Exposure to pollutants in the womb can affect children's cognition at the age of five. Researchers from the Columbia Center for Children's Environmental Health in New York studied 214 children born to healthy, non-smoking women in Krakow, Poland. The women in the study wore backpack air monitors and provided blood samples during their pregnancy and the children's intelligence was tested at the age of five. Those children exposed to most polycyclic aromatic hydrocarbons (PAHs) had a significant reduction in their intelligence scores. PAHs are produced when fossil fuels are burnt but are also found in cereals, oils and fats.