (13, 14).DDD

and DDE are 5.2 and 32 times less toxic to H. azteca, respectively,

in water exposures (averaging results of refs 15 and 16),

suggesting the sediment LC50s for these organochlorine compounds

are approximately 1300 and 8300 íg/g oc, respectively.

No sediment toxicity data are available for C. tentans, but

in water exposures the species is 12 times less sensitive to

DDT than H. azteca and 4.3 and 1.3 times more sensitive to

DDDand DDE, respectively (16). These factors,whenapplied

to H. azteca sediment LC50 values, yield the C. tentans

sediment LC50 estimates of Table 3.

Dieldrin. Ten-day sedimentLC50 values for C. tentans have

been measured at 35 and 78 íg/g oc, averaging 57 íg/g oc.

Values have ranged from 1100 to 3700 íg/g oc for H. azteca

and average 2000 íg/g oc (17).

Endrin. Sediment 10-d LC50 for C. tentans was measured

as part of this study and found to be 4.22 íg/g oc (c.i. )

0.70-8.11). Ten-day sediment LC50s to H. azteca range from

54 to 257 íg/g oc and average 140 íg/g oc (13, 14). Information

on the relative aquatic toxicities of endrin and its aldehyde

and ketone degradation products was lacking, but all three

compounds were summed when determining the TUs of

endrin present. While the validity of this assumption is

unclear, it is of little consequence since at those stations

with the highest total endrin concentrations, endrin itself

comprised >85% of the total.

Methoxychlor. Methoxychlor 10-d LC50 values were measured

for this study and found to be 36.7 (c.i. ) 27.2-46.8)

D 9 ENVIRON. SCI. & TECHNOL. / VOL. xx, NO. xx, xxxx

and 85.8 íg/g oc (c.i. ) 72.1-102.6) for C. tentans and H.

azteca, respectively.

Endosulfan. C. tentans 10-d LC50 values were measured

for this study and found to be 0.96 (c.i. ) 0.41-1.46), 3.24

(c.i. ) 1.46-4.27), and 5.22 íg/g oc (c.i. ) 3.23-5.82) for

alpha- and beta-endosulfan and endosulfan sulfate, respectively.

H. azteca 10-d LC50 values were measured as 51.7 (c.i.

) 38.6-61.6), >1000, and 873 íg/g oc (c.i. ) 660-1139) for

the same compounds.

BHC.The24-h sedimentEC50 ofgamma-BHCto C. riparius

is 0.73 íg/g oc (18). This estimate is shown in Table 3 as the

best available data, although the actual 10-dLC50 for C. tentans

is likely to be less considering our 10-d exposure and the fact

that C. tentans is more sensitive to gamma-BHC than is C.

riparius (19). No sediment LC50 data were available for H.

azteca, but in 10-d water exposures, the LC50 of the species

is 75% of that of C. riparius (20), and that conversion factor

was used to derive an estimated sediment LC50 for H. azteca

of 0.55 íg/g oc. In calculating TUs present at the sampling

sites, only the sediment concentration of the gamma-isomer

wasused since other isomers ofBHChavemuchlower aquatic

toxicities (21).

In most of the 10 samples toxic to C. tentans, the TU

approach suggests that several of the measured analytes were

present in concentrations that could account for the observed

mortality (Table 3). In the tailwater pond samples (FL and

LL) where near total mortality was observed, bifenthrin,

lambda-cyhalothrin, permethrin, endrin, and endosulfan

were all in sufficient concentrations in most of the samples

so that any one of these pesticides alone could account for

the toxicity. One sample (LL, March 2003) contained 78 TUs

of endosulfan.

To account for cumulative effects of multiple pesticides,

the TUs of individual pesticides were summed to determine

a totalTUin each sample. This approach implicitly presumes

additivity of toxicity as is common among pesticides (22),

though the data do not exist to demonstrate whether specific

combinations of our analytes are greater or less than additive.

The default presumption of additivity is made more defensible

by the fact that since the organochlorines only had

appreciable TUs at a few sites, the sum TU is largely a

summation of TUs of the individual pyrethroids for which

a common mode of toxic action is more likely.

