US EPA

Thallium compounds are used in the semiconductor industry, the manufacture of optic lenses and low-melting glass, low-temperature thermometers, alloys, electronic devices, mercury lamps, fireworks, and imitation germs, and clinically as an imaging agent in the diagnosis of certain tumors. EPA's assessment of noncancer health effects and carcinogenic potential of thallium compounds was last prepared and added to the IRIS database between 1988 and 1990. The IRIS program is preparing an assessment that will incorporate current health effects information available for thallium and compounds, and current risk assessment methods. The IRIS assessment for thallium compounds will consist of a Toxicological Review and IRIS Summary. The Toxicological Review is a critical review of the physiochemical and toxicokinetic properties of a chemical, and its toxicity in humans and experimental systems. The assessment will present reference values for the noncancer effects of thallium compounds (RfD and Rfc), and a cancer assessment. The Toxicological Review and IRIS Summary have been subject to Agency review, Interagency review, and external scientific peer review. The final product will reflect the Agency opinion on the overall toxicity of thallium and compounds.

Thallium exists in monovalent (Tl⁺¹) and trivalent (Tl⁺³) states. Thallium is released to the environment through the combustion of fossil fuels, refinement of oil fractions, the smelting of ferrous and non-ferrous ores, and by some other industrial processes such as cement production and brick works. In the past, thallium was used as a depilatory agent and as a treatment for ringworm, venereal diseases, TB, and malaria. It was banned for use as a pesticide in the United States in 1972. Currently, thallium compounds are used in the semiconductor industry, the manufacture of optic lenses and low-melting glass, low-temperature thermometers, alloys, electronic devices, mercury lamps, fireworks, and imitation gems, and clinically as an imaging agent in the diagnosis of certain tumors.

EPA is undertaking an Integrated Risk Information System (IRIS) health assessment for thallium and compounds. IRIS is an EPA database containing Agency scientific positions on potential adverse human health effects that may result from chronic (or lifetime) exposure to chemicals in the environment. IRIS contains chemical-specific summaries of qualitative and quantitative health information in support of two steps of the risk assessment paradigm, i.e., hazard identification and dose-response evaluation. IRIS assessments are used in combination with specific situational exposure assessment information to evaluate potential public health risks associated with environmental contaminants.

Following the External Peer Review, the final assessment will be published on the IRIS database.

U.S. EPA. IRIS Toxicological Review of Thallium and Compounds (External Review Draft). U.S. Environmental Protection Agency, Washington, DC, EPA/635/R-08/001, 2008.

Comments on the assessment may be submitted and reviewed using the e-Government Regulations.gov Web site. From the site, select Environmental Protection Agency and the keyword EPA-HQ-ORD-2008-0057 (for the docket ID) to comment on this report.

Contact Information

Octavia Conerly
by phone at: 202-566-1094
by fax at: 202-566-1140
by email at: conerly.octavia@epa.gov

Susan Rieth
by phone at: 703-347-8582
by fax at: 703-347-8699
by email at: rieth.susan@epa.gov