Predicting Arsenic Relative Bioavailability Using Multiple in Vitro Assays: Validation of in Vivo-in Vitro Correlations

Assessment of the stabilization effect of ferrous sulfate for arsenic-contaminated soils based on chemical extraction methods and in vitro methods: Methodological differences and linkages

Stabilization of arsenic-contaminated soils with ferrous sulfate has been reported in many studies, but there are few stabilization effects assessments simultaneously combined chemical extraction methods and in vitro methods, and further explored the corresponding alternative relationships. In this study, ferrous sulfate was added at FeAs molar ratio of 0, 5, 10 and 20 to stabilize As in 10 As spiked soils. Stabilization effects were assessed by 6 chemical extraction methods (toxicity characteristic leaching procedures (TCLP), HCl, diethylenetriamine pentaacetic acid (DTPA), CaCl2, CH3COONH4, (NH4)2SO4), and 4 in vitro methods (physiologically based extraction test (PBET), in vitro gastrointestinal method (IVG), Solubility Bioaccessibility Research Consortium (SBRC) method, and the Unified Bioaccessibility Research Group of Europe method (UBM)). The results showed that the HCl method provides the most conservative assessment results in non-calcareous soils, and in alkaline calcareous soils, (NH4)2SO4 method provides a more conservative assessment. In vitro methods provided significantly higher As concentrations than chemical extraction methods. The components of the simulated digestion solution as well as the parameters may have contributed to this result. The small intestinal phase of PBET and SBRC method produced the highest and lowest ranges of As concentrations, and in the range of 127-462 mg/kg and 68-222 mg/kg when the FeAs molar ratio was 5. So the small intestinal phase of PBET method may provide the most conservative assessment results, while the same phase of SBRC may underestimate the human health risks of As in stabilized soil by 51 %(at a FeAs molar ratio of 5). Spearman correlation analysis indicated that the small intestinal phase of PBET method correlated best with HCl method (correlation coefficient: 0.71). This study provides ideas for the assessment of stabilization efforts to ensure that stabilization meets ecological needs while also being less harmful to humans.

Arsenic, cadmium, lead, antimony bioaccessibility and relative bioavailability in legacy gold mining waste

Bioaccessibility and relative bioavailability of As, Cd, Pb and Sb was investigated in 30 legacy gold mining wastes (calcine sands, grey battery sands, tailings) from Victorian goldfields (Australia). Pseudo-total As concentration in 29 samples was 1.45-148-fold higher than the residential soil guidance value (100 mg/kg) while Cd and Pb concentrations in calcine sands were up to 2.4-fold and 30.1-fold higher than the corresponding guidance value (Cd: 20 mg/kg and Pb: 300 mg/kg). Five calcine sands exhibited elevated Sb (31.9-5983 mg/kg), although an Australian soil guidance value is currently unavailable. Arsenic bioaccessibility (n = 30) and relative bioavailability (RBA; n = 8) ranged from 6.10-77.6% and 10.3-52.9% respectively. Samples containing > 50% arsenopyrite/scorodite showed low As bioaccessibility (<20.0%) and RBA (<15.0%). Co-contaminant RBA was assessed in 4 calcine sands; Pb RBA ranged from 73.7-119% with high Pb RBA associated with organic and mineral sorbed Pb and, lower Pb RBA observed in samples containing plumbojarosite. In contrast, Cd RBA ranged from 55.0-67.0%, while Sb RBA was < 5%. This study highlights the importance of using multiple lines of evidence during exposure assessment and provides valuable baseline data for co-contaminants associated with legacy gold mining activities.

Immobilisation remediation of arsenic-contaminated soils with promising CaAl-layered double hydroxide and bioavailability, bioaccessibility, and speciation-based health risk assessment

Arsenic (As)-contaminated soil poses great health risk to human mostly through inadvertent oral exposure. We investigated CaAl-layered double hydroxide (CaAl-LDH), a promising immobilising agent, for the remediation of As-contaminated Chinese soils. The effects on specific soil properties and As fractionation were analyzed, and changes in the health risk of soil As were accurately assessed by means of advanced in vivo mice model and in vitro PBET-SHIME model. Results showed that the application of CaAl-LDH significantly increased soil pH and concentration of Fe and Al oxides, and effectively converted active As fractions into the most stable residual fraction, guaranteeing long-term remediation stability. Based on in vivo test, As relative bioavailability was significantly reduced by 37.75%. Based on in vitro test, As bioaccessibility in small intestinal and colon phases was significantly reduced by 25.65% and 28.57%, respectively. Furthermore, As metabolism (reduction and methylation) by the gut microbiota inhabiting colon was clearly observed. After immobilisation with CaAl-LDH, the concentration of bioaccessible As(Ⅴ) in the colon fluid was significantly reduced by 61.91%, and organic As (least toxic MMA(V) and DMA(V)) became the main species, which further reduced the health risk of soil As. In summary, CaAl-LDH proved to be a feasible option for immobilisation remediation of As-contaminated soils, and considerable progress was made in relevant health risk assessment.

