Enhanced Monitoring for Hexavalent Chromium in Drinking Water
In response to a draft scientific review released in September 2010, the EPA has issued guidance to all public water systems (PWS) recommending enhanced monitoring and sampling programs specifically for hexavalent chromium [also known as chromium-6 or Cr(VI)] in drinking water.
In a memo dated January 11, 2011 the EPA recommended that all PWS request their laboratories use a modified version of EPA Method 218.6, “Determination of Dissolved Hexavalent Chromium in Drinking Water, Groundwater and Industrial Wastewater Effluents by Ion Chromatography” (Rev. 3.3, 1994; www.nemi.gov) when testing drinking water samples. These modifications allow for improved low concentration measurement and are outlined in Dionex Corp. Application Update 144 “Determination of Hexavalent Chromium in Drinking Water by Ion Chromatography” found at www.dionex.com/en-us/webdocs/4242-AU144_V18.pdf. With appropriate modifications, laboratories are capable of attaining a detection limit as low as California’s proposed public health goal of 0.02 µg/L (ppb) and can support the EPA’s recommended reporting limit of 0.06 µg/L (ppb).
The holding time for a sample to be tested for chromium-6, under method 218.6, is 24 hours. However, as part of EPA’s guidance on hexavalent chromium, they issued a temporary extension for chromium-6 drinking water samples to 5 days, provided samples are properly collected and treated with an ammonium sulfate/ammonium hydroxide buffer to maintain an alkaline pH in the 9.0 to 9.5 range. The EPA stated that the holding time of 24 hours prescribed in Method 218.6 was based upon the most conservative holding times for wastewater and sludge extracts, also covered by the method, and not the stability of chromium-6 in drinking water matrices. However, the State of California has questioned the ability of the buffer to stabilize chromium-6 for 5 days and is currently performing studies to answer that question.
It is important to emphasize that, in spite of the EPA’s guidance document, the lowest total chromium maximum contaminant level (MCL) required anywhere in the US, except for California, is 100 ppb. In California the regulated level is 50 ppb for total chromium. Under the existing regulations, total chromium testing does not distinguish between how much of the total chromium is chromium-6 (the chromium form considered toxic) and how much is chromium-3 (an essential nutrient in our diets).
If a water agency wants to be prepared for the possible lowering of the MCL, they will need to determine which level they want to measure and identify a laboratory capable of meeting those detection limits. Possible changes to the MCL include the adoption of:
• California’s MCL of 50 ppb for total chromium,
• EPA’s recommended level of 0.06 ppb for chromium-6, or
• California’s newly proposed public health goal of 0.02 ppb for chromium-6.
In an effort to address the availability of laboratories that can currently meet the required detection limits, the EPA has stated they will accept data from any lab that is certified by a state, by the National Environmental Laboratory Accreditation Program (NELAP) or by a federal agency to perform an approved ion chromatography method and meet the detection limits of either 0.02 ppb or 0.06 ppb for chromium-6.1
The EPA is continuing to assess the new data and plans to issue a final assessment on chromium-6, in accordance with the Safe Drinking Water Act, sometime this year.
Columbia Analytical can meet the most stringent detection limit requirement. Visit this site for more information on testing for hexavalent chromium.
1 “Laboratories that have the necessary equipment and are certified by an accrediting authority to conduct an approved ion chromatography method (e.g., EPA Method 300.0, SM 4110B, ASTM D4327) should be given preferential consideration to provide this analytical support”; Hexavalent Chromium in Drinking Water EPA Guidance Information, How can I find a laboratory to measure chromium-6? http://water.epa.gov/drink/info/chromium/guidance.cfm, January 2011
Tags: 218.6, ammonium hydroxide, ammonium sulfate, California, chromium-3, chromium-6, Cr(VI), Drinking Water, EPA, EPA Method 218.6, Hexavalent Chromium, Ion Chromatography, maximum contaminant level, MCL, Method, municipal water, National Drinking Water Advisory Council, National Environmental laboratory Accreditation Program, NELAP, NEMI, public water systems, Safe Drinking Water Act, total chromium, USEPA