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Common class of insecticides may be detrimental for children’s cognition

Posted:  Friday, July 03, 2015

The chilling results of a new study on insecticide exposure in children may want you to abandon that mosquito repellent from home. French researchers found evidence of neurotoxicity in humans when exposed to a common class of household insecticide, namely pyrethroids. They found increased urinary output of 2 pyrethroid metabolites in children to be associated with significant decrease in cognitive performance, especially verbal comprehension and working memory.

For the study published in the journal Environment International, the researchers evaluated 287 mother-child pairs from the PELAGIE cohort between 2002 and 2006. They collected urine samples at 2 time points, between the 6th and 19th weeks of pregnancy and on the child’s 6th birthday. They analysed these samples for the presence of 5 metabolites: 3-phenoxybenzoic acid (3-PBA), 4-F-3-phenoxybenzoic acid (4-F-3-PBA), cis and trans-dimethylcyclopropane carboxylic acid (cis and trans DCCA), and cis-3-(2,2-dibromovinyl)-2,2- dimethylcyclopropane carboxylic acid (cis-DBCA).

Additionally, psychologists assessed the child’s neurocognitive performance using the WISC scale (verbal comprehension index, VCI, and working memory index, WMI) and also the environmental stimuli that may have influenced intellectual development. The researchers found that increase in the levels of 2 metabolites, namely 3-PBA and cis-DBCA in children’s urine was indicative of significant cognitive decline. This association was however not noted for the other 3 metabolites or for exposure to pyrethroid insecticides during pregnancy.

Pyrethroid insecticides are commonly found in agricultural insecticides, veterinary medications and in domestic products such as lice shampoo and mosquito repellents. They work by blocking neurotransmission in insects leading to paralysis. Although safe for humans, children are vulnerable due to proximity to dust (stores pollutants), frequent hand-to-mouth contact, and exposure to lice shampoos.

"Although these observations must be reproduced in further studies in order to draw definite conclusions, they indicate the potential responsibility of low doses of deltamethrine in particular (since the metabolite cis-DBCA is its main metabolite, and selective for it), and pyrethroid insecticides in general (since the metabolite 3-BPA is a degradation product of some twenty of these insecticides),"said the researchers summing up the study results.

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