Validation of the predictive capabilities of the Sbrc-G in vitro assay for estimating arsenic relative bioavailability in contaminated soils

Bioaccessibility and human health risks of arsenic from geological origin in lateritic red soil on construction land

Current human health risk assessments of soil arsenic (As) contamination rarely consider bioaccessibility (IVBA), which may overestimate the health risks of soil As. The IVBA of As (As-IVBA) may differ among various soil types. This investigation of As-IVBA focused As from geological origin in a typical subtropical soil, lateritic red soil, and its risk control values. The study used the SBRC gastric phase in vitro digestion method and As speciation sequential extraction based upon phosphorus speciation extraction method. Two construction land sites (CH and HD sites) in the Pearl River Delta region were surveyed. The results revealed a high content of residual As (including scorodite, mansfieldite, orpiment, realgar, and aluminum arsenite) in the lateritic red soils at both sites (CH: 84.9%, HD: 91.7%). The content of adsorbed aluminum arsenate (CH: 3.24%, HD: 0.228%), adsorbed ferrum arsenate (CH: 8.55%, HD: 5.01%), and calcium arsenate (CH: 7.33%, HD: 3.01%) were found to be low. The bioaccessible As content was significantly positively correlated with the As content in adsorbed aluminum arsenate, adsorbed ferrum arsenate, and calcium arsenate. A small portion of these sequential extractable As speciation could be absorbed by the human body (CH: 14.9%, HD: 3.16%), posing a certain health risk. Adsorbed aluminum arsenate had the highest IVBA, followed by calcium arsenate, and adsorbed ferrum arsenate had the lowest IVBA. The aforementioned speciation characteristics of As from geological origin in lateritic red soil contributed to its lower IVBA compared to other soils. The oxidation state of As did not significantly affect As-IVBA. Based on As-IVBA, the carcinogenic and non-carcinogenic risks of soil As in the CH and HD sites decreased greatly in human health risk assessment. The results suggest that As-IVBA in lateritic red soil should be considered when assessing human health risks on construction land.

Can arsenic bioavailability be predicted in soils using in vitro gastro-intestinal simulation?

Many gastrointestinal simulation methods have been used to predict bioavailability, but the suitability of different methods for the same metal(loid)s varies widely, which inevitably affects the accuracy of human health risk assessment. Arsenic is a common and important contaminant in many contaminated land situations. It can be readily absorbed and has teratogenic and mutagenic toxicity. Therefore, in this study, four the most commonly used in vitro simulation methods (the Physiologically Based Extraction Test (PBET), In Vitro Gastrointestinal Method (IVG), Soluble Bioavailability Research Consortium (SBRC), the Unified BARGE Method (UBM)) were tested against an in vivo animal live model, to evaluate their effectiveness for the prediction of soil As bioavailability in 10 industrially contaminated soils. The soil As relative bioavailability (RBA) varied between 15% and 68% in the different soils. As bioaccessibility differed between the 4 gastro-intestinal simulation methods. Gastric phase of UBM (UBMG) predicted As relative bioavailability the best of the 4 assays (R2 = 0.81). This study provides theoretical and technical support to refine human health risk assessment of As in soils from urban industrial legacy contaminated sites.

The effect of particle size on oral bioavailability and bioaccessibility of soil Ni from different sources

The goal of the work was to contribute to a unified approach to assessing the risk to human health of soil ingestion, for contaminated sites with elevated [Ni]. Robust relationships between in vitro bioaccessibility and in vivo bioavailability of Ni in various soils, with mechanistic understanding, would enable site-specific assessments of human exposure through soil ingestion. Four soils (three ultramafic Brunisols with geogenic Ni and one Organic soil with anthropogenic Ni) were sieved into PS < 10 μm, 10-41 μm, 41-70 μm, 70-105 μm, 105-150 μm, and 150-250 μm, the [Ni]T for which ranged from 560 to 103000 mg/kg. Mass fraction-adjusted [Ni]IVBA (SBRC gastric) for each soil fraction was similar whether calculated for all particles <250 μm or <150 μm %NiIVBA ranged from 3% to 16% of [Ni]T and %NiABA (accumulated Ni in urine, kidneys, and small intestine of Sprague Dawley rats gavaged with a soil) ranged from 0% to 0.49%. The correlation between these two measurements was weak (R2 = 0.06). Multiple linear dose response relationships attributing variation in %NiABA to %NiIVBA plus soil physicochemical parameters known to influence trace element availability in soils were developed. As many soil properties measured in this study were highly correlated, ridge regression enabled a predictive relationship where the effect of each parameter was its true contribution to variation in %NiABA. Using a ridge constant (k) of 0.012, %NiABA could be predicted from %NiIVBA adjusted for soil absorptive entities (OrgC, and Fe oxides (negative coefficients)) and soil pH (positive coefficient). %NiABA predicted from this relationship was very close to 1:1 with the observed %NiABA except at the lowest observed values which were lower than predicted. This study shows that as the conditions increasingly favour soil Ni solubility, more of the Ni was bioavailable; this generalization was true regardless of particle size or soil origin.

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.

Environmental and health impacts assessment of long-term naturally-weathered municipal solid waste incineration ashes deposited in soil-old burden in Bratislava city, Slovakia

