Toxic chemicals can affect male fertility over several generations, a new US study carried out on rats suggests. The research, published in Science, shows that a common fungicide and a pesticide cause fertility problems in male rats that are passed on to nearly every male in subsequent generations. The study authors, based at Washington State University, say that no other known toxins have been shown to have this effect.
Previous research had already shown that when pregnant rats are exposed to high doses of vinclozolin - a fungicide used in the wine industry - then their male offspring are sterile. In the latest study, the scientists injected vinclozolin into the abdomen of pregnant rats during days 8-15 of gestation. Although the male offspring's testes appeared normal, and the animals could reproduce, their sperm count dropped by 20 per cent compared to normal rats. Their sperm motility was also 25-35 per cent lower, and the cells in the testes showed a higher rate of apoptosis - 'cell suicide'.
The researchers then bred the male rats with females born to other rats also treated with the fungicide. Surprisingly, more than 90 per cent of the males born in this generation showed very similar reproductive abnormalities, as did the males in the subsequent two generations. The team got the same results when they bred males born to vinclozolin-treated mothers with normal females, but not when they bred normal males with females born to treated mothers. A pesticide called methoxychlor had a similar effect.
The results suggest that both chemicals somehow affected the genetic material of the male fetus' germ cells - the cells that grow into sperm. Since the changes affect almost every male rat descended from a treated mother, team leader Michael Skinner thinks that they are 'epigenetic' - changes that affect the 'on-off' switches of genes, rather than their DNA sequence. 'It's a new way to think about disease', said Skinner, adding 'we believe this phenomenon will be widespread and be a major factor in understanding how disease develops'. He says that a similar effect could be responsible for the higher rates of breast and prostate cancer.
The rats were given much higher doses of the toxins than would be experienced by people, even agricultural workers handling the chemicals routinely. However, the scientists still think that human male fertility could be affected by lower doses. 'The hazards of environmental toxins are much more pronounced than we realised', said Skinner. Toxicologist Earl Gray, of the US Environmental Protection Agency described the findings as 'remarkable observations', adding 'if they're solid and reproducible, they are going to have a large impact on how we look at these kinds of chemicals'. UK expert Alan Boobis, of Imperial College London said the study was interesting, but that there was no need for people to be alarmed. 'We need to find out whether this trans-generational effect is translated to much lower doses', he told BBC News Online.