Arsenic Bioaccessibility Research Articles

Arsenic bio-accessibility and bioaccumulation in aged pesticide contaminated soils: A multiline investigation to understand environmental risk.

Bio-accessibility and bioavailability of arsenic (As) in historically As-contaminated soils (cattle tick pesticide), and pristine soils were assessed using 3 different approaches. These approaches included human bio-accessibility using an extraction test replicating gastric conditions (in vitro physiologically-based extraction test); an operationally defined bioaccessibility extraction test - 1.0M HCl extraction; and a live organism bioaccumulation test using earthworms. A sequential extraction procedure revealed the soil As-pool that controls bio-accessibility and bioaccumulation of As. Findings show that As is strongly bound to historically contaminated soil with a lower degree of As bio-accessibility (<15%) and bioaccumulation (<9%) compared with freshly contaminated soil. Key to these lower degrees of bio-accessibility and bioaccumulation is the greater fraction of As associated with crystalline Fe/Al oxy-hydroxide and residual phases. The high bio-accessibility and bioaccumulation of freshly sorbed As in pristine soils were from the exchangeable and specifically sorbed As fractions. Arsenic bioaccumulation in earthworms correlates strongly with both the human bio-accessible, and the operationally defined bioavailable fractions. Hence, results suggest that indirect As bioavailability measures, such as accumulation by earthworm, can be used as complementary lines of evidence to reinforce site-wide trends in the bio-accessibility using in vitro physiologically-based extractions and/or operationally defined extraction test. Such detailed knowledge is useful for successful reclamation and management of the As contaminated soils.

Bioaccessibility in risk-benefit analysis of raw and cooked seabream consumption

The composition of raw and cooked gilthead seabream (Sparus aurata) was analysed. The bioaccessibility of arsenic (As), selenium (Se), mercury (Hg), and methylmercury (MeHg) in raw and cooked fish was studied by an in vitro model. A risk-benefit assessment was performed taking into account bioaccessibility. The content of contaminants Hg and As displayed a significant increase for every culinary treatment, only As content in boiled fish did not increase. Regarding bioaccessibility, while bioaccessible As was high (over 96%), the share of Hg (and MeHg) available for intestinal absorption was reduced by cooking, especially by grilling, 39% (60%) and roasting, 38% (55%). The risk-benefit probabilistic assessment leads to an advice of not exceeding one weekly meal of gilthead seabream. This recommendation concerns mainly pregnant and nursing women. However, Se bioaccessibility was high —minimum of 85% in boiled seabream—, thus helping to balance the deleterious effects of MeHg.

Assessment of influences of cooking on cadmium and arsenic bioaccessibility in rice, using an in vitro physiologically-based extraction test

The health risks associated with rice consumption may decrease if consumers use cooking practices which can reduce the bioaccessibility of metal(loid)s. The effects of cooking on the Cd and As bioaccessibility, at three contamination levels of rice, were studied. Results indicated that cooking reduced bioaccessibility of Cd and As in rice. Cooking resulted in a significant increase (p<0.01) of Cd and As concentrations in the residual fraction. Low volume water-cooking of rice to dryness reduced total Cd by about 10% for rices A and B, while medium or high volume water-cooking had no effect on Cd bioaccessibility in all rice types. In contrast, low volume cooking did not remove As, but a significant decrease (p<0.05) was observed when cooking with higher volumes of water. This study provides information for a better understanding of more realistic estimation of metal(loid)s exposure from rice and the possible health risks.

Variability of arsenic bioaccessibility and metabolism in soils by human gut microbiota using different in vitro methods combined with SHIME

Arsenic (As) speciation analysis is essential when evaluating the risks upon oral exposure to As-contaminated soils. In this study, we first investigated the variability in the As bioaccessibility and speciation using a combination of five common in vitro methods (SBRC, PBET, DIN, UBM and IVG) (gastric and small intestinal phases) and the SHIME model (colon phase). Our results indicate that the As bioaccessibility varies in the colon phase. An increase in the As bioaccessibility for SBRC and PBET, and a decrease for UBM and IVG were observed in the colon phase. In addition, we found different extents of methylation and large amounts of arsenite [As(III)] due to microbial reduction in the colon digests. The UBM-SHIME method displayed a higher methylation percentage of 13.5–82.1%, but a lower methylation percentage of 0.2–21.8% was observed in the SBRC-SHIME method. Besides, The MMAV levels in the colon digests were positively correlated with those of As(III) and DMAV, so DMAV can be considered an indicator to evaluate the As metabolic speed of in vitro cultured human gut microbiota. Based on the standard reference soil of NIST 2710a, the As bioaccessibility in the colon phase of PBET-SHIME and SBRC-SHIME were the closest to the in vivo results. Combining in vitro methods and SHIME will remarkably affect the accurate assessment of potential risks to human health associated with oral exposure to soil As.

