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RADON-222 [10]
CASRN: 14859677

Update: March 2007

Current Massachusetts Regulatory Limit
ORSGL = 10,000 pCi/L.

The ORSGL is actually an "Action Limit". When concentrations of Rn-222 in water equal or exceed the Action Limit of 10,000 pCi/l, indoor air should be tested (see paper written by K. Martin and C.R. West; March, 1987).

Federal Regulatory Limit
The U.S. EPA has not published a final MCL for radon-222. The U.S. EPA proposed an MCL of 300 pCi/l on 7/18/91 [56 FR 33050]. This value is equal to the practical quantitation limit and is associated with an ELCR of 2 x 10-4. In 1994, the U.S. EPA provided a report to Congress on the multimedia risks from exposure to radon. It then withdrew the proposed MCL in 1997. In 1999 (64 FR59246) the U.S. EPA proposed a multimedia approach for reducing radon risk in indoor air while protecting public health from the highest levels of radon in drinking water. A 4000 pCi/L option was proposed for states where multimedia radon mitigation programs were implemented; otherwise a 300 pCi/L limit was to apply. This proposal has not been finalized as of 2007.

Basis for Criteria
Review of exposure studies of radon in water indicates that for a given concentration of radon in water, the dose to the lung outweighs the dose to the stomach by three to twelve times. Lung cancer is the main health effect attributed to radon and its progeny. The action level of 10,000 pCi/L is based on considerations of the distribution of background radon concentrations in the U.S. A waterborne radon concentration of 10,000 pCi/L would not be expected to contribute to an indoor air radon progeny level in excess of normal background levels (Martin and West, 1987).

Critical Effects
Radon 222 is a naturally occurring element. Upon nuclear decay, alpha particles are emitted from the decaying nucleus. Alpha particles are considered carcinogenic and therefore human exposures should be limited.

Cancer Assessment: The cancer assessment for radon has been withdrawn.


Analytical Information
: 300 pCi/L

Analytical Methods
U.S. EPA 913; liquid scintillation

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 US EPA Drinking Water Analytical Methods .

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 US EPA Current Drinking Water Health Advisories .

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 18, 1991. Part II. Environmental Protection Agency. 40 CFR Parts 141 and 142. National Primary Drinking Water Regulations; Radionuclides; Proposed Rule. (56 FR 33050).

Martin, K.A. and West, C.R. March 1987. Interim action limit for radon in drinking water. Office of Research and Standards. Massachusetts Department of Environmental Protection.

[10] Exceedance of this guideline indicates that air sampling for Radon-222 should be done. EPA proposed guidelines for radon (64 FR 211; Tuesday, November 2, 1999) which have not been finalized.