CDC Pegs Human Exposures to Chemicals

CATHERINE M. COONEY / Environmental Science & Technology 1may03

Signifying “a quantum leap forward” on understanding environmental chemicals and how much is being absorbed by humans, officials with the U.S. Centers for Disease Control and Prevention (CDC) released their Second National Report on Human Exposure to Environmental Chemicals. It contains good news about declining children’s blood lead levels and exposures to tobacco smoke for nonsmokers, but some say it raises concerns about mercury levels.

We are “pretty excited,” says David Fleming, CDC’s deputy director for science. “It is almost the most extensive study ever made of exposures to environmental chemicals.”

The report is four times larger than CDC’s first 2001 document and relies on blood and urine specimens taken in 1999 and 2000. It includes data on 116 chemicals, 89 of which have never been measured in the U.S. population, such as polycyclilc aromatic hydrocarbons and carbamate insecticides. The first report measured levels of four groups of chemicals: metals, tobacco smoke, organophosphate pesticides, and phthalates. The second expands on these and reports on 12 groups of chemicals, including dioxins, furans and PCBs, herbicides, pest repellents, disinfectants, and phytoestrogens.

The report establishes exposure baselines, or reference ranges, that public health investigators can refer to when deciding whether an acute exposure, such as an accidental factory release, has harmed nearby residents. Regulators, too, can refer to the baselines to evaluate the effectiveness of controls. A more difficult but potential use would be to evaluate multiple exposures, suggests George Lucier, former director of the National Toxicology Program.

Released in January, the data support government efforts to control substances suspected of a human health link, the authors maintain, especially with respect to bans on tobacco smoke. For example, levels of cotinine, a metabolite of nicotine, have decreased 58% for children, 55% for adolescents, and 75% for adults when compared with levels measured in 1991–1994. At the same time, recent data show that cotinine levels in kids were more than twice the levels of adults, and levels in African Americans were more than twice the levels of Mexican Americans or whites. “Continued efforts to reduce exposure to environmental tobacco smoke are warranted,” the authors say.

Children were also found to have twice the levels as adults of chlorpyrifos and other commonly used organophosphate insecticides in their bodies. Levels of phthalates commonly found in soft PVC plastic products, particularly the more toxic phthalates, were higher in children than in adolescents and adults.

The data, however, doesn’t link exposures to disease, cautions Richard Jackson, director of CDC’s National Center for Environmental Health. From a regulatory perspective, there weren’t enough people in the study to determine whether the exposures exceed regulatory levels, and for many of the chemicals, there are no regulatory levels, adds Lynn Goldman, a former EPA official, and now a professor with the Johns Hopkins School of Public Health. Except perhaps for mercury, Goldman and several other researchers add. “As I looked at those 116 chemicals, the ones that showed levels that were close to or at levels that could cause effects in people, methyl mercury stood out,” says Lucier. The data show that “somewhere between 5 and 10% of women of childbearing age would exceed EPA’s [oral reference dose] for methyl mercury. This is far too many,” Lucier adds.

Public health advocacy groups hailed the report, and several released their own studies designed to interpret CDC’s data or to link exposures and disease risk.

Others called on Congress to provide states with better biomonitoring capabilities. “A comprehensive biomonitoring capacity could be used to do double duty, to protect our nation’s health by detecting environmental exposures and potential terrorism events,” says Shelley Hearne, executive director of Trust for America.

CDC officials plan to release future reports of exposure to cover two-year periods, with the next for 2003-2004. For a copy of the report, go to www.cdc.gov/exposurereport.