Municipal solid waste incineration (MSWI) is an effective method for reducing the volume/mass of waste. However, MSWI ashes contain high concentrations of many substances, including trace metal (loid)s, that could be released into the environment and contaminate soils and groundwater. In this study, attention was focused on the site near the municipal solid waste incinerator where MSWI ashes are deposited on the surface without any control. Here, combined results (chemical and mineralogical analyses, leaching tests, speciation modelling, groundwater chemistry and human health risk assessment) are presented to assess the impact of MSWI ash on the surrounding environment. The mineralogy of ∼forty years old MSWI ash was diverse, and quartz, calcite, mullite, apatite, hematite, goethite, amorphous glasses and several Cu-bearing minerals (e.g. malachite, brochantite) were commonly detected. In general, the total concentrations of metal (loid)s in MSWI ashes were high, following the order: Zn (6731 mg/kg) > Ba (1969 mg/kg) ≈ Mn (1824 mg/kg) > Cu (1697 mg/kg) > Pb (1453 mg/kg) > Cr (247 mg/kg) > Ni (132 mg/kg) > Sb (59.4 mg/kg) > As (22.9 mg/kg) ≈ Cd (20.6 mg/kg). Cadmium, Cr, Cu, Pb, Sb and Zn exceeded the indication or even intervention criteria for industrial soils defined by the Slovak legislation. Batch leaching experiments with diluted citric and oxalic acids that simulate the leaching of chemical elements under rhizosphere conditions documented low dissolved fractions of metals (0.00-2.48%) in MSWI ash samples, showing their high geochemical stability. Non-carcinogenic and carcinogenic risks were below the threshold values of 1.0 and 1 × 10^-6, respectively, with soil ingestion being the most important exposure route for workers. The groundwater chemistry was unaffected by deposited MSWI ashes. This study may be useful in determining the environmental risks of trace metal (loid)s in weathered MSWI ashes that are loosely deposited on the soil surface.

Molecular speciation controls arsenic and lead bioaccessibility in fugitive dusts from sulfidic mine tailings

Communities nearby mine wastes in arid and semi-arid regions are potentially exposed to high concentrations of toxic metal(loid)s from fugitive dusts deriving from impoundments. To assess the relation between potentially lofted particles and human health risk, we studied the relationship between pharmacokinetic bioaccessibility and metal(loid) molecular speciation for mine tailings dust particulate matter (PM), with elevated levels of arsenic and lead (up to 59 and 34 mmol kg-1, respectively), by coupling in vitro bioassay (IVBA) with X-ray absorption spectroscopy (XAS). Mine tailing efflorescent salts (PMES) and PM from the surface crust (0-1 cm, PMSC) and near surface (0-25 cm) were isolated to <10 μm and <150 μm effective spherical diameter (PM10 and PM150) and reacted with synthetic gastric and lung fluid for 30 s to 100 h to investigate toxic metal(loid) release kinetics. Bioaccessible (BAc) fractions of arsenic and lead were about 10 and 100 times greater in gastric than in lung fluid simulant, respectively, and 10-100% of the maximum gastric BAc from PM10 and PM150 occurred within 30 s, with parabolic dissolution of fine, highly-reactive particles followed by slower release from less soluble sources. Evaporite salts were almost completely solubilized in gastric-fluid simulants. Arsenate within jarosite and sorbed to ferrihydrite, and lead from anglesite, were identified by XAS as the principal contaminant sources in the near surface tailings. In the synthetic lung fluid, arsenic was released continuously to 100 h, suggesting that residence time in vivo must be considered for risk determination. Analysis of pre- and post-IVBA PM indicated the release of arsenic in lung fluid was principally from arsenic-substituted jarosite, whereas in synthetic gastric fluid arsenic complexed on ferrihydrite surfaces was preferentially released and subsequently repartitioned to jarosite-like coordination at extended exposures. Lead dissolved at 30 s was subsequently repartitioned back to the solid phase as pyromorphite in phosphate rich lung fluid. The bioaccessibility of lead in surface tailings PM was limited due to robust sequestration in plumbojarosite. Kinetic release of toxic elements in both synthetic biofluids indicated that a single IVBA interval may not adequately describe release dynamics.

Can the mouse model successfully predict mixed metal(loid)s bioavailability in humans from contaminated soils?

Mouse models have been employed by many scientific research groups worldwide to predict the bioavailability of metal (loid)s and other chemicals in humans. Their suitability for predicting mixed metal (loid) bioavailability has been questioned and debated for decades by many research teams. In this study soils contaminated by lead (Pb) and arsenic (As), either in the field or by spiking in the laboratory, were used in bioavailability and bioaccessibility tests. The spiked soils were aged for more than a year prior to testing to achieve steady state and eliminate soil ageing effects, as reported in previous research. The bioavailability of, firstly, Pb in the presence of As and secondly, As in the presence of Pb was determined using mice. Furthermore, bioaccessibility was determined using a range of in vitro methods: relative bioaccessibility leaching procedure (RBALP), the Unified Bioaccessibility Research Group Europe (BARGE) method (UBM) gastric and intestinal phases, and the National Institute for Public Health and the Environment (RIVM) gastric and intestinal phases. The correlations between Pb and As bioavailability and their in vitro bioaccessibility when they were present in mixtures were analysed. The results indicated that the bioavailability of Pb in mice kidney tissues significantly correlated with bioaccessibility of Pb in RBALP (p < 0.01), UBM gastric (p < 0.01) and intestinal phases (p < 0.01) and RIVM gastric phases when Pb is present in metal (loid) mixtures. Results of the current study reveal that the RBALP, and UBM gastric and intestinal phase were by far the best methods for predicting the RB of Pb when it is present in metal (loid) mixtures. Consequently, the mouse model can successfully explain the in vivo in vitro correlation (IVIVC) of Pb when it is present in metal (loid) mixtures. However, we did find that a mouse model may not be the best one to explain the IVIVC of As when it is present in metal (loid) mixtures.

Effect of Nanoscale Zero-Valent Iron on Arsenic Bioaccessibility and Bioavailability in Soil

Hand-to-mouth activity is considered to be the main way for children to come into contact with contaminated soil, and bioavailability is an important factor affecting their health risk. To reduce soil As risk to humans by oral exposure, nanoscale zero-valent iron (nZVI) has been extensively studied for immobilizing As-contaminated soil, but its efficiency has not been investigated using in vitro assay and its influence on As-RBA. In this study, two contaminated soil samples (A and B) were amended with 1% and 2% (w/w) nZVI for 56 days to study its effect on As fraction by sequence extraction, As bioaccessibility by SBRC assay, and As relative bioavailability (RBA) by the mouse liver and kidney model. Based on the sequence extraction, the As associated with the E1 (exchangeable fraction) and C2 (carbonate fraction) fractions were decreased from 3.00% to 1.68% for soil A and from 21.6% to 7.86% for soil B after being treated with 2% nZVI for 56 days. When assessing As bioaccessibility in all soils treated with nZVI by SBRC assay, it was found that As bioaccessibility was significantly higher in the gastric phase (GP) and lower in the intestinal phase (IP) (p < 0.05), and the bioaccessible Fe concentration decreased significantly from the gastric to intestinal phase at the same time. Based on the mouse liver–kidney model, the As-RBA in soil A increased from 21.6% to 22.3% and 39.9%, but in soil B decreased from 73.0% to 55.3% and 68.9%, respectively. In addition, there was a significant difference between As bioaccessibility based on GP or IP of SBRC assay and As-RBA in two soils after being treated with nZVI for 56 days. To more accurately assess the effects of nZVI human arsenic exposure, As-RBA should be considered in concert with secondary evidence provided through fraction and bioaccessibility assessments. In addition, it is necessary to develop a suitable in vitro assay to predict As-RBA in nZVI-amended soils.

