When too much fish makes men infertile

By Debora MacKenzie MERCURY, which is known to damage the nervous system and disrupt mental development, can also cause infertility in men at levels well below those the WHO says are safe. Mike Dickman, a biologist at the University of Hong Kong, and Clement Leung of the In Vitro Fertilisation Centre in Hong Kong measured mercury levels in men with fertility problems. They found that the hair of men with slow, deformed or sparse sperm contained on average 40 per cent more mercury than that of men with normal sperm. At any given age, men with 3.7 parts per million or more of mercury in their hair were twice as likely to be subfertile as men with 2 ppm or less. The WHO’s safety limit is 10 ppm. Acute mercury poisoning is known to harm sperm formation in mice and monkeys. But this is the first clear association between reduced fertility in men and environmental exposure to mercury. The results will be published in The Science of the Total Environment in June. The men got their mercury from seafood, says Dickman. Volcanoes and coal-fired power stations release the metal into the environment. It is converted to methyl mercury by marine bacteria and taken up by fish. “Men in Hong Kong who eat four or more seafood meals per week have significantly more mercury than those who eat less,” he says. The authors say the WHO’s recommended safe level for mercury in food of 0.5 ppm is too high for places such as Hong Kong where people eat lots of seafood. Last year,
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