Relative Bioavailability and Bioaccessibility and Speciation of Arsenic in Contaminated Soils

National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA.
Environmental Health Perspectives (Impact Factor: 7.98). 07/2011; 119(11):1629-34. DOI: 10.1289/ehp.1003352
Source: PubMed


Assessment of soil arsenic (As) bioavailability may profoundly affect the extent of remediation required at contaminated sites by improving human exposure estimates. Because small adjustments in soil As bioavailability estimates can significantly alter risk assessments and remediation goals, convenient, rapid, reliable, and inexpensive tools are needed to determine soil As bioavailability.
We evaluated inexpensive methods for assessing As bioavailability in soil as a means to improve human exposure estimates and potentially reduce remediation costs.
Nine soils from residential sites affected by mining or smelting activity and two National Institute of Standards and Technology standard reference materials were evaluated for As bioavailability, bioaccessibility, and speciation. Arsenic bioavailability was determined using an in vivo mouse model, and As bioaccessibility was determined using the Solubility/Bioavailability Research Consortium in vitro assay. Arsenic speciation in soil and selected soil physicochemical properties were also evaluated to determine whether these parameters could be used as predictors of As bioavailability and bioaccessibility.
In the mouse assay, we compared bioavailabilities of As in soils with that for sodium arsenate. Relative bioavailabilities (RBAs) of soil As ranged from 11% to 53% (mean, 33%). In vitro soil As bioaccessibility values were strongly correlated with soil As RBAs (R² = 0.92). Among physicochemical properties, combined concentrations of iron and aluminum accounted for 80% and 62% of the variability in estimates of RBA and bioaccessibility, respectively.
The multifaceted approach described here yielded congruent estimates of As bioavailability and evidence of interrelations among physicochemical properties and bioavailability estimates.

