Pesticide Action Network Updates Service (PANUPS)
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.