23 June 2005
New Evidence For Environmental Chemicals Damaging Sperm
by George Atkinson

In previous research, it was shown that certain chemicals known to mimic the female sex hormone, estrogen, could affect the correct functioning of mouse sperm. Now, in new research, it has been found that when certain chemicals are combined, they have an even stronger effect. Researcher Lynn Fraser said that when she tested one chemical, genistein (found in soy and legumes), on human sperm, she found that the human sperm were much more sensitive to it than mouse sperm. The smallest doses could cause human sperm to "burn out" and lose fertility.

"Given that these environmental chemicals are effective at very low concentrations, with combinations of compounds being even more potent, these results could have important negative implications for human fertility for two reasons. Firstly, humans are likely to be exposed to more than one such compound at any given time and, secondly, our results show that human sperm are even more sensitive to these compounds than mouse sperm," said Fraser, from King's College London. Fraser and her co-researchers tested combinations of three chemicals: genistein, 8-prenylnaringenin (found in hops), and nonylphenol (found in paints, herbicides, pesticides and cleaning products). They investigated the effect the chemicals had on capacitation, the stage when a sperm acquires the ability to fertilize an egg. "We found that combinations of small quantities of these three chemicals stimulated sperm far more than when used individually," she said. In particular, the chemicals caused the head of the sperm to rupture and release penetrative enzymes before it reaches the egg. In such cases, fertilization is unable to take place because the sperm has lost special "docking" molecules that allow it to bind to the egg.

"Human sperm proved to be even more responsive than mouse sperm to genistein. These compounds are classified as environmental estrogens, but they are very weak, so normally you would expect them to have to be in concentrations around 1,000 times stronger to get a response similar to that prompted by the naturally occurring estrogen, estradiol. Yet human sperm are responding to very low concentrations - well within the amounts that have been measured in people's blood," said Fraser. "At a time when there are concerns that the incidence of infertility may be rising, this research flags up important warning signs. The sensitivity of human sperm to these chemicals means that further investigations should be carried out to determine whether such environmental compounds might contribute to a decrease in human fertility," she concluded.

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