Phthalates do not bioaccumulate. That is, they do not build up in the body. Humans break them down quickly and dispose of them within 12 to 24 hours.
Phthalates do not biomagnify in the food chain. That is, they do not build up in the bodies of fish or animals that larger animals or humans ingest.
Substances encountered in the environment can find their way into plants and animals, and into 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. 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 increase with increasing levels in the food chain. If a small 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 large fish in this example or humans, could face a risk if the substance is harmful and if enough of the substance accumulates in the organism’s tissues.
The Centers for Disease Control and Prevention (CDC) has undertaken a program to analyze human blood and urine, looking for hundreds of different substances. The CDC's Fourth National Report on Human Exposure to Environmental Chemicals, , issued in 2009 with updated tables issued in September of 2013, 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 humans, this occurs within 12 to 24 hours. Thus, phthalates do not bioaccumulate, nor do they biomagnify in food chains.
Human Exposure & Biomonitoring
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 more than 300 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 8,000 for certain phthalates.
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, Updated Tables, September 2013, U.S. Centers for Disease Control and Prevention.
3 An RfD is an exposure level defined by EPA as "an estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime."