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March 21, 2001 7:26 AM

Major Findings 
First-Time Information About Exposure Levels for the U.S. Population 
U.S. Population-Based Reference-Range Information for Physicians and Health Researchers 
Blood Lead Levels Decline Among Children Since 1991-1994 
Better Assessment of Children's and Women’s Exposure to Mercury 
Setting Priorities for Research on Phthalates 
Reduced Exposure of the U.S. Population to Environmental Tobacco Smoke 

First-Time Information About Exposure Levels for the U.S. Population

The Report provides information to scientists, public health officials, and the public about exposure to environmental chemicals in the U.S. population. It provides measures of exposure for 27 chemicals in the U.S. population based on blood and urine samples from people participating in the 1999 National Health and Nutrition Examination Survey (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 on the U.S. population’s exposure to 24 additional environmental chemicals (metals, organophosphate pesticides, and phthalates). Because the sample size in any one year of NHANES is relatively small and because the 1999 survey was only conducted in 12 locations across the country, data from additional years of the survey will be needed to confirm these findings.
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U.S. Population-Based Reference-Range Information for Physicians and Health Researchers

The 1999 Report provides unique reference range values that are based on a sampling of the U.S. population. CDC had previously determined U.S. population-based reference ranges for lead, cadmium, and cotinine using NHANES data; the 1999 Report provides U.S. population-based reference-range results for 24 additional environmental chemicals.

Physicians use "normal" ranges for laboratory results to determine whether their patients have high or low values that would indicate a health problem. These normal ranges are obtained from people who are generally healthy. In the 1999 Report, CDC determined "reference ranges" for 24 environmental chemicals from a group of people from the general population who were selected without regard to known exposure to these chemicals. Sometimes these reference ranges are referred to as background exposure levels.

Reference ranges are extremely helpful to physicians and health researchers because levels above the reference range usually indicate exposure to a particular source. For example, if a physician was concerned about a patient's potential exposure to cadmium and measured a cadmium level in the patient’s urine, the results could be compared with the population reference range in the 1999 Report. A cadmium level similar to those found in the Report would indicate exposure no different from those found in the general population, and a level much higher than those found in the Report would indicate that there may have been an unusual exposure to cadmium worthy of further investigation.
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Blood Lead Levels Decline Among Children Since 1991-1994

Since 1976, CDC has measured levels of lead in blood as part of the NHANES surveys. 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 (mg/dL), from 2.7 mg/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, and highlights the success of public health efforts to decrease the exposure of children to lead. Nevertheless, 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 major public health concern

For more information see CDC’s Childhood Lead Poisoning Prevention Program http://www.cdc.gov/nceh/lead/lead.htm.
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Better Assessment of Children's and Women’s Exposure to Mercury

The 1999 Report provides important new data on levels of mercury in blood levels among children 1 to 5 years old and among women of childbearing age (16-49 years old). The geometric mean of blood mercury levels among children (0.3 mg/L) was about 25% of the geometric mean of blood mercury levels among women of childbearing age (1.2 mg/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.
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Setting Priorities for Research on phthalates

Phthalates are compounds commonly used in such consumer products 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 the 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 1999 Report showed levels of metabolites of DEP and DBP to be much higher in the population than 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 the levels of their metabolites are much higher in the general U.S. population. 
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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. ETS has been identified as a known human carcinogen. From 1988 through 1991, as part of the NHANES III survey, 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 U.S. population to environmental tobacco smoke since the period 1988-1991. However, since more than half of American youth are still exposed, ETS remains a major public health concern. 


For more information see CDC’s National Tobacco Control Program at http://www.cdc.gov/tobacco.

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