Throughout our lives, humans are exposed to both natural and synthetic chemicals in our environment. Although scientists have long understood that our bodies absorb some amount of these substances, today’s scientific techniques allow researchers to measure trace amounts in the body.
This measurement process is referred to as biological monitoring, or biomonitoring. Biomonitoring is the analysis of blood, urine or other body tissues or fluids of volunteers who provide samples from 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.”1
Population-based biomonitoring studies are on-going in the United States and in Europe. The U.S. Centers for Disease Control and Prevention (CDC) publishes periodic national reports on human exposure to environmental chemicals as part of the National Health and Nutrition Examination Survey (NHANES). The NHANES survey now includes biomonitoring for 212 substances, including a number of phthalates. Other U.S. government organizations, including the Environmental Protection Agency (EPA) and the National Institutes of Health, are conducting and sponsoring biomonitoring studies.
The CDC reports provide a snapshot of the U.S. population’s exposure to chemicals, including some phthalates, in our environment. These data can be very useful in understanding exposure to particular substances and providing guidance for additional research into the relationship between environmental substances and the human body. As CDC notes in its Fourth National Report on Human Exposure to Environmental Chemicals: “[t]he measurement of an environmental chemical in a person’s blood or urine is an indication of exposure; it does not by itself mean that a chemical causes disease or an adverse effect.”2
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 CDC’s First National Report on Human Exposure to Environmental Chemicals. 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 confirm that the trace levels of phthalates detected are well within safety levels established by EPA and other regulatory agencies and, therefore, should not pose a concern for human health. The table below shows how the exposures for various demographic groups compare to the Reference Dose (RfD)3 set by EPA or safety levels set by other regulatory/scientific bodies.
Phthalate Exposures Based on Fourth CDC National Exposure Report
Expressed as Micrograms per Kilogram of Body Weight per Day
1 National Research Council, Human Biomonitoring for Environmental Toxicants, Committee on Human Biomonitoring for Environmental Toxicants, National Academy Press, 316 pages (2006).
2 The Fourth National Report on Human Exposure to Environmental Chemicals, U.S. Centers for Disease Control and Prevention, December 2009.
3 An RfD is an exposure level defined by EPA as "a numerical estimate of a daily oral exposure to the human population, including sensitive subgroups such as children, that is not likely to cause harmful effects during a lifetime."