Changes of arsenic fractionation and bioaccessibility in wastewater-irrigated soils as a function of aging: Influence of redox condition and arsenic load

Redox conditions and arsenic (As) loads may affect the aging mechanisms of As in soils. A batch experiment of one wastewater-irrigated soil under four different conditions was performed to investigate the impact of redox conditions and As loads on the aging mechanisms of As in soils in this study. The results showed that the aerobic condition substantially decreased the more labile fractions and increased the less mobilizable or immobilizable fractions in soils over time, which was likely due to the oxidation of As(III) to As(V) and the decomposition of organic matter. The redistribution of the strongly adsorbed and organically bound fraction (F4) occurred in all soils during the aging process, and both low As load and aerobic conditions accelerated this redistribution. The aging processes of As were characterized by three stages in various soils except the low As load soil with two stages within 180days: The transformations of As fractions were from three former fractions to three later ones in all soils in the first stage (0day–10days), while the main transformations after 10days were from F4 to bound to Fe and Mn/Al oxides fraction (F5) and from water soluble fraction (F1) to F5 in soils with low and high As loads, respectively; In contrast, the main transformations in the second stage were from F1 to F4 and from F1 to F5 in soils at low oxygen and aerobic conditions, respectively, and were from F4 to F5 in the third stage in both redox conditions. The bioaccessibility of As in the low As load soil decreased markedly from approximately 40% down to <10% due to the aging and more remarkably from >70% down to <20% in three other soils. Both high As load and low oxygen conditions preserved higher bioaccessibility of As in soils after long aging process. In terms of As bioaccessibility, high As load and aerobic condition prolonged the aging process of arsenic in soils.

Effect of Stabilizer Addition on Soil Arsenic Speciation and Investigation of Its Mechanism

Arsenic toxicity, mobility and bioaccessibility are influenced by its different speciation in soil, which exerts different impacts on the environment. In this study, coal fly ash, dried sludge, ferrous sulfate and broken peanut shell were used as stabilizers to investigate their stabilizing effects on As in soil as well as relationships between pH, soil organic matter content, cation exchange capacity and speciation of soil As. The results showed rise in soil pH, soil organic matter content and residual arsenic content after the addition of stabilizers. Addition of 10% coal fly ash and 10% dried sludge led to the decrease in the content of exchangeable As, carbonate bound As, Fe-Mn oxide bound As, organic bound As by 34.2%, 17.5%, 19.9%, 53.7%, respectively. Addition of ferrous sulfate could preferably stabilize As in soil. When 10% coal fly ash, 10% dried sludge and 1% ferrous sulfate were added concurrently, the decrease in the content of exchangeable As, carbonate bound As, Fe-Mn oxide bound As, organic bound As was 62.3%, 55.2%, 29.6%, 58.2%, respectively, with an increase in residual arsenic content by 8.1%. After the addition of 10% coal fly ash, 10% dried sludge, 1% ferrous sulfate and 1% broken peanut shell, a most conspicuous decrease in the content of exchangeable As by 73.3% was observed. Appropriate application of coal fly ash, dry sludge and ferrous sulfate converted a proportion of exchangeable, carbonate bounded, Fe-Mn bounded, organic bounded As into residual As, which reduced As's toxicity. The rise in pH led to increasing residual As content and decreasing exchangeable As, carbonate bounded As, Fe-Mn bounded As and organic bounded As content, and As was most stable at the approach of neutral condition. The rise in organic matter content led to increasing carbonate bounded As and residual As content and decreasing exchangeable As, Fe-Mn bounded As, organic bounded As content. The rise in cation exchange capacity led to increasing residual As content and decreasing exchangeable As, carbonate bounded As, Fe-Mn bounded As and organic bounded As content.

