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Substances encountered in the environment can find their way into plants and animals, and humans. Most of what finds its way into us, from eating, drinking, breathing, even touching, finds its way out again. That is, we break down some of these substances and excrete or exhale them, whereas others may simply pass through. But some substances are not broken down or excreted so readily; these substances can build up and are usually stored in fatty tissue. This process is known as bioaccumulation. As the concentrations increase, a health risk could arise no matter whether the substance is "foreign" to the body (like lead or mercury) or whether it is needed by the body at lower concentrations (like vitamins or trace elements, e.g., selenium).
A related process called biomagnification is also very relevant to human health; it involves how materials may be passed up the food chain. If a little fish bioaccumulates a substance, and a bigger fish eats the smaller fish and, if both fish are incapable of metabolizing the substance, then the substance could magnify in concentration within each higher organism. Organisms at the top of the food chain, like the big fish in this example, could face a risk if the substance is harmful and if enough of the substance accumulates. In some cases, humans could be at the top of the food chain and receive a high concentration of a substance.
The Centers for Disease Control and Prevention (CDC) has undertaken a program of analysis of blood and urine samples of persons from around the country, looking for some of the hundreds of different substances that can usually be found in humans. The CDC's second National Exposure Report, issued in January 2003, showed that the "breakdown" products (also known as metabolites) of some phthalates were found in most of the samples. (The full CDC report may be found at http://www.cdc.gov/exposurereport/). Some have incorrectly concluded that the presence of these metabolites in these samples means that phthalates will continually build up in the body.
Phthalate exposures indicated by the CDC measurements were far below the safety levels set by the Environmental Protection Agency (EPA). Other studies have shown that phthalates are readily broken down by biological organisms such as fish and mammals. For people this occurs within 12 to 24 hours of entry. Thus, phthalates do not pose a bioaccumulative concern, nor do they biomagnify in food chains. Based on the science behind these conclusions, last year, both the EPA Office of Solid Waste and the State of Washington decided not to include phthalates on their lists of persistent, bioaccumulative and toxic materials.
Panel statements on both CDC exposure reports may be found in the Media Center section (2001, 2003) of www.phthalate.org.
Last Updated: May 27, 2003
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