According to one US study, each microgram per decilitre increase in blood lead results in a 1 per cent drop in IQ. Richard Canfield, a senior researcher in Cornell's Division of Nutritional Sciences and senior author of a study in the journal Environmental Health Perspectives said: "We found that the average IQ scores of children with blood level leads of only 5 to 10 micrograms were about five points lower than the IQ scores of children with less than five micrograms."
Other researchers have found that the impact is greater at the lowest levels. The world would have hundreds of thousands more geniuses were it not for the effects of lead.
According to recent research, levels of airborne heavy metal particles are 10-20 times higher on average in China than in the US.
Hong Kong and China have levels of 10 micrograms - double the 5 microgram US pollution standard.Governments around the world are slowly tightening legislation regulating air polluters, but enforcement lags regulation and is not enough to keep pace with the increase in pollution generated by economic growth
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