A five-year study involving 214 children born to healthy, non-smoking Caucasian women in Krakow, Poland, has found that those prenatally exposed to high levels of polycyclic aromatic hydrocarbons (PAHs) had a significant reduction in scores on a standardized test of reasoning ability and intelligence at age 5 (an estimated average decrease of 3.8 IQ points). The mothers wore small backpack personal air monitors for 48 hours during pregnancy to estimate their babies' PAH exposure. The finding persisted after mother’s intelligence, secondhand smoke exposure, lead and dietary PAH were taken into account. Previously, prenatal exposure to PAHs was found to adversely affect children's IQ at age 5 in children of nonsmoking African American and Dominican American women in New York City. PAHs are released into the air from the burning of fossil fuels.
 Prenatal Exposure to Airborne Polycyclic Aromatic Hydrocarbons and Children’s Intelligence at Age 5 in a Prospective Cohort Study in Poland. Environmental Health Perspectives [Internet]. 2010 . Available from: http://ehsehplp03.niehs.nih.gov/article/fetchArticle.action?articleURI=info%3Adoi%2F10.1289%2Fehp.0901070