New U.S. research is suggesting that chemicals can change the way genes work and that toxic chemicals that poisoned your great-grandparents may also damage your health.
A team from Washington State University has produced worrying evidence that some inherited diseases may be caused by poisons polluting the womb.
The researchers found in their work on rats,an indicatation that man-made environmental toxins may alter genetic activity, giving rise to diseases that pass down at least four generations.
Lead researcher Dr Michael Skinner says it is a new way to think about disease.
The scientists exposed pregnant rats to two agricultural chemicals during the period that the sex of their offspring was being determined.
The compounds used were vinclozolin, a fungicide commonly used in vineyards, and the pesticide methoxychlor, both are known as endocrine disruptors, chemicals that interfere with the normal functioning of reproductive hormones.
The team found that the rats exposed to the compounds produced male offspring with low sperm counts and poor fertility, and when these rats were then mated with females that had not been exposed to the toxins, they were still able to produce young, but their male offspring had the same problems.
This effect persisted through at least four generations, impairing the fertility of more than 90% of male offspring in each generation.
The researchers found the damage was not caused by alterations in the DNA code, but changes in the way the genes work. They say these epigenetic changes, are caused by small chemicals that become attached to the DNA, modifying its activity.
Epigenetic changes have been observed before, but were not previously known to pass onto later generations.
Skinner believes they may contribute to diseases such as breast cancer and prostate cancer, and says they need to find out whether this trans-generational effect is translated to much lower doses of the toxins.
Both diseases are becoming more common, and Dr Skinner says that cannot just be down to genetic mutations.
The researchers believe their findings suggest exposure to environmental toxins may play a key role in the evolutionary process which may not necessarily be driven just by genetic mutations, as commonly thought.
Dr Skinner believes this phenomenon will be widespread and will be a major factor in understanding how disease develops, but he emphasises that more work is needed to corroborate the findings.
Professor Alan Boobis, a toxicologist at Imperial College London, UK, says the findings are interesting, but says there was no need for people to be alarmed, as the levels of chemicals the rats were exposed to were very high and much higher than people normally ever encounter.
The research is published in the journal Science.