Outside of the tailwater ponds, the combined effects of

bifenthrin, lambda-cyhalothrin, and endosulfan may have

contributed to the mortality in both replicates of station FS,

since they together contribute nearly 1 TU. The combined

concentrations of endrin and endosulfan account for about

another TU at this site. DDT, dieldrin, and BHC most likely

did not contribute to the observed toxicity to C. tentans in

any sample. In 3 of the 10 toxic samples (GS, FR, DC) the

measured analytes could not account for the toxicity.

TUcalculations for samples not toxic to C. tentans are not

shown in Table 3 to conserve space, but for each analyte the

number of nontoxic samples that contained at least 0.5 TU

is shown. The 0.5 TU threshold is arbitrary but suggests a

strong likelihood that the analyte makes a substantial

contribution to the observed mortality. Bifenthrin, lambdacyhalothrin,

and endrin were the only pesticides for which

mortality was expected but not seen, with only one nontoxic

sample for each compound having g0.5 TU.

A similar TU analysis for the H. azteca toxicity data (Table

4) indicates bifenthrin, lambda-cyhalothrin, and permethrin

concentrations were sufficiently high (g0.5 TU) that each

compound individually could have had a substantial contribution

to the mortality in six of the 23 toxic samples.

Esfenvalerate concentrations were g0.5 TU in five samples.

Cumulatively, pyrethroids were likely responsible for much

of the toxicity in 17 of the 23 toxic samples. The most extreme

cases were the tailwater ponds where the combined effect

of all four pyrethroids created up to 12.9 TUs, and 98%

mortality to H. azteca was observed.

As was the case for C. tentans, the TU calculations for H.

azteca indicated that most of the legacy organochlorine

compounds were present at concentrations far too low to

account for the observed toxicity. The only exception to this

generality was endrin, which was found at 0.4 TU in one

irrigation canal toxic to H. azteca and at 0.5 TU in another

nontoxic canal sample. Among the current use organochlorines,

methoxychlor approached toxic thresholds in one creek

(Stone Corral Creek, AD18), and endosulfan may have

contributed to mortality in a tailwater pond. None of the

measured analytes could explain toxicity at AD11 and AD21.

Amongsamples without significant H. azteca toxicity there

were only rare instances of samples containing g0.5 TU of

any pesticide (one sample for lambda-cyhalothrinandendrin,

two for permethrin). The only exception was bifenthrin for

which four samples contained g0.5 TU of the compound

but were nontoxic. Nevertheless samples containing g0.5

TU bifenthrin were more than three times as likely to be

toxic than nontoxic, suggesting our bifenthrin LC50 estimate,

while perhaps slightly low, is not grossly in error. Overall, the

TABLE 3. C. tentans Toxicity Units (TU) of the Pesticide Analytes at All Stations Exhibiting Significant Toxicity to C. tentansa

toxicity units of individual pesticides

sample Mort Bif Esf Lam Per DDT Diel Endr Met Endo BHC ªTUs

LL, Nov 2002, rep. 1 100 ( 0 0.3 0.2 1.3 2.0 b b 0.7 b 4.7 b 9.2

LL, Nov 2002, rep. 2 100 ( 0 1.9 0.3 0.8 1.7 b b 0.6 0.05 3.3 b 8.7

LL, Mar 2003 100 ( 0 1.1 b 0.2 1.0 b b 1.8 b 74.6 b 78.7

FL, Nov 2002, rep. 1 98 ( 4 b b b 2.0 b b 0.5 b 1.3 b 3.8

GS, Mar 2003 62 ( 8 b b b b b b b b b b b

FL, Nov 2002, rep. 2 60 ( 17 0.2 b b 0.9 b b 0.4 b 1.0 b 2.5

FR, July 2002, rep. 2 58 ( 36 b b b b b b b b b b b

FS, Aug 2002, rep. 2 54 ( 11 0.2 b 0.3 0.05 b b 0.3 b 0.5 b 1.4

DC, July 2002 50 ( 28 b b b b b b b b b b b

FS, Aug 2002, rep. 1 44 ( 24 0.3 b 0.3 0.07 b b 0.4 b 0.6 b 1.7

# nontoxic samples

with g0.5 TU ( n)31)

1 0 1 0 0 0 1 0 0 0

LC50 used to derive

TUs (íg/g o.c.)

