April 23, 2012

What Do We Know About Low Doses of Chemicals and Our Health?

Researchers from a number of universities and the National Institute of Environmental Health Sciences recently published an article in the journal Endocrine Reviews that explores how much exposure to certain chemicals is needed to cause harm, and suggests that “fundamental changes in chemical testing and safety determination are needed to protect human health.”

The researchers, led by Laura Vandenberg, looked at endocrine-disrupting chemicals (EDCs) – chemicals like BPA and DES that interfere with the body’s hormone systems. In their review, they explore complex issues around dose – the effects of low doses, how “low dose” is defined, and what happens when effects of a chemical aren’t directly correlated to the dose.

As the authors explain:

For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of “the dose makes the poison,” because EDCs can have effects at low doses that are not predicted by effects at higher doses.

As a result, what we know about exposure to a chemical from following people after a one-time large exposure might not predict what happens when people are exposed to very small amounts of a chemical over a longer time.

The implications are that some of our assumptions about harms from low doses, the reliability of current testing methods, and safe thresholds might be incorrect, because harmful effects of chemicals might vary in unexpected ways at different doses, in different people, or at different stages of development. The authors point out several things researchers should do to improve our understanding of these issues, like carefully considering dose ranges and timing to study.

For the general public, the regulatory implications of the review may be most important. As the authors explain:

For decades, regulatory agencies have tested, or approved testing, of chemicals by examining high doses and then extrapolating down [from where observable effects are thought to start] to determine safe levels for humans and/or wildlife. As discussed earlier, these extrapolations use safety factors that acknowledge differences between humans and animals, exposures of vulnerable populations, interspecies variability, and other uncertainty factors. These safety factors are informed guesses, not quantitatively based calculations. Using this traditional way of setting safe doses, the levels declared safe are never in fact tested. Doses in the range of human exposures are therefore also unlikely to be tested.This has generated the current state of science,where many chemicals of concern have never been examined at environmentally relevant low doses.

In other words, for many chemicals,  regulations are based on best guesses about safety, rather than specific safety data. Additionally, the authors suggest that guessing about low doses based on higher doses really doesn’t work for endocrine-disrupting chemicals, and new approaches to assessing their safety should be developed. The authors also call for greater testing at low doses when new chemicals are developed and approved:

We further recommend greatly expanded and generalized safety testing and surveillance to detect potential adverse effects of this broad class of chemicals. Before new chemicals are developed, a wider range of doses, extending into the low-dose range, should be fully tested.

A related editorial from the director of the National Institute of Environmental Health Sciences also calls for “appropriate actions to protect human and wildlife populations from these harmful chemicals and facilitate better regulatory decision making.”

In an opinion piece, lead author Vandenberg writes more about their research and implications of EDCs for women:

We found overwhelming evidence that these hormone-altering chemicals have effects at low levels, and that these effects are often completely different than effects at high levels. For example, a large amount of dioxin would kill you, but a very small dose, similar to what people are exposed to from eating contaminated foods, increases women’s risk of reproductive abnormalities.

The full review is freely available online. There is also coverage over at Moms Rising, and a summary of the research at Environmental Health News.


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