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2,3,7,8-TCDD (Dioxin)
CASRN: 1746016

Update: August 1993

Current Massachusetts Regulatory Limit
MMCL = 3 x 10-8 mg/L. ORS has adopted the MCL published by the U.S. EPA as part of the Phase V rule (57 FR 31776: 7-17-92).

Federal Regulatory Limit
The MCL of 3 x 10-8 mg/L is set at the PQL for TCDD of 3 x 10-8 mg/L. The MCLG is set to zero.

Basis for Criteria
An MCLG of zero is assigned for TCDD based on the evidence for carcinogenic potential. The MCL is based on the TCDD PQL.

Critical Effects
Acute exposure to 2,3,7,8-TCDD, for relatively short periods of time, at levels above the MCL, could result in liver damage, weight loss, wasting of the thymus gland and immunosuppression. Chronic lifetime exposure to concentrations above the MCL may result in a variety of reproductive effects, from reduced fertility to birth defects and cancer.

Cancer Assessment: 
2,3,7,8-TCDD is a potent carcinogen in rats and mice. A number of bioassays have produced adenomas or carcinomas of the thyroid, hepatocellular carcinomas, carcinomas of the tongue and hard palate, and adenomas of the adrenal gland (Kociba et al., 1978a; Toth et al., 1979; NTP, 1980).

The U.S. EPA derived an oral cancer slope factor for 2,3,7,8-TCDD of 1.56 x 10-5 (mg/kg/day)-1 (U.S. EPA, 1987).

Chlorinated Organic

Analytical Information
: 3 x 10-8 mg/L

Analytical Methods
U.S. EPA Method 1613

PQLs and analytical methods may have been updated since this guidance value was last revised. Updated analytical methods for drinking water and their associated PQLs may be found at

Other Regulatory Data
Any Health Advisories, Reference Doses (RfDs), cancer assessments or Cancer Potency Factors (CPFs) referenced in this document pertain to the derivation of the current guidance value. Updated information may be obtained from the following sources:

Health Advisories - The U.S. EPA provides guidance for shorter-term exposures for chemicals based on their non-cancer effects. Current health advisories may be more current than those used to derive MCLs and may be found at

RfDs, cancer assessments and CPFs - For specific information pertaining to derivation of drinking water criteria, consult the Federal Register notice that announces the availability of the most current guidance for that chemical. In addition, information on other current RfDs and CPFs as well as cancer assessments for specific chemicals may be found in the U.S. EPA Integrated Risk Information System (IRIS) at Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.

Federal Register. July 25, 1990. Part II. Environmental Protection Agency. 40 CFR Part 141 et al. National Primary and Secondary Drinking Water Regulations; Synthetic Organic Chemicals and Inorganic Chemicals; Proposed Rule. (55 FR 30370)

Federal Register. July 17, 1992. Part III. Environmental Protection Agency. 40 CFR Parts 141 and 142. National Primary Drinking Water Regulations; Synthetic Organic Chemicals and Inorganic Chemicals; Final Rule. (57 FR 31776).

Kociba, R.J., D.G. Keyes. J.E. Beyer et al. 1978a. Results of a two-year chronic toxicity and oncogenicity study of 2,3,7,8-tetrachlorodibenzo-p-dioxin in rats. Toxicol. Appl. Pharmacol. 46(2):279-303.

NTP (National Toxicology Program). 1980. Bioassay of 2,3,7,8-tetrachloro-dibenzo-p-dioxin for possible carcinogenicity (gavage study). Carcinogenesis testing program, NCI, NIH, Bethesda, MD. NTP, Research Triangle Park, NC. DHHS Publ. No. (NIH) 82-1765.

Toth, K., S. Somfai-Relle, J. Sugar and J. Bence. 1979. Carcinogenicity testing of herbicide 2,4,5-trichlorophenoxyethanol containing dioxin and of pure dioxin in Swiss mice. Nature. 278(5704):548-549.

U.S. EPA. March 31, 1987. 2,3,7,8-Tetrachlorodibenzo-p-dioxin Health Advisory. Office of Drinking Water.

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