VIENNA, Austria, July 3, 2002 (ENS) - An estrogen found in synthetic cleaners, paints, herbicides, and pesticides, as well as other estrogens found in soy and hops, may reduce the fertilizing ability of sperm, a British research team has found. A beer drinking, vegetarian painter could be at even greater risk for reduced fertility than a person exposed to one environmental estrogen alone.
Dr. Lynn Fraser told the annual conference of the European Society of Human Reproduction and Embryology (ESHRE) in Vienna Tuesday that her team has produced the first direct evidence that estrogens from the environment, as well as those that occur naturally in the human body, affect the ability of sperm to fertilize an egg.
"Other studies, using indirect tests that do not assess actual sperm function, have reported that estrogens affect sperm," she said. "Our study is the first to provide both indirect and direct evidence that natural and environmental estrogens significantly affect sperm fertilizing ability."
Fraser, who is professor of reproductive biology at Kings College London, England, and a former chairman of ESHRE, investigated how three environmental estrogens and one natural estrogen affected the final stage of development of sperm when it acquires the ability to fertilize an egg. This stage is known as capacitation.
Fraser and her team studied this effect in mouse sperm in the test tube, but Fraser says she suspects these estrogens have a similar effect on human sperm.
The environmental estrogens studied were genistein, found in soy beans as well as in other peas and beans, 8-prenylnaringenin, an estrogen found in hops, and nonylphenol, which is found in industrial products such as synthetic cleaners, paints, herbicides and pesticides, emulsifiers, wetting agents, and foam reducing agents.
The natural estrogen tested was oestradiol 17ß, which is present in the female vagina and in seminal plasma, the fluid containing the sperm.
In sperm which had not completed capacitation, all the estrogens accelerated development so that they became fertile more quickly.
The estrogens stimulated sperm motility, capacitation and the acrosome reaction - when the cap at the head of the sperm ruptures to release enzymes which enable the sperm to penetrate the barriers surrounding the egg.
Successful sperm only undergo the acrosome reaction when they make contact with an egg. If the acrosome reaction takes place before contact, then they cannot fertilize an egg.
In sperm which were already capacitated, the natural estrogen had no major effect, but all the environmental estrogens "significantly" stimulated the acrosome reaction. These sperm developed too soon, before they found an egg to fertilize.
Fraser said, "At first sight these results might suggest that estrogens, particularly those found in the environment, could help fertility. However, the responses we have seen could have negative effects over time."
"In natural reproduction it could be a problem, but for IVF [in vitro fertilization] techniques it might be a benefit," she said.
The researchers now want to investigate the effect on sperm of a combination of environmental estrogens.
"My suspicion is that combinations of environmental estrogens, even in very weak amounts, would still have a significant effect," she said.
"These findings could be important in understanding how different compounds, known to be present in our environment, might affect sperm function in humans," Fraser said. "Given that the environmental estrogens are very potent and that we are probably being exposed to several at the same time, it is important to know whether they might have cumulative effects."
One of the estrogens Fraser's team studied, nonylphenol is a raw material for the manufacture of nonylphenol ethoxylates which are used in hair colors, shampoos, hair styling aids and cosmetics. They are often identified as nonoxynol or octoxynol. Nonoxynol-9 is also commonly used as a spermicide.
Products containing nonylphenol polyethoxylate (NPE) are used in textile processing, pulp and paper processing, paints, resins and protective coatings, oil and gas recovery, steel manufacturing, pest control products and power generation. A variety of cleaning products, degreasers and detergents are also available for institutional and domestic use.
In a June 2001 Assessment Report, Environment Canada said, "nonylphenol and its ethoxylates are entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long term harmful effect on the environment or its biological diversity," although they do not "constitute a danger to the environment on which life depends."