APPENDIX
II-AG: Synergy – Blood Brain Barrier – Kepner.
This
article cites: 5 Abou-Donia,
M. B., et al. 2001. Effects of daily dermal application of
DEET and permethrin,
alone and in combination, on sensorimotor
performance, blood-brain barrier, and blood-testis barrier in rats. Journal of Toxicology and Environmental Health 62:523-541.This
article states: “The neurological indicators included: sensorimotor
performance and permeability of the blood-brain barrier,5”
This article is from:
http://www.beyondpesticides.org/infoservices/pesticidesandyou/Winter%2003-04/Synergy.pdf
Beyond Pesticides/National Coalition Against
the Misuse of Pesticides
Vol. 23, No. 4, 2004 Pesticides and You Page 17
Synergy: The Big Unknowns of
Pesticide Exposure
Daily combinations of pesticides and pharmaceuticals untested
By John Kepner
Pesticide exposures in the real world are not isolated
incidents.
Rather, they are a string of incidents marked by
combinations of
exposures. As a result, scientists have argued for years that
toxic
exposures to pesticides should be measured as they would normally
occur, in combination with one another. Yet, current federal
law does not require this type of testing for pesticides on
the
market, except in very limited instances. This issue has been
fueled
during the recent
by researchers at
Medicine, who found that exposure to a popular
insect repellent when combined with
exposure to a popular insecticide caused
a synergistic, or magnified, effect greater
than the individual chemical effects
added together. The debate has also
heated up around the question of potential
interactions between pesticides and
pharmaceuticals. A law requiring the testing
of drug-pesticide combinations was adopted
by Congress and then dropped by the Food and
Drug Administration (FDA) in the
1960’s.
How much do we really know about the
pesticides that are widely used in our communities,
schools, homes, offices, hospitals,
parks, on lawns and golf courses and in West
Not as much as we should to be able to
make sound decisions that are protective of public
health and the environment. Sometimes limitations in protection
are a function of a regulatory failure to carry out the
mandate of
a federal statute. But, in this case, the underlying
statutes that
govern pesticide use, allowable residues (and exposure), and
risk
assessment are wholly deficient. The laws simply do not require
testing that is ultimately essential in determining the safety
of
pesticide use, as typically used every day. No amount of improved
enforcement of law or additional dollars for EPA will correct this
situation until the mandates in law change.
This piece by John Kepner
tracks the current situation and history
on this critical issue of public health and safety. It
leaves us
with a greater sense of the importance of efforts to
eliminate on a
daily basis exposure to pesticides and opt for alternative
pest management
approaches that do not rely on pesticides. The burden
must shift to those who want to use pesticides to show that
basic
questions of health protection have been answered. Pointing to a
pesticide label or citing an EPA pesticide product registration is
no
assurance of safety. —JF
lntroduction
In the summer of 2001, the mosquito-borne
hit
Maryland Departments of Health and Agriculture worked
together to monitor, treat, contain and eradicate the disease.
Permanone, a synthetic pyrethroid-based
insecticide
containing the active ingredient permethrin,
emerged as
the pesticide of choice for combating the adult
mosquitoes that could be carrying the virus. Aside
from spraying Permanone from
foggers mounted
on the backs of trucks, the state also instructed
its residents to empty standing water on
their property to reduce mosquito
breeding grounds, and encouraged
residents to use mosquito repellants
containing the active ingredient N, Ndiethyl-
m-toluamide (DEET).
Both DEET and permethrin are
registered
as pesticides by the Environmental
Protection Agency (EPA) and
have been, or are in the process of being,
individually tested for adverse health effects.
Based on these results, EPA has determined that
the risks posed by these pesticides do not outweigh
the benefits, namely killing and repelling mosquitoes.
However, many of the residents of
to these pesticides individually. Real world pesticide exposures
rarely occur as individual, isolated incidents. Many residents
could have applied DEET to their bodies as recommended
by the state when the mosquito trucks fog their neighborhoods.
Or because permethrin has a
half-life of 30 to 38 days, they
could be exposed to the combination anytime they are wearing
DEET for weeks to come. Although not all pesticide combinations
show increased toxicity, recent studies out of Duke
University’s
synergistic effects of this particular pesticide combination. These
studies will be discussed in greater detail below.
