New study points to inadequate testing of pesticides

June 23, 1999

New study points to inadequate testing of pesticides

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 ground water 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 ground water", 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 foetus are most at risk from pesticide-fertiliser 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, a herbicide; and nitrate, a chemical fertiliser. All three are in wide use worldwide and are the most ubiquitous contaminants of ground water in the United States.

In the 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 ground water. Effects were most noticeable when a single pesticide was combined with nitrate fertiliser.

The apparent influence of pesticide and fertiliser mixtures on the endocrine system may also result in changes in the immune system and affect foetal 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.

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 US are fundamentally flawed.

[From Pesticide Action Network Updates Service.]

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