Risk assessment of antimony-arsenic contaminated soil remediated using zero-valent iron at different pH values combined with freeze-thaw cycles

Soil in mining wastelands is seriously polluted with heavy metals. Zero-valent iron (ZVI) is widely used for remediation of heavy metal-polluted soil because of its excellent adsorption properties; however, the remediation process is affected by complex environmental conditions, such as acid rain and freeze-thaw cycles. In this study, the effects of different pH values and freeze-thaw cycles on remediation of antimony (Sb)- and arsenic (As)-contaminated soil by ZVI were investigated in laboratory simulation experiments. The stability and potential human health risks associated with the remediated soil were evaluated. The results showed that ZVI has a significant stabilizing effect on Sb and As in both acidic and alkaline soils contaminated with dual levels of Sb and As, and the freeze-thaw process in different pH value solution systems further enhances the ability of ZVI to stabilize Sb and As, especially in acidic soils. However, it should be noted that apart from the pH=1.0 solution environment, ZVI's ability to stabilize As is attenuated under other circumstances, potentially leading to leaching of its unstable form and thereby increasing contamination risks. This indicates that the F1 (2% ZVI+pH=1 solution+freeze-thaw cycle) processing exhibits superior effectiveness. After F1 treatment, the bioavailability of Sb and As in both soils also significantly decreased during the gastric and intestinal stages (about 60.00%), the non-carcinogenic and carcinogenic risks of Sb and As in alkaline soils are eliminated for children and adults, with a decrease ranging from 60.00% to 70.00%, while in acidic soil, the non-carcinogenic and carcinogenic risks of As to adults and children is acceptable, but Sb still poses non-carcinogenic risks to children, despite reductions of about 65.00%. These findings demonstrate that soil pH is a crucial factor influencing the efficacy of ZVI in stabilizing Sb and As contaminants during freeze-thaw cycles. This provides a solid theoretical foundation for utilizing ZVI in the remediation of Sb- and As-contaminated soils, emphasizing the significance of considering both pH levels and freeze-thaw conditions to ensure effective and safe treatment.

In vivo-in vitro correlations (IVIVC) for the assessment of pyrethroid bioavailability in honey

Bioaccessibility/bioavailability is an important factor in assessing the potential human health risk via oral exposure. However, methods for accurately predicting the bioaccessibility/bioavailability of pesticide residues are still limited, preventing accurate measurements of actual exposure to pesticide residues. In this study, pyrethroid bioavailability in honey were analysed using a mouse bioassay and bioaccessibility via in vitro methods with Tenax extraction. The results demonstrated that the combined liver plus kidney data served as an appropriate biomarker to estimate the relative bioavailability. Notably, significant in vivo-in vitro correlations (IVIVC) were observed between bioavailability and bioaccessibility (R2 = 0.7898-0.9793). Estimation of the bioavailability of honey from different nectar plants using derived IVIVC confirmed that different contents and physicochemical properties might affect its bioavailability. The findings provide insight into assessing human exposure to pesticides based on bioavailability and can decrease the uncertainty about the assessment of the risk of dietary exposure to pesticides.

Importance of arsenic bioaccessibility in health risk assessment based on iron "Minette" rocks and related soils

Total element concentrations by themselves are not always good predictors of toxicity and are therefore not suitable for eco- and/or human toxicological risk determination. In addition, despite the growing call for harmonization, countries show significant variation in risk assessment tools, screening/background values, protocols and legal management of soils. By incorporating mobility and bioaccessibility/availability into soil risk assessments, location-specific physico-chemical and geological conditions can be considered in routinely applied general risk assessment methodologies. Minette soils and rocks are a great case in point since they often are associated with high geogenic As concentrations and consequently potential risks. Minette iron ores form the world largest Fe ore deposits since the "great oxidation". For the first time, oral bioaccessibility during direct ingestion was assessed on Minettes from Luxembourg by applying the in vitro Solubility/Bioavailability Research Consortium (SBRC) method. Out of > 180 samples, 25 representative samples were selected providing a unique dataset which showed an average gastric bioaccessibility of ∼10% (7.8 ± 4.0 mg/kg) of the total As-concentration, with a maximum of 45% (17.9 mg/kg). Of importance is that bioaccessibility of As in Minette rocks and soils are controlled by, and can be estimated from, lithology, mineralogy and total Ca content. Soils and ooid grainstones with an iron oxide or clayey matrix, are characterized by average gastric bioaccessible As concentrations < 6 mg/kg. Gastric As bioaccessibility is highest in Fe-bearing calcite-cemented bioclastic grainstones (∼12 mg/kg). Importantly, for all samples the maximal bioaccessible As concentrations remain below the threshold from which significant adverse non-carcinogenic and/or carcinogenic health effects are expected. These new results are in strong contrast with what total As concentrations might suggest. Considering bioaccessibilities, consequently, can help to avoid disproportionate, costly and environmentally impacting risk management strategies. Furthermore, this study illustrates the importance of cross-disciplinary collaboration between geo- and health scientists.

Oral bioaccessibility of PTEs in soils: A review of data, influencing factors and application in human health risk assessment

Understanding the behavior of metal(loi)ds transported from soil to humans is critical for human health risk assessment (HHRA). In the last two decades, extensive studies have been conducted to better assess human exposure to potentially toxic elements (PTEs) by estimating their oral bioaccessibility (BAc) and quantifying the influence of different factors. This study reviews the common in vitro methods used to determine the BAc of PTEs (in particular As, Cd, Cr, Ni, Pb, and Sb) under specific conditions (particularly in terms of the particle size fraction and validation status against an in vivo model). The results were compiled from soils derived from various sources and allowed the identification of the most important influencing factors of BAc (using single and multiple regression analyses), including physicochemical soil properties and the speciation of the PTEs in question. This review presents current knowledge on integrating relative bioavailability (RBA) in calculating doses from soil ingestion in the HHRA process. Depending on the jurisdiction, validated or non-validated bioaccessibility methods were used, and risks assessors applied different approaches: (i) using default assumptions (i.e., RBA of 1); (ii) considering that bioaccessibility value (BAc) accurately represents RBA (i.e., RBA equal to BAc); (iii) using regression models to convert BAc of As and Pb into RBA as proposed by the USA with the US EPA Method 1340; or (iv) applying an adjustment factor as proposed by the Netherlands and France to use BAc from UBM (Unified Barge Method) protocol. The findings from this review should help inform risk stakeholders about the uncertainties surrounding using bioaccessibility data and provide recommendations for better interpreting the results and using bioaccessibility in risk studies.

