By: Centers for Disease Control and Prevention
Source: Centers for Disease Control and Prevention. National Report on Human Exposure to Environmental Chemicals. Atlanta, March 2001.
About the Organization: The U.S. Centers for Disease Control (CDC), an agency of the Department of Health and Human Services, is the premiere authority on U.S. health matters, especially those pertaining to infectious disease. The federal agency began in 1946 as the Communicable Disease Center, with the mission to fight malaria and typhus in the Deep South. The CDC, headquartered in Atlanta, Georgia, includes a dozen centers and institutes across the United States.
Rachel Carson is credited with bringing the hazards of toxic pollution to the attention of the American public in her 1962 book Silent Spring, which documented the danger of the powerful pesticide DDT (dichlorodiphenyltrichloroethane). DDT was applied directly to people during World War II (1939–1945) to control malaria and typhus. DDT is neurotoxic, meaning its toxic effects are targeted at the brain and central nervous system. It was banned in the United States in 1973.
By the 1990s, Americans had become much more aware of potential toxic substances lurking in the environment. Most arise from electricity production, automobile exhaust emissions, manufacturing industries, incinerators, pesticides, herbicides, and fertilizers. However, even such mundane things as cooking fumes, carpets, and copy machine toner contain toxic chemicals. Several federal laws, such as the Toxic Substance Control Act and the Federal Insecticide, Fungicide, and Rodenticide Act, are meant to protect human health, wildlife, and the environment from toxic substances.
It is important for federal agencies like the U.S. Centers for Disease Control (CDC) and the Environmental Protection Agency (EPA) to know exactly what toxic substances humans are coming into contact with and which ones are actually getting into our bodies. Toxic substances can be inhaled into the lungs, ingested through the mouth, or absorbed through the skin. Once inside the body, the toxic substance itself or a metabolite will end up in blood and eventually in urine.
In the 1990s, technological advances in molecular biology and analytical chemistry allowed the CDC to measure small amounts of many chemicals directly in blood and urine samples. Before this, the CDC measured blood levels of only one or two substances, such as lead. They estimated exposure to most other things by the levels found in air, water, or soil. The first National Report on Human Exposure to Environmental Chemicals measured twenty-seven chemicals in four main groups: metals, tobacco smoke, organophosphate pesticides, and phthalates.
One of the toxic metals the CDC checked for was mercury. The effects of this toxic metal are targeted at the brain and central nervous system. Because of its unique property—the only metal that exists as a liquid at room temperature—mercury was used in a wide variety of products, such as batteries, fungicides, and electrical switches. Mercury is also emitted into the air from coalfired electric power plants.
We are exposed to mercury from eating fish. Mercury is emitted into the air and travels through the atmosphere until it falls back to the earth in rainwater and from there, into lakes, rivers, and oceans. Bacteria in the water convert it into a more toxic form called methylmercury, which makes its way up the food chain to accumulate in larger fish. Even fish from pristine lakes contain mercury. Many states have fish consumption advisories that provide guidelines for how much of certain types of fish it is safe to eat.
The first National Report on Human Exposure to Environmental Chemicals provided information about the levels of twenty-seven chemicals in the blood or urine of the U.S. population. The CDC looked for four main groups of substances: metals, including lead, mercury, cadmium, and uranium; one metabolite of tobacco smoke, cotinine; the metabolites of pesticides such as diazinon, parathion, and chlorpyrifos; and metabolites of the ubiquitous compounds called phthalates, present in many common everyday products.
The results of the report helped the CDC, the EPA, and others zero in on potential health threats from the measured toxic substances. The importance of monitoring the public's exposure to toxic substances is illustrated by the metal lead, which affects the brain and nervous system. Lead poisoning can lead to learning and behavior problems, headaches, and even seizures and death. In the early 1970s, data on lead concentrations in the blood of Americans was very high, helping persuade Congress to enact laws mandating the removal of lead from gasoline in 1972. In turn, blood lead data gathered between 1976 and 1990 indicated that the ban on leaded gasoline had worked, as blood lead levels were much lower. The 1999 report also checked for lead and found that, except for a small segment of children, blood lead levels were even lower than they had been around 1990. Still worrisome, though, were the lead levels for poor urban children, who are usually exposed to lead from old buildings where lead-based paint still on the walls is chipping and peeling away. These results allowed the CDC to focus on providing health treatments for urban children and signaled to the EPA the need to remove the source of the problem.
Reports on human exposures to toxic substances have proven extremely helpful to scientists, medical professionals, and the government. The CDC released a second national exposure report in early 2003, which quadrupled the number of toxic chemicals measured to 116. The CDC intends to collect data on the levels of toxic substances in American blood and urine every year and to include a greater number of chemicals when possible. As data is collected over the years,researchers will be better able to protect humans from toxic exposures.
Primary Source: National Report on Human Exposure to Environmental Chemicals [excerpt]
SYNOPSIS: Some of the major findings of the 1999 CDC report, such as the levels of chemicals present in the blood and urine of Americans, are outlined in the following excerpts.
