About 5 percent of the US population aged 20 years and older had urinary cadmium at or near 1 microgram per gram of creatinine, a level that may be associated with subtle kidney injury and an increased risk for low bone mineral density.

These are some of the key findings in The Third National Report on Human Exposure to Environmental Chemicals, released yesterday by the Centers for Disease Control and Prevention (CDC).

"This is the most extensive assessment ever of Americans’ exposure to environmental chemicals," said CDC Director Dr. Julie Gerberding. "It shows we’re making tremendous progress, and that’s good news.... However, many challenges remain. CDC is steadfast in its commitment to health protection, including protection from environmental threats."

Children More Vulnerable to Secondhand Smoke

Levels of a chemical called cotinine, which is a marker of exposure to secondhand smoke in nonsmokers, have dropped significantly since levels were first measured from 1988 to 1991. Compared with median levels for 1988 to 1991, median cotinine levels measured from 1999 to 2002 have decreased 68 percent in children, 69 percent in adolescents, and about 75 percent in adults.

Still, some populations remain at greater risk; the third report shows that non-Hispanic blacks have levels twice as high as those of non-Hispanic whites or Mexican Americans, and children’s levels are twice as high as adults’ levels.

New data on blood lead levels in children aged 1 to 5 years show that for 1999 to 2002, 1.6 percent of children aged 1 to 5 years had elevated blood lead levels (levels of 10 micrograms per deciliter or greater -- the CDC blood lead level of concern). This percentage has decreased from 4.4 percent in the early 1990s.

"Lowering blood lead levels in children is one of the major environmental health accomplishments of the past 30 years," said Dr. Jim Pirkle, Deputy Director for Science at CDC’s Environmental Health Laboratory.

"However, CDC is still concerned about exposure to lead from lead-based paint and lead-contaminated house dust, soil and consumer products," Dr. Pirkle added. "There is no safe blood lead level in children. Children are best protected by controlling or eliminating lead sources before they are exposed."

Cadmium Levels Ringing Alarm Bells

Urine levels of the metal cadmium as low as 1 microgram per gram of creatinine may be associated with subtle kidney injury and an increased risk for low bone mineral density, recent studies have shown. About 5 percent of the US population aged 20 years and older had urinary cadmium at or near these levels, according to the CDC report.

Cigarette smoking is the likely source for these higher cadmium levels. More research is needed on the public health consequences of these levels in people in this age group, says the CDC.

CDC’s Environmental Health Laboratory measured 148 chemicals -- 38 of which have never been measured in the US population -- or their breakdown products (metabolites) in blood or urine for the latest report.

The samples were collected from approximately 2,400 people who participated in CDC's National Health and Nutrition Examination Survey (NHANES) from 1999 to 2002. NHANES is an ongoing national health survey of the general US population.

The report provides exposure data on the US population by age, sex, and race or ethnicity.

Research Priorities

In addition to lead and cadmium, the report includes extensive data for mercury and other metals; phthalates; organochlorine pesticides; organophosphate pesticides; pyrethroid insecticides; herbicides; polycyclic aromatic hydrocarbons; dioxins and furans; polychlorinated biphenyls; and phytoestrogens.

CDC conducts this research to learn more about the effectiveness of public health interventions and better understand the health risks of exposure to chemicals in the environment.

Research separate from the report’s findings is needed to determine the relationship between levels of chemicals in the blood or urine and health effects. The results presented in this and future reports will help set priorities for research on human health risks resulting from exposure to environmental chemicals.

The Third National Report on Human Exposure to Environmental Chemicals and an executive summary are available online.