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Low-Level Pesticide Exposure In Utero Linked to Impacts on Behavior and Hormones

(Beyond Pesticides, November 17, 2009) According to a new study by researchers at the University of Wisconsin-Madison, exposure to low levels of the organophosphate insecticide chorpyrifos during pregnancy can impair learning, change brain function and alter thyroid levels of offspring into adulthood for tested mice, especially females. The study, “Long-term sex selective hormonal and behavior alterations in mice exposed to low doses of chlorpyrifos in utero,” was led by Beyond Pesticides board member and professor of zoology and environmental toxicology, Warren Porter, PhD.

Read the full analysis of the study on the Rodale Institute website.

On June 8, 2000, the Environmental Protection Agency (EPA) and Dow AgroSciences, reached an agreement to stop the sale of most home, lawn and garden uses for chlorpyrifos because of its health risks to children. However, its use continues in agriculture. According to advocates, this new study provides further evidence for the need to ban chlorpyrifos and fully protect farmworkers, their families, and rural communities from the toxic hazards of this outdated, unnecessary pesticide.

According to the Rodale Institute, which provided part of the funding for the study, “The new animal study accentuates the risk of ultra-low levels of the common pesticide chlorpyrifos to cause long-lasting birth defects in female offspring of exposed mothers. The daughters exhibited learning delays, disturbed brain function and altered thyroid levels. Significantly, these symptoms resulted from low toxicity exposure during late gestation—an impact route not even part of current regulatory pesticide testing. Damage at these doses highlights vulnerability during gestation from toxins even at the parts per billion level.”

The following is taken from the Rodale Institute’s analysis of the study.

Pregnant mice were injected with 0, 1 or 5 mg CPF per kg of body weight. Their offspring were evaluated for several types of learning ability in a foraging maze from the age of 60 days to 150 days of age. The mice were evaluated for their ability to find food, how fast they found it, how well they remembered where it was. Thyroid hormone levels were checked at the end of the test.

Results demonstrate “a long-term, dose dependent, sex selective impairment of foraging behavior and as well as learning latency in female mice exposed to CPF in utero.” The traces of pesticide, even at the lower 1 mg CPF/kg of body weight level, did not impact the learning ability male mice, but had significant impacts on the females. Further, the CPF dosing of their mothers did not change the serum thyroid hormone level of the male mice, but correlated directly to the mother’s dose in female offspring. The detrimental changes persisted into adulthood for the female mice.

Dr. Porter points out that most pesticide testing is done on male rats, which are probably the most resistant to showing response to toxicants, while female mice may be the most sensitive.

Females exhibite “diminished foraging ability in a dose dependant manner due to in utero CPF exposure,” the paper says. In food recognition and food position learning assessments (a novel food in a novel place), the young mice with no exposure learn at a steady rate, while the lower-dosed group takes longer to reach the same level. The higher dose group never attains the same level of success in these foraging ability tests.

The authors conclude that the study is further evidence that chlorpyrifos and all organophosphates should be evaluated for endocrine disrupting potential, and that all EPA pesticide registrations should include in utero multi-generational toxicity testing.

For more information on chlorpyrifos, see the Pesticide Gateway and the Daily News Blog archives.


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