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

Abstract

Bioaccessibility is a measurement of a substance's solubility in the human gastro-intestinal system, and is often used in the risk assessment of soils. The present study was designed to determine the variability among laboratories using different methods to measure the bioaccessibility of 24 inorganic contaminants in one standardized soil sample, the standard reference material NIST 2710. Fourteen laboratories used a total of 17 bioaccessibility extraction methods. The variability between methods was assessed by calculating the reproducibility relative standard deviations (RSDs), where reproducibility is the sum of within-laboratory and between-laboratory variability. Whereas within-laboratory repeatability was usually better than (<) 15% for most elements, reproducibility RSDs were much higher, indicating more variability, although for many elements they were comparable to typical uncertainties (e.g., 30% in commercial laboratories). For five trace elements of interest, reproducibility RSDs were: arsenic (As), 22–44%; cadmium (Cd), 11–41%; Cu, 15–30%; lead (Pb), 45–83%; and Zn, 18–56%. Only one method variable, pH, was found to correlate significantly with bioaccessibility for aluminum (Al), Cd, copper (Cu), manganese (Mn), Pb and zinc (Zn) but other method variables could not be examined systematically because of the study design. When bioaccessibility results were directly compared with bioavailability results for As (swine and mouse) and Pb (swine), four methods returned results within uncertainty ranges for both elements: two that were defined as simpler (gastric phase only, limited chemicals) and two were more complex (gastric + intestinal phases, with a mixture of chemicals).

Keywords:

• Bioaccessibility
• variability
• multiple methods
• NIST 2710

Acknowledgments

Other participants are Kim House (laboratory supervisor) and Jessica Harris (analyst) from the Royal Military College of Canada; Tammie Morgan-Gray (risk assessor) and Andrea Amendola (risk assessor) from Golder Associates Ltd.; Marc Chénier (analyst) from Health Canada (HC); Shane Whitacre (analyst) from Ohio State University (OSU); Ben Smith (toxicologist/ risk assessor) from Stantec; Luba Vasiluk (analyst) from University of Guelph (UG); Linda Pinto (analyst) from Simon Fraser University (SFU); Bruno Welfringer (analyst) from École Polytechnique de Montréal (EPM); and Brian Laird (coordinator) and Kim Dekker (analyst) from University of Saskatchewan (US). Funding was provided by Health Canada, Contaminated Sites Division, as an Expert Support Department within the Federal Contaminated Sites Action Plan (FCSAP).

Notes

The Relative Bioavailability Leaching Procedure (RBALP) is also referred to as the Solubility and Bioavailability Research Consortium (SBRC) method, the Simple Bioaccessibility Extraction Test (SBET), and the In Vitro Bioaccessibility Assay (IVBA) for Pb in soil.

Spikes were prepared from Pb(NO₃)₂ and As₂O₃, rather than Pb(CH₃COO)₂ and NaH₂AsO₄ used in the bioavailability studies. Although the Pb²⁺ 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(V) species (H₂AsO₄ ⁻ ↔ HAsO₄ ²⁻).