A report published in the journal of Science provided direct evidence that environmental exposure to toxins can alter gene expression, affecting male offspring and subsequent generations.
Pregnant rats were injected with vinclozolin (a fungicide used on wine grapes) and methoxychlor (a pesticide) by a researcher at Washington State University. Male offspring that were exposed in the womb to these toxins exhibited reproduction problems. Sperm produced by these males swam slowly and died early. Ninety percent of their sons had the same problem, and the problem extended to their grandsons and great-grandsons.
Anway, M. et al, "Epigenetic Transgenerational Actions of Endocrine Disruptors and Male Fertility", Science, June 3, 2005; Vol. 308:1466-1469.