1,4-DICHLOROBENZENE (p-DCB) 
Update: August 1993
Current Massachusetts Regulatory Limit
MMCL = 0.005 mg/L.
Federal Regulatory Limit
The MCL for 1,4-dichlorobenzene is 0.075 mg/L.
Basis for Criteria
In 1988, ORS determined that there were sufficient data to classify p-dichlorobenzene as a group B2 (probable) human carcinogen (ORS 1988). In keeping with the U.S. EPA evaluation protocol, the standard for B2 carcinogens is set as close to zero as feasible. Feasibility is determined by considering treatment costs of reducing the concentration, the availability of Best Available Technology (BAT) and the lowest practical quantitation limit (PQL) available from the existing analytical methods. ORS determined that 0.005 mg/L was feasible.
The U.S. EPA promulgated an MCL for p-dichlorobenzene of 0.075 mg/L on January 31, 1991. The MCL is based on an MCLG of 0.075 mg/L derived from a long-term study in dogs where liver effects were the critical effect. Since the U.S. EPA classifies this compound as a group C (possible) human carcinogen, a safety factor of 10 was added to the usual calculation for non-cancer effects to account for possible cancer effects in humans.
ORS has calculated an Excess Lifetime Cancer Risk (ELCR) of approximately one in one hundred thousand from ingestion, inhalation and dermal exposures to p-dichlorobenzene at the ORS standard of 0.005 mg/L. A Cancer Potency Factor (CPF) of 0.024 (mg/kg/day)-1 was used for the calculation (U.S. EPA 1988, 1994).
non-cancer: liver effects; cancer
Cancer Assessment: B2/C
PQL: The PQL used as the basis for the MMCL is 0.005 mg/L.
502.1 GC 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 US EPA Drinking Water Analytical Methods .
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 US EPA Current Drinking Water Health Advisories .
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.
U.S. EPA (U.S. Environmental Protection Agency). 1988. Health Effects Assessment Summary Tables (HEAST).
U.S. EPA (U.S. Environmental Protection Agency). 1994. Health Effects Assessment Summary Tables (HEAST).
ORS (Office of Research and Standards). March 4, 1998. Memorandum from Carol Rowan West.
 The MMCL for this chemical is more stringent than the federal MCL.