Update: March 1994
Current Massachusetts Regulatory Limit
MMCL = 10 mg/L. ORS has adopted the MCL published by the U.S. EPA (56 FR 3526: 1/30/91 and 56 FR 30266: 7/1/91).
Federal Regulatory Limit
The MCL for xylenes is equal to its MCLG of 10 mg/L.
Basis for Criteria
The MCLG is based on the RfD presented below and assumes that a 70 kg adult ingests 2 L/day of water. A relative source contribution factor of 20% is incorporated into the final value.
RfD: 2.0 mg/kg/day
UF: 100 (10 intraspecies; 10 interspecies)
MF: 1 Confidence in RfD: medium
The RfD is based on a 103-week rat gavage study (NTP 1986) that identified a NOAEL of 250 mg/kg/day. Hyperactivity, decreased body weight gain and increased mortality were observed at higher doses.
Cancer Assessment: D; not classifiable as to human carcinogenicity
The U.S. EPA currently classifies xylenes as a group D carcinogen (insufficient evidence of carcinogenicity).
PQL: 0.005 mg/L
U.S. EPA 502.1; gas chromatography
U.S. EPA 503.1; gas chromatography
U.S. EPA 524.2; gas chromatography-mass spectrometry
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.
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 8, 1987. Part II. Environmental Protection Agency. 40 CFR Parts 141 and 142. National Primary Drinking Water Regulations-Synthetic Organic Chemicals; Monitoring for Unregulated Contaminants; Final Rule. (52 FR 25690).
NTP (National Toxicology Program) 1986. NTP Technical Report on the Toxicology and Carcinogenesis of xylenes (mixed) [60.2% m-xylenes, 13.640 p-xylene, 17.0% ethylbenzene and 9.1% o-xylene] (CAS No. 1330-20-7) in F344/N rats and B6C3F1 mice (gavage studies). US-DHHS, PHS, NIH, RIP, Research Triangle Park, NC. NTP TR. 327. NIH. publ. No. 86-2583.