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What are persistent, bioaccumulative toxic chemicals?

Persistent, bioaccumulative toxic chemicals (PBTs) are chemicals that:

1. Persist in the environment. They either biodegrade very slowly or not at all. Once released into the environment, they stay there virtually forever.

2. Bioaccumulate in living tissue. Once these chemicals are ingested by a person or other organism, they remain in the body. Because they increase in concentration as they move up the food chain, they can reach dangerous levels in living creatures ­ even when released in small, legally allowed quantities.

3. Are toxic. These chemicals are harmful to human health and to the environment, and have been associated with cancer, nerve damage, reproductive disorders, and other serious health problems.

Mercury fever thermometers provide a good example of the dangers posed by PBTs. When a discarded thermometer is burned in a trash incinerator, mercury (a PBT) can be released into the air, later falling back onto our lakes, rivers, and land as rain or snow. When a thermometer breaks in the sink, the mercury can go down the drain and eventually contaminate rivers and other water bodies. And a thermometer that is sent to a landfill can leach mercury into aquifers ­ underground water bodies that sometimes supply drinking water. In water, mercury can build up in fish, reaching levels a million times higher than that of the water itself.

Consumption of mercury-contaminated fish by humans can result in birth defects and damage to the kidneys and nervous system. Over 2500 water bodies in 47 states across the US contain fish with such high levels of mercury or other PBTs that the US Environmental Protection Agency (EPA) has issued a warning that children and pregnant women limit the amount of local fish that they eat. Moreover, in January 2001, the US Food and Drug Administration (FDA) warned women of child-bearing age not to eat any shark, swordfish, king mackerel, or tilefish (see http://www.fda.gov/bbs/topics/ANSWERS/2001/ANS01065.html).