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

Marine microplastics enhance release of arsenic in coastal aquifer during seawater intrusion process

Microplastics (MPs), omnipresent contaminants in the ocean, could be carried by seawater intrusion into coastal aquifers, which might affect the fate of heavy metals existing in aquifers. Herein, we investigated the release behavior of arsenic (As) in coastal aquifers during MPs-containing seawater intrusion by applying laboratory experiment and numerical simulation. We found that seawater with marine MPs enhanced the release of As in aquifers, especially for dissolved As(V) and colloidal As. Negatively charged MPs competed with As(V) for the adsorption sites on iron (hydr)oxides in aquifers, resulting in the desorption of As(V). In addition, MPs could promote the release of Fe-rich colloids by imparting negative charge to its surface and providing it with sufficient repulsive force to detach from the matrix, thereby leading to the release of As associated with Fe-rich colloid. We also developed a modeling approach that well described the transport of As in coastal aquifer under the impact of MPs, which coupled variable density flow and kinetically controlled colloids transport with multicomponent reactive transport model. Our findings elucidated the enhancement of MPs on the release of As in aquifers during seawater intrusion, which provides new insights into the risk assessment of MPs in coastal zones.

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.

Enhanced Gastric/Lung Arsenic Bioaccessibility from Lignite Fly Ashes: Comparing Bioaccessibility Rates with Multiple Environmental Matrices

Inorganic arsenic (As), a carcinogenic element to humans, is among the most dangerous and flammable substances that coal-burning plants could release. When coal is burned, large portions of arsenic are captured on fly-ash (FA) particles, but it could also contribute significantly to stack emissions of fine fly-ash particles. The aim of this study was to evaluate the oral and respiratory bioaccessibility of arsenic in lignite fly-ash (LFA) samples, and their contribution to total As exposure. Arsenic bioaccessibility fractions via ingestion and inhalation showed significant differences, suggesting the presence of highly soluble As-bearing phases in the studied LFA samples. The bioaccessible As fractions (BAF%) in the simulated gastric fluids (UBM protocol, ISO 17924:2018) showed a range of 45-73%, while the pulmonary bioaccessibility rates in the simulated lung fluid (artificial lung fluid (ALF)) exhibited significantly enhanced levels ranging from 86% to 95%. The obtained arsenic bioaccessibility rates were compared with previous data for multiple environmental matrices such as soil and dust-related materials, revealing that LFA exhibited significantly higher bioaccessibility (%) for the inhalation pathway.

Transport and transformation of arsenic in coastal aquifer at the scenario of seawater intrusion followed by managed aquifer recharge

Release of contaminants from aquifers at the coastal area is of increasing concern, but remains unclear due to the complex groundwater dynamics and hydrochemistry. Specifically, frequently occurring seawater intrusion and the subsequent engineering measures of managed aquifer recharge (MAR) could alter the groundwater regime, which might affect the fate and behaviors of contaminants. In this work, we investigated the transport and transformation of arsenic (As) in the coastal aquifer at the scenario of seawater intrusion followed by the injection-based MAR process. Results showed that seawater intrusion induced 10.3% more release of aqueous As in aquifers, which was attributed to the competitive desorption as a result of elevated anion concentration and pH, and the reduction of As(V) to As(III) due to the reduced redox potential and enriched As-reducing bacteria. Furthermore, seawater intrusion inhibited the recrystallization of iron (hydr)oxides and instead facilitated its conversion to iron sulfide with lower affinity to As. The subsequent MAR introduced oxygenated recharge water into aquifers and increased the redox potential, leading to the dissolution of iron sulfide followed by formation of amorphous iron (hydr)oxides. However, the competitive desorption of As with rich HCO₃^- under increased pH dominated continuous increase in the aquifer aqueous As during MAR process. A constructed numerical model for describing As transport based on the experimental data showed that As transported along the interface between seawater and freshwater, and MAR enhanced the release of As and expanded the spread range of As. Our findings reveal that both seawater intrusion and subsequent MAR could cause the release, transport, and transformation of As, which provides new insight on the understanding of geochemical process of As in coastal aquifers.

Effect of soil particle size and extraction method on the oral bioaccessibility of arsenic

Recent findings indicate that incidental ingestion of soil by humans primarily involves soil particles <150 µm, rather than <250 µm-sized fraction previously used for most oral bioaccessibility and bioavailability studies. It was postulated that a greater soil surface area in the finer fraction (<150 versus <250 µm) might increase oral bioaccessibility of arsenic (As) in soil. Bioaccessibility and concentrations of As were compared in <150 and <250 µm fractions of 18 soil samples from a variety of arsenic-contaminated sites. The two methods used to measure bioaccessibility were compared - EPA Method 1340 and the California Arsenic Bioaccessibility (CAB) method. Arsenic concentrations were nearly the same or higher in the <150 fraction compared with <250 µm. EPA Method 1340 and the CAB method presented significantly different bioaccessibility results, as well as estimated relative oral bioavailability (RBA) based upon algorithms specific to the methods, but there was no marked difference for <150 and <250 µm soil fractions within either method. When compared with RBA determined previously for these soil samples in vivo in non-human primates, EPA Method 1340 was generally more predictive than the CAB method. Data suggest that soil- or site-specific factors control bioaccessibility under either method and that the test method selected is more important than the particle size fraction (<150 or <250) in using these in vitro methods to predict As RBA for use in risk assessment.