Environmental and human health risk assessment of sulfidic mine waste: Bioaccessibility, leaching and mineralogy

Sulfidic mine waste can pose environmental and human health risks, especially when it contains high levels of mobile metal(loid)s. To assess the environmental and health risks of mine waste originating from three historic and active sulfidic Pb-, Zn- and/or Cu-mines in Europe, mineralogical and chemical characterizations were conducted in combination with in vitro bioaccessibility tests, sequential extractions and leaching tests. Results indicated that most samples contained highly elevated levels of metal(loid)s and key minerals consisting of pyrite, sphalerite and cerussite. The orally bioaccessible fraction varied amongst samples: Cd (13-100%), Zn (9-69%), Pb (4-67%), Cu (8-41%) and As (1-11%). Given these bioaccessible levels, the human health risk assessment indicated carcinogenic and non-carcinogenic risks for most investigated samples in a worst-case exposure scenario. The leaching tests revealed a high mobility of metal(loid)s, especially Pb, posing potential environmental risks. The sequential extractions coupled with mineralogical analyses highlighted the highly mobile levels of Cd, Pb and Zn, posing environmental and health risks. Cerussite dissolved in the easily exchangeable fraction, releasing elevated levels of Pb, while pyrite never completely dissolved. In conclusion, the studied wastes pose environmental and health risks, but the high mobility of some elements also provides opportunities for the valorization of the waste.

Gastric bioaccessibility and human health risks associated with soil metal exposure via ingestion at an E-waste recycling site in Kumasi, Ghana

Over 1000 people make a living by processing electronic and electrical waste (E-waste) and scrap metals for the recovery of valuable metals and integrated circuits at Dagomba Line, Kumasi, Ghana. The processing includes activities such as dismantling, open burning and open dumping of E-waste which can potentially release toxic metals into the environment and thus impact the health of recyclers and nearby residents. This study investigated the distribution of toxic metals (As, Cd, Cr, Cu, Hg, Ni, Pb, Sb and Zn) in surface soils at the E-waste recycling sites and determined the associated human health risk via ingestion incorporating bioaccessibility measurements. Metal concentrations in the activity sites were highly elevated, significantly higher than those in the surrounding area and exceeded international soil quality guidelines such as the Canadian soil quality guidelines for residential land use and the Dutch Intervention Value. Bioaccessibility was high for Pb (70.8%), Cd (64.1%), Cu (62.3%) and Ni (53.6%) which could be credited to the existence of oxidized species as a result of the E-waste burning. Non-carcinogenic effects were unacceptably high (hazard indices > 1) at 14 out of 31 sites, and the cancer risk for arsenic for adult workers was greater than 1 × 10^-5 at five of the sampling sites.

Bioaccessible arsenic in soil of thermal areas of Viterbo, Central Italy: implications for human health risk

Thermal waters near the city of Viterbo (Central Italy) are known to show high As contents (up to 600 µg/l). Travertine is precipitated by these waters, forming extended plateau. In this study, we determine the As content, speciation and bioaccessibility in soil and travertine samples collected near a recreational area highly frequented by local inhabitants and tourists to investigate the risk of As exposure through accidental ingestion of soil particles. (Pseudo)total contents in the studied soils range from 17 to 528 mg/kg, being higher in soil developed on a travertine substrate (197 ± 127 mg/kg) than on volcanic rocks (37 ± 13 mg/kg). In travertines, most As is bound to the carbonatic fraction, whereas in soil the semimetal is mostly associated with the oxide and residual fractions. Accordingly, bioaccessibility (defined here by the simplified bioaccessibility extraction test, SBET; Oomen et al., 2002.) is maximum (up to 139 mg/kg) for soil developed on a travertine substrate, indicating a control of calcite dissolution on As bioaccessibility. On the other hand, risk analysis suggests a moderate carcinogenic risk associated with accidental soil ingestion, while dermal contact is negligible. By contrast, ingestion of thermal water implies a higher carcinogenic and systemic health risk.

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.

Prediction on the combined toxicities of stimulation-only and inhibition-only contaminants using improved inverse distance weighted interpolation

The evaluation of ecological risks of contaminant mixtures to organisms is very challenging due to the non-linear response of organisms to each component, especially under the co-existence of both stimulators and inhibitors. Whether the stimulatory effect can reduce or even offset the inhibitory effect would be critical to the risk assessment and the treatment measures of mixed pollutants. Here, the combined toxicity of sodium fluoride (NaF), a stimulator with stimulation rate >100%, and six compounds that cannot induce hormesis (four ionic liquids (ILs) and two pesticides) were studied. The time-dependent toxicity of each toxicant on Vibrio qinghaiensis sp.-Q67 was investigated at 0.25, 2, 4, 6, 8, 10 and 12 h. Results showed that four ILs and two pesticides failed to induce hormesis, while NaF induced hormesis from 2 to 6 h and induced stimulation only after 6 h and reached its maximum (650%) at 12 h. All mixture rays with NaF induced hormesis at different times. In the four NaF-IL mixture systems, the absolute value of maximum stimulation demonstrated an upwards and then a downwards trend with the increasing of mixture ratio of IL. In two NaF-pesticide systems, the maximum stimulation effect declined with the increasing of the mixture ratio of pesticide. The toxicities of the mixture were successfully predicted by the improved inverse distance weighted interpolation, which are not able to be predicted by the commonly used concentration addition or independent action models. This paper shed lights on evaluating the hormesis of mixtures and the ecological risk of fluoride.

