Throughout their lives, humans and other organisms are continually exposed to both naturally occurring substances and synthetic substances in our environments. Some chemicals are generated within our bodies; others are absorbed through eating, breathing, drinking and through contact with our surroundings. 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/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 minute traces - a millionth of a gram or even less - of certain chemicals or their metabolites (breakdown products) in blood or urine. Starting in 1999, advanced methods have been used by the Centers for Disease Control and Prevention (CDC) to test blood and urine samples from thousands of Americans for the presence of more than a hundred chemicals, from components of soybeans to phthalates.

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.

Prior to the CDC reports, scientists typically estimated human exposure to chemicals based on possible routes of exposure and on estimates of amounts of the chemicals present in the environment. Phthalates are among the materials for which such exposure estimates were developed. The estimated exposure levels for phthalates were well below the safety levels set by federal regulators. When the CDC began releasing the results of its biomonitoring, the prior estimates proved to be on the mark or to have erred on the side of safety by overestimating exposure.

The CDC reports are, in all, very good news because the trace levels of phthalates found are well within EPA safety levels 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 set by the EPA.

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^a.Third National Report on Human Exposure to Environmental Chemicals, U.S. Centers for Disease Control and Prevention, January 2003.

^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). Exposure to phthalate esters. Environmental Health Perspectives 108(10):A440. The values given by this methodology are very similar to values derived by a separate methodology used by the CDC and the National Institute for Environmental Health Sciences. Kohn, M., et al. (2000). Human exposure estimates for phthalates. Environmental Health Perspectives 108(10):A440-442.

Last Updated: April 26, 2007