Toxic Tuesdays

CHEJ highlights several toxic chemicals and the communities fighting to keep their citizens safe from harm.

Epigenetic Toxicity

The way scientists think about how chemicals cause their toxic effects is changing. Recent scientific research tells us that the traditional notion of how chemicals act is being replaced by a better understanding of the actual features of exposures that influence how chemicals express their adverse effects in people. These features include the timing and vulnerability of exposures, exposures to mixtures, effects at low doses and genetic alterations called epigenetics.

It wasn’t too long ago that scientists believed that the DNA in our cells was set for life, that our genes would be passed on from one generation to the next, and that it would take generations to change our genetic makeup. This is no longer the case.

A new research area, called epigenetics, is perhaps the fastest growing field in toxicology and it is changing the way we think about chemical exposures and the risks they pose. Epigenetics is the study of changes in DNA expression (the process of converting the instructions in DNA into a final product, such as blue eyes or brown hair) that are independent of the DNA sequence itself.

Researchers are learning is that the “packaging” of the DNA is just as important as a person’s genetic make-up in determining a person’s observable traits, such as eye color, or their susceptibility to diseases such as adult on-set diabetes or lupus.

We are learning that the environment is a critical factor in the control of these packaging processes. We may be born with our genes, but epigenetic changes can occur because of environmental influences and exposures during development and throughout life. These influences include reactions to the chemicals in the food we eat, the air we breathe, the water we drink, and they appear to contribute to the development of cancer and other diseases.

Researchers have found that the genome, which is a person’s complete set of DNA, responds to toxic chemicals in the environment that a person is exposed to. It can lead to changes in gene expression, not by mutating the genes, but by sending subtle signals that stops gene activity or turns them on at the wrong times. Researchers believe that the genome has evolved from adapting to stressful survival situations to becoming more vulnerable to adverse environmental exposures, which leads to direct changes in people’s health based on how they respond to toxic chemicals in their environment. Linda Birnbaum, the former director of the National Institute of Environmental Health Sciences and the National Toxicology Program, put it this way: exposure to gene-altering substances, particularly in the womb and shortly after birth, “can lead to increased susceptibility to disease. The susceptibility persists long after the exposure is gone, even decades later. Glands, organs, systems can be permanently altered.”

This growing field of epigenetic toxicity may explain the long-term effects of chemical substances and the predisposition to disease that some people have due to environmental factors including exposure to chemicals. Epigenetics may also help to explain why certain people develop diseases and others do not, or why the person who smoked for 30 years never developed lung cancer.

There is still much to learn, but an early lesson to take away from this emerging science is that we need to rethink our traditional ideas of how chemicals affect our health. This is especially true since regulators and public health scientists who make decisions about safe levels of exposure to toxic chemicals are not considering epigenetic toxicity in their evaluations and are missing a critically important piece of the toxic chemical exposure puzzle. This may help explain why government is constantly telling people that the testing that has been done shows no cause for concern, while the people who have been exposed have symptoms and illnesses with no explanation for why they are sick.  

For more information on epigenetic toxicity, see these resources:



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