Researchers Model Personal Pollution Exposure

Ansgar Walk (Wikipedia)

Northern Exposure A diet rich in marine mammal fat such as seal blubber makes Arctic inhabitants especially susceptible to pollutant exposure.

Environmental toxicologists would like to better predict how much organic chemical pollution settles into our bodies, but two roadblocks stand in their way. Scientists don't know the exact emission rates of these chemicals or how quickly they biodegrade in the environment. A new study sidesteps these data gaps (Environ. Sci. Technol., DOI: 10.1021/es1009339) and finds that people's diets matter more than their local environment.

Organic contaminants, such as plasticizers and pesticides, make a long, complicated trip through the environment to us. "This complexity leads to great variability in human exposure between ecosystems," says Emma Undeman, an environmental chemist at Stockholm University in Sweden. For example, even though pollution emissions in the Arctic are very low, people who live there accumulate greater levels of harmful chemicals than people living in higher-emitting temperate regions.

Undeman and her colleagues wanted to find a novel way to predict this variability that overcame toxicologists' two roadblocks. They started by asking a question: If different ecosystems, such as the tropics or the Arctic, had identical emission levels and you compared people's contaminant loads in each region, how would they differ?

To answer their question, the scientists combined two models: one that calculates how chemicals move in an ecosystem and one that analyzes how the chemicals behave in that region's food chain. The models took into account environmental factors such as temperature and precipitation along with details about people's diet from each region.

With their linked-up models, the researchers set pollution emission rates equal for all ecosystems and estimated a person's average pollutant exposure in each region. They then normalized each region's estimates to that of the temperate zone to create an exposure susceptibility index, which allowed them to rank exposures for each region.

Not surprisingly, the Arctic came out on top. But the gap between the Arctic and other regions was larger than expected: A person living in the Arctic is about 520 times more susceptible to some pollutant exposures than a person eating a mixed diet in the temperate zone, the scientists estimated.

And, surprisingly, diet was the key factor, Undeman says. "The Arctic is a very susceptible environment because people there eat seal, which is a very good exposure vector for chemicals," she says. Seals and other marine mammals pack a high pollutant load because they live longer and feed on predatory fish that bioaccumulate contaminants. Because vegetables sit at the bottom of the food chain and amass fewer pollutants, vegans in temperate zones were the least susceptible, the researchers concluded.

Frank Wania, an environmental chemist at the University of Toronto, Scarborough in Canada and a co-author of the study, says that these calculations show that policymakers can't take risk assessments for the well-studied temperate region and apply them elsewhere, because the risks vary by several orders of magnitude.

Tom McKone, an environmental health scientist at the University of California, Berkeley, agrees that these susceptibility calculations could be powerful tools for policymakers: "It takes a complicated set of processes and integrates it into a single number that makes sense."

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