Innovative accumulative risk assessment strategy of co-exposure of As and Pb in medical earthworms based on in vivo-in vitro correlation

Recent studies on risks assessment of heavy metal(loid) are usually based on their total concentrations. Nevertheless, such an analysis does not assess their real amounts absorbed by human body. To scientifically assess the health risks, in this study medical earthworms were analyzed for relative bioavailability (RBA) of arsenic (As) and lead (Pb) using a multiple gavage mouse model with liver, kidneys, brain, and leg bones as biomarkers for the first time. Metal(loid) bioaccessibility was determined using in vitro physiologically based extraction (PBET) assay. We are the first to develop a novel accumulative health risk assessment strategy by combinational analyzing bioavailability of heavy metal(loid) levels to calculate target organ toxicity dose (TTD) modification of the HI and total cancer risk (TCR), which has capacity to evaluate the health risks of co-exposure of Pb and As in medical earthworms. As a result, As-RBA ranged from 7.2% to 45.1%, and Pb-RBA ranged from 16.1% to 49.8%. Additionally, As and Pb bioaccessibility varied from 6.7% to 48.3% and 7.8% to 52.5%, respectively. Moreover, strong in vivo-in vitro correlations (IVIVCs) were observed between metal-RBA and bioaccessibility, indicating the robustness of the in vitro PBET assay to predict metal-RBA in medical earthworms. The refined accumulative assessment strategy revealed that when adjusted by heavy metal(loid) bioavailability, the TTD modification of HI method typically exhibited an acceptable health risk caused by the co-exposure of Pb and As for cardiovascular, hematological, neurological, and renal system. The TCR levels associated with exposure to Pb and As due to the ingestion of medical earthworms were also acceptable after adjustment by bioavailability. Collectively, our innovation on accumulative risk assessment based on in vivo-in vitro correlation provides a novel approach engaging in assessing the risks due to co-exposure of As and Pb in medical earthworms.

Role of microbial iron reduction in arsenic metabolism from soil particle size fractions in simulated human gastrointestinal tract

Gut microbiota provides protection against arsenic (As) induced toxicity, and As metabolism is considered an important part of risk assessment associated with soil As exposures. However, little is known about microbial iron(III) reduction and its role in metabolism of soil-bound As in the human gut. Here, we determined the dissolution and transformation of As and Fe from incidental ingestion of contaminated soils as a function of particle size (<250 μm, 100-250 μm, 50-100 μm and < 50 μm). Colon incubation with human gut microbiota yielded a high degree of As reduction and methylation of up to 53.4 and 0.074 μg/(log CFU/mL)/hr, respectively; methylation percentage increased with increasing soil organic matter and decreasing soil pore size. We also found significant microbial Fe(III) reduction and high levels of Fe(II) (48 %-100 % of total soluble Fe) may promote the capacity of As methylation. Although no statistical change in Fe phases was observed with low Fe dissolution and high molar Fe/As ratios, higher As bioaccessibility of colon phase (avg. 29.4 %) was mainly contributed from reductive dissolution of As(V)-bearing Fe(III) (oxy)hydroxides. Our results suggest that As mobility and biotransformation by human gut microbiota (carrying arrA and arsC genes) are strongly controlled by microbial Fe(III) reduction coupled with soil particle size. This will expand our knowledge on oral bioavailability of soil As and health risks from exposure to contaminated soils.

Risks of applying mobilising agents for remediation of arsenic-contaminated soils: Effects of dithionite-EDTA and citric acid on arsenic fractionation, leachability, oral bioavailability/bioaccessibility and speciation

Arsenic (As) mobilisation assists in remediating As-contaminated soils but might increase ecological and health risks. In this study, risks of applying two mobilising agents were assessed, i.e. an emerging reducing-chelating composite agent [dithionite (Na₂S₂O₄)-EDTA] and a classical low-molecular-weight organic acid (LMWOA) [citric acid (C₆H₈O₇)]. Results showed that both agents induced sharp increase in leachability-based ecological risk of As. Interestingly, the two agents had opposite performances regarding health risks. Na₂S₂O₄-EDTA significantly increased As relative bioavailability (RBA) to 1.83 times that in controls based on in vivo mouse model, and As bioaccessibility to 1.96, 1.65 and 1.20 times in gastric, small intestinal and colon phases based on in vitro PBET-SHIME model. Besides, it caused significant increase of highly toxic As(Ⅲ) in colon fluid. In contrast, C₆H₈O₇ significantly reduced RBA and bioaccessibility of soil As in colon by 44.44% and 14.65%, respectively. Importantly, C₆H₈O₇ restrained bioaccessible As(V) reduction and promoted bioaccessible As(Ⅲ) methylation, further reducing health risk. The phenomena could mainly be attributed to excessive metal components release from soil by C₆H₈O₇ and gut microbiota metabolism of C₆H₈O₇. In summary, C₆H₈O₇ and similar LMWOAs are recommended. The study contributes to mobilising agent selection and development and provides a reference for managing remediation sites.

Predictive capabilities of in vitro colon bioaccessibility for estimating in vivo relative bioavailability of arsenic from contaminated soils: Arsenic speciation and gut microbiota considerations

Arsenic (As) transformation by human gut microbiota has been evidenced to impact As toxicity and human health. However, little is known about the influence of gut microbiota on As bioavailability from incidental ingestion of soil. In this study, we assessed As relative bioavailability (RBA) using an in vivo mouse model and As bioaccessibility in the colon phase of in vitro assays. Strong in vivo-in vitro correlations (R² = 0.70-0.92, P < 0.05) were observed between soil As RBA (10.2%-57.7%) and colon bioaccessibility (4.8%-49.0%) in 13 As-contaminated soils. Upon in vitro incubation of human colon microbiota, we found a high degree of As transformation and 65.9% of generated As(III) was observed in soil residues. For in vivo mouse assay, DMA(V) accounted for 79.0% of cumulative urinary As excretion. Except for As(V), dominant As species including As(III), DMA(V) and As sulfides were also detected in mouse feces. Gut bacteria (families Rikenellaceae and Marinifilaceae) could be significantly correlated with As intake and excretion in mice (P < 0.05). Our findings provide evidence that gut microbiota can affect transformation, bioavailability, and fate of the orally ingested soil As in human gastrointestinal tract.

