Trying to understand our chemical exposure
Our modern-day environment is loaded with man-made chemicals. We breath car exhaust, gasoline fumes and secondhand smoke, and we eat food laced with pesticides and plasticizers and cooked in pans with nonstick coatings.
FOR THE RECORD:
Biomonitoring: An article in the Oct. 11 Health section on traces of man-made chemicals in human bodies incorrectly named an environmental advocacy group. It is the Natural Resources Defense Council, not the National Resources Defense Council.
We use cosmetics on our skin, cleaning products in our houses and lawn products in our yards. We decorate our homes and clothe our kids with flame-retardant fabrics. And we drink municipal water that contains traces of pharmaceuticals and other chemicals.
What’s the health fallout of this? In some cases, such as those for lead and mercury, the effects of environmental chemicals are clear. Not so much for others, such as bisphenol A and flame retardants. It’s difficult to link disease to chemical exposure, partly because of the uncertainty of just who is exposed, to how much and for how long.
To get at part of the puzzle, since 1999 the national Centers for Disease Control and Prevention has been doing biomonitoring studies — sampling blood and urine from a broad swath of Americans to see what chemicals are regularly found in people.
“For the public, I think the basic point is just the understanding that chemicals … in our environment do in fact actually get into your body,†says Dr. John Osterloh, the chief medical officer of the CDC’s division of laboratory sciences. And with that information, he adds, scientists have a starting point for understanding the medical consequences.
The list of man-made chemicals now found in human tissue samples is long, encompassing 212 environmental chemicals. The latest report, published in 2009, added 75 chemicals to the list, including bisphenol A, found in many plastics; triclosan, found in antibacterial soap; a dozen perfluorinated chemicals, such as PFOA used in the manufacture of nonstick cookware; and 29 volatile chemicals, such as the gasoline additive MTBE.
The exposure report shows how pervasive many of these chemicals are in the environment, that they are found in a representative sample of Americans living in different communities across the country. Each of the surveys — there have been four so far — included about 2,500 people.
The CDC cautions that the mere presence of chemicals doesn’t necessarily mean that they pose a risk. But scientists who study environmental health risks say that each widespread chemical is like a human experiment. “If you want to expose millions of people to something, just intermingle it with the food supply,†says Thomas Burke of the Johns Hopkins Bloomberg School of Public Health, speaking about the bisphenol A in food can linings. (Burke chairs an advisory panel on risk assessment for the Environmental Protection Agency.)
Scientists and advocates alike hail the biomonitoring effort as a good thing because the data can be used in so many ways. Researchers can mine the data for associations between exposure and disease, regulators can monitor for new contaminants and policymakers can track changes in contaminant levels following regulations.
But some advocacy organizations wish the CDC had taken additional steps to be more user-friendly. “It’s very stripped of interpretation, of how these chemicals may affect human health,†says Sonya Lunder, senior analyst for the Environmental Working Group, a Washington, D.C.-based environmental advocacy organization.
For example, she says, chemicals such as PCBs are reported individually — and there are dozens — so you’d have to add them up to calculate the entire body burden for these pesticides. Ditto for the 11 brominated fire retardants.
Biomonitoring is not new, say Dr. Sarah Janssen, a public health doctor at the National Resources Defense Council. Screening lead levels in children, for example, has been done for decades because the substance is known to cause developmental and behavioral problems. Lead paint and leaded gasoline were banned in the late 1970s. “As the levels went down in those products, the levels in kids’ bodies also went down,†Janssen says.
The levels are still declining, according to the CDC biomonitoring reports. In children 1 to 5 years old, 1.4% have blood lead levels of concern — at least 10 micrograms per deciliter. This finding from the 1999-2004 reporting period is lower than the 4.4% seen in the period of 1988-1994.
What is new is the number of man-made chemicals we carry around in our body tissues. This reflects the massive increase in their use in the U.S., says Michael Wilson, an environmental health expert at the UC Berkeley School of Public Health who studies “green chemistry,†the development of safer useful chemicals. (Wilson serves on the scientific guidance panel for a separate biomonitoring program in California.) Data collected under the Toxic Substances Control Act show that 74 billion pounds of industrial chemicals are made in or imported to the country every day — this does not include pharmaceuticals, pesticides or fuel.
Some chemicals are extremely persistent in the environment, such as those PCBs that were banned in the 1970s but are still found in Americans today, even in children who weren’t even born when the ban took effect. However, the levels have decreased by more than 80% since the 1980s.
Other substances, such as perfluorinated chemicals used in manufacturing, can build up in our bodies to levels higher than what’s in the environment. In animal studies, they have been shown to cause cancer, liver toxicity and interfere with growth and development. Two common ones, PFOS and PFOA, were found in nearly all people tested.
In contrast, bisphenol A, an endocrine disruptor that has been shown to cause reproductive problems in animal studies, is thought to be metabolized fairly quickly, but it was still found in 93% of the participants sampled. “It means we’re taking it in as fast as our bodies can eliminate it,†Janssen says.
Scientific studies using the CDC data have found links between certain contaminants and disease. A 2010 study published in Pediatrics, for example, reported a 55% increased risk of attention deficit hyperactivity disorder in 1,139 children who had 10 times the organophosphate pesticide levels than average in their bodies. A 2010 study published in Environmental Health Perspectives found an association between higher PFOA levels and thryoid disease in 3,974 adults.
And a 2008 study of 1,455 adults published in the Journal of the American Medical Assn. reported that higher urinary bisphenol A levels correlated with somewhere between 18% and 63% higher rates of cardiovascular disease and diabetes.
These kind of studies cannot conclude that a substance is causing a disease: The illness might have preceded exposure, for example. “It’s just a snapshot of one time period,†Janssen says. “It’s more of a hypothesis-generating study.â€
California has its own biomonitoring program that’s modeled after the CDC’s but is tailored to the state’s concerns. For example, California law requires upholstered furniture meet a flammability standard, so the state’s biomonitoring program tests a more comprehensive list of fire retardants, filling that gaps in the CDC survey.
California’s program also surveys for additional phthalates and antibacterial substances that aren’t tested by the CDC.
To get a better handle on environmental chemicals and risks, Burke says, policymakers and regulatory agencies need to move away from a one-by-one approach to risk assessment. “We can argue forever how much disease bisphenol A or some of the other contaminants might play, but there’s no argument that there’s lots of things we can do in the environment a lot better.â€
