Metrohm and the EPA improve Cr-VI analyses

Like most Hollywood movies, Erin Brockovich brought the hexavalent chromium issue to the masses for a brief moment in time—but in the 10 years following, and through the future, the EPA and Metrohm continue to investigate ways that will improve the detection and monitoring of this contaminant in our drinking water.

What’s so special about Hexavalent Chromium — also called Hexachrome, Chrome-6, Cr-VI and Cr(VI)?

Well, it’s been cited as more toxic, more soluble and more mobile than its metallic (Cr-0) or other oxidative states (e.g., Cr(III)). In fact, a review of Cr-VI toxicity studies by the National Toxicology programme in 2008 showed “clear evidence of carcinogenic activity” in laboratory animals. And a toxicological review drafted in September 2010 concluded that the presence of Cr-VI in tap water may be carcinogenic to humans.

What are the current testing limits set for Cr-VI analysis?

The EPA has set the current drinking water standard for total Chromium (including Cr(III), Cr-VI and other forms) at 0.1 mg/L; although the EPA has not set a limit, the state of California has set a “safe” limit at 0.06 µg/L, with a goal of 0.02 µg/L.

The Environmental Working Group (EWG) used California’s “safe limit” of 0.06 µg/L when they conducted their 35-city test of municipal drinking water. Their findings showed 31 of those cities had contamination readings above this limit, which prompted the EPA to re-evaluate Method 218.6.

What modifications to Method 218.6 have been evaluated?

Even before these new toxicology studies came out, we noticed room for improvement in the methodology. Working closely with the EPA for years, an updated system and revisions to the method were evaluated; tests show the new system is reproducibly detecting hexachrome limits that are even less than California’s proposed 0.02 µg/L goal.

Modifications regarding the buffer solutions and maximum hold time for sample preservation that optimize the methodology were also tested, as well as the handling of common interferences, such as transition metals, disinfectants (e.g., chlorine and its compounds), oxidizers and reducers.

Download the latest EPA Method 218.7.

What other supporting documentation is available for this new method?

We're so glad you asked! We have a new Application Work that shows Metrohm Cr-VI systems achieve a 12.5 ng/L (ppt) quantifiable chromatogram.

Because we are in such close collaboration with the EPA, we suggest keeping connected with us, as we will continually send and post updated information as we receive it.

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