Research on chemical toxicity, early life nutrition, smoking and radiation has found evidence of harm even in offspring with no direct exposure to specific contaminants. These findings are important and have already begun transforming regulation of hazardous chemicals, from focusing primarily on the direct consequences of individual substances to assessing the potential impacts on an exposed woman's child. Greater understanding of epigenetics amplifies the need for a more protective approach to chemical risk assessment that would consider effects beyond the exposed generation.
Groundbreaking research by Mohan Manikkam and Michael Skinner of Washington State University at Pullman helped establish the principle of transgenerational toxicity by showing that the effects of toxic chemicals can extend even to the third generation of offspring.
In one study, the researchers tested the transgenerational impacts of mixtures of chemicals to which people are commonly exposed in everyday life, including bug repellents, plastics additives and jet fuel. After exposing pregnant rats to these chemical mixtures, they bred three subsequent generations of animals and did not expose them to the contaminants.
Despite no direct exposure to the chemicals, the third-generation rats had damaged reproductive systems. Females had earlier onset of puberty and fewer undeveloped eggs in their ovaries. Male rats had higher levels of dead sperm.
In a subsequent study of similar design, the researchers observed a 50 percent increased risk of obesity for the unexposed great-grandchildren of rats exposed to the banned pesticide DDT during pregnancy. The team found altered epigenetic markers in those third-generation rats.
At this point, however, there are very few studies of multigenerational toxicity in people. Such studies focus on the health effects on grandchildren of people with unusual psychological stress, poor nutrition, or exposure to radiation or prescription drugs during pregnancy. Studying people is complicated because we live much longer than rats, so experimental research is necessary to learn more about this phenomenon.