Male Fertility May Be Harmed By Mix Of Endocrine Disrupters

Many young men have a low sperm count and more and more boys are born with malformed sexual organs. A little less than five per cent of all Danish boys are, for example, born with hypospadias, where the opening of the urethra is on the underside of the penis. Substances disturbing the hormonal balance during the foetal development have long been suspected of being one of the causes of such birth defects.

"Several animal tests have shown that endocrine-disrupting chemicals, which have an effect on the male sex hormone testosterone, can result in such malformations in young male rats. In vitro testing and short-term animal testing have also suggested that concurrent exposure to several chemical substances can result in endocrine-disrupting effects even if exposure to each individual substance does not show any effect. We are now able to document that this is actually the case," says Ulla Hass, senior scientist at the National Food Institute, Technical University of Denmark.

Significant cocktail effects

The National Food Institute, Technical University of Denmark, has carried out comprehensive studies in which pregnant rats were exposed to a cocktail consisting of three chemicals that all inhibit the effect of the male sex hormone testosterone: The drug flutamide and the pesticides vinclozolin and procymidone.

The three chemicals were administered in doses which are harmless individually. Concurrent exposure to the three substances did, however, show significant cocktail effects. The male rats did, among other things, develop female characteristics in the form of retained nipples and severely malformed external sexual organs. Sixty per cent of the male rats were, for example, born with hypospadias.

Underestimated risk

Today, risk assessments of chemicals and establishing reference values are performed for one substance at a time although people are exposed to many different chemical substances every day.

"Our studies show that concurrent exposure to several endocrine-disrupting substances in small doses can increase the frequency of malformations such as hypospadias even though the doses are harmless individually. It is therefore not sufficient to establish reference values only by looking at one substance at a time," concludes Sofie Christiansen, PhD student at the National Food Institute, Technical University of Denmark.

"In order not to underestimate the risk of chemicals to humans, it is important to include the possible concurrent exposure of two or more chemicals in the risk assessment. To establish an adequate protection level for consumers, potential cocktail effects should be taken into account, and thus the way a chemical may interact with other chemicals," adds Ulla Hass.

Journal reference: International Journal of Andrology: http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2605.2007.00866.x