The Search for Environmental Carcinogens

In the search for carcinogens, competing interests can complicate and compromise the case.

The science that connects any particular exposure to cancer takes a long and convoluted path, often with false starts and detours along the way. But there are other reasons why the identification of and protection against environmental exposures are not as straightforward as some people might hope. It’s not just that the science can be messy. Those who have a stake in the answer can influence the direction of research—as the Long Island women showed—to both the benefit and detriment of obtaining an answer. Sometimes patients themselves may fixate on the wrong threats. Sometimes industry, which benefits from as much scientific murkiness as possible, can keep doubt alive long after most scientists agree on an answer. (The tobacco industry proved to be quite successful at this technique.) And even after the research is done, different voices come to the table when government officials have to take the data and make decisions about which exposures need to be limited and by how much. “The landscape can get very complicated,” says Jonathan Samet, MD, director of the University of Southern California Institute for Global Health in Los Angeles.

The Toxic Substances Control Act, which was passed in 1976 and remains the law, does not require registration and health-effects testing of a chemical before it is put on the market (although it does require premanufacturing notification of new chemicals).

The Cancer Panel calculated that of the more than 80,000 chemicals in use today, only a few hundred have been tested for safety. We are literally born with them; nearly 300 chemicals have been found in umbilical cord blood. And even when something is known to cause cancer, that still doesn’t mean that it will be banned or that exposures will be heavily regulated. (Consider tobacco.)

That’s because, when deciding whether some exposure contributed to your cancer, the answer is: It depends.

“It depends on what it is and how you’re exposed,” Samet says. Something may be known to cause cancer but is still allowed on the market because the amount of exposure needed to cause cancer is more than someone would reasonably be exposed to. Or an exposure may cause cancer in animals, but not people. Remember the saccharine scares? Studies in animals in the 1970s suggested high levels of the artificial sweetener might contribute to bladder cancer. Only later did researchers determine that the cancer risk applied only to rats.

Some chemicals, such as the insecticide dichlorodiphenyltrichloroethane (DDT), are considered so toxic that their use is not allowed at all in the U.S. But most potential carcinogens are not so dangerous. Then the question becomes where to draw the line. Because they regulate different entities, the Environmental Protection Agency has different standards than the Food and Drug Administration, which has different standards than the Occupational Safety and Health Administration. And all during the process of setting the bar, politics can interfere. In June 2011, the government classified formaldehyde—which millions of Americans are exposed to daily—as a known human carcinogen, yet it remains a staple of plywood, hair salons, cosmetics and other products. Adding formaldehyde to the federal government’s 12th Report on Carcinogens was opposed by the chemical industry, despite studies that had long raised concerns.

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