Air pollution cuts male birth rate, says study

Air pollution decreases the proportion of babies born male, according to a study suggesting that the level of pollution in many cities is high enough to alter the natural sex ratio.

Researchers at the University of Sao Paulo in Brazil used 15 pollution monitoring stations around the city. They then checked the sexes of 48,023 babies born within a 2km range of each station from 2001 to 2003.

Even over a narrow range of pollution, sex differences across the city were marked. In low pollution areas, the proportion was 51.7% male, whilst in the most polluted, it dropped to 50.7%.