Exposure to low levels of environmental toxins may reduce male sperm counts, research in sheep suggests.
Chemicals such as cosmetics, detergents and pollutants are part of our daily life: we inhale, consume and come into direct contact with them. A year-long study by researchers at the Universities of Glasgow, Aberdeen and Edinburgh, and the French National Institute for Agricultural Research investigated the effects of these chemicals on the testicles of adult rams.
The study compared groups of sheep fed on untreated pastures with those fed on grass treated with sewage sludge, a by-product of sewage and wastewater treatment. Sewage sludge is routinely used as fertiliser, including on land used for grazing, and results in only small increases in the levels of environmental chemicals in the soil.
Yet despite the low doses, five of the 12 rams fed on sludge-treated grass had abnormalities in their sperm-producing germ cells that the team say could result in low sperm counts. These alterations were not the same in all the rams, and did not correspond to differences in testicle size or hormone levels in the blood.
'These findings emphasise that even when the concentration of chemicals in the environment may be very low, it is hard to predict what the health effects are when an individual is exposed to a mixture of chemicals', co-author Professor Neil Evans from the University of Glasgow said.
The study, which was published in the International Journal of Andrology, examined sheep whose mothers had also been grazed on sludge-treated land, so these rams had been exposed to the chemicals from before birth until after puberty. It follows previous data from the same group that showed environmental chemicals have an effect on male and female reproductive organs, some systems that regulate reproduction and even altered fetal development.
Unlike humans, rams are able to store their sperm, which the researchers believe explains why sperm counts in their ejaculate were normal despite the low counts in their testicles. In their report they suggest that the effect of these chemicals on men could be more serious, potentially explaining the rise in IVF treatments in recent years.
No studies have yet looked at whether these findings, so far only observed in a small number of sheep, can be applied to humans. However, the fact that some of the sheep were more affected than others might help to explain why infertility only affects some men.
Professor Paul Fowler, one of the authors from the University of Aberdeen, said: 'The key now is to work out why these everyday chemicals affect some individuals more than others'.