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Pesticides, Children & Aggression

Peter Montague

For the past 25 years, tens of millions of Americans in hundreds of cities and towns have been drinking tap water that is contaminated with low levels of insecticides, weed killers, and artificial fertilizer. They not only drink it, but they also bathe and shower in it, thus inhaling small quantities of farm chemicals and absorbing them through the skin. Naturally, the problem is at its worst in agricultural areas of the country.

The most common contaminants are carbamate insecticides (aldicarb and others), and triazine herbicides (atrazine and others), and nitrate nitrogen. For years government scientists have tested each of these chemicals individually at low levels in laboratory animals – searching mainly for signs of cancer – and have declared each of them an “acceptable risk” at the levels typically found in groundwater.

Now a group of biologists and medical researchers at the University of Wisconsin in Madison, led by Warren P. Porter, has completed a five-year experiment putting mixtures of low levels of these chemicals into the drinking water of male mice and carefully measuring the results. They reported recently that combinations of these chemicals – at levels similar to those found in the groundwater of agricultural areas of the U.S. – have measurable detrimental effects on the nervous, immune and endocrine (hormone) systems. Furthermore, they say their research has direct implications for humans.

Dr. Porter and his colleagues point out that the nervous system, the immune system, and the endocrine (hormone) system are all closely related an in constant communication with each other. If any one of the three systems is damaged or degraded the other two may be adversely affected. The Wisconsin researchers therefore designed their experiments to examine the effects of agricultural chemicals on each of the three systems simultaneously. To access immune system function, they measured the ability of mice to make antibodies in response to foreign proteins. To access endocrine system function, the measured thyroid hormone levels in the blood. And to access nervous system function they measured aggressive behaviour in the presence of intruder mice introduced into the cages. They also looked for effects on growth by measuring total body weight and the weight of each animal’s spleen.

The experiments were replicated many times, to make sure the results were reproducible. The found effects on the endocrine system (thyroid hormone levels) and the immune system, and reduced body weight, from mixtures of low levels of aldicarb and nitrate, atrazine and nitrate, and atrazine, aldicarb and nitrate together. They observed increased aggression from exposure to atrazine and nitrate, and from atrazine, aldicarb and nitrate together.

In the five-year experiment, thyroid hormone levels rose or fell depending upon the mixture of farm chemicals put into the drinking water. Dr Porter and his colleagues present evidence from other studies showing that numerous farm chemicals can affect the thyroid hormone levels of wildlife and humans. PCBs and dioxins can have similar effects, they note. Proper levels of thyroid hormone are essential for brain development of humans prior to birth. Some, though not all, studies have shown that attention deficit and/or hyperactivity disorders in children are linked to changes in the levels of thyroid hormone in the blood. Children with multiple chemical sensitivity (MCS) have abnormal thyroid levels. Furthermore, irritability and aggressive behaviour are linked to thyroid hormone levels.

Interviewed recently by Keith Hamm of the Santa Barbara Independent, Dr. Porter explained. “Earlier work had shown that thyroid hormone typically changed when exposure to these pesticides occurred. Thyroid hormone not only affects and controls your metabolic rate, that is, how fast you burn food, it also controls your irritability level. For example, Type A personalities are more assertive, more aggressive, more hyper. These people tend to have higher levels of thyroid hormone. Type B personalities – people that are really laid back, really take things very easily – have lower levels of thyroid hormone. We expected that changes in thyroid [would] change in irritability levels. This was a concern because there was information that kids are getting more hyper and [that their] learning abilities are going down,” Dr. Porter said.

In the interview with Keith Hamm, Dr. Porter expressed concern for the overall effect of pesticides on the nation’s children:

Hamm: “I would assume that most people in this country are eating conventionally grown food. If that’s the case, wouldn’t the problems be more apparent? Why are there not more hyperaggressive dim-witted people with poor immune systems?”

Porter: “If we really looked carefully at what’s been happening in this county, you might find exactly that happening.”

Because of recent violence in small cities and towns (such as Littleton, Colorade, Laramie, Wyoming, and Jasper, Texas), this is a time when Americans are searching for the causes of violence in their society. Some are blaming a decline in religious upbringing. Others are blaming households with the parents working and no one minding the kids. Some say the cause is violent movies, violent TV, and extremist internet sites, combined with the ready availability of cheap guns. Still others point to a government that has often sanctioned the violence of “gunboat diplomacy” to open foreign markets for U.S. corporations.

No one seems to be asking whether pesticides, fertilisers, and toxic metals are affecting our young people’s mental capacity, emotional balance, and social adjustment.

From the work of Warren Porter, Elizabeth Guillette [see below], and others, it is apparent that these are valid questions.

Pesticides and Children: A Case Study

A recent study 4- and 5-year-old children in Mexico specifically noted a decrease in mental ability and an increase in aggressive behaviour among children exposed to pesticides (“An Anthropological Approach to the Evaluation of Preschool Children Exposed to Pesticides in Mexico,” Environmental Health Perspectives, June 1998). Elizabeth A. Guillette and colleagues studied two groups of Yaqui Indian children living in the Yaqui Valley in northern Sonora, Mexico. One group of children lives in the lowlands dominated by pesticide-intensive agriculture (45 or more spraying each year) and the other group lives in the nearby upland foothills where their parents make a living by ranching without the use of pesticides. The pesticide-exposed children had far less physical endurance in a test to see how long they could keep jumping up and down; they had inferior hand-eye coordination; and they could not draw a simple stick figure of a human being, which the upland children could readily do.

Notably, in the Guillette study we find this description of the behaviour of pesticide-expose children: “Some valley children were observed hitting their siblings when they passed by, and they became easily upset or angry with minor corrective comment by a parent. These aggressive behaviours were not noted in the [pesticide-free] foothills [children].” – P. Montague