Environmental and human-health risks of As in soils with abnormal arsenic levels located in irrigated agricultural areas of Paracatu (MG), Brazil

The municipality of Paracatu (Brazil) is notorious for its large irrigated agricultural area and by abnormal arsenic (As) levels in selected soils of the region. Concerns regarding As exposure via ingestion of water and food are frequent, yet little is known about the behavior of arsenic in irrigated agricultural soils, as well as on As bioaccessibility/bioavailability in agroecosystems of this region. This work evaluated total and available As in agricultural soils cultivated under irrigation and in soils under native vegetation in Paracatu. We also assessed reactive arsenic fractions and As bioaccessibility in the soil, as well as arsenic levels in plant shoots to estimate As risks in these agroecosystems. Soil (different depths) and plant tissue samples were collected in 6 irrigated agricultural areas (CA1 to CA6) and 4 reference areas (RA1 to RA4). Total soil-As did not differ between soil depths, reinforcing that the source of As in agricultural soils is natural. This was evident when counterpointing arsenic and phosphorus contents at different soil depths, as both accumulate on the surface of oxidic soils when added to agroecosystems by anthropogenic routes (e.g., phosphate fertilization for P and irrigation for As). Available As levels in soils and plants were very small (below detection limit). Furthermore, all soils presented very low oral As bioaccessibility. Our findings revealed that the irrigated soils are not As polluted due to the low enrichment and accumulation of arsenic, as well as the prevalence of low ecological risks. There is no non-carcinogenic risk for the local population, except for children in RA2. The estimated carcinogenic risk for children followed the order RA2 > CA3 > CA4 > RA3 > CA2, and for adults, RA2 > CA3. Ultimately, the strategy of comparing the behavior of P and As in the soils of this study proved to be efficient in showing that there are no major risks to humans and the environment in the investigated area. However, periodic monitoring of As bioavailability in these areas is recommended.

An interlaboratory evaluation of the variability in arsenic and lead relative bioavailability when assessed using a mouse bioassay

Animal bioassays have been developed to estimate oral relative bioavailability (RBA) of metals in soil, dust, or food for accurate health risk assessment. However, the comparability in RBA estimates from different labs remains largely unclear. Using 12 soil and soil-like standard reference materials (SRMs), this study investigated variability in lead (Pb) and arsenic (As) RBA estimates employing a mouse bioassay in 3 labs at Nanjing University, University of Jinan, and Shandong Normal University. Two performances of the bioassay at Nanjing University in 2019 and 2020 showed reproducible Pb and As RBA estimates, but increasing the number of mouse replicates in 2020 produced more precise RBA measurements. Although there were inter-lab variations in diet consumption rate and metal accumulation in mouse liver and kidneys following SRM ingestion due to differences in diet composition, bioassays at 3 labs in 2019 yielded overall similar Pb and As RBA estimates for the 12 SRMs with strong linear correlations between each 2 of the 3 labs for Pb (R² = 0.95-0.98 and slope = 0.85-1.02) and As RBA outcomes (R² = 0.46-0.86 and slope = 0.56-0.79). The consistency in RBA estimates was attributed to the relative nature of the final bioavailability outcome, which might overcome the inter-lab variation in diet consumption and metal uptake in mice. These results increased the confidence of use of mouse bioassays in bioavailability studies.

Antibiotic exposure decreases soil arsenic oral bioavailability in mice by disrupting ileal microbiota and metabolic profile

Oral bioavailability of arsenic (As) determines levels of As exposure via ingestion of As-contaminated soil, however, the role of gut microbiota in As bioavailability has not evaluated in vivo although some in vitro studies have investigated this. Here, we made a comparison in As relative bioavailability (RBA) estimates for a contaminated soil (3913 mg As kg^-1) using a mouse model with and without penicillin perturbing gut microbiota and metabolites. Compared to soil exposure alone (2% w/w soil in diets), addition of penicillin (100 or 1000 mg kg^-1) reduced probiotic Lactobacillus and sulfate-reducing bacteria Desulfovibrio, enriched penicillin-resistant Enterobacter and Bacteroides, and decreased amino acid concentrations in ileum. With perturbed gut microbiota and metabolic profile, penicillin and soil co-exposed mice accumulated 2.81-3.81-fold less As in kidneys, excreted 1.02-1.35-fold less As in urine, and showed lower As-RBA (25.7-29.0%) compared to mice receiving diets amended with soil alone (56 ± 9.63%). One mechanism accounted for this is the decreased concentrations of amino acids arising from the gut microbiota shift which resulted in elevated iron (Fe) and As co-precipitation, leading to reduced As solubilization in the intestine. Another mechanism was conversion of bioavailable inorganic As to less bioavailable monomethylarsonic acid (MMA^V) and dimethylarsinic acid (DMA^V) by the antibiotic perturbed microflora. Based on in vivo mouse model, we demonstrated the important role of gut microbiota and gut metabolites in participating soil As solubilization and speciation transformation then affecting As oral bioavailability. Results are useful to better understand the role of gut bacteria in affecting As metabolism and the health risks of As-contaminated soils.

Simultaneous immobilization of Pb, Cd and As in soil by hybrid iron-, sulfate- and phosphate-based bio-nanocomposite: Effectiveness, long-term stability and bioavailablity/bioaccessibility evaluation

Here, the bio-nanocomposite (n-HFP + n-HFS)@An was developed to simultaneously immobilize Pb, Cd and As in the severely contaminated soil. The immobilization rates of diethylenetriaminepentaacetic acid (DTPA)/decarbonate-extracted bioavailable Pb, Cd and As were 59.87%, 31.28% and 62.30%, and the immobilization rates of their water-soluble forms were 63.12%, 60.02% and 89.39%, respectively. Moreover, the ten-year acid rain simulated leaching assay showed that the maximum cumulative release contents of Pb, Cd and As in the treated soil samples were decreased by 2.94, 2.46 and 40.60 times, comparing to the un-treated ones. Additionally, the results of SBRC (Solubility Bioaccessibility Research Consortium) revealed that the bioaccessible rates of the three metals in intestinal phase were lower than in gastric phase, and both of them decreased with increasing the immobilization time. The gastric bioaccessibility of Pb, Cd and As had a higher correlation with the contents of water-soluble forms, while the intestinal bioaccessibility was more strongly positively associated with the bioavailable forms.

