Evaluation of Two In Vitro Protocols for Determination of Mercury Bioaccessibility: Influence of Mercury Fractionation and Soil Properties

Abstract

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.

The bioaccessibility of soil-based mercury as determined by physiological based extraction tests and human biomonitoring in children

“…The results of the current in vitro assessment of soil-based mercury bioaccessibility are of the same order of magnitude when compared to previous publications (Barnett and Turner, 2001;Welfringer and Zagury, 2009;Guney et al, 2013) and indicate that a conservative estimate of mercury bioaccessibility would be provided through the use of a two-phase PBET mimicking both the gastric and intestinal conditions relative to a single-phase test. Similar results were found by Welfringer and Zagury (2009) in which bioaccessibility measured using the IVG (In Vitro Gastrointestinal) method (Rodriguez et al, 1999) ranged from 1.1% to 4.5% for Phase 1, and from 1.5% to 7.5% for Phase 1+2.…”

“…As a result, a default of 100% relative bioavailability is typically used in risk assessment for inorganic mercury in ingested soils despite common acceptance that this represents an overly conservative assumption (Canady et al, 1997). A number of investigations have characterized the bioaccessibility of soil-based mercury through in vitro analysis (Barnett and Turner, 2001;Bloom et al, 2003;Welfringer and Zagury, 2009;Koch et al, 2013).…”

Bioaccessibility of mercury in selected Ayurvedic medicines

“…In the present study, the DOC concentrations, while not measured, were estimated to be 1.1 g/l in the PBET G phase, 1.6 g/l in the PBET GI phase, and 21 g/l in the FOREhST (all are unfiltered concentrations), based on the chemical content of the extraction fluids. Like in Welfringer and Zagury (2009), these increasing DOC concentrations are associated with increasing percent bioaccessibility (solubility) of insoluble inorganic mercury in the medicines, and with decreasing percent bioaccessibility of soluble methylmercury (74% bioaccessibility in the PBET-G solution) in DORM-2. Thus, the same components that remove methylmercury from solution may help to complex and solubilize the insoluble inorganic mercury.…”

“…Other forms, such as kleinite (Hg 2 N(Cl,SO4)•n(H 2 O)), terlinguaite (Hg + Hg 2+ ClO), calomel (Hg 2 Cl 2 ), and montroydite (HgO), have been found to be present in samples with higher percent bioaccessibility values (6-18%) but the mineralogy was not well defined and the association of the mineralogical forms with higher percent bioaccessibility was not systematic (Gray et al, 2010). One of the highest percent bioaccessibility values for mercury in soil reported to date is in the certified reference material, CRM 025-050 (35-64%) Welfringer and Zagury, 2009), and the mercury in this sample has been postulated to be associated with sulfate, possibly as HgSO 4 .…”

Solid–liquid separation method governs the in vitro bioaccessibility of metals in contaminated soil-like test materials

“…500-12 000g) (Rieuwerts et al, 2006;Sarkar et al, 2007;Tang et al, 2008;Nagar et al, 2009), microfiltration (e.g. 0.2-0.45 lm) (Yamada et al, 2003;Welfringer and Zagury, 2009;Roussel et al, 2010), and/or ultrafiltration (e.g. 5-10 kDa) (Oomen et al, 2002;Laird et al, 2007;Van de Wiele et al, 2007).…”