What is synergy?
The concept of interaction is fundamental to understanding
the processes by which chemical mixtures act. If the effect
is
simply additive, the sum of the effects is the same as if we
were
exposed to each chemical individually. Synergy occurs when
Beyond
Pesticides/National Coalition Against the Misuse of
Pesticides
Page 18 Pesticides and
You Vol. 23, No. 4, 2004
the effect of a mixture of chemicals is greater than the sum
of
the individual effects.1 (If the effect of a mixture is less
than the
sum of the individual effects, it is called antagonism).
For example, a population exposed to neither “Pesticide
A” nor “Pesticide B” experiences a background level
of a certain health effect at 5%. In a population exposed
only to “Pesticide A,” the effect is seen at 10%
(5% + the 5% background). In a population exposed
only to “Pesticide B,” the effect is seen at 20% (15%
+ the 5% background). If the two
pesticides are simply
additive, and not synergistic, we would expect
the effect to be observed at 25% (5% + 15% + the
5% background). If the observed effect is greater
than 25%, the combination is synergistic.
Prior to 1957, the combined effects of exposure
to a group of pesticides was assumed to be additive.
However, a study2 published that year documented
for the first time a case of pesticide synergy. The authors
postulated that the combined effects of exposure
to the organophosphate insecticides ethylpnitrophenyl
benzenethiophosphate (EPN) and
malathion would be additive. Instead, there was a 10-
fold synergistic effect in rats and a 50-fold synergistic
effect in dogs for the acute toxicity of EPN and
malathion administered simultaneously.
Regulatory history
Faced with potential interactions between pesticides and
pharmaceuticals,
the Food, Drug and Cosmetic Act was amended
with the following in 1962: “Pesticide chemicals that cause
related pharmacological effects will be regarded, in the absence
of evidence to the contrary, as having an additive deleterious
action. For example, many pesticide chemicals within
each of the following groups have related pharmacological
effects: chlorinated organic pesticides, arsenic-containing
chemicals, metallic dithiocarbamates,
cholinesterase-inhibiting
pesticides.” While this language assumed only additive
and not synergistic effects, it still considered, for the
first time,
the adverse impact of cumulative chemical exposures.
However,
in 1967, FDA abandoned the regulation on the grounds
that the “requirement has failed to serve any useful
purpose.”
During its first 85 years, federal pesticide law did not
require
testing for adverse health effects of pesticide combinations.
In 1996, EPA was required for the first time to consider
cumulative pesticide exposures in limited circumstances
under the Food Quality Protection Act (FQPA). FQPA,
which
amends the Federal Insecticide, Fungicide and Rodenticide Act
(FIFRA), recognizes that real-world pesticide exposures
do
not occur as single discrete exposures to a specific
pesticide,
but rather in combination to several pesticides at once.
Considering
dietary exposure alone, U.S. Department of Agriculture
(USDA) data shows that apples surveyed from across
the U.S. contained 22 different pesticide residues, and
peaches
surveyed contained 40 different pesticide residues. Many of
these residues remain even after thorough washing and
preparation
of food.
To address the issue of multiple pesticide exposures,
FQPA
directs EPA to consider combinations of pesticides that have a
common mechanism of toxicity when setting tolerances. This
means that only if EPA determines that two chemicals have
the same toxic mechanism in the body will the agency
aggregate the exposure value in its risk assessment calculation.
The first result of this mandate was released
in June 2002 when EPA published its Revised Organophosphate
Cumulative Risk Assessment,14 in which
the agency examined the combined hazard of exposure
to all organophosphate pesticides. Although
the report was seen as incomplete by the environmental
community and criticized by FIFRA’s
Scientific
Advisory Panel, the intent of the report is an
important first step in evaluating the combined effects
of several pesticides. Unfortunately, the current
Guidance on Cumulative Risk requires that only chemicals
sharing both a common toxic effect and a common
mechanism of toxicity be considered in determining
pesticide tolerances. In the real world, a liver
cannot tell the difference between two cancer-causing
chemicals because of the biochemical route each chemical
takes to cause that cancer. In other words, if a number
of pesticides and other substances cause liver cancer via a
number of different pathways, the end result is the same,
a
diseased liver. EPA should not use common mechanisms of
toxicity as a filter to decrease the number of chemicals it
considers.
