Silent Spring at 50
Sources and References
The Fourth Report on Human Exposure to Environmental Chemicals has measured 212 chemicals in people's blood or urine–75 of which have never before been measured in the U.S. population. The term environmental chemical refers to a chemical compound or chemical element present in air, water, food, soil, dust, or other environmental media (e.g., consumer products). Biomonitoring is the assessment of human exposure to chemicals by measuring the chemicals or their metabolites in such human specimens as blood or urine. A metabolite is a chemical alteration of the original compound produced by body tissues. Blood, serum, and urine levels reflect the amount of the chemical that actually gets into the body by all routes of exposure, including ingestion, inhalation, and dermal absorption. The measurement of an environmental chemical in a person's blood or urine is a measure of exposure; it does not by itself mean that the chemical causes disease or an adverse effect.
Widespread Exposure to Some Industrial Chemicals
Findings in the Fourth Report indicate widespread exposure to some commonly used industrial chemicals.
- Polybrominated diphenyl ethers are fire retardants used in certain manufactured products. These accumulate in the environment and in human fat tissue. One type of polybrominated diphenyl ether, BDE–47, was found in the serum of nearly all of the NHANES participants.
- Bisphenol A (BPA), a component of epoxy resins and polycarbonates, may have potential reproductive toxicity. General population exposure to BPA may occur through ingestion of foods in contact with BPA–containing materials. CDC scientists found bisphenol A in more than 90% of the urine samples representative of the U.S. population.
- Another example of widespread human exposure included several of the perfluorinated chemicals. One of these chemicals, perfluorooctanoic acid (PFOA), was a byproduct of the synthesis of other perfluorinated chemicals and was a synthesis aid in the manufacture of a commonly used polymer, polytetrafluoroethylene, which is used to create heat–resistant non–stick coatings in cookware. Most participants had measurable levels of this environmental contaminant.
For most of the environmental chemicals included in the Fourth Report, more research is needed to determine whether exposure at the levels reported is a cause for health concern. The Fourth National Report on Human Exposure to Environmental Chemicals 2009 and the Updated Tables, February 2011. Centers for Disease Control and Prevention. www.cdc.gov
Chlordane remains in the food supply because much of the farmland was treated with chlordane in the 1960s and 1970s, and it remains in some soil for over 20 years. However, since chlordane has been banned, the levels in soils would be expected to decrease with the passage of time. Chlordane may also be found in fish and shellfish caught in chlordane–contaminated waters. Agency for Toxic Substances and Disease Registry (ATSDR).
1994 Toxicological profile for chlordane. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
Polybrominated diphenyl ethers (PBDEs) are man–made chemicals found in plastics used in a variety of consumer products to make them difficult to burn. Very little is known about the health effects of PBDEs in people, but effects have been reported in animals. …We do not know whether PBDEs can cause cancer in humans. Rats and mice that ate food with decabromodiphenyl ether (one type of PBDE) throughout their lives, developed liver tumors. Based on this evidence, the EPA has classified decabromodiphenyl ether as a possible human carcinogen. PBDEs with fewer bromine atoms than decabromodiphenyl ether are listed by the EPA as not classifiable as to human carcinogenicity due to the lack of human and animal cancer studies. Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Toxicological Profile for Polybrominated Biphenyls and Polybrominated Diphenyl Ethers. Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
Levels of DDT and DDE in the U.S. Population
In the Fourth National Report on Human Exposure to Environmental Chemicals (Fourth Report), CDC scientists measured DDT and its metabolite DDE in the serum (a clear part of blood) of at least 1,956 participants aged 12 years and older who took part in CDC's National Health and Nutrition Examination Survey (NHANES) during 2003–2004. Prior survey periods of 1999–2000 and 2001–2002 are also included in the Fourth Report. By measuring DDT and DDE in the serum, scientists can estimate the amounts of these chemicals that have entered people's bodies.
- A small portion of the population had measureable DDT. Most of the population had detectable DDE. DDE stays in the body longer than DDT, and DDE is an indicator of past exposure.
- Blood serum levels of DDT and DDE in the U.S. population appear to be five to ten times lower than levels found in smaller studies from the 1970s.
Finding measurable amounts of DDT and DDE in serum does not mean that the levels of these chemicals cause an adverse health effect. Biomonitoring studies of serum DDT and DDE can provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of DDT and DDE than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.
DDT, DDE, and DDD have been found in at least 442 of the 1,613 current or former NPL sites. However, the total number of NPL sites evaluated for these substances is not known. As more sites are evaluated, the sites at which DDT, DDE, and DDD are found may increase. This information is important because exposure to these substances may harm you and because these sites may be sources of exposure.
Based on all of the evidence available, the Department of Health and Human Services has determined that DDT is reasonably anticipated to be a human carcinogen. Similarly, the International Agency for Research on Cancer (IARC) has determined that DDT is possibly carcinogenic to humans. EPA has determined that DDT, DDE, and DDD are probable human carcinogens. Agency for Toxic Substances and Disease Registry (ATSDR). 2002. DDT, DDE y DDD). September 2002