Literature review and meta-analysis of gastric and intestinal bioaccessibility for nine inorganic elements in soils and soil-like media for use in human health risk assessment

When soils become contaminated, a human health risk assessment (HHRA) is beneficial for determining whether identified contaminants of potential concern (COPCs) pose a risk to human health. In certain jurisdictions, when calculating doses from soil ingestion during the exposure assessment step of a HHRA, validated bioaccessibility methods may be used to accurately represent a contaminant's relative absorption factor (RAF). Where validated methods do not exist, risk assessors must either a) conduct their own literature search (which can be time consuming), b) create their own validation study (also a time consuming process), or c) use default assumptions (i.e., a RAF of 1). This literature search and meta-analysis characterizes the past 28 years of published analysis for aluminum (Al), antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), iron (Fe), lead (Pb), manganese (Mn), and mercury (Hg) from 13 different gastric and intestinal bioaccessibility methodologies. These elements were selected as they are often risk drivers in HHRAs and are sometimes identified as COPCs in HHRAs at contaminated sites. Results were compiled from soil deriving from a variety of sources and varying in physicochemical properties. The mean percent bioaccessibility and 95 percent upper confidence limit on the mean (95 UCL) were calculated to better inform further study and validation of methods for elements additional to Pb, As, and Cd, which may be applicable to future HHRAs. Although there has been plenty of study into effects of various soil and method parameters on elemental bioaccessibility, meta-analysis found limited evidence that these findings are generalizable. Meta-analysis was also limited by little variability in certain parameters, but a more targeted analysis identified some correlative influences of pH and particle size for well-studied elements within the dataset. High bioaccessibility variability indicates that moving away from default parameters to use percent bioaccessibility to represent contaminant RAF must still be completed on a site-specific basis. The study has identified that more bioaccessibility studies for Al, Cr, Sb, Fe, Mn, and Hg, particularly studies that seek to validate bioaccessibility testing of these elements, will be beneficial for more robust and informative future risk assessments.