5 December 2014. Pesticides are meant to be toxic to various pests, including insects. As our nervous system is quite similar to insect brains in regard to its biochemistry, pesticides that control insects may also present a hazard to the human nervous system. The current list of suspected brain drainers includes 100 pesticides. Each of them has caused neurological symptoms in adults. However, for most of them, we do not know whether they damage brain development in children. In order to find out, Dr. Helle R. Andersen decided to examine Danish children whose mothers had worked in greenhouse flower production during pregnancy.
Dr. Andersen recruited the mothers in 1997-2001 and obtained detailed information on their occupational exposure to pesticides. Some of the women were not exposed, as they worked in offices away from the greenhouses. But the study was complicated by the high-level of protection against exposures that can harm a pregnant woman and her fetus. According to Danish legislation, women with occupational exposure were moved to unexposed work functions or went on paid leave as soon as pregnancy was determined. As modern pesticides do not stay in the body for long, any exposure was therefore limited to the first several weeks of pregnancy.
All told, the women gave birth to 203 children, and about two out of three have now been examined at school age. The researchers used neuropsychological tests and evoked potentials (brainstem auditory response) to determine any deficits in brain functions.  The bad news is that Helle Andersen’s results – just published – suggest that even this high level of protection is insufficient when it comes to fetal brain development.
When comparing 112 prenatally exposed  children to unexposed controls (21 + 44 additional controls), the evoked potentials were delayed in the exposed children, and  impaired neuropsychological functions were found in exposed girls, while no effect was apparent in boys. The functions most clearly affected were language and motor speed, but similar tendencies were also seen for other brain functions in the girls.
The question is then if any individual pesticide can be singled out as the main cause of the exposure-associated deficits. Unfortunately, modern-day exposures are complex, and the greenhouse workers had applied about 200 different pesticide formulations, which represent 124 different active pesticide ingredients. There is no way to tell from this study which one or which ones were the culprit.
The researchers previously found that women with pesticide exposure showed signs of endocrine disruption. Serum from these women had greater estrogenicity activity and activated to a greater extent the estrogen receptor. Thus, pesticide toxicity may act via interference with hormone actions in the body. Could this explain why effects were so strong in the girls and not at all in the boys? Possibly. Recent studies in mice prenatally exposed to chlorpyrifos – a pesticide commonly used in the US and the EU – showed that brain functions in the two sexes are not affected similarly, perhaps because this pesticide is an endocrine disruptor. These experimental data support the notion that girls may be more vulnerable to some pesticides than boys.
So this new report adds to the concern that occupational exposures to modern pesticides, even under circumstances considered safe, are not safe for the next generation’s brains.