Contamination, oral bioaccessibility and human health risk assessment of thallium and other metal(loid)s in farmland soils around a historic TlHg mining area

In this study, tweenty-nine soil samples were collected from a historic TlHg mining area, located in southwest Guizhou, China. Total concentrations of metal(loid)s in soils and in vitro extracts were analysed by ICP-MS, and the bioaccessibility of metal(loid)s was conducted by two often used in vitro extraction methods, Simplified bioaccessibility Extraction Test (SBET) and Physiologically Based Extraction Test (PBET). The health risk assessment based on total concentrations of metal(loid)s, bioaccessibility of SBET and PBET through soil ingestion were investigated. Results indicated that the collected cultivated soils contained elevated concentrations of Tl (44.8 ± 67.7 mg kg^-1), Hg (110 ± 193 mg kg^-1), As (84.4 ± 89.2 mg kg^-1) and Sb (14.8 ± 24.8 mg kg^-1), exceeding the regional background values of Guizhou province, China and the Chinese farmland risk screening values. However, the bioaccessibility of Tl, Hg, As and Sb were relatively low, usually less than 30% for most samples and varied greatly among metal(loid)s and sampling sites. The average bioaccessibility values of Tl, Hg, As and Sb by SBET were lower than those by PBET. The non-carsinogenic risk (HQ and HI) and Carcinogenic Risk (CR) values were significantly reduced when incorporating the bioaccessibiltiy of metal(loid)s into health risk assessment. It is worth noting that the health risk to children exceeded adults. Moreover, Tl and As contributed the most to the risk, indicating that more attention should be paid on Tl and As during the daily environmental regulation and management of contaminated soils in Lanmuchang.

Environmental and human health risks of arsenic in gold mining areas in the eastern Amazon

Knowledge of arsenic (As) levels in gold (Au) mining areas in the Amazon is critical for determining environmental risks and the health of the local population, mainly because this region has the largest mineral potential in Brazil and one of the largest in the world. The objective of this study was to assess the environmental and human health risks of As in tailings from Au exploration in the eastern Amazon. Samples were collected from soils and tailings from different exploration forms from 25 points, and the total concentration, pollution indexes and human health risk were determined. Concentrations of As were very high in all exploration areas, especially in tailings, whose maximum value reached 10,000 mg kg^-1, far above the investigation value established by the Brazilian National Council of the Environment, characterizing a polluted area with high environmental risk. Exposure based on the daily intake of As demonstrated a high health risk for children and adults, whose non-carcinogenic risk indexes of 17.8, extremely above the acceptable limit (1.0) established by the United States Environmental Protection Agency. High levels of As in reactive fractions in underground, cyanidation, and colluvium mining areas, as well as extremely high gastric and intestinal bioaccessibility were found, suggesting that high levels may be absorbed by the local population. The results show that the study area is highly polluted through Au mining activities, putting the environment and population health at risk, and that there is an urgent need for intervention by the environmental control agencies for remediation.

Levels, sources, isotope signatures, and health risks of mercury in street dust across China

Spatial distribution and isotope signature of mercury (Hg) in street dusts across China were investigated by collecting dust samples from 14 cities and reviewing previously published data from an additional 46 cities. Potential sources of street dust and the associated health risks to humans were also assessed. The total Hg (THg) concentrations in street dust ranged from 0.020-39.1 mg kg^-1 with an average of 0.433 ± 0.185 mg kg^-1 in the 60 cities. Street dust samples collected from 14 cities were characterized by slightly negative δ²⁰²Hg (-0.61 ± 0.92‰) and near-zero Δ¹⁹⁹Hg (-0.03 ± 0.08‰) values, and coal combustion and industrial activities were estimated to be the major sources of Hg in street dust. The estimated average probable daily intake (PDI) of THg from street dust exposure for adults and children (1.36E-03 and 1.27E-02 μg d^-1 kg^-1, respectively) were comparable to their respective exposures via rice consumption in China. Children being exposed to THg in dust is a major concern in mercury mining areas (e.g., Wangshan and Xunyang), and may also be a concern in cities with major coal-based industries and nonferrous metal smelting. Results from this study suggest that exposure to street dust is not a primary MeHg exposure pathway in China.

Bioaccessibility and human health risk assessment of metal(loid)s in soil from an e-waste open burning site in Agbogbloshie, Accra, Ghana

Environmental pollution and human health issues due to unrestricted electronic waste (e-waste) recycling activities have been reported at a number of locations. Among different e-waste recycling techniques, open burning of e-waste releases diverse metal(loid)s into the environment, which has aroused concern worldwide. In human health risk assessments (HHRAs), oral ingestion of soil can be a major route of exposure to many immobile soil contaminants. In vitro assays are currently being developed and validated to avoid overestimation of pollutants absorbed by the human body when calculating total pollutant concentrations in HHRAs. In this study, Cu, As, Cd, Sb, and Pb bioaccessibility in polluted soils (n = 10) from e-waste open burning sites at Agbogbloshie in Accra, Ghana, was assessed using an in vitro assay, the physiologically based extraction test. A bioaccessibility-corrected HHRA was then conducted to estimate the potential health risks to local inhabitants. The in vitro results (%) varied greatly among the different metal(loid)s (Cu: 1.3-60, As: 1.3-40, Cd: 4.2-67, Sb: 0.7-85, Pb: 4.1-57), and also showed marked variance between the gastric phase and small intestinal phase. The particle sizes of soil samples and chemical forms of metal(loid)s also influenced bioaccessibility values. Using these bioaccessibility values, both the hazard index and carcinogenic risk were calculated. The hazard index was above the threshold value (>1) for 5/10 samples, indicating a potential health risk to local inhabitants.