2.0 4.8 1.3 23 DDT ) 3100

DDD ) 300

DDE ) 6400

57 4.2 36.7 R ) 0.96

â ) 3.2

sulf ) 5.2


a Mort ) % mortality; Bif ) bifenthrin; Esf ) esfenvalerate; Lam ) lambda-cyhalothrin; Per ) permethrin; DDT ) sum TU of DDT, DDD, DDE;

Diel ) dieldrin; Endr ) endrin; Met ) methoxychlor; Endo ) sum TU of alpha- and beta-endosulfan and endosulfan sulfate; BHC ) gamma-BHC.

b <0.05 TU.

VOL. xx, NO. xx, xxxx / ENVIRON. SCI. & TECHNOL. 9 E

rarity of high TU values among nontoxic samples for all

analytes suggests our LC50 estimates are reasonable.


There have been few measurements of pyrethroids in

sediments of agriculture-influenced water bodies, and fewer

still that have incorporated toxicity testing of these sediments.

We found that pyrethroid residues can be widespread in

sediments from regions of intensive agriculture, and in some

locations are present in concentrations likely to cause toxicity

to sensitive species. The tailwater ponds represented the most

extreme instance, containing at least four pyrethroids that

were present at concentrations that, even if considered

individually, were capable of causing substantial mortality.

Sediments collected from creeks, rivers, and the irrigation

canals that discharge to them did not show the extreme

pesticide concentrations found in the tailwater ponds but

nevertheless frequently showed toxicity to the test species.

Statistically significant mortality to C. tentans or H. azteca

was observed in 32% of the 77 sediment samples tested, and

42%of the locations sampled were toxic to at least one species

on at least one occasion. Toxicity was seen on occasion in

both major rivers sampled, eight of the 19 creeks and sloughs

sampled, and seven of the 17 irrigation canals. Six sites (14%

of those tested) showed >80% mortality in a test species on

at least one occasion.

It appears the analytes we measured were at sufficient

concentrations to explain the vast majority of observed

mortality. Pyrethroids were likely to have contributed to the

toxicity in 40% of samples toxic to C. tentans and nearly 70%

of samples toxic to H. azteca (excluding tailwater ponds).

Endrin, endosulfan, and methoxychlor may have been

important in a few instances, but for the remaining toxic

samples, it was not possible to determine if pesticides or

other substances were responsible for the toxicity. There are

over 130 pesticides used in the Central Valley, and since the

concentrations of most are not measured in any monitoring

program, their contribution to toxicity is unknown.

Our toxicity data are supported by an independent study

that overlapped with two sampling locations. California’s

Central Valley Regional Water Quality Control Board sampled

the Del Puerto Creek site three times from June to October

of 2002 and found 39-100% mortality to H. azteca (J. Rowan,

personal communication), compared to our observation of

78% mortality in August 2002. The same agency sampled the

Orestimba Creek site in September 2002 and found 59%

mortality to H. azteca, compared to our determination of

60% mortality in March, 2003.

In considering the frequency of toxicity and the sediment

concentrations of pesticides, it should be recognized that

sampling for the PUR-guided study was focused on areas of

high pyrethroid use or water bodies where water quality

degradation was likely. However, the irrigation return study,

which made up half the total samples, targeted water bodies

dominated by irrigation return flow with only minimal

consideration of pesticide use or crops grown. There was a

greater frequency of toxicity in the PUR-guided study (34%

vs 27% in irrigation return study) and in the frequency of

pyrethroid detection (85% vs 65%), but the results are still

quite striking even for the return flow study with minimal

site selection bias.

