Exposure to environmental toxins affects the health of generations of offspring, a new study shows.

Researchers at the University of Texas at Austin have shown that rats exposed to toxic chemicals generations earlier, passed down genetic health defects to their offsping.

“This, I think, is the first causal demonstration that environmental contamination may be the root cause of the great increase in obesity and the great increase in mental disorders,” study author David Crews, a professor of psychology and zoology, told Bloomberg in an interview.

“It’s as if the exposure three generations before has reprogrammed the brain so it responds in a different way to a life challenge.”

The study is another in a growing body of evidence suggesting that environmental toxin exposure harms the genetic make-up of future generations.

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The study looked at rats who descended from others that were exposed to the chemical vinclozolin, a fungicide that has been linked to hormone disruption, reported Phys Org.

Behavioral tests on the third generation rats found that they were more anxious and sensitive to stress than those whose descendents were not exposed to the chemical.

According to Bloomberg, third generation rats were chosen as this was meant to coincide with the advent of similar environmental toxins that humans were exposed to in the early 20th century such as the pesticide DDT.

The study is another in a growing body of evidence suggesting that environmental toxin exposure harms the genetic make-up of future generations.

The findings were published in the Proceedings of the National Academy of Sciences.