Polycyclic aromatic hydrocarbons (PAHs) are a group of pollutants that are produced and released into the environment as a byproduct of burning fossil fuels, tobacco, and other such substances. These substances are known to cause cancer (carcinogenic), genetic mutations (mutagenic), and birth defects (teratogenic). Newborns and fetuses children are thought to be especially susceptible to this form of pollution.
This study looked at the relationship between prenatal/early postnatal exposure to airborne PAHs and intelligence in a group of children in New York City.
To that end, a group of pregnant women was recruited from select area of New York City between 1998 and 2003. These women were between 18 to 23 years old, non-smokers, non-drug users, and in good health.
To measure prenatal exposure to PAHs the air quality in the women’s home environment was sampled during the third trimester of the pregnancy. The air was analyzed to determine the level of PAHs – the range of values was from 0.49 ng/m3 to 34.48 ng/m3 with the mean being 2.26 ng/m3.
Since the level of air pollution in New York City is stable and does not vary seasonally this level of exposure was used as the exposure of the children to PAHs during early childhood as well.
When the children reached their fifth birthday, they were given the Wechsler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R) to determine their IQ.
There were 249 children still participating in the study at age 5 who had enough data to be included in the results. The children were split into a low and high exposure group based on their mother's PAH exposure while pregnant. There were 140 children in the high exposure group (PAHs over 2.26 ng/m3) and 109 children in the low exposure group.
The data was adjusted for the mother's intelligence, the quality of the home environment, other exposures to PAHs (i.e. second hand smoke, dietary sources), as well as other factors.
The results indicate that the children in the high exposure group scored about 5 points lower on average on several measures of IQ than the low PAH group - this roughly translates to a 4% percent lower IQ.
To put it another way, chronic exposure to pollutants like these could very well negatively affect a child’s IQ in the same way that chronic exposure to low levels of lead does.
So what does this study have to do with autism? Well, the authors also included some of the other affects that PAHs are thought to have on fetuses and very young children :