Insolubility of Cr₂O₃in Bioaccessibility Tests Points to Requirement for a New Human Oral Reference Dose for Trivalent Chromium

Abstract

Bioaccessibility measurements have the potential to improve the accuracy of risk assessments and reduce the potential costs of remediation when they reveal that the solubility of chemicals in a matrix (e.g., soil) differs markedly from that in the critical toxicity study (i.e., the key study from which a toxicological or toxicity reference value is derived). We aimed to apply this approach to a brownfield site contaminated with chromium, and found that the speciation was Cr III , using a combination of alkaline digestion/diphenylcarbazide complexation and X-ray absorption near edge structure analysis. The bioaccessibility of Cr 2 O 3 , the compound on which a reference dose for Cr III is based, was substantially lower (<0.1%) than that of the Cr III in the soils, which was a maximum of 9%, giving relative bioaccessibility values of 13,000% in soil. This shows that the reference dose is based on essentially an insoluble compound, and thus we suggest that other compounds be considered for toxicity testing and derivation of reference dose. Two possibilities are CrCl 3 ·6H 2 O and KCr(SO 4 ) 2 ·12H 2 O, which have been used for derivation of ecological toxicity reference values and are soluble at a range of dosing levels in our bioaccessibility tests.

Variability of bioaccessibility results using seventeen different methods on a standard reference material, NIST 2710

“…Although the Pb 2+ species are not expected to differ much in solubility behaviour, the use of the spike from the present study for As is not ideal, since the neutral As(III) species (As(OH) 3 ) used in the spike may be less reactive with solution components (e.g., organic biomolecules) than anionic As spike recoveries under certain conditions, such as that seen for Pb [27] and Cr. [28] As and Pb RBAs in NIST 2710 were determined at the Institut national de l'environnement industriel et des risques (INERIS) according to methods published elsewhere. [5] Swine were used and the positive controls were sodium arsenate (NaH 2 AsO 4 ) and lead acetate (Pb(CH 3 COO) 2 ).…”