Comparative evaluation of in vivo relative bioavailability and in vitro bioaccessibility of arsenic in leafy vegetables and its implication in human exposure assessment

Arsenic (As) contamination in vegetables is a severe threat to human health. However, the evaluation of As relative bioavailability (As-RBA) or bioaccessibility in vegetables is still unexplored. The study sought to evaluate the As-RBA in commonly consumed ten leaf vegetables collected from As-polluted farmlands. Additionally, the As-RBA was determined using rat bioassay and compared with As bioaccessibility through five commonly used in vitro methods, including UBM (Unified BARGE Method), SBRC (Solubility Bioavailability Research Consortium), DIN (Deutsches Institut für Normung e.V.), IVG (In Vitro Gastrointestinal), and PBET (Physiologically Based Extraction Test). Results showed that the As-RBA values were 14.3-54.0% among different vegetables. Notably, significant in vivo-in vitro correlations (IVIVC) were observed between the As-RBA and the As bioaccessibility determined by the PBET assay (r² = 0.763-0.847). However, the other assays (r² = 0.417-0.788) showed a comparatively weaker relationship. The estimation of As-RBA using derived IVIVC to assess As exposure risk via vegetable consumption confirmed that As exposure risk based on As-RBA was lower than that the total As concentrations. Therefore, it was concluded that PBET could better predict the As-RBA in vegetables than other in vitro assays. Furthermore, As-RBA values should be considered for accurate health risk assessment of As in vegetables.

Interconnected soil iron and arsenic speciation effects on arsenic bioaccessibility and bioavailability: a scoping review

Extensive research has examined arsenic (As) bioavailability in contaminated soils and is routinely assessed using in vitro bioaccessibility (IVBA) assays. Analysis of differences in bioaccessibility measurements across IVBA assays and phases is expected to provide valuable insights into geochemical mechanisms controlling soil As bioaccessibility and bioavailability. Soil iron (Fe) content and As speciation are expected to significantly influence IVBA gastric and intestinal phases due to fluctuations in precipitation-dissolution chemistry and sorption reactivity as pH and assay chemical complexity changes. The aim of this review was to examine these relationships by 1) conducting a meta-analysis (n = 47 soils) determining the influence of total Fe on As bioaccessibility measurements and 5 IVBA assays and 2) investigating the effect of As speciation on gastric/intestinal phase IVBA and in vitro-in vivo correlations. Our findings indicate that soil Fe content and As speciation heterogeneity are important in elucidating variability of bioaccessibility measurements across IVBA assays and gastrointestinal phases. Greater focus on coupled As speciation and Fe precipitation chemistry may (1) improve our understanding of soil geochemical factors and assay constituents that influence As in vitro-in vivo correlations and (2) resolve variability in the precision of oral relative bioavailability (RBA) estimated using IVBA assays for soils possessing heterogenous As speciation and Fe composition.

Effects of aluminum and soil mineralogy on arsenic bioaccessibility

A comprehensive characterization was performed to investigate the composition and mineralogy of soils from a gold mining region and their correlation with arsenic (As) total concentration and its bioaccessible fraction. The arsenic bioaccessible (BAC) fraction was determined through in vitro test and calculated as the ratio between the amounts of As released and the total As concentration in the soil sample. Among the minor constituents of environmental concern, only arsenic is significantly higher (median of 748.0 mg kg^-1) than the national guidelines (agricultural, 35 mg kg^-1 and residential, 55 mg kg^-1). All the other trace elements showed concentrations below the investigation values established for residential areas. The mean bioaccessible As was 7.0 mg kg^-1, with a median value of 4.4 mg kg^-1, and a median As BAC percentage of 0.7%. The Brunauer-Emmett-Teller (BET) surface area showed a consistent increase with the increase of the acid-soluble Al content in the soil samples. The distribution of As in the soil samples is not correlated with the abundance of As-minerals and the fraction of adsorbed As. Arsenic was shown to be trapped in oriented aggregates of crystalline (Al-)Fe-(hydr)oxides nanoparticles (the main metalloid reservoirs), as demonstrated by scanning and transmission electron microscopy analyses. This unique pattern supports the significant difference between total As concentration and the bioaccessible amount. There was a positive correlation between soluble Al (within the Fe-(hydr)oxides phases and minor gibbsite) and As concentration in the soil samples, and a negative correlation with bioaccessible As. Therefore, although Al in the soil is associated with high As levels, it also makes the metalloid less bioaccessible. The risk to human health from As exposure to these soils is low.

Soil particle size fraction and potentially toxic elements bioaccessibility: A review

In the last decade, extensive studies have been conducted to quantify the influence of different factors on potentially toxic elements (PTE) bioaccessibility in soil; one of the most important is soil size fraction. However, there is no agreement about the size fraction and the methods to investigate bioaccessibility, as very few review articles are available on soil PTE bioaccessibility and none addressed the influence of particle size on PTE bioaccessibility. This study provides a review of the relations between PTE bioaccessibility and soil particle size fractions. The available research indicates that PTE bioaccessibility distribution across different size fractions varies widely in soil, but a general trend of higher bioaccessibility in finer size fraction was found. The different elements may exhibit different relationships between bioaccessibility and soil size fraction and, in some cases, their bioaccessibility seems to be more related to the source and to the chemico-physical form of PTE in soil. Often, soil pollution and related health risk are assessed based on PTE total concentration rather than their bioaccessible fraction, but from the available studies it appears that consensus must be pursued on the methods to determine PTE bioaccessibility in the fine soil size fractions to achieve a more accurate human health risk assessment.

