Prenatal exposure to common insecticide additive linked to mental delays

In utero exposure to piperonyl butoxide, an additive in pyrethroid insecticides, appears to be negatively associated with neurodevelopment in children who are 3 years old.

The recent shift from using organophosphorus insecticides to pyrethroid insecticides for residential pest control prompted investigators from Columbia University to evaluate the association between in utero exposure to piperonyl butoxide and permethrin and neurodevelopment at 36 months of age. Study results were published in the March issue of Pediatrics.

The researchers note that long-term neurotoxic effects after low-level exposure to pyrethroid insecticides had not been previously studied in people. Experimental data, however, raised safety concerns regarding exposure in utero and during early childhood.

Permethrin was chosen as the targeted pyrethroid because it is one of the insecticides most frequently detected in residential homes in the United States. According to the US EPA, pyrethroids, which are synthetic chemical insecticides, are sometimes formulated with synergists such as piperonyl butoxide to enhance effectiveness.

Investigators studied 725 mothers and their newborns in a prospective longitudinal study consisting of women who resided in 2 low-income areas of New York City. Personal air samples were collected via a personal ambient air monitor from 342 women in their third trimester of pregnancy to determine permethrin exposure. Samples also were collected from 230 women to measure piperonyl butoxide exposure. Maternal and umbilical cord plasma was analyzed for permethrin exposure in 272 women.

Piperonyl butoxide was found in 75.2% of air samples. Levels of permethrin in personal air samples and maternal and cord plasma were relatively low and ranged in values from 5.4% to 18.7%.

When the children of these mothers became 3 years old, they were tested for cognitive and motor development using the Bayley Scales of Mental Development, second edition, a commonly used measure that can diagnosis developmental delay and is sensitive to neurotoxic effects. It also generates the Mental Developmental Index.

Researchers found that the children who had higher exposures (at least 4.34 ng/m³) to piperonyl butoxide in air samples scored approximately 4 points lower on the Mental Developmental Index compared with children who had lower exposures. In contrast, prenatal exposure to permethrin in personal air samples and plasma was not linked with performance scores.

The investigators explain that many pyrethroid insecticides are not volatile, making their detection in personal air samples relatively low. These insecticides also are quickly metabolized and it is difficult to measure permethrin in maternal and cord plasma samples. Such difficulties in measuring permethrin may inhibit researchers from finding significant links to neurodevelopmental outcomes, they say.

Horton MK, Rundle A, Camann DE, Barr DB, Rauh VA, Whyatt RM. Impact of prenatal exposure to piperonyl butoxide and permethrin on 36-month neurodevelopment. Pediatrics. 2011;127(3):e693-e700.