Antagonistic Interactions between Arsenic, Lead, and Cadmium in the Mouse Gastrointestinal Tract and Their Influences on Metal Relative Bioavailability in Contaminated Soils

Soils are often co-contaminated with As, Pb, and Cd. To what extent ingested metal(loid)s interact with each other in the gastrointestinal tract and influence their RBA (relative bioavailability) is largely unknown. Three soils predominantly contaminated with As (MS, mining/smelting impacted), Pb (WR, wire rope production impacted), and Cd (EP, enamel pottery production impacted) were administered to mice individually or in binary and tertiary combinations with sodium arsenate, Cd chloride, and/or Pb acetate. In binary combinations, ∼10-fold higher Pb addition decreased As-RBA in MS (26.0 ± 6.28% to 17.1 ± 1.08%), while ∼10-fold higher As addition decreased Pb-RBA in WR (61.3 ± 2.41% to 28.8 ± 5.45%). This was possibly due to the formation of insoluble Pb arsenate in mouse intestinal tract, as indicated by the formation of precipitates when As and Pb co-occurred in water or simulated human gastrointestinal fluids. Due to competition for shared absorption transporters, ∼10- and 100-fold higher Pb addition decreased Cd-RBA in EP (95.8 ± 12.9% to 67.8 ± 12.8% and 62.8 ± 8.24%). Tertiary combinations showed that interactions between two metal(loid)s were affected by the presence of the third metal(loid). Our study suggests that As oxyanion could interact with Pb or Cd ions in the mouse gastrointestinal tract, and the interactions vary depending on concentration and solution characteristics.

The association of tryptophan and phenylalanine are associated with arsenic-induced skin lesions in a Chinese population chronically exposed to arsenic via drinking water: a case-control study

OBJECTIVES

We investigated the association of specific serum amino acids (AAs) with the odds of arsenic-induced skin lesions (AISL) and their ability to distinguish patients with AISL from people chronically exposed to arsenic.

DESIGN

Case-control study.

SETTING

Three arsenic-exposed villages in Wuyuan County, Hetao Plain, Inner Mongolia, China were evaluated.

PARTICIPANTS

Among the 450 residents aged 18-79 years, who were chronically exposed to arsenic via drinking water, 56 were diagnosed as having AISL (defined as cases). Another 56 participants without AISL, matched by gender and age (±1 year) from the same population, were examined as controls.

MAIN OUTCOME MEASURES AND METHODS

AA levels were determined by ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry-based metabolomics analysis. Potential confounding variables were identified via a standardised questionnaire and clinical examination. Multivariable conditional logistic regression model and receiver operating characteristic curve analyses were performed to investigate the relationship between specific AAs and AISL.

RESULTS

Tryptophan and phenylalanine levels were negatively associated with AISL (p<0.05). Compared with that in the first quartile, the adjusted OR of AISL in the second, third and fourth quartiles were decreased by 44%, 88% and 79% for tryptophan and 30%, 80% and 80% for phenylalanine, respectively. The combination of these two higher-level AAs showed the lowest OR for AISL (OR=0.08; 95% CI 0.02 to 0.25; p<0.001). Furthermore, both AAs showed a moderate ability to distinguish patients with AISL from the control, with the area under the curve (AUC; 95% CI) as 0.67 (0.57 to 0.77) for tryptophan and 0.70 (0.60 to 0.80) for phenylalanine (p<0.05). The combined pattern with AUC (95% CI) was 0.72 (0.62 to 0.81), showing a sensitivity of 76.79% and specificity of 58.93% (p<0.001).

CONCLUSIONS

Specific AAs may be linked to AISL and play important roles in early AISL identification.

TRIAL REGISTRATION NUMBER

NCT02235948.

Oral Bioavailability of As, Pb, and Cd in Contaminated Soils, Dust, and Foods based on Animal Bioassays: A Review

Metal contamination in soil, dust, and food matrices impacts the health of millions of people worldwide. During the past decades, various animal bioassays have been developed to determine the relative bioavailability (RBA) of As, Pb, and Cd in contaminated soils, dust, and foods, which vary in operational approaches. This review discusses the strengths and weaknesses of different animal models (swine and mice), dosing schemes (single gavage dose, repeated gavage dose, daily repeated feeding, and free access to diet), and end points (blood, urine, and tissue) in metal-RBA measurement; compares metal-RBA obtained using mouse and swine bioassays, different dosing schemes, and different end points; and summarizes key findings on As-, Pb-, and Cd-RBA values in contaminated soils, dust, and foods. Future directions related to metal-RBA research are highlighted, including (1) comparison of metal-RBA determinations between different bioassays and different laboratories to ensure robust bioavailability data, (2) enhancing the metal-RBA database for contaminated dust and foods, (3) identification of physiological and physicochemical mechanisms responsible for variability in metal-RBA values, (4) formulation of strategies to decrease metal-RBA values in contaminated soils, dust, and foods, and (5) assessing the impacts of cocontaminants on metal-RBA measurement.

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.

Bioaccessibility estimates by gastric SBRC method to determine relationships to bioavailability of nickel in ultramafic soils

Frameworks for human health risk assessment often include the opportunity to correct the estimate of exposure for bioavailability, which could be predicted from bioaccessibility. Lead and As are the only metallic elements for which bioavailability and bioaccessibility have been correlated across a spectrum of mineralogy and particle types. The objective of the present study is to correlate in vivo bioavailability with ex vivo bioaccessibility for elevated Ni in soils of ultramafic origin and explore attribution of any variation in this correlation to mineralogical characterization of the Ni. Ultramafic soils were field collected in British Columbia, CA. Rietveld quantitative X-ray diffraction was used for the characterization and quantification of crystalline materials containing Ni. Bioaccessible Ni was determined using the in vitro method developed by the Solubility/Bioaccessibility Research Consortium. Bioavailable Ni was determined by gavage dose of the soils to Sprague-Dawley rats. Urine and feces were collected every 24 h. At the end of 72 h, the animals were humanely sacrificed using carbon dioxide as per the approved animal care protocol. All organs were harvested, washed and preserved. Fecal elimination of gavaged Ni ranged from 35 to 95% including positive control. Relative bioavailability (RBA) ranged from 5 to 18%. In vitro bioaccessibility (IVBA) of soil Ni ranged from 0 to 17%; IVBA explained 86% of the variation in RBA. Normalizing both axes to soil olivine accounted for an additional 10% of the variation in RBA. For risk assessment of Ni contaminated soils, IVBA would be a useful and cost effective tool in estimating exposure of mammals through ingestion of soil particles, with some additional benefit of considering Ni mineralogy.

