Modification of an existing in vitro method to predict relative bioavailable arsenic in soils

Abstract

The soil matrix can sequester arsenic (As) and reduces its exposure by soil ingestion. In vivo dosing studies and in vitro gastrointestinal (IVG) methods have been used to predict relative bioavailable (RBA) As. Originally, the Ohio State University (OSU-IVG) method predicted RBA As for soils exclusively from mining and smelting sites with a median of 5,636 mg As kg. The objectives of the current study were to (i) evaluate the ability of the OSU-IVG method to predict RBA As for As contaminated soils with a wider range of As content and As contaminant sources, and (ii) evaluate a modified extraction procedure's ability to improve prediction of RBA As. In vitro bioaccessible (IVBA) by OSU-IVG and California Bioaccessibility Method (CAB) methods, RBA As, speciation, and properties of 33 As contaminated soils were determined. Total As ranged from 162 to 12,483 mg kg with a median of 73 mg kg. RBA As ranged from 1.30 to 60.0% and OSU-IVG IVBA As ranged from 0.80 to 52.3%. Arsenic speciation was predominantly As(V) adsorbed to hydrous ferric oxide (HFO) or iron (Fe), manganese (Mn), and aluminum (Al) oxides. The OSU-IVG often extracted significantly less As in vitro than in vivo RBA As, in particularly for soils from historical gold mining. The CAB method, which is a modified OSU-IVG method extracted more As than OSU-IVG for most soils, resulting in a more accurate predictor than OSU-IVG, especially for low to moderately contaminated soils (<1,500 mg As kg) with RBA As = 0.81 IVBA As + 3.2, r = 0.91.

Arsenic, lead, and cadmium bioaccessibility in contaminated soils: Measurements and validations

“…Though SBRC-GP assay was not the best based on our study (Li, Li, Cui, et al, 2015), based on two validation studies outside test soils, SBRC-GP assay was the best among the 5 in vitro assays as a surrogate for As-RBA in soils (Bradham et al, 2015). However, Whitacre et al (2017) reported that the SBRC-GP and IVG-GP assays were poor predictors of As-RBA for soils contaminated from gold mining activities, which were high in Fe concentrations. This leads to a modification of the IVG assay by including ascorbic acid, which is called California Bioaccessibility Method (Whitacre et al, 2017).…”

“…However, Whitacre et al (2017) reported that the SBRC-GP and IVG-GP assays were poor predictors of As-RBA for soils contaminated from gold mining activities, which were high in Fe concentrations. This leads to a modification of the IVG assay by including ascorbic acid, which is called California Bioaccessibility Method (Whitacre et al, 2017).…”

“…Arsenic bioaccessibility data are pooled from 10 studies, totaling 179 contaminated soils (Table 2). Among them, 47 soils were measured for As bioaccessibility using all 5 assays Juhasz et al, 2015;Bradham et al, 2011;Li, Li, Cui, et al, 2015), while 132 soils were measured using 1-2 assays (Rodriguez et al, 1999;Basta, Foster, Dayton, Rodriguez, & Casteel, 2007;Denys et al, 2012;Bradham et al, 2015;Whitacre et al, 2017). In addition, these soils were also measured for As-RBA using swine (116 soils) or mouse model (63 soils).…”

“…For example, 20-40 soils were used to validate SBRC-GP assay for As Bradham et al, 2015), while 19-38 soils were used to validate SBRC-GP assay for Pb (Drexler & Brattin, 2007;Li, Zhao, et al, 2016). Similarly, 15-33 soils were used to validate the IVG assay for As and Pb (Rodriguez et al, 1999;Whitacre et al, 2017;Schroder et al, 2004), while 16 soils were used to validate the UBM assay for As, Pb, and Cd (Denys et al, 2012). To increase the strength of in vitro assays, validation using large sample size is suggested.…”

“…In vivo animal bioassays are robust to determine metal bioavailability in soils, with swine and mouse models being commonly used (Juhasz, Herde, Herde, Boland, & Smith, 2015;Li, Li, Zhu, Juhasz, & Ma, 2015;Li, Li, Cave, Li, & Ma, 2015;Li, Li, Cui, et al, 2015;Li, Zhao, et al, 2016;Li, Liu, et al, 2017;. During in vivo bioassays, metal bioavailability in soils is often measured as relative bioavailability (RBA) (Brattin & Casteel, 2013;Ruby et al, 1999), which compares metal accumulation in animal tissues following exposure of soils to that of soluble references including sodium arsenate, Pb acetate, and cadmium chloride (Juhasz, Gancarz, et al, 2014;Juhasz, Herde, Herde, Boland, & Smith, 2014;Juhasz, Smith, Nelson, Thomas, & Bradham, 2014;Whitacre et al, 2017). In this case, the bioavailability values obtained using animals can be extrapolated to humans for risk assessment.…”