Studies in many western countries have shown an alarming decrease in men's average sperm count and an increase in testicular cancers and abnormalities such as undescended testes. In the UK, the incidence of testicular cancer has more than doubled since 1964, and the proportion of men with high sperm counts has declined from 50% in the 1930s to only 15% in the 1980s.
Researchers believe that environmental rather than genetic factors are to blame, and theories about precisely what factors are involved received fresh impetus with the publication of an article by British and Danish scientists.1 The authors argue that environmental exposure to oestrogens, or substances which mimic them, could affect the development of male reproductive tissue in the pre-natal period.
The strongest supporting evidence comes from the use of a synthetic oestrogen, diethyl-stilboestrol (DES), in the USA during the 1970s. The drug was administered to mothers to prevent miscarriages, but produced side effects in some male children, including reduced sperm counts, malformations of the reproductive system and increased risk of testicular cancer.
Exposures of laboratory animals to synthetic oestrogens, as well as to substances with oestrogenic activity such as dioxins and PCBs, produce similar effects on reproductive development in males. Even high natural oestrogen levels in mothers are known adversely to affect their male offspring.
Possible environmental sources of oestrogens include synthetic hormones used in oral contraceptives, dairy products, plant oestrogens in the diet, and pollutants such as some organochlorines and detergent breakdown products. Exposure to these sources is likely to have increased over the last 40-50 years, the researchers argue, creating what some scientists have described as a "sea of oestrogens".
Recent research has found that sewage effluents have an oestrogenic effect on fish (ENDS Report 216, pp 10-11 ). Synthetic hormones used in contraceptive pills were recognised as a likely cause, but detergent biodegradation products were also implicated. Professor John Sumpter of Brunel University is currently conducting research into the hormonal activity of the biodegradation products of alkyl phenol ethoxylates, a group of non-ionic detergents, now used mainly in industrial cleaners.
One of the paper's authors, Dr Richard Sharpe of the Medical Research Council's Unit of Reproductive Biology, told ENDS that it will be necessary to phase out compounds which act as hormonal mimics.