“…the presence of a chemical in a blood or urine specimen does not mean that the chemical causes a health risk or disease.” Centers for Disease Control and Prevention (2005)
Throughout our lives, humans are continually exposed to both naturally occurring and synthetic substances in our environments. Although scientists have long understood that our bodies absorb tiny amounts of chemical substances simply by interacting with our environment, today’s technology allows researchers to detect and measure trace concentrations of many environmental substances in the body.
The measurement of trace compounds in humans is referred to as biological monitoring, or biomonitoring. Biomonitoring usually involves the analysis of blood, urine or other body tissues and fluids. Typically, biomonitoring studies rely on volunteers to provide samples of fluid and/or tissue at a single point in time.
Scientists have now developed very sensitive tests that can find a millionth of a gram (3.5 hundred millionths of an ounce) or even less of certain chemicals or their metabolites (breakdown products) in blood or urine. In July 2006, an expert committee of the National Academy of Sciences (NAS) published the results of a comprehensive study of biomonitoring. The Committee expressed its view that, “In spite of its potential, tremendous challenges surround the use of biomonitoring, and our ability to generate biomonitoring data has exceeded our ability to interpret what the data mean to public health.”*
Many population-based biomonitoring efforts are taking place in the United States and in Europe. In the United States, the Centers for Disease Control and Prevention (CDC) publishes periodic national reports on human exposure to environmental chemicals in a representative sample of the U.S. population as part of the National Health and Nutrition Examination Survey (NHANES). The NHANES survey now includes biomonitoring for 275 substances, including a number of phthalates. Other government organizations, including EPA and the National Institutes of Health (NIH), are conducting and sponsoring biomonitoring studies.
These CDC reports provide a snapshot of the U.S. population’s exposure to phthalates and other substances in our environment, from naturally occurring compounds and food nutrients to the products and processes of modern life. This type of data can be very useful in understanding the extent to which people have been exposed to particular substances and providing guidance for additional research into the relationship between environmental substances and the human body. As CDC notes in its National Reports on Human Exposure to Environmental Chemicals, “the presence of a chemical in a blood or urine specimen does not mean that the chemical causes a health risk or disease.”
For phthalates, there have been three sets of such biomonitoring data generated by the CDC. The first was data for samples from 1,029 people, selected to be representative of the U.S. population. This information was released in March 2001 as part of the CDC’s First National Report on Human Exposure to Environmental Chemicals. Two more national reports have since been issued, and the total number of subjects for whom results have been released now totals more than 5,000.
The CDC reports are, in all, very good news because the trace levels of phthalates found are well within safety levels established by the Environmental Protection Agency (EPA) and therefore should not pose a concern for human health. The tables below show how the exposures for various demographic groups compare to the safety levels (the Reference Dose or RfD) set by the EPA.
Phthalate Exposures Based on Third CDC National Exposure Reporta Expressed as Micrograms per Kilogram of Body Weight per Dayb
Larger View
a Third National Report on Human Exposure to Environmental Chemicals, U.S. Centers for Disease Control and Prevention, July 2005.
b The urinary concentrations of phthalate monoesters reported by CDC were converted to daily intake of the parent phthalate using the methodology described in David, R. (2000).
* National Research Council, Human Biomonitoring for Environmental Toxicants, Committee on Human Biomonitoring for Environmental Toxicants, National Academy Press, 316 pages (2006).
