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Biomonitoring Data



  • 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.

Background

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 Issue

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.

The Evidence

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

 

Larger View

a Fourth National Report on Human Exposure to Environmental Chemicals, U.S. Centers for Disease Control and Prevention, December 2009.
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).
c Below the limit of detection.
d The RfDs for DEP, DBP, BBP, and DEHP are the reference doses derived by the U.S. Environmental Protection Agency (EPA), as presented in the Integrated Risk Information System (IRIS) database.. The value for DINP is the Acceptable Daily Intake recommended to the U.S. Consumer Product Safety Commission by its Chronic Hazard Advisory Panel in June 2001. The values for DMP and DnOP are estimated from available information reported in studies on laboratory animals; no reference levels have been established by regulatory agencies.

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