Environmental News Network (ENN), November 20, 2006


[Rachel's introduction: All the scientific advancements in risk assessment of the past 20 years are becoming overshadowed by biomonitoring, the capability to measure low levels of specific toxicants (or their breakdown products) in humans, typically urine or blood.]

By Dr. Gary Ginsberg

Nearly 25 years after the National Academies of Science codified the practice of environmental risk assessment with their 1983 "Red Book", this relatively young field now comes to a critical stage in its maturation.

As the key scientific method that underlies toxics regulations, the manner in which risk assessment is conducted is not trivial. Since 1983 it has gone through many refinements, from beginnings in crude, high dose animal tests, it has advanced to increasingly more sophisticated procedures that tell us how toxicants behave in animals and are likely to act in people. The newer models forecast dose and toxicity in young children, pregnant women and those whose metabolism may be deficient due to their unique genetic makeup. But all these advances are becoming overshadowed by biomonitoring, the capability to measure low levels of specific toxicants (or their breakdown products) in humans, typically urine or blood.

Why is this such an important breakthrough and why is it putting risk assessment at a precarious crossroads? First and foremost, biomonitoring is teaching us that the old adage "What goes around, comes around" is especially pertinent to toxic chemicals. It has taught us this lesson many times as specialty chemicals that were meant to stay in consumer products (e.g., flame retardants, Teflon coating, plasticizers) end up inside us, likely from in utero onwards.

This greatly raises the stakes for risk assessment because we're not just talking about possible exposures to theoretical receptors at some point in the future, but exposures happening right now to real people from whom we've just taken some blood. The October 2006 National Geographic spread on biomonitoring highlights the finding of many chemicals in one reporter's blood, with his levels of brominated flame retardants much higher than typical. Certainly he and the rest of the public want to know where all this exposure is coming from, what it means to one's health, and why aren't there answers given that most chemicals found have been used for decades. Everyone is taking a long look at risk assessment for answers.

As pointed out in a new National Academy report on biomonitoring (NAS, 2006), there is good news -- the techniques exist. But the bad news is that we are just starting to use them effectively, and even in those cases, there is a question of whether we will believe the results.

Ironically, one of the main techniques for anwering the questions raised by biomonitoring is... biomonitoring itself. Why use biomonitoring just to search for chemicals? Why not also use it to tell us whether people with lots of a chemical have more health problems than those who don't. This is the arena of epidemiology, a field that has many obstacles to overcome because people are much more difficult to study than lab rats.

One of its main difficulties is determining the level of exposure in study populations. Good biomonitoring data remove that mystery and puts epidemiology squarely on the path of dose-response and risk assessment. With more and more biomarkers available, epidemiologists can test all sorts of hypotheses, and are now finding plausible links between low dose chemical exposure and toxic effects in people. Risk assessors are typically toxicologists, trained in the highly artificial but well-controlled world of animal testing. Are risk assessors ready to embrace the new wave of epidemiology that is showing us that the controlled lab study may not tell us everything we need to know about risk?

Hopefully the answer is yes. It was yes for lead and mercury, cases in which biomonitoring in combination with decades of human testing showed clear risks at low dose, driving lead from paint and gasoline and causing us to warn pregnant women to cut down on fish consumption.

The new wave that's emerging is showing us that low levels of life's common ingredients, from phthalates present in cosmetics to a newly discovered dietary contaminant that's also in rockets and bombs (perchlorate), have the potential to impair fetal development (Swan, et al., 2005; Blount, et al., 2006). These findings are at low dose levels, commonly experienced by average Americans.

The greater sensitivity of human testing may be related to the fact that if we test enough people with biomonitoring-based epidemiology, we will find a sensitive subgroup if it exists. Animals used in toxicology testing are highly inbred so they are in another universe when it comes to variability. CDC's new findings with perchlorate are instructive: men and most women were insensitive to this chemical. However, the subgroup of women with compromised iodine intake were affected. These types of findings throw risk assessment into the crossroads of biomonitoring -- does it embrace these new findings and accept the caveats and uncertainties involved in human population testing, or does it stick to the better controlled laboratory studies, which as we are now finding out may be less sensitive than we had originally believed.

The pendulum in recent years has been swinging towards epidemiology for dose response information, limiting animal testing to demonstrate plausibility and mechanism. The cases of phthalates and perchlorate will show whether regulators are ready to fully accept the biomonitoring-based risk assessment paradigm, testing their resolve because it may mean more stringent regulation of cosmetics (phthalates, as already being done in Europe) and the diet and drinking water (perchlorate). The challenge for risk assessors will be to use biomonitoring data responsibly to protect public health and not let this new crossroads become bogged down by inaction and gridlock.


Blount, B. et al. (2006) Urinary Perchlorate and Thyroid Hormone Levels in Adolescent and Adult Men and Women Living in the United States Environ Health Perspect: doi:10.1289/ehp.9466. [Online 5 October 2006]

National Academy Science (2006) Human Biomonitoring for Environmental Chemicals. National Academy Press.

Swan, S. et al. (2005) Decrease in anogenital distance among male infants with prenatal phthalate exposure. Environ Health Perspect. 113:1056-61.

Dr. Gary Ginsberg is co-author of What's Toxic, What's Not (Berkley Books, pub date 12/05/06) and is a toxicologist at the Connecticut Department of Public Health. He is on the faculty of Yale University and the University of Connecticut School of Medicine. He served on the NAS Panel on Biomonitoring and currently serves on several other NAS and EPA panels. For more information go to www.whatstoxic.com.

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