Henry Falk, M.D., M.P.H.
National Center for Environmental Health
Agency for Toxic Substances and Disease Registry
Centers for Disease Control and Prevention
Current Science on Public Exposures to Toxic Chemicals
Committee on Environment and Public Works
Subcommittee on Superfund, Toxics and Environmental
United States Senate
Thursday February 4, 2010
Good morning Mr. Chairman and Members of the Subcommittee.
My name is Dr. Henry Falk, and I am the Acting Director of the National Center for Environmental Health at the Centers for Disease Control and Prevention (CDC), and of the Agency for Toxic Substances and Disease Registry (ATSDR).
I am pleased to appear today before the Subcommittee to discuss CDC’s work in assessing people’s exposure to chemicals. My testimony will focus on the biomonitoring program at CDC, and public health uses of biomonitoring.
For approximately three decades, CDC has been using biomonitoring to assess human exposure to selected chemicals (both manmade and naturally occurring). Biomonitoring is the direct measurement of chemicals and naturally occurring compounds or their metabolites in people’s blood, urine or tissue. It determines which chemicals—and how much of them—get into people after they have been exposed.
CDC’s Biomonitoring Program
I will describe two aspects of CDC’s biomonitoring program: assessment of the U.S. population’s exposure to chemicals, and targeted studies to examine exposure in vulnerable populations.
How CDC assesses the U.S. population’s exposure to chemicals: CDC’s Environmental Health Laboratory measures chemicals or their metabolites in blood and urine samples from participants in the National Health and Nutrition Examination Survey (NHANES). NHANES, which is conducted by CDC’s National Center for Health Statistics, involves a complete physical exam, a detailed questionnaire that collects more than 1,000 pieces of information, and the collection of blood and urine samples. The survey, which is nationally representative of the U.S. population, has been conducted multiple times since the 1970s and became a continuous survey in 1999 with two-year survey cycles. With some exceptions, most urine measurements are done in participants ages 6 years and older, and most serum measurements are done in participants age 12 years and older. Thus, the exposure information it provides on young children is limited, mostly due to the difficulty in obtaining large enough blood and urine samples from them. Currently blood levels of lead, cadmium, and mercury are measured in children aged 1 year and older, and cotinine, which is a marker for environmental tobacco smoke exposure, is measured in children aged 3 years and older.
CDC scientists publish significant biomonitoring findings from NHANES in peer-reviewed publications, and then CDC periodically publishes a summary report, the National Report on Human Exposure to Environmental Chemicals. The Fourth Exposure Report was released in December 2009, and summarizes blood and urine levels for 212 chemicals, including levels for 75 chemicals which had never before been measured in a representative sample of the U.S. population. Findings show evidence of widespread exposure in the U.S. population to some commonly-used commercial chemicals such as bisphenol-A (BPA), the perfluorinated compound known as PFOA, and a type of fire retardant known as BDE-47. The Fourth Exposure Report also notes continued progress in reducing children’s exposure to lead.
The data in the Fourth Exposure Report provide unique exposure information that can be used by scientists, physicians, and health officials for a variety of public health purposes, such as to: determine which chemicals get into Americans’ bodies and at what concentrations; determine what proportion of the population has levels above those associated with adverse health effects for chemicals with a known toxicity level; establish reference values that can be used by physicians and scientists to determine whether a person or group has an unusually high exposure; track over time trends in levels of exposure of the population; assess the effectiveness of public health efforts to reduce exposure of Americans to specific chemicals; determine whether exposure levels are higher among minorities, children, women of childbearing age, or other special groups; and direct priorities for research on human health effects from exposure.
Chemicals analyzed from the NHANES samples and reported in the Fourth Report were selected based on known or hypothesized exposure in the U.S. population; scientific data on the health effects known or thought to result from some levels of exposure; the need to assess the efficacy of public health actions to reduce exposure to a chemical with known health effects; the availability of an analytical method that is accurate, precise, sensitive, and specific; the availability of adequate blood or urine samples from the NHANES survey; and the analytical cost to perform the analysis. Also, CDC has solicited suggestions for candidate chemicals from the public and other government agencies.
