Gastric bioaccessibility is a conservative measure of nickel bioavailability after oral exposure: Evidence from Ni-contaminated soil, pure Ni substances and Ni alloys. (1st January 2021)

• Record Type: Journal Article
• Authors: Dutton, Michael D.; Thorn, Ryan; Lau, Wilson; Vasiluk, Luba; Hale, Beverly
• Is Part Of: Environmental pollution. Volume 268(2021)Part A
• Publication Date: 2021-01-01
• Subjects: Nickel -- Bioavailability -- Bioaccessibility -- Speciation -- Alloys; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2020.115830
• Languages: English
• ISSNs: 0269-7491

Abstract

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. Graphical abstract: Image 1 Highlights: Oral bioaccessibility (BAc) was studied in pure Ni substances and nickeliferous soils. All Ni BAc occurs in a leaching 'envelope' between Ni salts and green Ni oxide (bunsenite). In soil with elevated Ni, BAc also fell within the leaching envelope, in relation to Ni speciation. Oral BAc provides a meaningful, conservative, estimate of true oral bioavailability (BAv). Oral BAc is a valuable tool for estimating oral exposure, risk, and safety of Ni substances, including alloys. Abstract : Summary statement for review by environmental pollution: Leaching curves illustrate the principle of oral bioaccessibility (BAc). Validation of the oral Ni BAc/BAv (bioavailability) relationship supports BAc for exposure adjustment in risk assessment.