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. 2021 Jan 1;268(Pt A):115830.
doi: 10.1016/j.envpol.2020.115830. Epub 2020 Oct 14.

Gastric bioaccessibility is a conservative measure of nickel bioavailability after oral exposure: Evidence from Ni-contaminated soil, pure Ni substances and Ni alloys

Michael D Dutton  1 , Ryan Thorn  2 , Wilson Lau  3 , Luba Vasiluk  4 , Beverly Hale  5
Affiliations

Gastric bioaccessibility is a conservative measure of nickel bioavailability after oral exposure: Evidence from Ni-contaminated soil, pure Ni substances and Ni alloys

Michael D Dutton et al. Environ Pollut. .

Abstract

Oral bioaccessibility (BAc) is a surrogate for the bioavailability (BAv) of a broad range of substances, reflecting the value that the approach offers for assessing oral exposure and risk. BAc is generally considered to have been validated as a proxy for oral BAv for the important soil contaminants Pb, Cd, and As. Here, using literature data for Ni BAc and BAv, we confirmed that Ni BAc (gastric only, with HCl mimicking stomach conditions) is a conservative measure of BAv for the oral exposure pathway. Measured oral BAv of Ni in soil was shown to be 50-100 times less than the simplest oral BAc estimates (%BAv = 0.012(%BAc) - 0.023 (r = 0.701, 95%CI [0.456, 0.847], n = 30)) in rats, demonstrating a significant conservatism for exposure assessment. The relationship between the oral BAv and BAc of nickel sulfate hexahydrate (NSHH) was comparable to that of soil, with measured oral BAv of NSHH (1.94%) being a small fraction of NSHH gastric BAc (91.1%). BAc and BAv reflect the underlying Ni speciation of the sample, with the bioaccessible leaching limits being represented by the highly soluble Ni salts and the poorly soluble Ni monoxide, and the environmental (e.g. soil properties) or gastric (e.g. food present) conditions. BAc has potential utility for chemical classification purposes because pure Ni substances can be grouped by %BAc values(using standardized methodologies for the relevant exposure routes), these groupings reflecting the underlying chemistry and speciation of the samples of substances tested here, with 0.008% %BAc for alloys (SS304, SS316, Inconel, Monel), <1% in green NiO and Ni metal massives, 0.9-23.6% for Ni powders, 9.8-22.7% for Ni sulfides, 26.3-29.6% for black oxidic Ni, and 82-91% for the soluble Ni salts. Oral BAc provides realistic yet conservative estimates of BAv for the hazard classification and risk assessment of Ni substances.

Keywords: Alloys; Bioaccessibility; Bioavailability; Nickel; Speciation.

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Conflict of interest statement

Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The corresponding author (M. Dutton) included the following declaration in the submitted manuscript in the “Funding disclosure/competing interests” section at the end of the manuscript. “This work was first conceptualized when M. Dutton was an employee of Vale Canada Limited. Vale Canada Limited had no input into the completion of the work. Funding to complete the manuscript was provided toBioProcess Assist (BPA) Ltd.byNiPERA Inc. NiPERA provided comments on the manuscript, but the final product is that of the authors, led by M. Dutton. The research of W. Lau and R. Thorn were supported in part by grants-in-aid-of-research provided to B. Hale by Vale Canada Limited, Canada’sNatural Sciences and Engineering Research Council(NSERC), and from the University of Guelph. “

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