City pollution bad enough to skew male birth rate
The pollution in Sao Paulo is severe enough to change the natural ratio of male and female birth rates and the problem is likely affecting cities all over the world.
City pollution is reducing the rate of male births in mice - and in humans
Studies of the city's birth registries between January 2001 and December 2003 were checked against recording of pollution during that period and the results were then backed up by lab tests on mice.
The human results showed that in the least polluted areas and time frames 51.7% of babies being born were male, while in the periods and areas suffering the worst pollution the male birth rate had dropped by one percent to 50.7%.
While these figures may be less than striking, the tests on mice produced larger discrepancies.
Male mice were split into two groups, with half spending the first four months of their lives in the clean environment of an air-filtered chamber while the others were given no protection from the ambient pollution.
All the mice were then allowed to breed with females which had not been exposed to pollution.
53.7% of the offspring of those that had developed in the clean air were male while the figure was only 46.2% for those which had been exposed to the city's pollution.
As well as the clear difference in male/female birth rates, the pollution also affected the development of the sperm in the mice.
By Sam Bond
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