This leaves the majority of potential pesticide
interactions
untested and potentially dangerous.
Medical studies: proof
of
pesticide synergy
While the first study showing pesticide synergy was
published
in 1957, the topic has not been studied at the level necessary
to adequately inform officials making decisions regarding
human health. Despite the lack of depth, many studies
demonstrating
synergy between pesticides and other commonly
used chemicals have been documented in medical literature.
In the late 1960’s and early 1970’s, researchers Samuel
Epstein,
MD, at the time with the Children’s Cancer Research
Foundation
in Boston, MA and Keiji Fujii,
MD, of the National
Institute of Hygienic Sciences in Tokyo, Japan published
a
series of papers3,4 on the synergistic effects of carcinogens
and
co-carcinogens found in a variety of common pesticide products.
“Co-carcinogens” is a term used to describe
non-carcinogenic
chemicals that increase the rate of cancer when used
in combination with carcinogens. These papers highlighted
carcinogenicity between two chemicals used in combination,
even when the individual dosages were applied at
sub-carcinogenic
levels. One study produced the effect even when the
chemicals were applied as far as 200 days apart.
Much of the latest research on the synergistic effects of
pesticides
used in combination has come out of the Duke University
Medical Center in Durham, NC. In 2001, researchers in
the Department of Pharmacology and Cancer Biology published
Beyond
Pesticides/National Coalition Against the Misuse of
Pesticides
Vol. 23, No. 4, 2004
Pesticides and You Page 19
a
series of papers in the Journal of Toxicology and Environmental
Health and Experimental
Neurology looking closely at the synergistic
health effects of DEET, the active ingredient in most
insect repellents, and permethrin, a
pesticide commonly used
in community mosquito spray programs, as well
as many household bug killers.
To determine the effect of subchronic
dermal
application of these chemicals on the brain,
the researchers evaluated neurological indicators
after daily dermal doses of DEET,
permethrin or a combination of the two pesticides
for varying periods of time, from 24 hours
to 60 days. The neurological indicators included:
sensorimotor performance and permeability of
the blood-brain barrier,5 increased urinary excretion
of 6B-hydroxycortisol (a marker chemical
poisoning),6 release of brain mitochonrial
cytochrome-
c
(a result of cell death)7, and diffuse
neuronal cell (cells specialized to conduct nerve
impulses) death and cytoskeletal
(structural components of the
cell) abnormalities.8 In the first study, DEET alone caused a
decrease in the permeability of the blood-brain barrier and
impairment
of sensorimotor performance, and permethrin alone
showed no effect. In combination, the effect on the blood brain
barrier and sensorimotor performance
was amplified, a “0+1=2”
example of pesticide synergy. This “0+1=2” pattern was also
seen in the study examining increased urinary excretion of 6Bhydroxycortisol.
When the researchers looked
at the release of cytochrome c as an indicator
of brain cell death, no effect was seen when
the pesticides were used individually. However
in combination, a significant increase in
the release of cytochrome c was
seen 24 hours
after dosing, a “0+0=1” example of pesticide
synergy. In the study examining neuronal cell
death, damage was seen in all treatment
groups, but was accelerated in rats treated with
both DEET and permethrin.
The purpose of the Duke studies was to
determine a possible link between pesticides
and other chemicals used during the Persian
Gulf War and “Gulf War Syndrome,” neurological
disease characterized by headache, loss of memory,
fatigue, muscle and joint pain, and ataxia, which causes an
inability to coordinate muscular movements. The first work
in this area by this team of researchers, published in 1996,
studied the combination of DEET and permethrin
with pyridostigmine
bromide, a drug taken prophylactically
to counteract
toxic gas warfare agents.9 The study found that test animals
exposed to the three chemicals in combination experienced
neurological deficits similar to the symptoms of the
Gulf War veterans. However, when the chemicals were
administered
alone, even at doses three times the level soldiers
received, no effects were observed, a “0+0+0=1” effect. The
researchers theorized that many of the symptoms might be
seen without the pyrido-stigmine
bromide and continued to
study the interactions of DEET and permethrin.
