The Influence of Liquid to Soil Ratios on Arsenic and Lead Bioaccessibility in Reference and Field Soil

In vitro bioaccessibility testing is gaining popularity as a tool to estimate the oral bioavailability of contaminants in soil for human health risk assessment (HHRA). Bioaccessibility tests are used to measure the bioaccessible fraction of a contaminant in soil, which can then be used to estimate the bioavailable fraction. Inherent uncertainties are associated with bioaccessibility tests. Various test parameters need to be carefully considered in their development, including the liquid to soil (L/S) ratio employed. We used L/S ratios (v:wt) ranging from 25 ml:1 g to 1,000 ml:1 g in a modified relative bioaccessibility extraction procedure to investigate the effects on bioaccessibility of lead and arsenic in field and reference soils. General trends of increased percent bioaccessibility of lead and arsenic with increasing L/S ratio were observed in the reference soil. A similar positive relationship was observed for lead in the field soil; soluble arsenic concentrations were below the detection limit and data were insufficient to observe a trend. Percent bioaccessibility was significantly affected at each extreme of the L/S ratios tested (p < .05). Biological relevance, technical feasibility, and mathematical relationships with in vivo results should be considered when selecting an appropriate L/S ratio for bioaccessibility testing.