Feb. 26, 2009 -- For the second time in four years, scientists have measured levels of certain toxic chemicals in our bodies. Their results offer mixed news.
"The good news is that the levels in people in the United States are lower than they were two years ago," said Donald Patterson, formerly of the Centers for Disease Control and Prevention, and now president of a company called EnviroSolutions Consulting, Inc., in Jasper, Ga.
"The bad news is that we can still measure them," added Linda Birnbaum, director of the National Institute of Environmental Health Sciences in Research Triangle Park, N.C.
The chemicals in question include dioxins, PCBs, DDT, and a variety of other pesticides, insecticides, and fungicides, many of which are banned. All belong to a group of chemicals known as persistent organic pollutants (POPs).
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By definition, POPs take a long time to break down both in the environment and in our bodies, and they are known to be toxic.
Patterson and colleagues looked at levels of 68 of these chemicals in the blood of about 1,800 people, ages 12 and up. Blood was collected in 2003 and 2004 as part of the National Health and Nutrition Examination Survey (NHANES) survey, which uses interviews and physical exams to regularly sample the health and nutritional intake of American adults.
Compared to data collected in 2001 and 2002, results showed that overall, levels were lower in adults two years later. That's promising, Patterson said, but he cautioned that a third set of numbers will be necessary to know for sure if there really is a downward trend. Analyses for 2005 and 2006 are underway.
Even as levels have dropped, POPs continue to stick around, partly because it takes many years for the body to get rid of them. The new study found detectable levels of a banned fungicide called hexachlorobenzene in 99.9 percent of people tested, for example. DDE, which arises from the metabolism of DDT, appeared in 99.7 percent of the population.
"Many of these chemicals were banned, pulled from the market, or regulated years ago, and yet we still have them" in our bodies, Birnbaum said. "It's a wake up call -- a reminder that chemicals are very persistent in the environment and in the body, and they are going to be with us for a long time."
The study found higher levels in older people than in younger people, as well as differences between males and females and between ethnic groups.
It's not yet clear what the new study means for human health. But tracking changing levels of chemicals in our bodies should help researchers figure out where exposure is greatest and where chemical levels might increase in the future.
"We have a better measure of what's in Americans," Birnbaum said. "It gives us a baseline to work with."
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