Neurology experts give three possible reasons for the
synergistic
effects seen in the above experiments. First, the stress endured
by animals when exposed to a combination of chemicals
undermines the protective role of the blood brain barrier, allowing
the level of toxics to cross into the brain to be 100 times
higher. Second, tissue that has been exposed becomes more
sensitive
and receptive to other toxic substances. Third, certain
chemicals bind to enzymes that detoxify the body, making the
enzymes unavailable to protect the body from other intruding
chemicals. Dr. Goran Jamal, a
neurologist at the
makes the following comparison, “It’s like releasing 200
criminals in
usually on duty. There is bound to be some damage.”
Conclusion
Synergistic effects between multiple pesticides and/or
other
chemicals represent one of the greatest gaps in EPA’s ability to
protect the public from the adverse health effects associated
with pesticide use and exposure. The
that pesticide exposures occur in combinations and not
as unique events, yet has rules and regulations to test only a
Pesticide-Drug Synergy
In the summer of 1985, 30 year-old Thomas Latimer
was leading a good life in the suburbs of
was a vigorous, athletic man with a promising engineering
career. On one particular Saturday afternoon,
Mr. Latimer spent the day mowing the lawn, picking
up the clippings and edging the walkways. After about
an hour, he began to feel dizziness, nausea, tightness
in his chest and a pounding headache. Ten days later,
he felt even worse and went to see his doctor.
Over the next six years, Mr. Latimer found himself
unable to exercise and suffering from brain seizures.
He visited 20 different doctors and underwent numerous
tests to determine the source of his medical problems.
His symptoms were consistent with organophosphate
poisoning, most likely from the insecticide
diazinon that had been applied to his lawn. But because
his symptoms were so severe and the amount of
pesticide he was exposed to was so low, the doctors
continued to look for a complicating factor. After further
research, a toxicologist, three neurologists and two
neuro-ophthalmologists all concluded independently
that the popular ulcer drug Tagamet
that Mr. Latimer
was taking had suppressed his liver, making him more
susceptible to pesticide poisoning.
Alfredo A Sudan, a professor of neurology and
ophthalmology
at the
conducted extensive tests evaluating an eye disorder that
Mr. Latimer developed, estimates that taking a medication
like Tagamet “can make a person 100
to 1,000 times
more sensitive to organophosphate poisoning.”10
Beyond
Pesticides/National Coalition Against the Misuse of
Pesticides
Page 20 Pesticides and
You Vol. 23, No. 4, 2004
limited number of possible interactions. Given that there are
over 875 active ingredients currently registered for use, it
would be impossible to test all possible combinations, but we
must start somewhere. One approach would be to prioritize
pesticides most likely to act in combination. The following
recommendations would serve as a basis for beginning to look
at this very important aspect of pesticide safety:
■ Test for interactions
between pesticides commonly
used in combination in
both agricultural
and non-agricultural
settings. This would include
testing of groups of pesticides that are commonly used on
the same crops, like atrazine and chlorpyrifos, the most
common herbicide and insecticide applied to corn.11 Another
example would be DEET, used as an insect repellent
and permethrin, used as a mosquito
fog.
■ Test for interactions
between agricultural pesticides
and the most persistent
food contaminants.
FDA data shows chlordane, DDE (a breakdown product
of DDT), DDT, dieldrin, dioxin, endrin, heptachlor,
hexachlorobenzene, and toxaphene are frequent
contaminants
of the typical
■ Test for interactions
between the pesticides that
most commonly contaminate
drinking water. Like
all pesticide use patterns, water contamination will vary
greatly around the country, so it is imperative that these
combinations are tested for synergistic effects. The
State Laboratory of Hygiene has found 14 different
pesticides contaminating state water supplies.13
■ Test pesticides that
are most likely to drift and
cause non-target exposure. Based on formulations
and methods of application, pesticides often drift far from
their point of application. A July 2000 survey of air samples
Endnotes
For a fully cited version of this article, see www.beyondpesticides.org.
1 Working Group on Synergy in Complex Mixtures,
Public Health. 1986. Synergy: positive interaction among chemicals in
mixtures. Journal of Pesticide Reform, Summer.
2 Frawley, J.P., et al. 1957.
Marked potentiation in mammalian toxicity
from simultaneous administration of two anticholinesterase
compounds.
