Radon, Arsenic, Radionuclides, and Sulfates
— Timeline for Drinking Water Standards

EPA has identified radon, arsenic, and radionuclides as priority chemical contaminants that should be regulated in drinking water. The agency is also considering whether to regulate sulfate or not; EPA is still identifying the health effects of sulfate. Radon, arsenic, and radionuclides are known human carcinogens, and an interim drinking water standard for arsenic already exists. Although interim drinking water standards also currently exist for some radionuclides, the agency is trying to clarify existing radionuclide regulations while developing clear and consistent policies in the future. Additionally, the agency is considering establishing a standard for uranium.


Radon
To date, EPA has not established a regulation for radon in public drinking water. On July 18, 1996, the agency proposed a level of 300 pCi/L. However, concerns over this level arose, primarily over the cost of implementation and the larger risk to health from radon in indoor air coming from soil under private homes. While this risk may be greater, EPA estimates that approximately 19 million people drink water contaminated with radon at levels that could cause one case of cancer for every 5,000 people exposed.

Currently, EPA is studying the risk to health posed by radon and the cost to reduce the risk. The agency aims to finalize a radon standard in drinking water by August 2000.


Arsenic
In 1976, EPA set an interim standard of 50 micrograms per liter (or parts per billion — ppb) for arsenic in drinking water. This interim standard was based on the level set by the Public Health Service in 1943 and was supposed to be subject to revision in 1989. But citizens sued EPA for not proposing a revision by the 1989 deadline. Since then, EPA has postponed proposing a new standard for arsenic as new research has become available. The agency plans to finalize a new standard for arsenic by January 1, 2001.


Radionuclides (except Radon)
In 1977, EPA set an interim drinking water standard for radium 226/228 at 5 pCi/L. In 1991, the agency proposed a new, less stringent standard of 20 pCi/L for each isotope – a proposal that caused some public concern. EPA is now reviewing the proposal and will finalize a standard by August 2000.

In addition, the agency will finalize drinking water standards for alpha and beta/photon emitters by August 2000. Currently, the interim standards for alpha emitters and beta/photon emitters are 15 pCi/L and 4 mrem/year, respectively. Finally, EPA will finalize a drinking water standard for uranium by August 2000. Uranium is presently unregulated in drinking water.


Sulfate
After concluding that sulfate is a relatively low risk contaminant, EPA proposed a drinking water standard of 500 mg/l. However, the agency is still researching the adverse health effects caused by sulfate contamination. Once these studies are complete, EPA will decide whether or not to regulate sulfate in drinking water. The agency will make this decision by August 2001.

Currently, a "secondary" drinking water standard of 250 mg/l is set for sulfate. Secondary standards are established only as guidelines for taste, odor, and aesthetic effects and are not enforceable.