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    • "In addition to swine model, a mouse model has also been used to validate in vitro assays . Bradham et al. (2011) showed a strong correlation between As bioaccessibility by the gastric phase of SBRC method and As-RBA by a mouse urine model in contaminated soils from the USA (r 2 = 0.88). These studies demonstrated that As-RBA in contaminated soils can be predicted using in vitro methods and the established in vivo–in vitro correlations (IVIVC). "
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    ABSTRACT: Previous studies have established in vivo-in vitro correlations (IVIVC) between arsenic (As) relative bioavailability (RBA) and bioaccessibility in contaminated soils. However, their ability to predict As-RBA in soils outside the models is unclear. In this study, As bioaccessibility and As-RBA in 12 As-contaminated soils (22.2-4172mgkg(-1) As) were measured using five assays (SBRC, IVG, DIN, PBET, and UBM) and a mouse blood model. Arsenic RBA in the soils ranged from 6.38±2.80% to 73.1±17.7% with soils containing higher extractable Fe showing lower values. Arsenic bioaccessibility varied within and between assays. Arsenic bioaccessibility was used as input values into established IVIVC to predict As-RBA in soils. There were significant differences between predicted and measured As-RBA for the 12 soils, illustrating the inability of established IVIVC to predict As-RBA in those contaminated soils. Therefore, a new IVIVC was established by correlating measured As-RBA and As bioaccessibility for the 12 soils. The strength of the predictive models varied from r(2)=0.50 for PBET to r(2)=0.83 for IVG, with IVG assay providing the best prediction of As-RBA. When IVIVC were compared to those of Juhasz et al. (2014a), slopes of the relationships were significantly higher possibly due to different As-RBA measurements. Our research showed that IVG has potential to measure As bioavailability in contaminated soils from China though UBM and SBRC assays were also suitable. More research is needed to verify their suitability to predict As-RBA in soils for refining health risk assessment. Copyright © 2015. Published by Elsevier B.V.
    Science of The Total Environment 06/2015; 532. DOI:10.1016/j.scitotenv.2015.05.113 · 4.10 Impact Factor
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    • "Bioavailable As is defined as the fraction of As that reaches the systemic circulation in human gastrointestinal (GI) tract [4]. Common animal models including juvenile swine and mouse have been used to assess As bioavailability in contaminated soils [5] [6]. "
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    ABSTRACT: Arsenic bioaccessibility varies with in vitro methods and soils. Four assays including unified BARGE method (UBM), Solubility Bioaccessibility Research Consortium method (SBRC), in vitro gastrointestinal method (IVG), and physiologically based extraction test (PBET), were used to determine As bioaccessibility in 11 contaminated soils (22-4,172mgkg(-1)). The objective was to understand how bioaccessible As by different methods was related to different As pools based on sequential extraction and 0.43M HNO3 extraction. Arsenic bioaccessibility was 7.6-25, 2.3-49, 7.3-44, and 1.3-38% in gastric phase (GP), and 5.7-53, 0.46-33, 2.3-42, and 0.86-43% in intestinal phase (IP) for UBM, SBRC, IVG, and PBET, respectively, with HNO3-extractable As being 0.90-60%. Based on sequential extraction, As was primarily associated with amorphous (AF3; 17-79%) and crystallized Fe/Al oxides (CF4; 6.4-73%) while non-specifically sorbed (NS1), specifically sorbed (SS2), and residual fractions (RS5) were 0-10%, 3.4-20% and 3.2-25%. Significant correlation was found between As bioaccessibility by PBET and NS1+SS2 (R(2)=0.55-0.69), and UBM-GP and NS1+SS2+AF3 (R(2)=0.58), indicating PBET mostly targeted As in NS1+SS2 whereas UBM in NS1+SS2+AF3. HNO3-extractable As was correlated to bioaccessible As by four methods (R(2)=0.42-0.72) with SBRC-GP having the best correlation. The fact that different methods targeted different As fractions in soils suggested the importance of validation by animal test. Our data suggested that HNO3 may have potential to determine bioaccessible As in soils. Published by Elsevier B.V.
    Journal of Hazardous Materials 04/2015; 295:145-152. DOI:10.1016/j.jhazmat.2015.04.011 · 4.53 Impact Factor
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    • "Bradham et al. [7] found that Fe + Al (FeAl) accounted for the largest variation in RBA As and IVBA As and reported the following relationships (Equations 4 and 5) between RBA As, IVBA As, and soil FeAl (mol/kg) extracted by USEPA method 3051a. "
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    ABSTRACT: In order for in vitro methods to become widely accepted as tools that accurately assess soil arsenic (As) exposure through the oral ingestion pathway, a better understanding is needed regarding which fractions of soil As are being measured in the in vitro extraction. The objective of the current study is to (1) identify in vitro bioaccessible (IVBA) and non-IVBA fractions of soil As using sequential extraction; and (2) determine the sorptive phases of soil in non-IVBA As soil fractions. Nineteen soils with a range of soil properties were spiked with 250 mg/kg of sodium arsenate and aged. In vitro bioaccessible As (IVBA As) was then determined using The Ohio State University in vitro gastrointestinal method (OSU-IVG), and soil As was fractionated using sequential extraction into: (F1) non-specifically sorbed; (F2) specifically sorbed; (F3) amorphous and poorly crystalline oxides of Fe and Al; (F4) well-crystallized oxides of Fe and Al and residual As phases. The IVBA As across the 19 soil ranged from 0.36 to 2.75 mmol/kg (12 to 86%) with a mean of 1.26 mmol/kg (42%) in the gastric phase and from 0.39 to 2.80 mmol/kg (13 to 87%) in the intestinal phase with a mean of 1.32 mmol/kg (43%). The results of the sequential extraction showed that IVBA As extracted by the OSU-IVG is the As present in the first two fraction (F1 and F2) of the sequential extraction. In the non-IVBA fractions, highly significant relationships (P < 0.01) exist between F3 As and log transformed F3 Fe (r (2) = 0.74), but not F3 Al. In addition, the gastric extraction dissolves a significant fraction of soil Al, but not soil Fe, therefore As sorbed to Al oxides likely contributed to IVBA As and is accounted for in the F2 fraction of the sequential extraction. In vitro methods that demonstrate the ability to extract the similar soil fractions that occur in vivo across a wide range of soil types and As-contaminant sources is an important criteria for in vitro method validation. Further research that includes soils with multiple As-contaminant sources (mining, pesticide, etc.), soil As fractionation, and in vivo bioavailability is needed in order to determine if F1+F2 are the bioavailable As fractions in soils that vary in total As content and sorbed As species.
    Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering 05/2013; 48(6):620-8. DOI:10.1080/10934529.2013.731804 · 1.16 Impact Factor
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