Bioaccessibility and arsenic speciation in carrots, beets and quinoa from a contaminated area of Chile

Consumption of vegetables grown in arsenic (As)-contaminated soils is an important exposure route to the element for humans. The present study is focused on locally-grown, frequently-consumed vegetables, such as carrots (Daucus carota), beets (Beta vulgaris) and quinoa (Chenopodium) from the As-polluted Chiu Chiu area in Northern Chile. The latter region is affected both by As discharge from copper mining activity and natural As contamination, leading to a high As content in local food and water. For the selected vegetables, the following aspects were investigated: i) Their total As, Cu, Pb, Cr, Cd and Mn content; ii) Arsenic speciation in the edible part of the vegetables by liquid chromatography inductively-coupled plasma mass spectrometry (LC-ICPMS) analysis; iii) Arsenic bioaccessibility in the vegetables during in vitro gastrointestinal digestion; iv) Arsenic species present in the extracts obtained from in vitro gastrointestinal digestion; and v) Arsenic dietary exposure estimates for the assessment of the risk posed by the vegetables consumption.A significant degree of As contamination was found in the vegetables under study, their metal content having been compared with that of similar Spanish uncontaminated products. In vitro gastrointestinal digestion of the studied vegetables led to quantitative extraction of As from carrots and beets, whereas efficiency was about 40% for quinoa. For carrots, only As(III) and As(V) species were found, being their concentration levels similar. In the case of quinoa, around 85% of the element was present as As(V). For beets, inorganic As(V) and unknown overlapped As species (probably arsenosugars) were found. No significant transformation of the original As species was observed during in vitro gastrointestinal digestion. Arsenic dietary exposure values obtained for the three vegetables (0.017–0.021μg As person−1day−1) were much lower than the JFCFA's safety limit of 50μg As person−1day−1. Therefore, no toxicological risk would be expected from the intake of these vegetables.

Assessment of arsenic speciation and bioaccessibility in mine-impacted materials

Mine-impacted materials were collected from Victoria, Australia and categorized into three source materials; tailings (n=35), calcinated (n=10) and grey slimes (n=5). Arsenic (As) concentrations in these materials varied over several orders of magnitude (30–47,000mgkg−1), with median concentrations of 500, 10,800 and 1500mgkg−1, respectively. When As bioaccessibility was assessed using the Solubility Bioaccessibility Research Consortium (SBRC) assay, As bioaccessibility ranged between 4 and 90%, with mean gastric phase values of 30%, 49% and 82% for tailings, calcinated and grey slimes, respectively. An analysis of variance (ANOVA) determined that As bioaccessibility was significantly different (P<0.05) between source materials. This was due to differences in As mineralogy, soil particle size as well as the concentration and nature of Fe present. X-ray Absorption Near Edge Structure (XANES) analysis identified arseniosiderite, yukonite, realgar, loellingite and mineral sorbed arsenate species in mine-impacted materials. Despite differences in physicochemical properties, ‘mine wastes’ are often reported under a generic descriptor. Outcomes from this research highlight that variability in As bioaccessibility can be prescribed to As mineralogy and matrix physicochemical properties, while categorizing samples into sub-groups can provide some notional indication of potential exposure.

An evaluation of the bioaccessibility of arsenic in corn and rice samples based on cloud point extraction and hydride generation coupled to atomic fluorescence spectrometry

A simple, inexpensive and rapid method was proposed for the determination of bioaccessible arsenic in corn and rice samples using an in vitro bioaccessibility assay. The method was based on the preconcentration of arsenic by cloud point extraction (CPE) using o,o-diethyldithiophosphate (DDTP) complex, which was generated from an in vitro extract using polyethylene glycol tert-octylphenyl ether (Triton X-114) as a surfactant prior to its detection by atomic fluorescence spectrometry with a hydride generation system (HG-AFS). The CPE method was optimized by a multivariate approach (two-level full factorial and Doehlert designs). A photo-oxidation step of the organic species prior to HG-AFS detection was included for the accurate quantification of the total As. The limit of detection was 1.34μgkg−1 and 1.90μgkg−1 for rice and corn samples, respectively. The accuracy of the method was confirmed by analyzing certified reference material ERM BC-211 (rice powder). The corn and rice samples that were analyzed showed a high bioaccessible arsenic content (72–88% and 54–96%, respectively), indicating a potential human health risk.

