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Poisoning young minds? Methyl parathion may be linked to neurodevelopment problems.

Imagine a kindergartener who has difficult), remembering the story just read to her, who cannot sit still and gets angry, easily, and who can't seem to maneuver playground equipment as easily as other children. These are some examples of short-term memory loss, attention problems, and impaired motor function that can be caused by exposure to organophosphates, a group of chemicals that interfere with the transmission of nerve signals to muscle cells. In a study of children who were exposed to the organophosphate methyl parathion in the 1990s, Perri Zeitz Ruckart of the Agency for Toxic Substances and Disease Registry and colleagues find evidence that such exposure may contribute to neurobehavioral problems in children [EHP 112:46-51].

Methyl parathion is licensed only for use as an insecticide on certain crops in open fields. However, during the 1990s, this cheap, persistent, effective pesticide was used illegally for indoor cockroach control in homes in Alabama, Arkansas, Illinois, Louisiana, Michigan, Mississippi, Ohio, Tennessee, and Texas. Before this study, little was known about the effects of the chemical in children, as most research had been conducted on occupationally exposed adults.

The researchers examined study cohorts in Mississippi and Ohio. The children in each group, who were identified by their respective state health departments, were aged 6 years or younger when their homes were sprayed with methyl parathion. Exposure status was based on environmental wipe samples from inside the homes and biomarker levels for exposure in urine specimens. Residences in Mississippi were sprayed between 1994 and 1996, and tests to determine the extent of exposure were conducted in 1996 and 1997. The Ohio homes were sprayed between 1991 and 1994, and exposure monitoring tests were conducted in 1994. Groups of unexposed children the same age from the same localities provided a comparative control.

In 1999, all 279 children in the two cohorts took a standardized battery of tests to measure performance in learning, motor skills, and sensory perception. Parent interviews and questionnaires provided additional information for evaluating cognitive abilities and behavior.

Statistical analyses confirmed that exposed children had more difficulty with short-term memory and attention, and more problems in behavior and motor skills. These results are inconclusive, however, because there were some inconsistencies between the two cohorts. For example, in the Verbal Cancellation Test, which measures attention, one statistical method showed an effect in Ohio but not in Mississippi, whereas the other statistical method showed an effect in Mississippi but not in Ohio.

The children were retested in 2000 to see whether effects initially observed were temporary, or whether they persisted over time and thus could be expected to have a longer-lasting impact on the lives of the exposed individuals. The results suggest that, among children who performed lower than expected the year before, methyl parathion exposure was no longer associated with deficits.

One factor that may have contributed to the inconsistent results was the timing of exposure in relation to when neurobehavioral testing was conducted. Children in Mississippi were exposed two years later than children in Ohio; therefore, the Ohio children, who were older at the time of testing, may have outgrown any methyl paration-related neurobehavioral effects.

Despite the inconclusiveness of these findings, they do suggest that methyl parathion exposure may subtly impair memory, attention, and behavior. However, such exposure is not expected to impact general intelligence or integration of visual and motor skills.
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Title Annotation:Science Selections
Author:Eubanks, Mary
Publication:Environmental Health Perspectives
Date:Jan 1, 2004
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