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 to environmental chemicals. These features include the timing and vulnerability of exposures, exposures to mixtures, effects at low doses and genetic alterations called epigenetics.
Traditional thinking tells us that how much of a chemical you are exposed to (the dose) determines the effect. This principle assumes that chemicals act by overwhelming the body’s defenses at high doses. We’re learning now that this principle is not always accurate and its place in evaluating risks needs to be reconsidered. What we now know is that some chemicals cause their adverse effects at low exposure levels that are not predicted by classic toxicology.
Recent research has shown that environmental chemicals like dioxin or bisphenol A can alter genetic make-up, dramatically in some cases. These changes are so powerful that they can alter the genetic material in eggs and sperm and pass along new traits in a single generation, essentially by-passing evolution.
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. That’s no longer the case.
This new field – called epigenetics – is perhaps the fastest growing field in toxicology and it’s 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.
What 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 blue eyes, or their susceptibility to diseases such as adult on-set diabetes, or to the development of lupus.
The environment is a critical factor in the control of these packaging processes. We may be born with our genes, but epigenetics changes occur because of environmental influences during development and throughout life. These influences include 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.
Epigenetics may explain certain scientific mysteries, such as why certain people develop diseases and others don’t, 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.
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