When exposed in a laboratory to pollution levels comparable to those found in the atmosphere of the Amazon region during the forest and crop burning season, human lung cells suffer severe DNA damage and stop dividing. After 72 hours of exposure, over 30 percent of the cultured cells are dead. The main culprit appears to be retene, a chemical compound that belongs to the class of polycyclic aromatic hydrocarbons (PAHs). These results have been reported by a group of Brazilian researchers in the journal Scientific Reports.