Effect of biogeochemical interactions on bioaccessibility of arsenic in soils of a former smelter site in Republic of Korea.

The total concentration-based regulations for soil remediation do not consider the possible changes in bioaccessibility of remaining arsenic (As) in soils due to biogeochemical interactions after remediation. This study used As-contaminated soil and pore water samples that were collected from the rice paddy and forest/farmland located in the vicinity of a former smelter site in Republic of Korea to elucidate the changes in As bioaccessibility due to biogeochemical interactions. Bioaccessibility and chemical forms of As in soils were determined by using an in vitro method and sequential extraction, respectively, and soil microbial community was evaluated. Bioaccessibility of As in the rice paddy soil samples was higher than that in the forest/farmland soil samples. This could be attributed to relatively higher dependence of bioaccessible As in the rice paddy soils on the soil concentration of iron (Fe), aluminum, or manganese, which could lead to greater changes in bioaccessible As via reductive dissolution. The strong linear relationship (R 2=0.90, p value ≤0.001) between the pore water As and Fe concentrations, and the greater portion of bacterial species related to reductive dissolution of Fe oxides in the rice paddies can support the higher As bioaccessibility promoted by reductive dissolution. Therefore, it is necessary to consider the potential changes in the bioaccessible As due to biogeochemical interactions in remediation of As-contaminated soils, particularly when soils are likely to be reused under reductive dissolution-promoting conditions (e.g., flooded conditions).

Relationship of arsenic speciation and bioavailability in mine wastes for human health risk assessment

Environmental context X-ray absorption near-edge spectroscopy (XANES) was applied to give arsenic chemical forms directly in the solid phase of mine wastes from two mine sites, including fluvial dispersion. The arsenic speciation data explained the variation of in vitro bioaccessibility and in vivo bioavailability (rat uptake) data of the mine wastes. The As speciation from XANES fitting supported the hypothesis that when soil intake is adjusted for bioaccessibility, the potential health risk estimate to local residents is significantly lower. Abstract X-ray absorption near-edge spectroscopy (XANES) was used for arsenic speciation in mine processing and waste samples from two mines in northern Australia. XANES fitting of model compound spectra to samples was used, in combination with in vitro bioaccessibility data for the pure compounds, to predict bioaccessibility of each mine waste sample (Pearson’s correlation R2=0.756, n=51). The XANES fitting data for a smaller set of the samples (n=12) were compared with in vivo bioavailability and in vitro bioaccessibility data. The bioavailability of arsenic (As) in the mine wastes, which is dependent, at least in part, on its oxidation state, was found to be &lt;14% (0.9–13.5%) for arsenite (AsIII) and &lt;17% (3.5–16.4) for arsenate (AsV). Arsenic bioaccessibility in the mine wastes ranged from 8–36% in the stomach to 1–16% in the intestinal phase, indicating that a small portion of the total As concentration in the mine waste was available for absorption. A significant correlation showed that bioaccessibility can be used as a predictor of bioavailability. The XANES results support that bioavailability and bioaccessibility results were very similar and show a strong association with the presence of ferric arsenate and As sulfides. It can be concluded that, when soil intake is adjusted for bioaccessibility, the potential health risk estimate to local residents exposed to the mine waste was significantly lower than that estimated based on a 100% bioavailability often employed for the risk assessment.

Bioaccessibility and health risk assessment of arsenic in soil and indoor dust in rural and urban areas of Hubei province, China

Incidental oral ingestion is the main exposure pathway by which human intake contaminants in both soil and indoor dust, and this is especially true for children as they frequently exhibit hand-to-mouth behaviour. Research on comprehensive health risk caused by incidental ingestion of both soil and indoor dust is limited. The aims of this study were to investigate the arsenic concentration and to characterize the health risks due to arsenic (As) exposure via soil and indoor dust in rural and urban areas of Hubei province within central China. Soil and indoor dust samples were collected from schools and residential locations and bioaccessibility of arsenic in these samples was determined by a simplified bioaccessibility extraction test (SBET). The total arsenic content in indoor dust samples was 1.78–2.60 times that measured in soil samples. The mean As bioaccessibility ranged from 75.4% to 83.2% in indoor dust samples and from 13.8% to 20.2% in soil samples. A Pearson's analysis showed that As bioaccessibility was significantly correlated with Fe and Al in soil and indoor dust, respectively, and activity patterns of children were utilised in the assessment of health risk via incidental ingestion of soil and indoor dust. The results suggest no non-carcinogenic health risks (HQ<1) or acceptable carcinogenic health risks (1×10−6<CR<1×10−4) in all studied locations. Indoor activities comprised between 64.0% and 92.7% of the total health risk incurred during daily indoor and outdoor activities. The HQ and CR values for children in urban areas were 1.59–1.95 times those for children in rural areas. The HQ and CR values for children three to five years of age were 1.40–1.47 times those for children six to nine years of age. The health risk accounting for bioaccessibility was only 50.8–59.8% of that obtained without consideration of bioaccessibility.

