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CASRN: 7446-18-6

Update: March 1996

Current Massachusetts Regulatory Limit
MMCL = 0.0005 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
Though the MCLG for thallium is 0.0005 mg/L, the U.S. EPA has set the MCL at 0.002 mg/L.  The U.S. EPA usually bases such a decision on either the detection capability for the chemical or the technical feasibility of being able to achieve compliance with the MCL given the available treatment techniques.

Basis for Criteria
The MCLG is based on the RfD presented below and assumes that a 70 kg adult ingests 2 L/day drinking water. A relative source contribution factor of 20% is incorporated into the final value.

RfD: 6.7 x 10-5 mg/kg/day *
UF: 3000 (10 = subchronic to chronic; 10 = interspecies; 10 = intraspecies;
3 = lack of adequate reproductive studies)
MF: 1

* This RfD was determined from information used by the U.S. EPA to derive the Drinking Water Equivalent Level (DWEL) for this chemical for the Phase V Rule.

Critical Effects
Toxic effects of thallium in test animals include degenerative changes in mitochondria of the kidneys, liver, brain and intestines. The MCLG is based on a NOAEL of 0.2 mg/kg/day identified from a thirteen-week dietary study in which rats were given approximately 0.008 to 0.20 mg thallium/kg /day. Significant increases in blood levels of glutamic-oxaloacetic transaminase (SGOT), lactic dehydrogenase (LDH), and sodium levels were reported. No histopathologic changes were seen (with light microscopic or gross pathologic evaluation of organs and tissues) that would reveal a significant treatment-related effect. Alopecia was noted although light microscopic evaluation did not indicate changes in hair follicles. Uncertainty remains as to whether any effects would be found at the electron microscope level (Stoltz et al., 1983).

Cancer Assessment: D
The U.S. EPA has classified thallium in Group D based on inadequate evidence of carcinogenicity in humans or animals

Inorganic; Heavy metal

Analytical Information
: 0.001 mg/L

Analytical Methods
Standard Methods 3113 (atomic absorption; furnace)
U.S. EPA Method 279.2 (atomic absorption; furnace)
U.S. EPA Method 200.9 (atomic absorption, platform)
U.S. EPA Method 200.8 (ICP-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

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).

Stoltz, ML. Stedman, MA, Brown, LK, Laber, L. El-hawari, AM, 1986. Midwest Research Institute. Final Report. Subchronic (90-day) Toxicity of Thallium (I) Sulfate (CAS No. 7446-18-6) in Sprague-Dawley Rats. Project No. 8702-L. November 21, 1986.