Insecticides may affect cognitive development in children, according to a new study.

Pyrethroid insecticides are one of the most commonly used pesticides, with benefits in a variety of sectors including residential pest control, public health and agricultural purposes. They can also be found in many domestic products such as lice shampoo and mosquito repellent.

With more toxic compounds such as organochorides, organophosphates, and carbamate having been banned due to health concerns, pyrethroids are now increasingly popular, and considered relatively safe for humans and mammals.

Now, a study published in the journal Environment International provides new evidence of neurotoxicity in humans from pyrethroid insecticides. An increase in the urinary levels of two pyrethroid metabolites (3-PBA and cis-DBCA) in children is associated with a significant decrease in their cognitive performance, particularly in terms of verbal comprehension and working memory.

Pregnancy is also an important period of life for the future health of a child. So during the study, researchers from INSERM (or IRSET in English, standing for the Institute of Research in Environmental and Occupational Health) in Rennes, France studied a total of 287 mother-child pairs randomly selected from the PELAGIE cohort. This cohort, established between 2002 and 2006, considers exposure to pyrethroid insecticides during fetal life and childhood.

Psychologists assessed each child's neurocognitive performances using the WISC scale - a combination of the verbal comprehension index (VCI) and working memory index (WMI).

Simultaneously, exposure to pyrethroid insecticides was estimated by measuring levels of five metabolites (3-PBA, 4-F-3-PBA, cis-DCCA, trans-DCCA and cis-DBCA) in urine from the mother and the child.

They found that an increase in two metabolites - 3-PBA and cis-DBCA - in children was associated with a significant drop in cognitive performance. Such a drastic decline, however, was not exhibited for the other three metabolites.

"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)," lead author Cécile Chevrier, INSERM Research Fellow, explained in a press release.

Not only that, but what's also concerning is the fact that children are exposed to pyrethroids on a daily basis. That's because kids stand closer to the ground where there is pollutant-containing dust, and because they have more frequent hand-to-mouth contact, researchers say.

In children, pyrethroids are mainly absorbed via the digestive system, but are also absorbed through the skin. These chemicals are rapidly metabolized in the liver, and mainly eliminated in the urine as metabolites within 48 hours.

Given these contributing factors and the neurotoxicity of pyrethroid insecticides, the researchers believe these contaminants negatively impact the nervous system and its development in children.

"The consequences of a cognitive deficit in children for their learning ability and social development constitute a handicap for the individual and for society," added co-author Jean-François Viel. "The research effort needs to be pursued in order to identify causes that could be targeted by preventive measures."

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