Dennis Lincoln, director of the Medical Research Council's Reproductive Biology unit in Edinburgh, said falling sperm counts would lead to an increase in the number of childless couples by the turn of the century.
Two recent studies covering 20 years had confirmed that sperm counts were falling by 2 per cent a year.
Speaking at the British Association meeting, Professor Lincoln said 'wetting agents', called surfactants, mimic the action of female hormones, called oestrogens, once they enter the environment.
He said surfactants - used in a vast range of household cleaning agents, cosmetics and washing powders and in industry - become more oestrogen-like as they are degraded by bacteria. 'They also become more stable in the environment and develop the potential to bioaccumulate in the body.' This means that although they may not be terribly powerful oestrogens when compared with steroids, their effect increases once they enter the environment.
The falling sperm counts were not yet serious in terms of infertility, 'but if we were to project it to beyond the year 2005 then we might suspect that more men would begin to fall into that sub-fertile or infertile range'.
Danish data published in Copenhagen in 1993 had been strongly reinforced in the past month, he said, by two sets of studies on 1,000 men conducted in France and Belgium. 'These studies are very robust . . . they virtually superimpose on the data that was published a year ago from Copenhagen.' He said chemical pollutants that had accumulated in the environment appeared to be mimicking female osetrogens. These could include oestrogens from plants, the contraceptive pill, PCBs and dioxins.
Soya beans, found in many fast foods, were particularly rich in oestrogen-like chemicals. Other chemicals, such as fungicides, might also be playing a part by blocking testosterone production in males.
'I do not wish to suggest that this is a major environmental problem at this time but I think it is one we should be conscious of. We can already see what are very significant effects in wildlife with the levels of infertility there.' He cited recent sex changes observed in fish, and the measurable rise in oestrogen-like chemicals found in rivers.
Professor Lincoln said scientists had also observed a 'massive' increase in abnormalities in male children, such as testicular cancer.
Professor Lincoln said between 12 and 14 per cent of couples are infertile, with 40 per cent of these due to male infertility. It was hard to predict how many more couples would suffer infertility as a result of falling sperm counts because of the natural fluctuations in the sperm counts of individual men.
Men produce a very large excess of sperm - about 100 million per millilitre of semen. This would have to fall below 20 million per millilitre for the man to be considered infertile.
'Many men drop into sub-fertile range . . . this might put some of them over time into the totally infertile range.'
Some scientists remain sceptical that male fertility has fallen and believe the fluctuations may be natural.Reuse content