The role of soil arsenic fractionation in the bioaccessibility, transformation, and fate of arsenic in the presence of human gut microbiota

Soil arsenic (As) fractionation and its bioaccessibility are two important factors in human health risk assessment. However, data related to the impact of As minerals on the bioaccessibility with human gut microbiota involvement are scarce. In this study, speciation analysis was determined using HPLC-ICP-MS and XANES after incubation with colon microbiota from human origin, in combination with sequential extraction. Significant increase of colon As bioaccessibility was contributed primarily from As associated with amorphous and crystalline Fe/Al (hydr)oxides. We found a high degree of transformation at higher bioaccessibility (ave. 40 % of total As), which was predominantly present as liquid-phase As. In contrast, As transformation occurred mainly in the solid phase at lower bioaccessibility (< 5%), especially for soils containing As-S species. XANES spectroscopy revealed that As(III) increased by about 20 % in soil residues. Finally, the excreted As may be predominantly in association with (alumino)silicate minerals by SEM-EDX. It inferred that the priority sequence in As transformation by human gut microbiota was dissolved As(V), As(V) sorbed to mineral surfaces, crystalline As(V)-bearing minerals and As sulfides. This study will shed new light on the role of As-bearing minerals in evaluating health risks from soil As exposure.

One-pot synthesis of nZVI-embedded biochar for remediation of two mining arsenic-contaminated soils: Arsenic immobilization associated with iron transformation

Waste biomass derived biochar has been proven as an effective and friendly amendment for remediation of heavy metals-contaminated soil. However, biochar is less effective for soil arsenic (As) immobilization in most cases. To improve the ability of biochar for As immobilization, in this study, the composite of biochar embedded with nano zero valent iron (nZVI/BC) was prepared through simple one-step pyrolysis of biomass sawdust and Fe₂O₃ mixture and then applied for amendment of two mining As-contaminated soils. Pristine sawdust biochar (BC) and nZVI alone or in combination were included for comparison. Results show that the prepared nZVI/BC contained about 40% Fe which was mainly present as Fe°. All treatments except BC reduced As concentration in (NH₄)₂SO₄ extraction and gastrointestinal solution. Particularly, nZVI/BC reduced the labile As in (NH₄)₂SO₄ extraction in two soils by over 93% and bioaccessible As in gastrointestinal solution decreased by over 85%. Fe° on the surface of nZVI/BC was oxidized into amorphous FeOOH which adsorbed or co-precipitated with As. Meanwhile, Ca-Fe-As-O and Al-Fe-As-O co-precipitated at the interface between nZVI/BC and two soils enriched with Ca and Al, respectively. Results indicated that the simply-prepared nZVI/BC was a promising material for remediation of As-contaminated soils.

A descriptive bibliometric study on bioavailability of pesticides in vegetables, food or wine research (1976-2018)

A bibliometric analysis based on the Web of Science© (WOS) database was performed on bioavailability of pesticides in vegetables, food or wine related studies published from inception to 2018. A total of 1202 articles were subjected to examination. The results reveal that yearly production of scientific articles increased steadily. Journal and institution production, and author's keywords frequencies followed the Lotka's Law. Khan SU and White JC were the most productive authors. The most productive journals were Journal of Agricultural and Food Chemistry (55), and Journal of Ethnopharmacology (48), and the most common WOS subject category was Pharmacology & Pharmacy (419). USA (h-index of 40) produced 21.7 % of all articles, closely followed by China (20.6 %). Chinese Academy of Sciences (34) was the most productive research institutions. Finally, current and future trends in this area should focus on keywords such as pharmacokinetics, curcumin, in-vitro, nanoparticles, oral (bioavailability) and cell.

As, Cd, and Pb relative bioavailability in contaminated soils: Coupling mouse bioassay with UBM assay

The robustness of in vitro bioaccessibility assays to predict oral relative bioavailability (RBA) of multiple metals in contaminated soils requires validation using additional soil samples. In this study, 11 contaminated soils from mining/smelting areas were analyzed for As-, Cd-, and Pb-RBA using a mouse bioassay and metal bioaccessibility via the UBM gastric phase assay. Metal-RBA varied considerably among soils, with As-RBA (2.5-23%, mean 12%) being generally lower than Cd-and Pb-RBA (3.4-88 and 3.3-59%, mean 42 and 28%), due to higher proportions of As in the residual fractions. Metal-RBA generally decreased with increasing metal concentrations probably due to reduced labile metal fractions. In addition, strong negative correlations were observed between total Fe with As-, Cd-, and Pb-RBA (R² = 0.46-0.77), suggesting the role of Fe in controlling metal-RBA in soils. Like RBA, metal bioaccessibility by the UBM assay also varied among samples. However, strong in vivo-in vitro correlations (IVIVCs) were observed between metal-RBA and bioaccessibility (R² = 0.52-0.81). Further, there were little differences when As-, Cd-, and Pb-IVIVCs established using soils from this study and soils pooled from literature were compared, suggesting the robustness of the UBM assay to predict metal-RBA in contaminated soils.

