New Study Points to Inadequate Testing of Pesticides
March 26, 1999
A new study in the journal Toxicology and Industrial Health identifies
significant shortcomings in toxicological testing protocols currently
used to register pesticides in the United States. The five year study
suggests that combinations of commonly used agricultural chemicals
in concentrations that mirror levels found in groundwater can
significantly influence immune and endocrine systems as well as
neurological health.
"The single most important finding of the study is that common
mixtures, not the standard one-chemical-at-a-time experiments, can
show biological effects at current concentrations in groundwater,"
said Warren Porter, lead author and University of Wisconsin
professor of zoology and environmental toxicology. "Although they
frequently co-occur, tests for these compounds in combination are
very rare."
The experiments performed by Porter's group suggest that children
and the developing fetus are most at risk from pesticide-fertilizer
mixtures. Their influence on developing neurological, endocrine and
immune systems, said Porter, portend change in ability to learn and
in patterns of aggression.
The study focused on three commonly used farm chemicals:
aldicarb, an insecticide; atrazine, an herbicide; and nitrate, a
chemical fertilizer. All three are in wide use worldwide and are the
most ubiquitous contaminants of groundwater in the United States.
In the series of experiments, when mice were given drinking water
laced with combinations of pesticides and nitrate, they exhibited
altered immune, endocrine and nervous system functions. Those
changes, according to Porter, occurred at concentrations currently
found in groundwater. Effects were most noticeable when a single
pesticide was combined with nitrate fertilizer.
The apparent influence of pesticide and fertilizer mixtures on the
endocrine system, the system of glands such as the thyroid that
secrete hormones into the bloodstream, may also result in changes
in the immune system and affect fetal brain development. "Thyroid
disruption in humans has multiple consequences," Porter said. Some
of these include effects on brain development, level of irritability,
sensitivity to stimuli, ability or motivation to learn and altered immune
function.
A curious finding of the study is that animals may be more vulnerable
to the influence of such chemicals depending on the time of year:
"Our current working hypothesis is that animals are seasonally
vulnerable because of subtle modulation of natural seasonal
variation in hormone levels," according to Porter.
Need for new testing methods
The new study, Porter contends, adds to a growing body of evidence
that current testing methods required for the registration and use of
chemical pesticides in the U.S. are fundamentally flawed. The study
listed six important deficiencies in current testing protocols:
* Current tests do not require chemicals to be tested at low dose
pulse exposure. Pulse doses of low levels of pesticides at critical
times when developmental windows are open and body defenses
are unable to respond may lead to permanent changes in a fetus. It
is important to remember that the embryo has almost no defensive
systems against chemicals and no feedback systems to modulate
chemical concentrations early in its development.
* Toxicological tests have typically focused on cancer and mutation
endpoints and have not looked at other critical concerns such as
endocrine and immune system effects that can occur.
* Standard toxicological tests only evaluate one route of exposure at
a time, rather than all possible routes (oral, cutaneous and
respiratory).
* Most testing is done with pure forms of pesticidal active ingredients
rather than with commercial formulations. There are three types of
chemical additives that are missing from most testing: contaminants
of manufacturing processes, toxic waste deliberately added from
chemical reactor cleaning processes and "inert" ingredients.
* Current testing requirements do not evaluate exposure effects from
chemical mixtures. While it is impossible to examine all possible
mixtures, common combinations generated in specific areas due to
crop rotation and tillage practices could be examined.
* Laboratory animals generally live in an environment where climate,
nutrition and disease are carefully controlled. Researchers know that
when additional stresses are present, toxic responses to registered
chemicals occur that do not appear under current standard testing
procedures.
Sources: Warren Porter, et al., "Endocrine, immune and behavioral
effects of aldicarb (carbamate), atrazine (triazine) and nitrate
(fertilizer) mixtures at groundwater concentrations," Toxicology and
Industrial Health (1999) 15, 133-150. University of Wisconsin-
Madison press release, March 15, 1999.
Contact: PANNA.
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