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Why are there no longer any screening levels calculated for thallium?

April 26, 2017calculated levels longer screening Thallium

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Why are there no longer any screening levels calculated for thallium?

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The previous soil and tapwater screening levels were calculated using an oral reference dose (RfD) from IRIS. On September 30, 2009 a new IRIS assessment was posted for thallium, in which no toxicity values were derived. We no longer have any toxicity values which could be used to calculate screening levels. However, the MCL for public water supplies remains in effect and that value continues to be provided in the tables. If you have questions about the IRIS assessment for thallium, we invite you to contact EPA’s IRIS program at (202) 566-1676, or fax to (202) 566-1749 or regular mail at: IRIS Hotline, c/o EPA Docket Center, Mail Code 28221T, EPA-West Building, 1301 Constitution Avenue NW, Washington, DC 20005.