Toxic Chemicals Can Be Inherited in Utero

Researchers are finding even if toxic chemicals don’t persist, their effects on DNA function might—for up to five generations.

A growing body of research from Washington State University finds that exposing rats to toxic substances predisposes their offspring even five generations later to serious diseases. But the substances studied are not mutagens, which affect DNA directly; rather, the research shows the inherited effects are due to simple methyl molecules passed on during pregnancy.

Michael Skinner, Ph.D., and his research team have been exposing rats to chemicals, including Bisphenol-A (BPA), pesticides like vinclozolin and methoxychlor, and industrial chemicals such as dioxin. Again and again, diseases associated with each chemical surfaced in rats that were four and five generations down the line from the subject exposed.

The researchers credit this “transgenerational” inheritance not to mutated genes but rather to altered methyl groups that change the ability of a gene to function. The methyl groups are passed on in utero when they latch onto DNA in a fetus’s germ-line cells, which eventually become its eggs or sperm.

The implications for toxicology are significant. The studies concretely link environmental exposure to predisposing animals for diseases such as cancer, infertility, and obesity that are often purely attributed to genetics. Exposure levels in humans, especially during pregnancy, may have to be re-evaluated. The findings also suggest that current chemical risk assessments may be missing part of the picture by accounting only for first-generation effects.