A deterministic and stochastic assessment for exposure and risk of arsenic via ingestion of edible crops

Natural arsenic contamination is a critical problem for various places around the world. Simav Plain (Kutahya, Turkey) is one such area that was shown to have natural arsenic contamination in its waters and soils. Arsenic exposure through ingestion of edible crops cultivated in Simav Plain and associated health risks were assessed in this study. To achieve this objective, arsenic levels in 18 crop species were estimated based on measured soil arsenic concentrations. Individual and aggregate non-carcinogenic and carcinogenic risks associated with ingestion of arsenic-contaminated crops were then assessed with scenario-based deterministic point estimates and stochastic population estimates. Monte Carlo simulation was used for the estimation of population health risks. Accordingly, wheat was found as the highest-ranked crop specie for the both types of health risks, followed by tomato and potato, which are three of the most consumed crops in the region. The risk levels estimated in this study were relatively high, indicating consumption of crops grown in the plain may be posing significant health risks even at lower-bound estimates. Consuming wheat, tomato, potato, and their products from uncontaminated sources was found to reduce the aggregate risks up to 88% implicating the importance of proposing suitable management measures for similar risk-prone areas.

Long-term leaching of arsenic from pressure-treated playground structures in the northeastern United States

Wood used in playground structures built prior to 2004 was pressure-treated with chromated copper arsenate (CCA) which has been associated with negative health and environmental impacts. Given the prevalence and lack of maintenance of these aging play structures in rural northeastern US, the aim of this study was to determine the distribution of As (total, speciated and bioaccessible) in surface soil collected near and underneath four CCA-treated playground structures 16- and 26-years following installation. Note that one playground in southeastern MA was studied where surface soil samples were collected at various distances from the structures (0, 5, 15, and 30 cm). Total As in surface soil was measured by graphite furnace atomic absorption spectroscopy, whereas As speciation and bioaccessible As were determined by HPLC-ICPMS and in vitro SBRC-gastric assay, respectively. Near (≤5 cm) and underneath CCA-treated structures total As concentration in surface soil ranged from 143.4-213.5 mg/kg after 26 years of installation compared to 101.3-166.6 mg/kg ten years earlier. These concentrations exceeded the Massachusetts Residential Risk-Based Soil Standard by 5-10 times. In comparison, total As in background soil samples ranged from 4.6-6.6 mg/kg during the two study periods. While most of the As in surface soil were in the form of As(V), ≤29% was bioaccessible. Overall, our findings demonstrated that arsenic accumulation in soil surrounding aging playground structures continues to be a source of elevated exposure to children through contact with contaminated soil.

Low arsenic bioaccessibility by fixation in nanostructured iron (Hydr)oxides: Quantitative identification of As-bearing phases

A new analytical protocol was developed to provide quantitative, single-particle identification of arsenic in heterogeneous nanoscale mineral phases in soil samples, with a view to establishing its potential risk to human health. Microscopic techniques enabled quantitative, single-particle identification of As-bearing phases in twenty soil samples collected in a gold mining district with arsenic concentrations in range of 8 to 6354 mg kg^-1. Arsenic is primarily observed in association with iron (hydr) oxides in fine intergrowth with phyllosilicates. Only small quantities of arsenopyrite and ferric arsenate (likely scorodite) particles, common in the local gold mineralization, were identified (e.g., 7 and 9 out, respectively, of app. 74,000 particles analyzed). Within the high-arsenic subgroup, the arsenic concentrations in the particle size fraction below 250μm ranges from 211 to 4304 mg kg^-1. The bioaccessible arsenic in the same size fraction is within 0.86-22 mg kg^-1 (0.3-5.0%). Arsenic is trapped in oriented aggregates of crystalline iron (hydr)oxides nanoparticles, and this mechanism accounts for the low As bioaccessibility. The calculated As exposure from soil ingestion is less than 10% of the arsenic Benchmark Dose Lower Limit - BMDL_0.5. Therefore, the health risk associated with the ingestion of this geogenic material is considered to be low.

A Pooled Data Analysis to Determine the Relationship between Selected Metals and Arsenic Bioavailability in Soil

Chronic exposure to arsenic (As) is a global concern due to worldwide exposure and adverse effects, and the importance of incorporating bioavailability in the exposure assessment and risk assessment of As is increasing acknowledged. The bioavailability of As is impacted by a number of soil properties, such as pH, clay and metal concentrations. By retrieving 485 data from 32 publications, the aim of this study was to determine the relationship between selected metals (Fe and Al) and As bioavailability. In present study, the bioaccessibility (BAC) data measured by in vitro approaches were converted into bioavailability data based on the previously determined relationship between BAC and bioavailability. The As relative bioavailability (RBA) was summarized to be 24.36 ± 18.49%, which is in the range previously reported. A significant association between Fe concentration and the bioavailability of As was observed while this association varied for different types of RBA data. This disparity may suggest a non-reliable association between Fe and As bioavailability. The correlations between logarithmically transformed total content of Fe + Al and As bioavailability is then outlined: RBA = (−8.40 ± 1.02) × Ln(Fe + Al) + (58.25 ± 4.09), R² = 0.25, p < 0.001, n = 212. Jackknife resampling was also applied to validate the relation between total content of (Fe + Al) and As bioavailability, which suggested that the relation is robust. This is the first pooled study to address the relations between selected metal concentrations and As bioavailability, which may provide some implications to establish soil properties-based RBA prediction for As.

Assessing bioavailability of complex chemical mixtures in contaminated soils: Progress made and research needs

Understanding the distribution, behaviour and interactions of complex chemical mixtures is key for providing the evidence necessary to make informed decisions and implement robust remediation strategies. Much of the current risk assessment frameworks applied to manage land contamination are based on total contaminant concentrations and the exposure assessments embedded within them do not explicitly address the partitioning and bioavailability of chemical mixtures. These oversights may contribute to an overestimation of both the eco-toxicological effects of the fractions and the mobility of contaminants. In turn, this may limit the efficacy of risk frameworks to inform targeted and proportionate remediation strategies. In this review we analyse the science surrounding bioavailability, its regulatory inclusion and the challenges of incorporating bioavailability in decision making process. While a number of physical and chemical techniques have proven to be valuable tools for estimating bioavailability of organic and inorganic contaminants in soils, doubts have been cast on its implementation into risk management soil frameworks mainly due to a general disagreement on the interchangeable use of bioavailability and bioaccessibility, and the associated methods which are still not standardised. This review focuses on the role of biotic and abiotic factors affecting bioavailability along with soil physicochemical properties and contaminant composition. We also included advantages and disadvantages of different extraction techniques and their implications for bioavailability quantitative estimation. In order to move forward the integration of bioavailability into site-specific risk assessments we should (1) account for soil and contaminant physicochemical characteristics and their effect on bioavailability; (2) evaluate receptor's potential exposure and uptake based on mild-extraction; (3) adopt a combined approach where chemical-techniques are used along with biological methods; (4) consider a simplified and cost-effective methodology to apply at regulatory and industry setting; (5) use single-contaminant exposure assessments to inform and predict complex chemical mixture behaviour and bioavailability.

