Evaluation of two in vitro protocols for determination of mercury bioaccessibility: influence of mercury fractionation and soil properties.

Soil ingestion by children can be a significant exposure pathway to mercury (Hg). Unfortunately, no reliable in vivo results for Hg oral bioavailability determination in soils have been published. In vitro extractions enable the assessment of metals' bioaccessibility, which is an estimate of oral bioavailability. Therefore, the goal of this study was to evaluate two in vitro protocols (CDM (Camp Dresser and Mc Kee Inc.) and IVG (In Vitro Gastrointestinal)) for determination of Hg bioaccessibility in soils using pure Hg-compounds, reference materials (CRM 025-050 and ERM-CC580), and field-collected soils with elevated Hg concentrations. The influence of Hg fractionation and soil properties on Hg bioaccessibility was also investigated. In the field-collected soils, IVG bioaccessibility ranged from 1.5 to 7.5%, and was always below 3.15%, using the CDM method. Mercury bioaccessibility in CRM 025-050 was 61.5 and 34.7%, using IVG and CDM protocols, respectively, whereas Hg bioaccessibility was much lower in the certified sediment sample ERM-CC580 (<7%). Overall, the CDM protocol resulted in lower Hg bioaccessibility values. The water-soluble and exchangeable Hg fraction was highly correlated with gastrointestinal bioaccessibility (r=0.99, p<0.001 for both methods) and this fraction could be a potentially good indicator of Hg bioaccessibility. Because the IVG method is less time-consuming than the CDM protocol and includes organic physiological components which seem to increase Hg bioaccessibility, it might be preferred for determination of Hg bioaccessibility.