APPENDIX II-S: Communities Reject Adulticiding.
TO AMEND THE
FEDERAL WATER POLLUTION CONTROL ACT (33 U.S.C. 1342(1))
aka CLEAN WATER ACT
SUBCOMMITTEE ON WATER RESOURCES AND ENVIRONMENT
APPENDICES A - D
In 2003 the city of
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
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
landmass, used only larvicides and had 20 cases of WNv and 1 fatality.3
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
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
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.
Hhttp://www.yorkcounty.gov/eds/fishhatchery.htmH (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
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.
Hhttp://www.fortworth.gov/health/HP/mosqinees.aspH (viewed July 6, 2004)
8 Turrillion, G. 2002. Director of Mosquito Control Program in Nassau County, NY. Personal
9 Town of Marblehead, MA West Nile Virus Protocol and Response Plan. 2002.
Hhttp://www.beyondpesticides.org/mosquitoH (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.
Hhttp://www.cityofseattle.net/environment/Documents/WNV%20IPM.pdfH (July 2, 2004)
West Nile Virus and Mosquito Control
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
The prime reservoir of West Nile is the bird population. At
least 125 species of birds have been reported infected with
West Nile, 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, the great majority associated
with West Nile were Culex pipens. 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
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.
MOSQUITO LARVAL CONTROL
The CDC advises that mosquito control should focus
primarily on mosquito larval control and secondarily on
the less efficient adulticiding. 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.
ADULT MOSQUITO CONTROL
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
ULTRALOW VOLUME SPRAYING
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%. 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. Then in Cicero Swamp, FL, populations of
disease-carrying mosquito populations increased 15-fold
after spraying, 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.
Insecticide Effectiveness in Reaching
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. 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
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
Various adult mosquito traps and zappers are sold to
homeowners for control, but rarely do these units provide
continuous satisfactory control of mosquitoes. 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. For some individuals, the DEET
pesticide is reported to cause allergic reactions and may
interfere with the immune and endocrine systems for
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. http://www.environmentaldefense.org/
West Nile Virus and Mosquito Control 3
2. CDC. West Nile Virus: Statistics, Surveillance, and
Control; Centers for Disease Control: Atlanta, 2002.
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. http://skipper.physics.sunyb.edu/
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.
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. http://www.mosquitobuzz.com/control/
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
[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.
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
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
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
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, firstname.lastname@example.org, 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; www.cdpr.ca.gov). 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@ berkeley.edu.
† 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
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,
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
(kg in 2001)
crops on which most
(% 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%)
alfalfa (7%) lambda-cyhalothrin (44%) Mar (32%)
bifenthrin (38%) July (33%)
Madera 5224 pistachios (55%) permethrin (100%) May (38%)
Stanislaus 4809 almonds (46%) permethrin (79%) July (59%)
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
carbon Bif Esf Lam Per
BHC total DDT Diel
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
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
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.
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.
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
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
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
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 http://pubs.acs.org.
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Received for review October 31, 2003. Revised manuscript
received February 26, 2004. Accepted March 1, 2004.
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