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Human Exposure to Environmental Chemicals

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From time-to-time I report on toxic chemicals in the environment, whether it be in fish we eat (here), polluted streams (here), or toxic waste sites (here). People come into contact with these chemicals by eating contaminated food, drinking contaminated water, and breathing contaminated air. I thought it might be interesting to see whether people are carrying a dangerous load of toxic chemicals in their bodies.

It turns out that the Centers for Disease Control (CDC) was also interested, and they have systematically tested samples of the population of the USA to see which environmental chemicals people are carrying in their blood and urine, and at what levels. They have published their findings in a series of reports, most recently in 2009, and they regularly update the data associated with the report, most recently in 2017.

There is some basic information you need to know in looking at this data. First, the data covers 308 environmental chemicals. There are over 80,000 chemicals registered for use in the USA, however, and the American Chemical Society database contains over 50 million unique chemical substances that have been discovered or created. Very little is known about the toxicity of many of them.

Second, once a toxic chemical enters your body, it seldom remains in the bloodstream for very long. Some chemicals are cleared from the body relatively quickly (often in urine), others migrate into the body’s tissues, where they sometimes persist for decades. Thus, toxic chemicals have two kinds of effects on the body: acute symptoms (those related to high levels in the blood), and chronic effects (which can be caused by even small amounts of some chemicals remaining in the tissues of the body). The CDC surveyed blood and urine levels. Thus, their data would bear most directly on acute symptoms, and would have less to say about long-term chronic exposure at low levels.

Third, most of the chemicals tested by the CDC exist at some level in the environment. You can find them in just about everyone. In fact, many are essential for health. For instance, too much iron in the blood is toxic, but too little can cause iron deficiency anemia.

Our chemical tests have become so sophisticated that they can find traces of chemicals that are smaller than microscopic. Thus, the fact that people carry some level of a chemical in their body is not evidence that it is toxic. Many additional factors need to be taken into account. The CDC reports are intended to provide baseline data.

Rather than get into the hundreds of tables provided in the report, I’ll just report a few headline findings from the Executive Summary:

  • Exposure to some chemicals is widespread.
    • Polybrominated diphenyl ethers (flame retardants used in a wide variety of products) were found in almost all of the subjects tested. These accumulate in the environment and in fatty tissue.
    • Bisphenol A, a component of epoxy resins and polycarbonates, was found in the urine samples of more than 90% of tested subjects.
    • Perfluoroctanoic acid, used in the manufacture of non-stick coatings in cookware, was found in “most” subjects tested.
      .
  • Figure 1. Source: Centers for Disease Control and Prevention, 2009a.

    Because exposure to environmental chemicals is so widespread, it means that many (most?) people are carrying more than one in their body. Very little is known about how (if) they interact. Do they potentiate each other, making even low level exposure dangerous? We just don’t know.

  • Serum levels of lead in children have declined. The CDC has set the upper limit for lead in the blood of adults at 10 micrograms per deciliter. (This is not the safe level for children, but it does provide a marker against which change can be measured.) The percentage of children with a blood level greater than 10 µg./dl. has declined significantly since 1970 (Figure 1). Where once it was 88.2%, now it is 1.4%. This suggests that lead mitigation efforts have been tremendously successful. Some special populations remain at risk, however, especially children living in homes containing lead-based paint.

    Figure 2. Source: Centers for Disease Control and Prevention, 2009a.

  • For the first time, the report included data on exposure to mercury. The report found that mercury levels increase with age for all demographic groups, then begin to decline after age 50 (Figure 2). The levels were well below those associated with mercury poisoning. Non-hispanic blacks had the highest blood levels, then Mexican Americans, then non-hispanic whites. I reported on the bioaccumulation of mercury here. Thus, it makes sense that blood levels increase with age. What accounts for the decrease after age 50 and the racial differences? I would put my money on lifestyle differences (where you live, what you do for a living, what you eat), but I don’t really know.
    .
  • Perchlorate was found in the urine of all subjects. Perchlorate is a chemical used to manufacture fireworks, explosives, flares, and rocket propellant. It’s hard to imagine that those uses would make it ubiquitous in the environment, but on the other hand, 14 billion pounds of bombs were dropped by the United States during the Vietnam War alone. This chemical is known to affect thyroid function, but the maximum safe blood level has not yet been determined. This data will help scientists develop standards for safe and unsafe exposure.

I wish I could report on the chemical burden of people living in Missouri, but the CDC data is not broken out by state, and I have not been able to find a report that addresses the issue.

In summary, the report seems to find that environmental chemicals can be widely detected in the blood or urine of Americans. Safe blood levels have been established for some chemicals, and for those the data seem to show that the mean blood level across all significant groups is within the safe level. There may be special populations in which the blood or urine level is higher. Similarly, the number of chemicals tested is a small fraction of those that have been discovered or created, and about most of them, we know very little.

Sources:

American Chemical Society. 50 Million Unique Chemical Substance Recorded in CAS Registry. Viewed online 4/24/2017 at https://www.acs.org/content/acs/en/pressroom/newsreleases/2009/september/50-millionth-unique-chemical-substance-recorded-in-cas-registry.html?_ga=1.43194213.1375747815.1493039805.

Centers for Disease Control and Prevention. Executive Summary, Fourth National Report on Human Exposure to Environmental Chemicals: 2009. National Center for Environmental Health, Division of Laboratory Sciences, Mail Stop F-20, 4770 Buford Highway, NW, Atlanta, GA 30341-3724. Downloaded 4/22/2017 from https://www.cdc.gov/exposurereport.

Centers for Disease Control and Prevention. Fourth National Report on Human Exposure to Environmental Chemicals: Updated Tables, January 2017, Volumes One and Two.. National Center for Environmental Health, Division of Laboratory Sciences, Mail Stop F-20, 4770 Buford Highway, NW, Atlanta, GA 30341-3724. Downloaded 4/22/2017 from https://www.cdc.gov/exposurereport.

Centers for Disease Control and Prevention. Executive Summary, Fourth National Report on Human Exposure to Environmental Chemicals: 2009. National Center for Environmental Health, Division of Laboratory Sciences, Mail Stop F-20, 4770 Buford Highway, NW, Atlanta, GA 30341-3724. Downloaded 4/22/2017 from https://www.cdc.gov/exposurereport.

Clodfelter, Micheal. 1995. Vietnam in Military Statistics: A History of the Indochina Wars, 1792—1991. Jefferson, NC: McFarland & Company. Cited in Wikipedia. List of Bombs Used in the Vietnam War. Viewed online 5/4/2017 at https://en.wikipedia.org/wiki/List_of_bombs_in_the_Vietnam_War.

National Toxicology Program. About NTP. Viewed online 4/24/17 at https://ntp.niehs.nih.gov/about/index.html.

New York State Department of Health. Understanding Mercury Exposure Levels. Viewed online 4/24/2017 at https://www.health.ny.gov/environmental/chemicals/hsees/mercury/mercury_exposure_levels.htm.

Wikipedia. Iron Poisoning. Viewed online 2/24/2017 at https://en.wikipedia.org/wiki/Iron_poisoning.

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