Increased levels of air pollution and a decrease in the human and mouse male-to-female ratio in São Paulo, Brazil.

A significant negative association (R(2) = 0.7642; P=.013) between particulate matter and secondary sex ratio was found when evaluating people in the city of São Paulo, Brazil. An animal model with male mice raised in nonfiltered open-top chambers showed a significant reduction in the secondary sex ratio (P=.041), suggesting that ambient air pollution may interfere with sex distribution by altering the X:Y sperm proportion in pollution-exposed males.