While our work focused on smaller tributaries, there is

some indication of sediment quality impacts in the larger

rivers. One sample (of three) in the Feather River proved

toxic to C. tentans with the responsible agent unknown. Three

locations were sampled on the San Joaquin River: one in

July 2002 and all three in March 2003, with the July sample

showing H. azteca mortality due to unknown causes. Further

TABLE 4. H. azteca Toxicity Units (TU) of the Pesticide Analytes at All Stations Exhibiting Significant Toxicity to H. aztecaa

toxicity units of individual pesticides

sample Mort Bif Esf Lam Per DDT Diel Endr Met Endo BHC ªTUs

MA, Mar 2003 100 ( 0 1.2 b 1.6 0.1 b b b b b b 2.9

LL, Nov 2002, rep. 1 98 ( 4 1.1 0.5 4.4 6.8 b b b b 0.06 b 12.9

FL, Nov 2002, rep. 1 97 ( 5 b b b 6.9 b b b b b b 6.9

AD2, Apr 2003 97 ( 7 b b 0.5 0.2 b b b b b b 0.7

DP, Mar 2003, rep. 1 90 ( 14 0.4 0.1 0.2 0.1 b b b b b b 0.8

IC, Mar 2003, rep. 2 90 ( 14 b 0.4 0.3 0.2 b b b b b b 0.9

IC, Mar 2003, rep. 1 85 ( 13 0.3 0.2 0.5 0.1 b b b b b b 1.1

AD6, Aug 2003 85 ( 19 b 1.3 b b b b b b b b 1.3

AD2, Aug 2003, rep. 2 84 ( 9 b 0.4 b 0.1 b b b b b b 0.5

FL, Nov 2002, rep. 2 83 ( 6 0.7 0.1 b 3.0 b b b b b b 3.8

TL, Mar 2003, rep. 1 82 ( 18 1.3 b b b b b b b b b 1.3

AD2, Aug 2003, rep. 1 81 ( 18 b 0.3 b 0.09 b b b b b b 0.4

DP, Aug 2002 78 ( 16 3.4 1.2 0.6 0.6 b b b b b 0.2 6.0

LL, Mar 2003 76 ( 29 4.0 b 0.8 3.2 0.2 b 0.05 b 0.9 b 9.2

MS, Mar 2003 68 ( 33 b 0.4 b 0.1 b b b b b b 0.5

AD8, Aug 2003 67 ( 18 b 2.0 b b b b b b b b 2.0

DP, Mar 2003, rep. 2 58 ( 16 b 0.2 b 0.1 b b b b b b 0.3

AD5, Aug 2003 47 ( 27 b 0.5 b 1.2 b b b b b b 1.7

AD6, Apr 2003 39 ( 25 b 0.2 b 0.2 b b 0.4 b b b 0.8

AD18, Apr 2003 36 ( 28 b b b b b b b 0.3 b b 0.3

AD11, Mar 2003 34 ( 27 b b b b b b b b b b b

SJ, July 2002, rep. 2 34 ( 15 b 0.1 b b b b b b b b 0.1

AD21, Apr 2003 31 ( 17 b b b b b b b b b b b

# nontoxic samples

with g0.5 TU ( n)51)

4 0 1 2 0 0 1 0 0 0

LC50 used to derive

TUs (íg/g o.c.)

0.57 1.4 0.38 6.8 DDT ) 260

DDD ) 1300

DDE ) 8300

2000 140 85.8 R ) 52

â ) >1000

sulf ) 870


a Mort ) % mortality; Bif ) bifenthrin; Esf ) esfenvalerate; Lam ) lambda-cyhalothrin; Per )permethrin; DDT ) sum TU of DDT, DDD, DDE;

Diel ) dieldrin; Endr ) endrin; Met ) methoxychlor; Endo ) sum TU of alpha- and beta-endosulfan and endosulfan sulfate; BHC ) gamma-BHC.

b <0.05 TU.

F 9 ENVIRON. SCI. & TECHNOL. / VOL. xx, NO. xx, xxxx

sampling in the major rivers would be desirable to better

characterize regional impacts.

An important conclusion from these data is that legacy

organochlorines, while widely distributed in Central Valley

sediments, were far below acutely toxic concentrations to

sensitive aquatic invertebrates. The only exception to this

generalization was endrin, which was found at concentrations

of approximately half its LC50 in a few irrigation canals.

Current-use organochlorine compounds (endosulfan, methoxychlor)

were below acutely toxic thresholds in the majority

of samples, though they may have contributed to toxicity in

the tailwater ponds or a few irrigation canals where concentrations

exceeded several hundred ng/g.

