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Risk From Exposure To Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans Emitted From Municipal Incinerators

U.S. Environmental Protection Agency, Environmental Criteria and Assessment Office, Cincinnati, OH 45268, U.S.A.

David H. Cleverly

U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711, U.S.A.

Incineration of wastes seems to be one of the major sources of PCDDs and PCDFs (dioxins). Their prevalence and extreme stability in the environment, bioavailability and bioaccumulation in the biota and human adipose tissues and breast milk are of much concern. 2,3,7,8-TCDD is one of the most toxic chemicals known and has been found to have teratogenic and carcinogenic activities in animals. Exposure to TCDD can result in chloracne, general weakness, drastic weight loss, hyperpigmentation of skin, hirsutism, porphyria cutanea tarda, liver damage, changes in activities of various liver enzymatic levels, abnormal lipid metabolism, abnormalities of the endocrine and immune systems, and possible teratogenic effects in humans. Moreover, chronic bioassay data indicate that TCDD is one of the most potent carcinogens known. It promotes liver and skin carcinogeneses, and is an initiator for various target organs in rodent test systems. There is only a limited number of human epi-studies on carcinogenic outcome as a result of exposure to TCDD in isolated population.

According to the classification system of the International Agency for Research on Cancer (IARC), the qualitative evidence for carcinogenicity of TCDD is considered to be "sufficient" in animals and "inadequate" in humans. Consequently, this chemical has been placed in IARC's 2B category. A modification of the multistage model is utilized for extrapolating high-dose, two-year animal cancer bioassay data to estimate human cancer risk for long-term, low-dose human exposure. The upper limit of incremental cancer risk is 3.3 x 10-5 for a continuous lifetime exposure to 1 pg m^-3 of TCDD in ambient air. With the exception of 2,3,7,8-TCDD and a mixture of 1,2,3,6,7,8- and 1,2,3,7,8,9-HxCDDs, the chronic toxicity data on the rest of the 75 PCDD and 135 PCDF congeners are badly deficient. In the absence of chronic bioassay data on other PCDDs and PCDFs, several TCDD equivalent approaches have been proposed for risk assessment on other congeners or mixtures. This paper compares the various approaches.

Key Words: Dioxins • TCDD • TCDF • municipal incineration • health risk • isomer equivalents.

Waste Management & Research, Vol. 5, No. 1, 269-283 (1987)
DOI: 10.1177/0734242X8700500139


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