Update: March 1996
Current Massachusetts Regulatory Limit
MMCL: 0.2 mg/L. ORS has adopted the MCL published by the U.S. EPA (52 FR 25689 (7/8/87)).
Federal Regulatory Limit
The MCL of 0.2 mg/L is equal to its MCLG of 0.2 mg/L.
Basis for Criteria
The MCLG is based on a mouse inhalation study (49 FR 24329). The MCLG is derived based on the RfD presented below and assumes that a 70 kg adult ingests 2 L/day of drinking water. A relative source contribution factor of 20% is incorporated into the final value.
RfD: 0.035 mg/kg/day *
UF: 1000 (10 = subchronic to chronic; 10 = interspecies; 10 = intraspecies)
The dose associated with inhaling the minimum effect level (MEL) discussed below was derived, assuming that a 70 kg adult inhales continuously at a rate of 1 m3/hr. A 6-hour duration is assumed for this calculation as this is the exposure assumed to be saturable and therefore equivalent to exposure for a 24-hour period. An absorption factor of 0.3 is also applied. Thus, the inhalation MEL of 1365 mg/m3 is converted to an ingestion MEL dose:
1365 mg/m3 x 1 m3/hr x 6 hrs/day x 0.3)/70 kg = 35.1 mg/kg/day
(U.S. EPA, 1984)
* In the February 1984 Draft Criteria Document for 1,1,1-Trichloroethane, an Adjusted Allowable Daily Intake (AADI) is described as: (NOAEL or MEL in mg/kg)(70 kg)/(Uncertainty Factor)(2 liters/day). What we refer today as the RfD is referred to as the ADI (Allowable Daily Intake) in the document cited above and can be back calculated from the AADI by multiplying it by the ingestion rate divided by the body weight for an adult (i.e., 2 liters/day/70 kg. This value has been back calculated from the AADI of 1.22 mg/L (rounded to 1.0 mg/L).
The critical effect is liver toxicity in mice. McNutt et al. (1975) exposed male mice continuously via inhalation to 250 ppm (1365 mg/m3) or 1000 ppm (5460 mg/m3) 1,1,1-trichloroethane for 14 weeks. Significant changes were noted in centrilobular hepatocytes (including vesiculation of rough endoplasmic reticulum, with loss of attached polyribosomes, increased smooth endoplasmic reticulum, microbodies and triglyceride droplets). 250 ppm was assumed to be a minimum effect level (MEL) and was used as the basis upon which to derive an RfD (U.S. EPA, 1984).
Cancer Assessment: D
There are no data indicating that 1,1,1-trichloroethane is carcinogenic either in humans or animals.
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 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.
Federal Register. June 12, 1984. Part V. Environmental Protection Agency. 40 CFR Part 141. National Primary Drinking Water Regulations; Volatile Synthetic Organic Chemicals; Proposed Rulemaking. (49 FR 24329).
Federal Register. July 8, 1987. 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 25689).
McNutt, NS; Amster, RL; McConnell, EE; et al. 1975. Hepatic lesions in mice after continuous inhalation exposure to 1,1,1-trichloroethane. Lab Invest. 32:642-654.
U.S. EPA (U.S. Environmental Protection Agency). February 1984. Draft Criteria Document for 1,1,1-Trichloroethane. Health Effects Branch. Criteria and Standards Division. Office of Drinking Water.
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