First-time Information about Exposure Levels for the U.S. Population
The 1999 Report provides measures of exposure for levels of 27 chemicals in the U.S. population that are based on blood and urine samples obtained from people participating in NHANES 1999. For three chemicals—lead, cadmium, and cotinine—CDC has previously assessed the population's exposure through NHANES, and this Report provides new data for the 1999 calendar year. The Report provides information for the first time about the U.S. population's exposure to 24 additional environmental chemicals (metals, organophosphate pesticides, and phthalates). Because the sample size in one year of NHANES is relatively small and because the 1999 survey was conducted only in 12 locations across the country, data from additional years of the survey will be needed to confirm these findings.…
Decline in Blood Lead Levels among Children since 1991–1994
Since 1976, CDC has measured blood lead levels as part of NHANES. Results presented in the Report for 1999 show that the geometric mean blood lead level for children aged 1–5 years has decreased to 2.0 micrograms per deciliter (μg/dL), from 2.7 μg/dL, the geometric mean for the period 1991–1994. This decrease documents that blood lead levels continue to decline among U.S. children when considered as a group, highlighting the success of public health efforts to decrease the exposure of children to lead. However, special populations of children at high risk for lead exposure (e.g., those living in homes containing lead-based paint or lead-contaminated dust) remain a public health concern.
Reduced Exposure of the U.S. Population to Environmental Tobacco Smoke
Cotinine is a metabolite of nicotine that tracks exposure to environmental tobacco smoke (ETS) among nonsmokers. Higher cotinine levels reflect more exposure to ETS, which has been identified as a known human carcinogen. From 1988 through 1991, as part of NHANES III, CDC determined that the median level (50th percentile) of cotinine among nonsmokers in the United States was 0.20 nanograms per milliliter (ng/mL). Results from the 1999 Report showed that the median cotinine level among people aged 3 years and older has decreased to less than 0.050 ng/mL—more than a 75% decrease. This reduction in cotinine levels objectively documents a dramatic reduction in exposure of the general population to ETS since 1988–1991. However, since more than half of American youth are still exposed, ETS remains a major public health concern.
Better Assessment of Children's and Women's Exposure to Mercury
The 1999 Report provides important new data about blood mercury levels among children aged 1–5 years and among women of childbearing age (16–49 years old). The geometric mean of blood mercury levels among children (0.3μg/L) was about 25% of the geometric mean of blood mercury levels among women of childbearing age (1.2μg/L). Compared with an adult, the fetus and child are usually more vulnerable to the effects of metals. Consequently, when addressing mercury exposures, health officials are particularly careful to protect the fetus and child. The Report provides data for children and levels for women of childbearing age that reflect levels of mercury to which the fetus is exposed. Scientists will use these new data to better estimate health risks for the fetus, children, and women of childbearing age from potential sources of mercury exposure.
Setting Priorities for Research on PhthalatesPhthalates are compounds commonly used in consumer products such as soap, shampoo, hair spray, and many types of nail polish. Some phthalates are used in flexible plastics such as blood bags and tubing. Animal research has focused on evaluating reproductive effects of phthalates. For the 1999 Report, CDC scientists measured metabolites of seven major phthalates. Di-2-ethylhexyl phthalate (DEHP) and di-isononyl phthalate (DINP) are the two phthalates produced in greatest quantity, with diethyl phthalate (DEP) and dibutyl phthalate(DBP) produced in much lower quantities. However, data from the Report showed that levels of metabolites of DEP and DBP were much higher in the population than levels of metabolites of either DEHP or DINP. These new data have prompted CDC to conduct additional studies to explain these findings by examining the pathways by which these phthalates get into people's bodies. The data also indicate that health research needs to focus on DEP and DBP, given that levels of their metabolites are much higher in the general population than metabolite levels of phthalates produced in the largest quantities.
Colborn, Thomas, Dianne Dumanoski, and John Peterson Myers. Our Stolen Future: Are We Threatening Our Fertility, Intelligence, and Survival? A Scientific Detective Story. New York: Dutton, 1996.
Davis, Devra Lee. When Smoke Ran like Water: Tales of Environmental Deception and the Battle Against Pollution. New York: Basic Books, 2002.
Whelan, Elizabeth, A. Toxic Terror: The Truth Behind the Cancer Scares. Buffalo, N.Y.: Prometheus, 1993.
Ott, W.R., and J.W. Roberts. "Everyday Exposure to Toxic Pollutants." Scientific American, February 1998, 86–91.
Wakefield, Julie. "Human Exposure: The Key to Better Risk Assessment." Environmental Health Perspectives 108, no. 12, December 2000, A558.
National Library of Medicine. "ToxTown." National Library of Medicine. Available online at ; website home page: http://toxtown.nlm.nih.gov (accessed March 17, 2003).
U.S. Centers for Disease Control. "Second National Report on Exposures to Environmental Chemicals. The U.S. Centers for Disease Control. Available online at http://www.cdc.gov/exposurereport; website home page: http://www.cdc.gov (accessed March 17, 2003).
World Wild Life Fund. "Toxic Chemicals." World Wild Life Fund. Available online at http://www.worldwildlife.org/toxics/progareas/ed/index.htm; website home page: http://www.worldwildlife.org (accessed March 16, 2003).