Screening Levels
At this time, the EPA has not declared screening levels specifically for thorium. Depending on the decay chain (see below), thorium is grouped with uranium or radium. For Thorium-230, see uranium. For Thorium-232, see radium.
Maximum Contaminant Level
The Maximum Contaminant Level (MCL) is the highest level of a contaminant that is allowed in drinking water.
MCL: 15 pCi/L
National Primary Drinking Water Regulations for “Alpha/photon Emitters” (Last Updated by the EPA in May 2009)
Thorium-230
Thorium-230 is part of the Uranium-238 decay chain.
Thorium-232
Thorium-232 decays into Radium-228.
Units
| Abbreviation | Meaning | Notes |
|---|---|---|
| pCi/L | radioactivity of chemical (picocuries, pCi) per volume of water (liter, L) | A Curie is a unit of radioactivity equivalent to that of one gram of radium; pico means one-trillionth |
For more information about these units and their conversion factors, visit https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.files/fileid/14285.