Impact of temperature on the aging mechanisms of arsenic in soils: fractionation and bioaccessibility.

The present study focused on the influence of temperature variation on the aging mechanisms of arsenic in soils. The results showed that higher temperature aggravated the decrease of more mobilizable fractions and the increase of less mobilizable or immobilizable fractions in soils over time. During the aging process, the redistribution of both carbonate-bound fraction and specifically sorbed and organic-bound fraction in soils occurred at various temperatures, and the higher temperature accelerated the redistribution of specifically sorbed and organic-bound fraction. The aging processes of arsenic in soils at different temperatures were characterized by several stages, and the aging processes were not complete within 180 days. Arsenic bioaccessibility in soils decreased significantly by the aging, and the decrease was intensified by the higher temperature. In terms of arsenic bioaccessibility, higher temperature accelerated the aging process of arsenic in soils remarkably.

Drinking Water Treatment Residual Amendment Lowers Inorganic Arsenic Bioaccessibility in Contaminated soils: a Long-Term Study

Inorganic arsenical pesticides were used widely in agriculture for a long time, leaving large tracts of farmlands and orchards contaminated with high levels of arsenic. These contaminated soils pose a significant public health risk as residential developments encroach on these lands due to urban sprawl. Several studies have documented the effectiveness of iron and aluminum hydroxides in immobilizing arsenic in contaminated soils. Solid residues left from drinking water treatment (Drinking water treatment residuals, or WTRs) have been proposed as a low-cost and effective amendment, as they contain large amounts of aluminum (Al) and iron (Fe) oxides. By conducting in vitro tests after 1 year of equilibration, our group recently documented the effectiveness of two types of WTRs (Fe- and Al-based) in significantly (p < 0.01) lowering As bioaccessibility. However, long-term studies under realistic conditions are necessary to test the ability of WTRs in reducing soil arsenic bioaccessibility. In the current study, the effect of WTRs on inorganic arsenic bioaccessibility and distribution in two soils (Immokalee and Orelia) with variable properties was evaluated over a 3-year time period in a greenhouse setup. Results show that arsenic bioaccessibility decreased significantly (p < 0.001) from 100 to ~25 % after 3 years of equilibration, compared to the unamended controls. There was a significant (p < 0.001) decline in water-soluble arsenic with time, accompanied by an increase in Fe/Al and Ca/Mg-bound fractions, suggesting that these phases control the mobility of arsenic. The negative correlation between arsenic bioaccessibility Fe/Al- and Ca/Mg-bound fractions can be attributed to the transformation of soluble arsenic to less soluble mineral phases.

Oral bioaccessibility of arsenic, mercury and methylmercury in marine species commercialized in Catalonia (Spain) and health risks for the consumers

This study was aimed at characterizing the bioaccessibility of arsenic (As), mercury (Hg) and methylmercury (MeHg) in commercial fish and seafood species widely consumed by the population of Catalonia (Spain). An accurate evaluation on how bioaccessibility estimations may affect the outcomes of exposure assessment studies was also conducted. The concentrations of As, Hg, and MeHg in samples of fish and seafood incubated in a 3-compartmental (mouth, stomach, and small intestine) in vitro gastrointestinal model, were quantified and compared with the levels of these elements in cooked samples. Arsenic showed a high bioaccessibility in all the fish and seafood species, ranging from 72% (mackerel) to 89% (sardine). In contrast, the bioaccessibility of Hg was rather lower, being <50% for most species, while MeHg could be only quantified in swordfish and tuna. This study elucidates the potential overestimation of health risks to consumers, when the effects of bioaccessibility and cooking procedures are not taken into account in the risk assessment. Unlike As, whose risk is not generally overestimated, Hg and MeHg showed a lower and variable bioaccessibility in marine species, meaning an overestimation of health risks for the adult population. Further studies should assess the bioaccessibility of mercurial species for children.

