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Toxic Tuesdays

Transgenerational Toxicity

Toxic Tuesdays

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

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Transgenerational Toxicity

While getting cancer, liver disease or central nervous system damage is often associated with exposure to toxic chemicals, one of the most sensitive targets of toxic chemicals is the reproductive system. This has long been recognized for over 50 years (1, 2, 3). In recent years however, research has shown that toxic chemicals can not only directly affect the reproductive system of both women and men, but that these effects can be passed on to the next generation and can even skip a generation. The impact of toxic chemicals on children with no direct exposure to these chemicals is known as a transgenerational effect.

A recent review paper reported that research on chemical toxicity, early life nutrition, smoking and radiation found evidence of harm even in offspring with no direct exposure to specific contaminants. This paper pointed to groundbreaking research at Washington State University that helped establish the principle of transgenerational toxicity by showing that the effects of toxic chemicals can extend even to the third generation of offspring. Other review papers have found a growing body of evidence from epidemiological studies that suggests that environmental exposures early in development have a role in susceptibility to disease in later life and that some of these effects seem to be passed on through subsequent generations (6, 7).

One important study that made this clear was a follow-up study on the residents of Love Canal in Niagara Falls, NY. This study, conducted by the New York State Department of Health (DOH), found that maternal exposure to chemicals from the Love Canal landfill was associated with an elevated risk of bearing a child with an adverse reproductive outcome. The researchers found that women who lived in the designated emergency zone while pregnant prior to the time of evacuation had a higher risk of having a preterm birth compared to women from other regions of the state. This effect was statistically significant.

There was also a greater than expected frequency of congenital malformations among Love Canal boys born from 1983 to 1996. These birth defects occurred in infants born to mothers who previously lived at Love Canal. The rate of these birth defects was about 50% higher than in boys born to mothers who lived in upstate NY. In addition, the ratio of male to female births was lower for children conceived at Love Canal. Lastly, women exposed as children had an increased risk of giving birth to a low weight baby.

These findings are consistent with the initial findings at Love Canal that led to the evacuation of the community in 1978 and 1980. The initial findings identified lower birth weight and increased congenital birth defects in infants, but were limited in defining the risk of adverse pregnancy outcomes because of small sample sizes.

This study is extraordinary because it looked at the reproductive outcomes of women after their exposure had stopped compared to other studies which typically evaluate health effects at the time when exposures were ongoing. In some cases, exposures to Love Canal chemicals occurred only when the women were children! These remarkable findings point out the subtle impact of exposure to toxic chemicals. They are a red flag for health concerns – especially for women of child bearing age – at other contaminated sites across the country. This study also highlights how little we really know about low level exposures to toxic chemicals.

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Toxic Tuesdays

Epigenetic Toxicity

Toxic Tuesdays

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

< Back to Toxic Tuesdays

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:

1. https://www.healthandenvironment.org/environmental-health/social-context/gene-environment-interactions

2. https://www.sciencedirect.com/science/article/pii/S0278691517305240

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