In vivo and in vitro methods for evaluating soil arsenic bioavailability: relevant to human health risk assessment

Arsenic (As) is the most frequently occurring contaminant on the priority list of hazardous substances, which lists substances of greatest public health concern to people living at or near U.S. National Priorities List site. Accurate assessment of human health risks from exposure to As-contaminated soils depends on estimating its bioavailability, defined as the fraction of ingested As absorbed across the gastrointestinal barrier and available for systemic distribution and metabolism. Arsenic bioavailability varies among soils and is influenced by site-specific soil physical and chemical characteristics and internal biological factors. This review describes the state-of-the science that supports our understanding of oral bioavailability of soil As, the methods that are currently being explored for estimating soil As relative bioavailability (RBA), and future research areas that could improve our prediction of the oral RBA of soil As in humans. The following topics are addressed: (1) As soil geochemistry; (2) As toxicology; (3) in vivo models for estimating As RBA; (4) in vitro bioaccessibility methods; and (5) conclusions and research needs.

Investigation of bioaccessibility of Cu, Fe, Mn, and Zn in market vegetables in the colon using PBET combined with SHIME

The in vitro bioaccessibility of trace metals associated with oral ingestion of market vegetables (lettuce, pak choi, cole, and leaf lettuce) of Beijing, China was studied. The physiologically based extraction test (PBET) combined with the Simulator of Human Intestinal Microbial Ecosystem (SHIME) was applied to simulate stomach, small intestine, and colon of human. In the gastro-intestinal phases, the bioaccessibility of Cu, Fe, Mn, and Zn varied within 5.7–75.5%, 17.3–50.4%, 13.3–49.1%, and 19.9–63.7%, respectively. There was no significant difference in the metal bioaccessibility between the gastric and small intestinal phases, except for higher Cu bioaccessibility in the small intestine. Besides, the bioaccessibility of the four trace metals in the colon phase was first ever reported. A significant decline in Cu bioaccessibility (1.8–63.7%) and slight increases in the bioaccessibility of Fe (16.7–56.4%), Mn (21.2–71.6%), and Zn (15.7–69.7%) were revealed, which could mainly be attributed to the effect of colon microbiota. In addition, the estimated daily intakes (EDIs) of Cu, Fe, Mn, and Zn were worked out to be 0.7, 8.8, 2.7, and 4.5 μg kg⁻¹ body weight d⁻¹, based on which the potential influences of these trace metals in vegetables on the health of the local consumers was demonstrated.

Effect of phosphate amendment on relative bioavailability and bioaccessibility of lead and arsenic in contaminated soils

Hand-to-mouth activity is an important pathway for children's exposure to contaminated soils, which is often co-contaminated by Pb and As in mining and smelting sites. To reduce soil Pb risk to humans by oral exposure, phosphate amendments have been used to reduce Pb relative bioavailability (RBA), but its efficiency has not been investigated using validated in vitro assays nor its influence on As-RBA. Here, 5 contaminated soils (A-E) were amended with 0.5% phosphoric acid (PA) to study its effect on Pb- and As- RBA using a newly-developed mouse kidney model and bioaccessibility using 4 in vitro assays including UBM, SBRC, IVG, and PBET. Based on the mouse kidney model, Pb-RBA in PA-amended soils decreased from 14.2-62.5% to 10.1-29.8%. In contrast, As-RBA decreased from 26.5% to 15.9% in soil B but increased from 27.5 to 41.2% in soil D, with changes being insignificant in 3 other soils (35.8-58.8 to 28.1-61.1%). When assessing Pb bioaccessibility in PA-amended soils, decreased bioaccessibility were found using PBET and SBRC. For As, its bioaccessibility increased in PA-amended soils, inconsistent with in vivo data. Our results shed light on the importance of method selection to assess risk in Pb- and As-contaminated soils amended with phosphate.

Biomimetic Gastrointestinal Tract Functions for Metal Absorption Assessment in Edible Plants: Comparison to In Vivo Absorption

A biomimetic gastrointestinal tract, including in vitro digestion and biomimetic biomembrane extraction, has been proposed for absorption assessment of metals from edible plants. However, its validity is still unknown. Herein, two species of edible plants, Anoectochilus roxburghii and Radix astragali, were selected and digested in a bionic mouth, stomach, and intestine, and then trace metals (Cr, Mn, Fe, Ni, Cu, Zn, Se, Sr, As, and Pb) were transformed to their final metal species. To check model predictability, in vitro and in vivo metal absorption were imitated and tested by monolayer liposome extraction and rat stomach or single-pass duodenal intestine, respectively. A strong correlation was established between in vivo and in vitro metal absorption ratios, with 0.89 > R² > 0.66, and a significant relationship (p < 0.05) was exhibited for stomach, intestine, two plant species, and 10 metal species. Our biomimetic system could be used as low-cost alternatives to animal and clinical studies for multi-metal absorption.