Linking selective chemical extraction of iron oxyhydroxides to arsenic bioaccessibility in soil

The relationship between As bioaccessibility using the physiologically based extraction test (PBET) and As extracted by hydroxylamine hydrochloride (HH), targeting the dissolution of amorphous Fe oxyhydroxides, is established in soils from the British Geological Survey Geochemical Baseline Survey of SW England, UK, to represent low As background and high As mineralised/mined soils. The HH-extracted As was of the same order of magnitude as the As extracted in the bioaccessibility test and proved to be a better estimate of bioaccessible As than total As (bioaccessible As − total As: r = 0.955; bioaccessible As – HH-extracted As: r = 0.974; p-values = 0.000). These results provide a means of estimating soil As bioaccessibility on the basis of the HH extraction. Further selective extraction data, using hydrochloride acid that seeks to dissolve both amorphous and crystalline Fe oxyhydroxides, indicates a decrease in the As bioaccessible fraction with the increase of the soil Fe oxyhydroxide crystallinity.

Assessment of arsenic bioaccessibility in raw and cooked edible mushrooms by a PBET method

The present study reports arsenic analysis in Lentinula edodes, Agaricus bisporus and Pleurotus ostreatus before and after being cooked. Furthermore, arsenic in raw and cooked mushroom was determined in the gastric and gastrointestinal bioaccessible fractions obtained after simulating human digestion by means of an in vitro physiologically based extraction test (PBET). Several certified reference materials (SRM 1568a, SRM 1570a, CRM 7503-a, BC211 and IPE-120) were analysed to evaluate the proposed methods. Total arsenic content was 1393, 181 and 335μgAskg−1 for L. edodes, A. bisporus and P. ostreatus, respectively, and decreased by between 53% and 71% in boiled mushroom and less than 11% in griddled mushroom. High bioaccessibility was observed in raw, boiled and griddled mushroom, ranging from 74% to 89% and from 80% to 100% for gastric and gastrointestinal extracts, respectively, suggesting the need to consider the potential health risk of consumption of the mushrooms analysed.

Comparison of arsenic bioaccessibility in housedust and contaminated soils based on four in vitro assays

Few studies have assessed As bioaccessibility in housedust using different in vitro assays and compared to those in contaminated soils. We determined As bioaccessibility in 24 housedust samples (4.48–38.2mgkg−1) using SBRC, IVG, DIN, and PBET assays and they averaged 73, 68, 53, and 48% in the gastric phase and 26, 46, 55 and 43% in the intestinal phase of the 4 assays. The corresponding As bioaccessibility in 34 As-contaminated soils (22–6899mgkg−1) were 34, 25, 22, and 22% in the gastric phase and 18, 19, 21, and 20% in the intestinal phase, which was 1.5–2.7 fold lower than those in housedust possibly due to differences in contamination sources and properties. Based on the gastric phase of SBRC assay, As bioaccessibility was 44–96% in housedust and 2.3–80% in soils. Variation in As bioaccessibility among assays was similar for housedust and soils, with SBRC assay providing the highest bioaccessibility in gastric phase. In intestinal phase, dissolved As was probably adsorbed onto precipitated iron oxides, causing a sharp decrease in As bioaccessibility by SBRC assay. Unlike SBRC assay, gastric constituents (pepsin, mucin, phosphate, and citrate) in other 3 assays inhibited As adsorption and/or enhanced As dissolution, leading to greater As bioaccessibility. The greater As bioaccessibility in housedust than soil suggests the potential of greater health risk from As exposure to housedust than soil.

In vitro bioaccessibility and in vivo relative bioavailability in 12 contaminated soils: Method comparison and method development

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 r2=0.50 for PBET to r2=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.

Arsenic bioaccessibility in contaminated soils: Coupling in vitro assays with sequential and HNO3 extraction

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 (R2=0.55−0.69), and UBM-GP and NS1+SS2+AF3 (R2=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 (R2=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.