The extreme toxicity of sediment-associated pyrethroids

indicates the need to improve the detection limits achieved

in this study. The sediments tested had organic carbon

contents typically about 1%, and in such sediments the H.

azteca 10-d LC50 of cypermethrin is 3.6 ng/g (8). Based on

relative toxicityamongthe pyrethroids, in the same sediment

the LC50s for bifenthrin, cyfluthrin, and deltamethrin would

be on the order of 3-6 ng/g, the LC50s for esfenvalerate or

fenvalerate would be about 10-15 ng/g, and the LC50s for

permethrin and fenpropathrin would be about 60-90 ng/g.

Excluding permethrin and fenpropathrin, these estimates of

LC50 are only slightly above the one ng/g detection limit.

Thus, mere detection of any of the more toxic pyrethroids

at least raises the possibility of acute toxicity, even without

considering that other species may be more sensitive than

H. azteca or that chronic toxicitymayoccur at concentrations

less than the 10-d LC50 used in these estimates.

The data suggest that pyrethroid concentrations in aquatic

habitats of the Central Valley tend to be greater shortly after

their use rather than after heavy winter rains. Though there

is some dormant spraying of pyrethroids on orchard crops

during winter months, most Central Valley crops treated with

pyrethroids receive the greatest amounts in the summer.

During this period, the mechanisms for transport of residues

to aquatic systems would be irrigation return and spray drift

from aerial application. Potentially pesticide-bearing soils

are washed into aquatic systems by heavy rains, largely

confined to December through March. However, pyrethroids

typically have half-livesonthe order of 1-2 months in aerobic

soils (10), providing opportunity for substantial degradation

between summer application and winter rains. In this study,

65% of the sites with measurable pyrethroids had the highest

concentrations in the late summer and fall near the end of

the irrigation season. At only 35% of the sites were concentrations

greatest in March and April at the conclusion of the

rainy season.

The prevalence of sediment toxicity in this study, and

evidence that pyrethroids were likely to be responsible for

much of it, clearly shows the need for greater awareness of

the risks of particle-associated pyrethroids. There are considerable

data on the toxicity of dissolved-phase pyrethroids

to aquatic life that have been used in developing risk

assessments for the compounds (9, 12, 23, 24), but these risk

assessments have generally focused more on the water

column than on sediments. The bioavailability and toxicity

of sediment-bound residues have received little attention,

as indicated by the difficulty in locating direct sediment LC50

measurements for the compounds of interest in this study.

The log Koc for most pyrethroids ranges from 5 to 6 (10), and

they rapidly partition on to soils or sediments (8). Except in

close proximity to and shortly after application, pyrethroids

will largely be sediment associated (26). It has been argued

that the hydrophobicity of these compounds lessens their

bioavailability (12, 25), which may be the case for organisms

living within the water column (e.g., daphnids widely used

for toxicity testing). However, results from our study indicate

a substantial risk remains to benthic organisms under realistic

conditions of agricultural use. Our study did not differentiate

whether the primary route of toxicity was exposure to

dissolved phase pyrethroids within the pore water or ingestion

and digestive desorption of particle-associated residues.

Digestive routes of contaminant uptake often take on

increasing importance for strongly hydrophobic compounds

(26), and deposit-feeder digestive fluids are usually far more

effective extractants of hydrophobic organics than is water

(27). Regardless of the route of uptake, our findings of

widespread sediment toxicity indicate pyrethroid uptake by

and toxicity to benthic organisms, and particularly depositfeeding

species, deserves closer study.


We thank Shakoora Azimi-Gaylon of the Central Valley

Regional Water Quality Control Board for making possible

our work in the irrigation return study and the Aquatic

Toxicity Laboratory of the University of California, Davis for

collecting those samples. Minghua Zhang of the University

of California, Davis kindly providedmapsof pyrethroid usage

in the Central Valley. The laboratory work was done with the

assistance of Kristina Estudillo, Kathleen London, Jessica

Newman, and Nicole Ureda. This work was supported by

grants from the CALFED Bay-Delta Authority and California

State Water Resources Control Board.

Supporting Information Available

Sampling location details (Table S1), analytical chemistry

results for all samples (Table S2), and toxicity testing results

for all samples (Table S3). This material is available free of

charge via the Internet at

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Received for review October 31, 2003. Revised manuscript

received February 26, 2004. Accepted March 1, 2004.


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