An Evaluation of a Technical Holding Time for the Preparation and Analysis of Hexavalent Chromium in Soils/Sediments

Chromium (Cr) is routinely measured during environmental investigations involving soils and other solid matrix sampling. Regulatory-approved analytical methods are available to extract and quantify total Cr in various environmental media. However, due to significant toxicity differences between trivalent [Cr(III)] and hexavalent [Cr(VI)] valences, it is compelling that the two can be quantitatively distinguished. SW-846 Method 3060A is an effective extraction technique for soluble and insoluble Cr(VI). Several regulatory-approved methods exist for quantitating the Cr(VI) in extracts or aqueous samples. Although a 6-month holding time for total Cr is not encumbering, investigators are challenged by the typical 24-h holding time (sample collection through analysis) for Cr(VI) in aqueous samples and the 24- to 96-h holding time range for solid matrix samples typically set by regulators. This research report addresses quantitating Cr(VI) in solid matrices. Using SW-846 Methods 3060A/7196A, a scientifically defensible basis has been established for designating a 30-day holding time for Cr(VI) extraction from solid matrices and a 7-day holding time for Cr(VI) analysis once solubilized in the alkaline digestate. The study results indicate that a 30-day holding time, from sample collection to preparation, and a 7-day holding time, from digestion to analysis, are appropriate for Cr(VI) analysis.