Considerations for Determining Appropriate Reference Doses for Soluble and Insoluble Trivalent Chromium Compounds. P. A. Malsch, D. M. Proctor and M. L. Gargas, ChemRisk Division, McLaren/Hart Environmental Engineering, 29225 Chagrin Blvd., Cleveland, OH 44122
The current reference dose (RfD) for trivalent chromium, Cr(III), is relevant for insoluble forms of Cr(III) only; however, recent animal data indicate that more soluble forms of Cr(III) present a greater potential for toxicity. It is theorized that, in comparison to insoluble forms, water or acid soluble forms of Cr(III) are more bioaccessible and thus absorbed from the gastrointestinal tract to a greater extent resulting in a larger delivered dose to the target organ. These potential differences in Cr(III) absorption may, in part, explain the differences in observed toxicities, thus indicating the need for separate RfDs for soluble and insoluble species. This study examined the solubilities of three Cr(III) compounds, CrC13_6H2O,Cr2(SO4)3, and Cr2O3, under simulated stomach (gastric) conditions and used this information along with the existing toxicity database to derive appropriate RfDs. The solubilities of CrC13_6H2O,Cr2(SO4)3, and Cr2O3 were 165,000, 124, and 2.37 mg Cr(III)/L of solvent respectively, under simulated gastric conditions (250 mL of a pH 1.3 HCI solution, 37C, mild shaking for 2 hours). Using traditional methodology, RfDs for Cr2O3 (insoluble) and CrC13_6H2O (soluble) of 15 mg/kg-day and 0.03 mg/kg-day, respectively, were derived. The solubility data and calculated RfDs from this work, as well as qualitative solubility descriptions, were used to derive RfDs for CR(III) compounds of intermediate solubilities where no toxicity data are available. Using this technique, an RfD of 5 mg/kg-day was derived for Cr2(SO4)3 (slightly soluble). This analysis supports the use of separate RfDs in environmental health risk assessments for CR(III) compounds of varying gastric solubilities.