Comparison of in vitro digestion model with in vivo relative bioavailability of BDE-209 in indoor dust and combination of in vitro digestion/Caco-2 cell model to estimate the daily intake of BDE-209 via indoor dust

There is limited information on the BDE-209 relative bioavailability (RBA) of indoor dust and the absorption of BDE-209 after in vitro digestion was seldom studied. In the present study, BDE-209 RBA in 6 household dust samples measured using an in vivo mouse model was compared to BDE-209 bioaccessibility determined using physiologically based extraction test (PBET) and solubility bioaccessibility research consortium method (SBRC) assays. BDE-209 RBA obtained ranged from 45.9 ± 16.1 to 96.0 ± 17.4% and exhibited a significant relationship with PBET gastric phase (r² = 0.578, p = 0.080), small intestinal phase (r² = 0.728, p = 0.031) and total BDE-209 bioaccessibility (r² = 0.728, p = 0.031), which indicated PBET assay can serve as a surrogate to predict BDE-209 RBA to refine human health exposure. In addition, the absorption of BDE-209 by Caco-2 cell line was assessed. With the consideration of the corresponding bioaccessibility and absorption of BDE-209 by Caco-2 cell line, the human daily intake of BDE-209 via dust ingestion for adults and children was much lower than that estimated by total concentration.

Oral relative bioavailability of Dichlorodiphenyltrichloroethane (DDT) in contaminated soil and its prediction using in vitro strategies for exposure refinement

In this study, the bioavailability of DDTr (sum of DDT, DDD and DDE isomers) in pesticide-contaminated soil was assessed using an in vivo mouse model. DDTr relative bioavailability (RBA) ranged from 18.7±0.9 (As35) to 60.8±7.8% (As36) indicating that a significant portion of soil-bound DDTr was not available for absorption following ingestion. When DDTr bioaccessibility was assessed using the organic Physiologically Based Extraction Test (org-PBET), the inclusion of a sorption sink (silicone cord) enhanced DDTr desorption by up to 20-fold (1.6-3.8% versus 18.9-56.3%) compared to DDTr partitioning into gastrointestinal fluid alone. Enhanced desorption occurred as a result of the silicone cord acting as a reservoir for solubilized DDTr to partition into, thereby creating a flux for further desorption until equilibrium was achieved. When the relationship between in vivo and in vitro data was assessed, a strong correlation was observed between the mouse bioassay and the org-PBET+silicone cord (slope=0.94, y-intercept=3.5, r(2)=0.72) suggesting that the in vitro approach may provide a robust surrogate measure for the prediction of DDTr RBA in contaminated soil.

Arsenic and Environmental Health: State of the Science and Future Research Opportunities

BACKGROUND

Exposure to inorganic and organic arsenic compounds is a major public health problem that affects hundreds of millions of people worldwide. Exposure to arsenic is associated with cancer and noncancer effects in nearly every organ in the body, and evidence is mounting for health effects at lower levels of arsenic exposure than previously thought. Building from a tremendous knowledge base with > 1,000 scientific papers published annually with "arsenic" in the title, the question becomes, what questions would best drive future research directions?

OBJECTIVES

The objective is to discuss emerging issues in arsenic research and identify data gaps across disciplines.

METHODS

The National Institutes of Health's National Institute of Environmental Health Sciences Superfund Research Program convened a workshop to identify emerging issues and research needs to address the multi-faceted challenges related to arsenic and environmental health. This review summarizes information captured during the workshop.

DISCUSSION

More information about aggregate exposure to arsenic is needed, including the amount and forms of arsenic found in foods. New strategies for mitigating arsenic exposures and related health effects range from engineered filtering systems to phytogenetics and nutritional interventions. Furthermore, integration of omics data with mechanistic and epidemiological data is a key step toward the goal of linking biomarkers of exposure and susceptibility to disease mechanisms and outcomes.

CONCLUSIONS

Promising research strategies and technologies for arsenic exposure and adverse health effect mitigation are being pursued, and future research is moving toward deeper collaborations and integration of information across disciplines to address data gaps.

CITATION

Carlin DJ, Naujokas MF, Bradham KD, Cowden J, Heacock M, Henry HF, Lee JS, Thomas DJ, Thompson C, Tokar EJ, Waalkes MP, Birnbaum LS, Suk WA. 2016. Arsenic and environmental health: state of the science and future research opportunities. Environ Health Perspect 124:890-899; http://dx.doi.org/10.1289/ehp.1510209.

Using the SBRC Assay to Predict Lead Relative Bioavailability in Urban Soils: Contaminant Source and Correlation Model

Using in vitro bioaccessibility assays to predict Pb relative bioavailability (RBA) in contaminated soils has been demonstrated, however, limited research was performed on urban soils having lower Pb levels. In this study, 162 soils from urban parks in 27 capital cities in China were measured for Pb bioaccessibility using the SBRC assay, with Pb-RBA in 38 subsamples being measured using a mouse-kidney assay. Total Pb concentrations in soils were 9.3-1198 mg kg(-1), with 92% of the soils having Pb concentrations <100 mg kg(-1). Lead bioaccessibility in soils was 20-94%, increasing with Pb concentration up to 100 mg kg(-1) (r = 0.44), however, limited variability in Pb bioaccessibility (60-80%) was observed for soils with Pb > 100 mg kg(-1). On the basis of a stable isotope fingerprinting technique, coal combustion ash was identified as the major Pb source, contributing to the increased Pb bioaccessibility with increasing soil Pb concentration. Lead-RBA in soils was 17-87%, showing a strong linear correlation with Pb bioaccessibility (r(2) = 0.61), with cross validation of the correlation based on random subsampling and leave-one-out approaches yielding low prediction errors. On the basis of the large sample size of 38 soils, this study demonstrated that the Pb-RBA predictive capability of the SBRC assay can be extended from mining/smelting impacted soils to urban soils with lower Pb levels.