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1,2-DICHLOROBENZENE (o-DCB)
CASRN: 95501

Update: March 1993

Current Massachusetts Regulatory Limit
MMCL = 0.6 mg/L. ORS has adopted the MCL promulgated by the U.S. EPA as part of the Phase II rule 56 FR 3526 (1-30-91); FR 30266; (7-1-91).

Federal Regulatory Limit
The MCL is equal to the MCLG of 0.6 mg/L.

Basis for Criteria
The MCLG is based on the potential for hepatic toxicity reported in subchronic rat and mouse studies (NTP, 1985). The MCLG assumes that a 70 kg adult ingests 2 L/day of water and incorporates a relative source contribution factor of 0.2.

RfD: 9 x 10-2 mg/kg/day
UF: 1000 (10 = intraspecies; 10 = interspecies; 10 = no repro. studies or 2nd chronic study)
MF: 1

Critical Effects
Exposure to 1,2-dichlorobenzene at high doses produces a variety of toxic effects, including central nervous system depression, kidney and liver damage. In a study in which mice and rats were given 1,2-dichlorobenzene by gavage at doses of 30, 60, 125, 250 and 500 mg/kg/day, five days per week for thirteen weeks, no effects were noted at the three lowest doses (NTP, 1985). A NOAEL of 125 mg/kg/day was identified from these studies. Since animals were only dosed five days per week, the NOAEL was time-adjusted to 89.2 mg/kg/day by multiplying by 5 days/7 days.

Cancer Assessment: D
Data are inadequate to make a judgment regarding the potential for increased cancer in humans or animals.

Class
VOC

Analytical Information

Analytical Methods
502.1; Purge and trap

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 http://www.epa.gov/safewater/methods/methods.html.

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 http://www.epa.gov/waterscience/drinking/standards/dwstandards.pdf.

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 http://www.epa.gov/iris/. Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.

References
Federal Register. January 30, 1991. Part II. Environmental Protection Agency. 40 CFR Parts 141, 142, and 143. National Primary Drinking Water Regulations; Final Rule. (56 FR 3526).

Federal Register. July 1, 1991. Environmental Protection Agency. 40 CFR Parts 141, 142, and 143. National Primary Drinking Water Regulations; Monitoring for Volatile Organic Chemicals; MCLGs and MCLs for Aldicarb, Aldicarb Sulfoxide, Aldicarb Sulfone, Pentachlorophenol, and Barium; Final Rule. (56 FR 30266).

National Toxicology Program (NTP) 1985. Toxicology and Carcinogenesis studies of 1,2-dichlorobenzene (o-dichlorobenzene) in R344/N rats and B6C3R1 mice (gavage studies). NTP R 255 NIH Publ. No. 86-2511