J. Pharmacol. Exper. Therap. 121:96-106.
3 Epstien,
Samuel S., et al. 1967. Synergistic
toxicity and carcinogenicity
of freons and piperonyl
butoxide. Nature, 214:526-528.
4 Epstein, Smauel
S. and Keiji Fujii. 1970. Synergism in Carcinogenesis
with particular reference to synergistic effects of piperonyl butoxide and
related insecticidal synergists. Chemical
Tumor Problems. Ed. Nakahara,
5 Abou-Donia,
M. B., et al. 2001. Effects of daily
dermal application of
DEET and permethrin, alone and
in combination, on sensorimotor performance,
blood-brain barrier, and blood-testis barrier in rats. Journal
of
Toxicology and Environmental Health 62:523-541.
6 Abu-Qare, Aqel W. and Mohamed B. Abou-Donia. 2001. DEET (N,N-Diethyl-
m-Toluamide) alone and in
combination with permethrin increased
urinary excretion of 6B-hydroxycortisol in rats, a marker of
hepatic cyp3a
induction. Journal of Toxicology and Environmental Health 64:373-384.
7 Abu-Qare, Aqel W. and Mohamed B. Abou-Donia. 2001. Combined exposure
to DEET (N,N-Diethyl-m-Toluamide) and permethrin-induced
release of rat brain mitochondrial cytochrome
c. Journal of Toxicology
and Environmental Health 63:243-252.
8 Abdel-Rahman,
Ali, et al. 2001. Subchronic
Dermal Application of N,NDiethyl
m-Toluamide (DEET) and Permethrin to Adult
Rats, Alone or
in Combination, Causes Diffuse Neuronal Cell Death and Cytoskeletal
Abnormalities in the Cerebral Cortex and the Hippocampus,
and Purkinje
Neuron Loss in the Cerebellum. Experimental Neurology 172:153-171.
9 Abou-Donia, M.B., et. al. 1996. Neurotoxicity
resulting from coexposure
to pyridostigmine bromide, DEET, and permethrin: Implications of Gulf
War chemical exposures. J. Toxicol. Environ. Health
48:35-56.
10 Allen, Frank Edward. 1991. One Man’s Suffering Spurs
Doctors to Probe
Pesticide-Drug Link. The Wall Street Journal.
October 14.
11
Field Crops Summary. < http://usda.mannlib.cornell.edu/reports/nassr/
other/pcu-bb/agcs0502.txt>
12 Schafer, K. S. and S. E. Kegley. 2002.
Persistent toxic chemicals in the
13
water.
<http://www.slh.wisc.edu/ehd/pamphlets/pesticide.html>
14 Environmental Working Group. 2001. Every breath you take: airborne
pesticides in the
everybreathyoutake/everybreath.pdf>
15 Cecchine, Gary, et. al. 2000. Review of the
Scientific Literature as it Pertains
to Gulf War Illnesses, Volume 8: Pesticides.
in
carbaryl, chlorpyrifos and
trifluralin.14
■ Test interactions
between the most common pharmaceuticals
and the most common
pesticides. According
to the National Defense Research Institute, DEET
has been reported to accelerate the dermal absorption of
pharmaceuticals and possibly other pesticides.15
Recognizing the unlikely reality of testing even the most
common
pesticide combinations, another approach would be to
reduce pesticide risk by limiting exposure. When weighing
the benefits of a pesticide against the risks to public
health,
we must err on the side of safety. In registering pesticides,
EPA should assume interactions between chemicals will
occur.
Limiting exposure, and therefore
limiting synergistic
health effects, could be accomplished through decreased
pesticide
use and tighter restrictions to minimize pesticide drift
and runoff. For example, ban drift-prone application
technologies,
like cropdusting and ultra-low
volume foggers; establish
buffer zones around populated areas; require notification
to nearby residents before a pesticide application, so
appropriate precautions may be taken; and encourage lower
exposure formulations such as containerized baits. By taking
the appropriate steps, we could minimize harmful synergistic
health effects.
Overall, this deficiency in data and the difficulty
associated
with its collection calls for a national policy of pesticide
use reduction and national adoption of the Precautionary
Principle
that seeks to avoid pesticide use in favor of alternatives.
John Kepner, project director
at Beyond Pesticides, has been with
the organization since 1999. He graduated with a B.S. in
biology
from
Relations in 1998.