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Friday, September 1, 2000, 12:00 p.m. EDT
For the first time, scientists from the Centers for Disease Control and Prevention (http://www.cdc.gov) 's (CDC's) National Center for Environmental Health (http://www.cdc.gov/nceh/) have been able to measure in humans the presence of metabolites of seven phthalates, chemicals used in plastics, solvents, detergents, and many other products.
Because of ongoing concern that some animal studies have shown that phthalates may cause cancer or interfere with reproduction, the study was initiated as part of a collaboration between the National Toxicology Program (NTP), which is headquartered at the National Institute of Environmental Health Sciences (http://www.niehs.nih.gov) (NIEHS), and CDC to measure levels of phthalate metabolites in humans. Titled "Levels of Seven Urinary Phthalate Metabolites in a Human Reference Populations" the study was published electronically on September 1 in the October edition of the NIEHS journal Environmental Health Perspectives.
This study confirmed most of the earlier estimates of human exposure that are based on the amount of chemicals produced and used. However, it also indicated that there is one phthalate found at higher exposure levels than anticipated in humans. Additional studies will need to be done to examine possible sources of the exposures, as well as the need for more insight into the safety and health effects of these chemicals.
Those phthalates found at the highest levels in this study are used in detergents, lubricating oils, and solvents and can be found in a wide variety of products including cosmetics and wood finishes. They are diethyl phthalate (DEP), dibutyl phthalate (DBP), and benzylbutyl phthalate (BzBP). Other phthalates that are produced in larger quantities but whose metabolites were not highest in the urine sampled are used primarily as plasticizers in flexible polyvinyl chloride products (PVCs) such as blood bags, building products, food packaging, and children's toys. Di-(2-ethylhexyl) phthalate (DEHP) is the primary phthalate in this group.
"This is important," said Richard Jackson, director of CDC's National Center for Environmental Health. "For the first time, phthalate metabolites have been measured in human samples, and we can see which phthalates show the highest level of exposure in people. It is important to know what is in the environment, but even more important to know what is in our own bodies. This study is an example of how we should assess environmental exposures in the future."
"This joint study provides a huge step forward in the gathering of real exposure data, which is too often the missing data we need for scientifically sound conclusions regarding human environmental health risks," said Kenneth Olden, director of NIEHS and NTP.
For the study, CDC scientists analyzed urine samples of 289 adults aged 20-60 for seven metabolites associated with exposure to various phthalates. The samples were randomly selected from participants in the Third National Health and Nutrition Examination Survey (NHANES-III) from 1988 to 1994. NHANES, conducted by CDC's National Center for Health Statistics, is the only national survey that includes medical examinations or collection of biologic samples from participants, including blood and urine
Because phthalates are found throughout our environment, measuring the chemicals after they have actually been processed by the body yields important information about actual human exposure levels. By looking at metabolites, the scientists are looking at human exposures rather than simply measuring chemicals in the environment. However, at what level of exposure causes illness, is still unknown.
"By directly measuring levels of phthalate metabolites in urine, we have markedly improved our understanding of human exposure to phthalates and also improved our ability to determine potential health risks from exposure," said John Brock, senior chemist at CDC and phthalates team leader.
Of the seven phthalate metabolites measured in the human samples, four were found in more than 75% of the samples analyzed. The phthalate levels measured ranged from below detection to as high as 15 parts per million. DEHP is produced in higher quantities than the other phthalates but did not show as high a level of metabolites as DEP, DBP, or BBP. DEP and DBP are commercially produced in considerably lower amounts than DEHP. The sources of exposure are still being investigated.
This phthalate study included only a small sample of participants from NHANES and was not designed to be representative of the U.S. population. However, phthalate analyses are included in the current NHANES survey, which began in 1999. As part of this survey, CDC will be assessing a larger number of samples for phthalate levels, including urine samples among children aged 6 and older. This will be the first time children's phthalate exposure levels are measured. Also, CDC is collaborating on several additional health studies that include measurement of human levels of phthalates.
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