Article

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

ABSTRACT

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.
    Full-text · Article · Jun 2015 · Science of The Total Environment
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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.
    Full-text · Article · Apr 2015 · Journal of Hazardous Materials
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    • "Recently, the inadvertent oral ingestion of soil has been considered an important exposure pathway for As, especially for children through outdoor hand-to-mouth activities (Ljung et al. 2006). Thus, risk assessors account for limitations in the release and subsequent absorption of contaminants by incorporating bioaccessibility and bioavailability parameters into exposure assessments (Bradham et al. 2011). There are many in vitro methods to assess bioaccessibility, such as simple bioavailability extraction test (SBET), physiologically based extraction test (PBET), and Unified BARGE Method (UBM) (Kim et al. 2002; Ruby et al. 1996; Wragg et al. 2011). "
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    ABSTRACT: Purpose Bioaccessibility is always a factor in human health risk assessment; the accurate determination of arsenic (As) dynamic dissolution in the gastric and small intestinal phases can provide a better understanding of its potential impact on human health. Materials and methods Eighteen soil samples were collected from different sites in Hunan, China, and the factors controlling the bioaccessibility and dynamic dissolution of soil As were investigated. The bioaccessibility of soil As was determined by the physiologically based extraction test (PBET). Results and discussion The results indicated that the bioaccessibility ranged from 6.9 to 59.5 % and 5.9 to 83.2 % in the gastric and small intestinal phases. Among all the soil properties, the concentrations of oxalate-extractable Fe, Mn, and total As were important for controlling bioaccessible As. In the gastric phase, the bioaccessible As concentrations increased rapidly in the first 20 min and kept steady state after 1 h. In the small intestinal phase, the bioaccessible As concentrations kept steady state rapidly after 2 h. Moreover, the more soluble fraction of As-bearing metal minerals had enhanced solubility in the gastric phase under acidic conditions, and most of the metal oxyhydroxides formed were usually unstable in the small intestinal phase under neutral conditions. By the interaction between kinetic laws and simple linear correlation, the dissolution rate of As for soils with lower pH was faster in the gastric phase; thus, the soil pH and dissolution of Fe, Mn, and Al minerals may be the main factors controlling the As dissolution rate. Conclusions The As bioaccessibility in the small intestinal phase was higher, and the prescribed 4 h duration of the PBET method can meet As complete dissolution. The dynamic dissolution of As from soil in the gastric and small intestinal phases was strongly controlled by the concentrations of dissolved Fe, Mn, and Al.
    Full-text · Article · Mar 2015 · Journal of Soils and Sediments
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