Chemical damage has been caused in laboratory animals

Now they say that several symptoms - malformations of the penis and testicles, as well as subnormal sperm counts and cancer - may be caused by maternal exposure to chemicals which disrupt the endocrine system.

They say difficulty in observing the chemicals' effects may be caused by their affecting only a genetically susceptible sub-population.

Skakkebaek and Sharpe say animal data show that maternal exposure to oestrogens, and especially to anti-androgens, can cause defects in the sexual development of male offspring.

Because some animals, even at the same level of exposure, show no abnormality, there has been considerable dispute over the real effects of hormones from external sources.

Danish evidence

But the researchers suggest that animals as well as humans may have different genetic susceptibilities.

They say there is evidence of growing human ill-health in Denmark:

• almost 1% of (mostly young) Danish men are treated for testicular cancer
• 5-6% of boys have undescended testicles
• almost 1% have abnormalities of the penis at birth
• more than 40% of young men have subnormal sperm counts.

"Gender-benders" are thought to be affecting wildlife

They say: "As the rise in the incidence of the various symptoms of TDS occurred rapidly over a few generations, the etiological impact of adverse environmental factors such as hormone disrupters, probably acting upon a susceptible genetic background, must be considered."

The researchers note that exposure in the womb of laboratory animals to some phthalates can cause effects very similar to TDS, and recent data show that human exposures to phthalates are higher than expected.

Tighter controls

And they argue for a re-examination of phthalates' human reproductive toxicity, for more data on exposure levels, and for studies of the effects of exposure to combinations of chemicals.

WWF, the global environment campaign, is urging precautionary action now, because it says testicular cancer and lowered sperm counts occur decades after exposure.

It wants the European Union to agree a presumption against the use of endocrine disrupters.

Dr Rob Taalman, of Cefic, the European Chemical Industry Council, told BBC News Online: "We do know about the theory that TDS exists. We think the hypothesis that there are people genetically susceptible to phthalates and other endocrine disrupters must be tested."