How toxic are these pesticides?
Ways toxins affect the body:
Neurotoxicity In the United States, most episodes of acute occupational poisoning are due to organophosphate and carbamate insecticide exposure.
Four common pollutants found in household dust may help make a popular bug-killer more toxic, researchers said . The insecticide, chlorpyrifos, is meant to destroy an insect's nervous system but could also have bad effects in people,the team at Johns Hopkins University in Baltimore said.
In a report in the journal Toxicology Letters, they said four common components of house dust, known as polycyclicaromatic hydrocarbons (PAHs), themselves work against the human nervous system.
When added to chlorpyrifos ( pesticide) , the chemicals increased its effects on cholinesterase, a neurotransmitter or message-carrying chemical, they reported. The four PAHs they tested are pyrene, benzopyrene, fluoranthene,and anthracene.
"When acetylcholinesterase was incubated with chlorpyrifos-oxon together with the PAHs, the inhibitory effect on acetylcholinesterase was additive," David Jett, an assistant professor of environmental health sciences at Johns Hopkins who led the study, said in a statement.
Cancers: The cumulative effects of widespread chronic low-level exposure to pesticides only partially is understood. However, mounting evidence suggests a strong correlation between pesticide exposure and the development of cancer in humans
."Of the 80,000 pesticides and other chemicals in use today, 10 percent are recognized as carcinogens. Cancer-related deaths in the United States increased from 331,000 in 1970 to 521,000 in 1992, with as estimated 30,000 deaths attributed to chemical exposure.
A recent study of pesticides and childhood brain cancers has revealed a strong relationship between brain cancers and compounds used to kill fleas and ticks. The specific chemicals associated with children's brain cancers were pyrethrins and pyrethroids (which are synthetic pyrethrins, such as permethrin, tetramethrin, allethrin, resmethrin, and envalerate), and chlorpyrifos (trade name: Dursban).
Exposure to pesticides, whether in laboratory experiments, animal studies, or epidemiologic studies in humans, clearly shows a significant effect on the immune system, such as T- and B-cell function, macrophage phagoeytosis, and host resistance (Arch Environ Health. 1993;48:81,88 and 1991;46:249-253). Pesticide use "could be a hidden killer"-especially in developing countries, where infections are a leading cause of death. ref. Robert Repetto, vice president of the Washington, D.C.-based World Resources Institute (WRI)
RACHEL'S ENVIRONMENT & HEALTH WEEKLY #648 .April 29, 1999--- .
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, 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), the 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 5-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 and 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 assess immune system function, they measured the ability of mice to make antibodies in response to foreign proteins. To assess endocrine system function, they measured thyroid hormone levels in the blood. And to assess nervous system function they measured aggressive behavior 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. They found effects on the endocrine system (thyroid hormone levels) and the immune system, and reduced body weight, from mixtures of low levels of aldicarb & nitrate, atrazine & nitrate, and atrazine, aldicarb & nitrate together. They observed increased aggression from exposure to atrazine & nitrate, and from atrazine, aldicarb & nitrate together.
The Wisconsin research team wrote, "Of particular significance in the collective work of Boyd and others, Porter and others, and our current study is that THYROID HORMONE CONCENTRATION CHANGE was consistently a response due to mixtures, but NOT usually to individual chemicals."
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 behavior are linked to thyroid hormone levels.
Interviewed recently by Keith Hamm of the SANTA BARBARA [CAL.] 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 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.
A recent study of 4 and 5 year-old children in Mexico specifically noted a decrease in mental ability and an increase in aggressive behavior among children exposed to pesticides. 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 sprayings 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.
 Jack E. Barbash and Elizabeth A. Resek, PESTICIDES IN GROUND WATER (Chelsea, Michigan: Ann Arbor Press, 1996); Richard Wiles and others, TAP WATER BLUES (Washington, D.C.: Environmental
Working Group, 1994);
 Warren P. Porter, James W. Jaeger and Ian H. Carlson, "Endocrine, immune and behavioral effects of aldicarb (carbamate), atrazine (triazine) and nitrate (fertilizer) mixtures at groundwater concentrations," TOXICOLOGY AND INDUSTRIAL HEALTH Vol. 15, Nos. 1 and 2 (1999), pgs. 133-150.
 C.A. Boyd, M.H. Weiler and W.P. Porter, "Behavioral and neurochemical changes associated with chronic exposure to low-level concentration of pesticide mixtures," JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH Vol. 30, No. 3 (July 1990), pgs. 209-221.
 W.P. Porter and others, "Groundwater pesticides: interactive effects of low concentrations of carbamates aldicarb and methamyl and the triazine metribuzin on thyroxine and somatotropin levels in white rats," JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH Vol. 40, No. 1 (September 1993), pgs.
Special risks to children's health:
Worries over pesticides and their special risks to children are well-founded. Experimental tests in lab animals have found the young to be more vulnerable than adults to the toxic effects of many chemicals simply because their bodies still are developing.
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