Centers for Disease Control and Prevention. 2003. Second National Report on Human Exposure to Environmental Chemicals. NCEH Pub. No. 02-0716.

A sampling of press coverage:
TomPaine.com
Detroit Free Press
Newsday
New York Times
San Francisco Chronicle
San Francisco Chronicle op-ed
Washington Post
MSNBC

In the largest and most extensive survey of American body burdens of environmental chemicals ever undertaken, the Centers for Disease Control found widespread low-level contamination in a random sample of Americans in 1999-2000.

The good news is that steps taken to reduce exposures are having a positive effect, and that current levels of most of the chemicals measured are beneath those known to cause harm.

The bad news?

• Some chemicals are present at levels associated with health effects. Among the most troubling findings are:

  confirmation of an earlier, smaller CDC study that documented widespread exposure to phthalates.

  levels of phthalates are highest in children and women of reproductive age, creating the potential for developmental effects on the fetus and children.

  up to 10% of American women carry mercury concentrations near the level considered to put fetal development at risk to neurological damage.

• While this is the most ambitious body burden survey ever undertaken, it measured only 116 of the thousands of chemicals in modern use. Many of those thousands are unlikely to have health effects. But the survey left out many compounds, like arsenic, bisphenol A and the polybrominated diphenyl ethers, now known to be biologically active at low levels and known to interfere, in animals, with important developmental processes. These compounds are used in processes and products that certainly create human exposures.

• The health implications of most of the exposures the CDC found are largely unknown, because few of the chemicals measured have thorough toxicological profiles. Indeed most have received little study, particularly of developmental effects, which are likely to be the most sensitive to low level exposures. None have been studied thoroughly for health impacts in the mixtures in which they were found.

What did they do? Scientists and health professionals collaborating with the CDC obtained blood and urine samples from subjects participating in the National Health and Nutrition Examination Survey (NHANES) during 1999 and 2000. This survey is one of a series conducted by the CDC to track the health and nutritional status of people living in the US. These samples were then analyzed by CDC chemists to determine blood or urine levels of 116 chemicals.

Choice of which chemicals to analyze was based on several considerations, including potential importance to health, cost and availability of suitable assays. No standardized analytical techniques have been developed for many compounds of potential interest.

The compounds measured included an array of metals like lead, cadmium, colbalt and uranium, organochlorine pesticides like DDT, metabolites of organophosphate pesticides, other modern use pesticides including atrazine and chemicals like dioxins and furans produced as byproducts of industrial processes and incineration. The pesticide measurements usually focused on metabolites of the compounds rather than the pesticide itself.

What did they find? For several contaminants for which historical data are available, body burdens are down significantly. For example, the percentage of children with blood lead levels above 10 µg/dL, the level at which current data indicate children suffer neurological impacts, has been cut in half since the last survey in 1991-94.

DDT and PCB levels are also down markedly. Hexachlorobenzene, another organochlorine pesticide banned from use in the US in 1984, was detected in only 0.6% of people sampled. Dioxins, furans and co-planar PCBs were not detectable in most people measured, although the small amount of blood sampled from each person and the detection limits of the analytical techniques limits the conclusions that can be drawn from this dioxin result.

All these declines reflect the impacts of strong protective measures put in place to restrict or eliminate use of the compound.

Metabolic traces of some agricultural pesticides were noticably higher in Mexican Americans than in African Americans or non-Hispanic whites. This was found for several compounds now banned in the US, for example DDT and hexachlorocylclohexane, as well at least one current-use pesticide, parathion. The average DDE level found in Mexican Americans was 674 ng/g compared to 295 ng/g and 217 ng/g in African Americans and non-Hispanic whites, respectively.

For most of the chemicals measured, too few historical data exist to allow any assessment of trends. This study will serve as an important benchmark against which to measure future progress. Residential uses of chlorpyrifos, for example, ended in 2001; parathion use will be banned in 2003. The next CDC body burden assessment should find reduced levels.

Time trends on mercury are not available, although ongoing large-scale liberation of mercury into the environment (particularly via combustion of coal) and incorporation thereafter into the food chain (particularly fish) would indicate that body burdens are rising (see the United Nations Global Mercury Assessment, January 2003). Average levels observed in American women and children are, respectively, approximately 1/50th and 1/100th the lowest level known to cause neurodevelopmental problems (58 µg/L). Approximately 10% of US women, however, carry mercury at blood concentrations much closer to this level. Over time, the recurring pattern in studies of neurodevelopmental risks is for new research to reveal greater sensitivity, as research designs become more sophisticated. Hence the gap between that concentration known to cause effects and levels experienced by many women is not reassuring.

Results on phthalates confirmed and extended the CDC's 2000 finding that virtually all Americans carry a body burden of these plasticizers. As with the previous work, phthalate contamination levels were determined by measuring urinary metabolites of the phthalates, not the parent compound itself. In this survey, different types of phthalates showed different patterns.

For example, the metabolite of dibutyl phthalate (commonly used in cosmetics) reaches higher levels in women than in men; is higher in African Americans than in non-Hispanic whites; and is higher in children than in adults.

The metabolite of di-2-ethylhexyl phthalate (used as a plasticizer in polyvinyl chloride and thus common in toys, flexible tubing, shower curtains, etc.) is also higher in children than adults. The FDA has recently recommended that DEHP be removed from medical equipment that might create exposures for fetal and infant males, and the European Union has banned the use of DEHP in toys intended for young children's use.

In November 2002 the EU also mandated removal of dibutyl phthalate and di-2-ethylhexyl phthalate from cosmetics.

The phthalate levels reported in this study by the CDC are very similar in magnitude to those found by a Harvard study published in 2003 to be associated with sperm damage in men living in the Boston area.

What does it mean? This study offers new insights into patterns of contamination of people living in America. Its clearest message is that public decisions to reduce exposures can yield dramatically positive results. Lead and DDT are two prime examples.

The report brings additional value by providing a baseline against which future measurements can be compared, allowing trends to be tracked, and by providing health professionals a snapshot of typical contamination patterns. This may be helpful in diagnostic work because it will be a benchmark against which to compare contamination burdens of their patients.

These contributions are important, but equally important is the spotlight that this report shines on ignorance. Too little information is available on the human health impacts of the vast majority of chemicals surveyed, one-by-one and especially their effects in complex mixtures. Indeed, too few of the thousands of potential chemicals that are likely to be part of the human body burden were sampled by this study.

With growing evidence, mostly from animal experiments, that low-level exposures to biologically-active contaminants are plausibly linked to a range of human health effects, this state of ignorance is unacceptable.

In the absence of dramatically stronger, scientifically-based assurances of safety, efforts to reduce exposures to biologically-active compounds should be redoubled. Those assurances now rest on the absence of data—the requisite studies simply haven't been done—instead of on carefully conducted studies demonstrating no harm.