Man-made pesticides blamed for fall in male fertility over past 50 years

By Steve Connor, Science Editor
03 June 2005

Pesticides and other man-made chemicals may lower male fertility for
at least four generations, according to new research.

Pregnant rats exposed to fungicide sprayed on vineyards and pesticide
sprayed on crops had male offspring with a sperm count reduced by 20
per cent.

If confirmed by further experiments, the findings could help explain
the decline in human male fertility over the past 50 years.

The study was carried out on laboratory rats that received high
levels of vinclozolin, a fungicide widely used in vineyards, and
methoxychlor, a pesticide used to replace DDT when it was banned more
than 30 years ago. Scientists found that the male offspring of the
exposed rats suffered a sharp decline in the quality and quantity of
their sperm and that these traits continued to be passed on down the
male line.

Yet the researchers believe that the chemicals did not mutate the
genes of the rats - a proven way of passing on damaging traits - but
instead may have altered the way the genes work.

Michael Skinner of Washington State University, who led the research
team, said nearly all the male rats born in each generation were
affected by sperm damage or low sperm counts. He said that the
findings, published today in the journal Science, suggest that toxins
may play a role in heritable diseases that were previously thought to
be caused solely by genetic mutations.

"It's a new way to think about disease. We believe this phenomenon
will be widespread and be a major factor in understanding how disease
develops," Dr Skinner said.

The rats were exposed to much higher levels of the toxic chemicals
than would be experienced even by agricultural workers handling the
products on a daily basis. But the scientists believe that this does
not rule out the possibility that a similar effect may result from
exposure to low doses.

Both of the chemicals are known to be toxic in high doses and each is
considered capable of interfering with the functioning of
reproductive hormones - a feature of toxins known as endocrine

The scientists exposed pregnant rats to the chemicals at the crucial
moment in gestation when the sex of the offspring is determined. The
result was that male offspring suffered a 20 per cent decline in
sperm counts, and sperm motility - its ability to swim - fell by up
to 35 per cent.

What was surprising was that these traits were also seen in 90 per
cent of the male offspring born to three more subsequent generations
yet the scientists found no obvious mutations in the DNA of the

One possibility is that the toxic substances altered the natural
chemicals, called methyl groups, that normally surround the DNA
molecule and these subtle changes were inherited by the male

"We are mostly describing a new phenomenon... The hazards of
environmental toxins are much more pronounced that we realised," Dr
Skinner said.