Pollution characteristics, sources, and health risk assessment of human exposure to Cu, Zn, Cd and Pb pollution in urban street dust across China between 2009 and 2018

Since heavy metal pollution is widespread in street dust in China, the effects of heavy metals in street dust on human health cannot be ignored. However, studies estimating heavy metal pollution in street dust nationwide are limited. In this study, the concentrations of Cu, Zn, Cd and Pb in street dust at 3877sites throughout China were obtained from the published scientific literature. Based on these data, the contamination levels, spatial distributions, sources and potential health risks of heavy metals in street dust were comprehensively estimated. The results revealed that Cu, Zn, Cd and Pb levels are generally higher in the southeast provinces than in northwest China. In addition, traffic emissions and industrial activities are determined to be the two main sources of heavy metal pollution in street dust. The health risk assessment indicated that ingestion is the most important pathway of exposure to metal pollution in street dust for both children and adults, followed by dermal contact and inhalation. The spatial distribution of health risks suggested that the health risks are more serious in southeast China than in northwest China. The noncarcinogenic risks posed by Pb are relatively higher than those posed by the other three metals for both children and adults. Meanwhile, none of the hazard index (HI) values exceeded the safe level (1.0), with the exception of Pb in Daye city for children (HI = 1.074). The HI values for children were higher than those for adults. Therefore, children should be prioritized for protection from heavy metal pollution.

Oral bioaccessibility of metal(loid)s in dust materials from mining areas of northern Namibia

Ore mining and processing in semi-arid areas is responsible for the generation of metal(loid)-containing dust, which is easily transported by wind to the surrounding environment. To assess the human exposure to dust-derived metal(loid)s (As, Cd, Cu, Pb, Sb, Zn), as well as the potential risks related to incidental dust ingestion, we studied mine tailing dust (n = 8), slag dust (n = 5) and smelter dust (n = 4) from old mining and smelting sites in northern Namibia (Kombat, Berg Aukas, Tsumeb). In vitro bioaccessibility testing using extraction in simulated gastric fluid (SGF) was combined with determination of grain-size distributions, chemical and mineralogical characterizations and leaching tests conducted on original dust samples and separated PM₁₀ fractions. The bulk and bioaccessible concentrations of the metal(loid)s were ranked as follows: mine tailing dusts < slag dusts ≪ smelter dusts. Extremely high As and Pb bioaccessibilities in the smelter dusts were caused by the presence of highly soluble phases such as arsenolite (As₂O₃) and various metal-arsenates unstable under the acidic conditions of SGF. The exposure estimates calculated for an adult person of 70 kg at a dust ingestion rate of 50 mg/day indicated that As, Pb (and also Cd to a lesser extent) grossly exceeded tolerable daily intake limits for these contaminants in the case of slag and smelter dusts. The high risk for smelter dusts has been acknowledged, and the safety measures currently adopted by the smelter operator in Tsumeb are necessary to reduce the staff's exposure to contaminated dust. The exposure risk for the local population is only important at the unfenced disposal sites at Berg Aukas, where the PM₁₀ exhibited high levels of bioaccessible Pb.

Arsenic in Playground Soils from Kindergartens and Green Recreational Areas of Bratislava City (Slovakia): Occurrence and Gastric Bioaccessibility

In this study, playground soils of kindergartens and green recreational zones in Bratislava were investigated for the occurrence and gastric bioaccessibility of arsenic (As) in the < 150 μm soil size fraction. Eighty topsoil (0-10 cm) samples were collected from playgrounds in kindergartens and green recreational zones throughout the urban area. Bioaccessibility measurements of As were performed using the Simple Bioaccessibility Extraction Test that mimics the human gastric environment, and resulting extracts were analyzed by hydride generation-atomic absorption spectrometry to assess bioaccessible As concentrations in the collected playground soils. Single selective chemical extractions using hydroxylamine hydrochloride-hydrochloric acid and dithionite-citrate-bicarbonate solutions also were used to determine the amount of As associated with amorphous and amorphous/crystalline Fe oxy-hydroxides in soils, respectively. The results showed that the spatial distribution of total As concentrations was related to the historical development of the city, with higher soil concentrations of As found in the old city centre and related urban zones and the lower ones on the outskirts of Bratislava. There was a variation in the values of bioaccessible concentrations and fractions of As, with ranges from 0.40 to 5.60 mg/kg and 7.29 to 56.1%, respectively. Correlation and multivariable linear regression analyses revealed that bioaccessible concentrations of As were linearly related to its total concentrations in the soils, whereas dithionite-citrate-bicarbonate extractable Fe (Fe_DCB) was the main soil property, controlling the bioaccessibility of As. When the amount of Fe_DCB in the soils increased, As bioaccessibility decreased, confirming an importance of Fe bound to amorphous and crystalline iron oxy-hydroxides to the limitation of As bioaccessibility in urban playground soils of Bratislava. Additionally, single selective extractions showed that As concentrations extracted by hydroxylamine hydrochloride (As_HH) and dithionite-citrate-bicarbonate (As_DCB) were positively correlated with its bioaccessible concentrations (Spearman r = 0.75 and 0.62, respectively; p < 0.001).

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.

