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CAS Number: 7440-48-4
Synonyms: Co-57, Co-58, Co-59, Co-60
Contaminant Type: Radiological

Some drinking water sources have very low levels of radionuclides (radioactive elements).  While stable cobalt isotopes exist in nature, cobalt has two radionuclides that can be detected in drinking water. Cobalt-58 and cobalt-60 are both anthropogenic nuclides that mey be present from the cooling water used in nuclear power facilities. The primary anthropogenic source of cobalt-60 originates from nuclear power plants when neutrons from the nuclear reaction process bombard natural cobalt (cobalt-59) present in the metal making up the reactor itself.  Both nuclides are beta particle emitters and are regulated under the USEPA's Radionuclides Rule due to its radiotoxicity.  The half lives of cobalt-58 and cobalt-60 are 71 days and 5.27 years, respectively.  [1762]  Because of its prevalence and activity, cobalt-60 is a larger concern for water utilities.  Cobalt-57 is also radioactive and used in medical and scientific research.  Its half life is 272 days. 

Emitted particles ionize or destabilize atoms as they pass through the body's cells damaging chromosomes, which can lead to cancer. Radioactive cobalt exposure has been shown to cause a reduction in white cell counts and cause reproductive harm and even temporary sterility. [1762]

Radioactive cobalt and other beta particle emitters are regulated by USEPA in drinking water with a combined maximum contaminant level of 4 mrem per year [584] or 8 picoCuries/L. 

USEPA has identified ion exchange and reverse osmosis as Best Available Technologies (BATs) for the control of beta particles in drinking water. [566] 

In the National Inorganics and Radionuclides Survey (NIRS) of ground waters, gross beta-particle activity detects exceeded the survey screening level of 50 pCi/L in 9 of 990 public water supplies. [586]  Because radioactive cobalt is able to travel with percolating waters to underlying layers of soil and into groundwater, it is found in both surface and ground waters. [1762]

Naturally-occurring cobalt (cobalt-59) is present in most rocks, soil and plants.  It can be found in water in dissolved ionic form.  Cobalt typically combines with other elements such as oxygen, sulfur, and arsenic in nature and is critical in the formation of vitamin B-12.  Cobalt chloride has been used in pharmaceuticals.  

Non-radioactive cobalt has some health effects (possible fetal development, possible human carcinogen).  It will be monitored with unregulated contaminants as a part of the UCMR3 and is on the CCL3 for consideration for regulation in drinking water.      

Date of Literature Search: August 2010

566 USEPA; 2002; Implementation Guidance for Radionuclides; Implementation Guidance for Radionuclides; EPA-816-F-00-002. Office of Ground Water and Drinking Water, USEPA, Washington, DC.
584 USEPA; 2007; Basic information about radionuclides in drinking water; http://www.epa.gov/safewater/radionuclides/basicinformation.html; As posted on August 27, 2007. Office of Ground and Drinking Water, USEPA, Washington, DC.
586 USEPA; 2000; Radionuclides Notice of Data Availability: Technical Support Document; Radionuclides Notice of Data Availability: Technical Support Document; Targeting and Analysis Branch Standards and Risk Management Division, Office of Ground Water and Drinking Water, US EPA, Washington, DC.
1762 Agency for Toxic Substances and Disease Registry U.S. Public Health Services and U.S. Environmental Protection Agency; 2004; Toxicological Profile for Cobalt; Toxicological Profile for Cobalt; 183:193; U.S. Public Health Service and U.S. Environmental Protection Agency

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