TABLE 4-2 The “Dirty Dozen” Identified in United Nations Environment Programme

The “Dirty Dozen”

Aldrina

Chlordanea

DDTa

Dieldrina

Endrina

Heptachlora

Hexachlorobenzenea,b,c

Mirexa

Toxaphenea

Polychlorinated biphenyls (PCBs)b,c

Polychlorinated dibenzo-p-dioxins (Dioxins)c

Polychlorinated dibenzo-p-furans (Furans)c

NOTES: The United States has taken strong domestic action to reduce emissions of POPs. Currently, none of the pesticide POPs are registered for sale and distribution in the United States. In 1978, the US Congress prohibited the manufacture of any new PCBs and severely restricted the use of remaining stocks.

aPesticides.

bIndustrial Chemical.

cBy-products.

SOURCES: UNEP Global Environmental Facility, 2003; IISD, 1998.

sources within the continental United States. Regulatory action has resulted in a 77 percent decline in total dioxin and furan releases between 1987 and 1995 (US EPA, 2005) (for more information see also US EPA 1987, 1991, 1994, 1995). Overall, levels of dioxins and DLCs in the environment have been declining for the past three decades. However, since dioxins are persistent compounds, they can be expected to remain in the environment and the food supply for many years to come (IOM, 2003).

Toxic Equivalency Factors (TEFs) are a convenient method for assessing the toxicity of mixtures containing dioxins and DLCs but there are uncertainties associated with calculating TEF values for individual congeners because of variability in their half-lives and differences in toxicity to humans. The reference compound for the TEF is the dioxin compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). WHO recommends a tolerable daily intake of DLCs and PCBs of 1–4 pg/TEQ/kg/day (IOM, 2003). The US EPA has estimated 0.001 pg/kg/day of TCDD as the level associated with a 1 in 1 million excess risk for human health effects from exposure to DLCs and PCBs (IOM, 2003). The NRC committee on EPA’s Exposure and



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