Mineralogical Controls on the Bioaccessibility of Arsenic in Fe(III)-As(V) Coprecipitates

X-ray amorphous Fe(III)-As(V) coprecipitates are common initial products of oxidative As- and Fe-bearing sulfide weathering, and often control As solubility in mine wastes or mining-impacted soils. The formation conditions of these solids may exert a major control on their mineralogical composition and, hence, As release in the gastric tract of humans after incidental ingestion of As-contaminated soil. Here, we synthesized a set of 35 Fe(III)-As(V) coprecipitates as a function of pH (1.5-8) and initial molar Fe/As ratio (0.8-8.0). The solids were characterized by synchrotron X-ray diffraction, FT-IR spectroscopy, and electrophoretic mobility measurements, and their As bioaccessibility (BA_As) was evaluated using the gastric-phase Solubility/Bioavailability Research Consortium in vitro assay (SBRC-G). The coprecipitates contained 1.01-4.51 mol kg^-1 As (molar Fe/As_solid: 1.00-8.29) and comprised varying proportions of X-ray amorphous hydrous ferric arsenates (HFA_am) and As(V)-adsorbed ferrihydrite. HFA_am was detected up to pH 6 and its fraction decreased with increasing pH and molar Fe/As ratio. Bioaccessible As ranged from 2.9 to 7.3% of total As (x̅ = 4.8%). The BA_As of coprecipitates formed at pH ≤ 4 was highest at formation pH 3 and 4 and controlled by the intrinsically high solubility of the HFA_am component, possibly enhanced by sorbed sulfate. In contrast, the BA_As of coprecipitates dominated by As(V)-adsorbed ferrihydrite was much lower and controlled by As readsorption and/or surface precipitation in the gastric fluid. Bioaccessible As increased up to 95% with increasing liquid-to-solid ratio, indicating an enhanced solubility of these solids due to interactions between Fe and the glycine buffer. We conclude (i) that natural Fe(III)-As(V) coprecipitates exhibit a particularly high solubility in the human gastric tract when formed at pH ∼ 3-4 in the presence of sulfate, and (ii) that the in vitro bioaccessibility of As in Fe(III)-As(V) coprecipitates as assessed by tbe SBRC-G assay depends critically on their solid-phase concentration in As-contaminated soil and mine-waste materials.

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.

Elemental concentrations and in vitro bioaccessibility in Canadian background soils

Elemental concentrations and bioaccessibility were determined in background soils collected in Canada as part of the North American Geochemical Landscapes Project. The concentrations of As, Cr, Cu, Co, Ni and Zn were higher in the C-horizon (parent material) compared to 0-5 cm (surface soil), and this observation along with the regional distribution suggested that most of the variability in concentrations of these elements were governed by the bedrock characteristics. Unlike the above-stated elements, Pb and Cd concentrations were higher in the surface layer reflecting the potential effects of anthropogenic deposition. Elemental bioaccessibility was variable decreasing in the order Cd > Pb > Cu > Zn > Ni > Co > As > Cr for the surface soils. With the exception of As, bioaccessibility was generally higher in the C-horizon soils compared to the 0-5 cm soils. The differences in metal bioaccessibility between the 0-5 cm and the C-horizon and among the provinces may reflect geological processes and speciation. The mean, median or 95th percentile bioaccessibility for As, Cr, Cu, Co, Ni and Pb were all below 100 %, suggesting that the use of site-specific bioaccessibility results for these elements will yield more accurate estimation of the risk associated with oral bioavailability for sites where soil ingestion is the major contributor of human health risk.

Using Delaunay triangulation and Voronoi tessellation to predict the toxicities of binary mixtures containing hormetic compound

Concentration addition (CA) was proposed as a reasonable default approach for the ecological risk assessment of chemical mixtures. However, CA cannot predict the toxicity of mixture at some effect zones if not all components have definite effective concentrations at the given effect, such as some compounds induce hormesis. In this paper, we developed a new method for the toxicity prediction of various types of binary mixtures, an interpolation method based on the Delaunay triangulation (DT) and Voronoi tessellation (VT) as well as the training set of direct equipartition ray design (EquRay) mixtures, simply IDV_equ. At first, the EquRay was employed to design the basic concentration compositions of five binary mixture rays. The toxic effects of single components and mixture rays at different times and various concentrations were determined by the time-dependent microplate toxicity analysis. Secondly, the concentration-toxicity data of the pure components and various mixture rays were acted as a training set. The DT triangles and VT polygons were constructed by various vertices of concentrations in the training set. The toxicities of unknown mixtures were predicted by the linear interpolation and natural neighbor interpolation of vertices. The IDV_equ successfully predicted the toxicities of various types of binary mixtures.

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.

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.

Predicting oral relative bioavailability of arsenic in soil from in vitro bioaccessibility

Several investigations have been conducted to develop in vitro bioaccessibility (IVBA) assays that reliably predict in vivo oral relative bioavailability (RBA) of arsenic (As). This study describes a meta-regression model relating soil As RBA and IVBA that is based upon data combined from previous investigations that examined the relationship between As IVBA and RBA when IVBA was determined using an extraction of soil in 0.4 M glycine at pH 1.5. Data used to develop the model included paired IVBA and RBA estimates for 83 soils from various types of sites such as mining, smelting, and pesticide or herbicide application. The following linear regression model accounted for 87% of the observed variance in RBA (R(2) = .87): RBA(%) = 0.79 × IVBA(%) + 3. This regression model is more robust than previously reported models because it includes a larger number of soil samples, and also accounts for variability in RBA and IVBA measurements made on samples collected from sites contaminated with different As sources and conducted in different labs that have utilized different experimental models for estimating RBA.

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.

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 (22.2-4172 mg kg(-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.

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

In this study, previously established arsenic (As) in vivo-in vitro correlations (IVIVC) were assessed for their validity using an independent data set comprising As relative bioavailability (RBA) and bioaccessibility values for 13 herbicide- and mine-impacted soils. The validation process established the correlation between As RBA (swine model) and bioaccessibility (five in vitro assays), determined whether correlations differed significantly from previous relationships and assessed model bias and error. The capacity of in vitro assays to predict As RBA was demonstrated by the strength of IVIVC; goodness of fit ranged from 0.53 (DIN-I) to 0.74 (UBM-I). When compared to previous IVIVC (Juhasz et al. Environ. Sci. Technol. 2009 , 43 , 9487 ; Juhasz et al. J. Hazard. Mater. 2011 , 197 , 161 ), there was no significant difference (P < 0.01) in the slope and y-intercept for IVG-G, UBM-G, and UBM-I indicating the consistency of these assays for predicting As RBA. However, variability in model bias and prediction error was observed with significantly lower (P < 0.01) error determined for IVG-G suggesting that As RBA predictions using IVG-G may be more robust compared to UBM-G and UBM-I. In contrast, differences in the slope and/or y-intercept were observed for SBRC-I, IVG-I, PBET-G, PBET-I, DIN-G, and DIN-I suggesting that these methodologies may not be suitable for predicting As RBA.