Targeted studies: Each year CDC’s Environmental Health Laboratory works with states, other federal agencies, academic institutions and international organizations on 50-70 studies that examine vulnerable populations, particularly newborns, children, pregnant women and population groups or communities known or likely to have higher exposures. For example, one important current partnership is with the Eunice Kennedy Shriver National Institute of Child Health and Human Development at the National Institutes of Health. This partnership involves a pilot study of 525 pregnant women in which CDC is lending analytical and biomonitoring expertise. Scientists at CDC's Environmental Health Lab will measure chemicals in pregnant women’s blood and urine and, after delivery, in the newborn’s cord blood and mother’s breast milk. Cord blood is a promising way to assess prenatal exposure to certain chemicals. However, cord blood is not the best way to measure exposures to chemicals that pass through the body more quickly; these generally are best measured in urine.
Public Health Uses
As distinguished from measurements in environmental samples, such as air, soil, water, food, and consumer products, biomonitoring measurements have the advantage of indicating the amount of a chemical that actually gets into people, rather than extrapolating from measurements of environmental media. Although biomonitoring is far ahead of the science of interpreting what exposures mean for health, biomonitoring data is valuable, and CDC uses it for a range of public health purposes, including to establish reference ranges in the population and to identify groups of people with higher levels of exposure than those typical for the U.S. population. In addition, by tracking exposures in the U.S. population, we can detect trends in people over time, and assess whether a chemical is present in large numbers of people, or is disproportionately present in vulnerable subgroups, such as children. This information can be used by scientists and policy makers as one of the considerations in setting priorities for evaluating health impacts of chemicals. Biomonitoring thereby serves as one important tool in identifying and reducing or preventing exposures and potential health problems.
A National Research Council review of biomonitoring noted that it has been a key tool in some landmark public health actions (NRC, 2006). One example is lead. Our laboratory has been measuring lead in the NHANES blood samples since 1976. Many of the effects of lead can be benchmarked to blood lead concentrations. Lead is highly toxic, especially to young children, and can harm a child’s brain, kidneys, bone marrow, and other body systems. It can cause decrements in cognitive ability and IQ and at very high levels can cause coma, convulsions, and death.1 Our laboratory analysis of the NHANES samples, which showed that the American population’s blood lead levels were declining in parallel with declining levels of lead in gasoline, provided critical support for the Environmental Protection Agency (EPA) regulations that reduced lead in gasoline (GAO, 2000). CDC and EPA have used this decline in blood lead levels over time to demonstrate that the removal of lead from gasoline had a dramatic impact on the levels of lead in the U.S. population. Today, the most common source of children's exposure to lead is from dust and soil derived from lead-based paints in older homes.2 In the late 1970s, CDC used the NHANES data to document that 88 percent of children had blood lead levels above 10 μg/dL, the current level of concern. Data from the Fourth Exposure Report demonstrate that collaborative public health efforts by CDC, EPA, NIEHS, the Department of Housing and Urban Development, and others reduced children’s exposure to lead. For the period 1999–2004, only 1.4% of children aged 1 to 5 years had elevated blood lead levels.
Biomonitoring also can be used to monitor the effectiveness of interventions designed to reduce exposures. In the early 1990s, our laboratory analysis of cotinine data from NHANES showed that 88 percent of the nonsmoking population was exposed to secondhand tobacco smoke. This finding was used by state and local areas as a justification for restricting smoking in public places. Over the past 15 years, NHANES data have shown that exposure to secondhand smoke in nonsmokers has decreased about 70 percent, indicating that public health interventions to reduce exposure have been successful.
In conclusion, biomonitoring provides solid human data that can assist in making important health decisions. Better exposure information means that we can make better decisions to protect the health of the public.
CDC is fully committed to working with other federal agencies and partners to improve the uses and benefits of biomonitoring. Thank you Mr. Chairman and members of the Subcommittee. I look forward to answering any questions you may have.
National Research Council (2006). Human Biomonitoring for Environmental Chemicals. The National Academies Press, Washington, D.C.
United States General Accounting Office (2000). Toxic Chemicals: Long-Term
Coordinated Strategy Needed to Measure Exposures in Humans. Washington, D.C.
Fourth National Report on Human Exposure to Environmental Chemicals:
NHANES Web Site: http://www.cdc.gov/nchs/nhanes.htm
1 Eliminating Childhood Lead Poisoning: A Federal Strategy Targeting Lead Paint Hazards. Washington, DC: President’s Task Force on Environmental Health Risks and Safety Risks to Children; 2000.
2 Lanphear BP, Roghmann KJ. Pathways of lead exposure in urban children. Environ Res. 1997
Last revised: June 18, 2013