Synergistic Impacts of Arsenic and Antimony Co-contamination on Diazotrophic Communities

Nitrogen (N) shortage poses a great challenge to the implementation of in situ bioremediation practices in mining-contaminated sites. Diazotrophs can fix atmospheric N₂ into a bioavailable form to plants and microorganisms inhabiting adverse habitats. Increasing numbers of studies mainly focused on the diazotrophic communities in the agroecosystems, while those communities in mining areas are still not well understood. This study compared the variations of diazotrophic communities in composition and interactions in the mining areas with different extents of arsenic (As) and antimony (Sb) contamination. As and Sb co-contamination increased alpha diversities and the abundance of nifH encoding the dinitrogenase reductase, while inhibited the diazotrophic interactions and substantially changed the composition of communities. Based on the multiple lines of evidence (e.g., the enrichment analysis of diazotrophs, microbe-microbe network, and random forest regression), six diazotrophs (e.g., Sinorhizobium, Dechloromonas, Trichormus, Herbaspirillum, Desmonostoc, and Klebsiella) were identified as keystone taxa. Environment-microbe network and random forest prediction demonstrated that these keystone taxa were highly correlated with the As and Sb contamination fractions. All these results imply that the above-mentioned diazotrophs may be resistant to metal(loid)s.

Can acid sulfate soils from the southern Baltic zone be a source of potentially toxic elements (PTEs)?

The mobility of Cr, Cu, Ni, Pb, and Zn in acid sulfate (AS) soils in the reverse delta of the Świna River, NE Poland was studied using extraction of the target metals using the BCR protocol, which targets acid-extractable (F1), reducible (F2), oxidizable (F3) fractions, and aqua regia digestion for residual (F4) fraction. It was assumed that the content of mobile forms determined in air-dried samples during consequent steps of BCR extraction refers to two scenarios of possible release of selected metals from the studied soils: (1) attributed to seasonal soil moisture variation or (2) caused by artificial drainage. The studied AS soils had thin organic layers (muck, peat and mud) overlaying deltaic sands, and contained hypersulfidic material. The field pH was 6.2 ± 0.5 and significantly decreased to 4.3 ± 1.4 after the 8-weeks incubation period. This can be explained by low buffering properties (e.g. lack of carbonates). Total concentrations of metals (Cr 17.9-61.6, Cu 5.7-27.7, Ni 6.2-47.0, Pb 2.2-17.7, and Zn 13.6-130 mg∙kg^-1) in the AS soils were diversified but none of the concentrations exceeded the Polish legal limits. Despite the relative low content of analyzed metals, the studied soils can be a potential source of metal contamination affecting the coastal environment in the southern Baltic Sea region that has been overlooked so far. This is confirmed by the high proportion (44-82%) of Cr, Cu, Ni, and Zn in the F1-F3 fractions which can potentially be released as assumed in two scenarios. The BCR protocol seems to be a useful tool for understanding the chemical behavior and fate of metals in AS soils. Challenges in the assessment of metal mobility in the oxidized and unoxidized zones of individual soil profiles occurred due to their complex morphology resulting from the heterogeneous depositional environment under the human impact.

Elucidating of potentially toxic elements contamination in topsoils around a copper smelter: Spatial distribution, partitioning and risk estimation

Soil pollution by potentially toxic elements (PTEs) as one of the major environmental hazards is associated with metal exploration and refining acting. In this study, forty-five topsoil samples surrounding a copper smelter factory were taken and analysed using standard routine methods. The total concentration, chemical fractionation and the mobility potential of As, Cd, Cr, Cu, Pb and Zn were analysed. Additionally, the spatial distribution of PTEs, the potential ecotoxicological, and human health risks was assessed. The range of total Cu was 1478-4718 mg kg^-1, reaching up to 501.5, 21.6, 118.4, 573.5 and 943.3 mg kg^-1 for total contents of As, Cd, Cr, Pb and Zn, respectively. The potentially available fractions after sequential extraction reveal all studied PTE were dramatically mobile and available in the studied area (86%, 69.3%, 59.5%, 87.2%, 84% and 68% for As, Cd, Cr, Pb, Zn and Cu, respectively), reflecting that the concentration and accumulation of these elements are profoundly affected or originated by smelting activities and deposition of atmospheric emissions of the Cu smelting factory. The spatial distribution of all PTEs indicated that concentrations of these element near the smelter Cu-factory were elevated. Accordingly, the ecotoxicology status of the studied area suggests that significantly high risks are posed by the measured PTEs. Non-carcinogenic effects of As, Pb and Cu were significantly much higher than the recommended value (HI = 1), suggesting that these three PTEs could adversely impact children's health. For adults, only the HI value of As was greater than one.

An integrated approach combining magnetic, geochemical and particle-based techniques to assess metal(loid) loadings in urban venues frequented by children

Urban venues frequented by children, such as playgrounds, are potentially important sources of exposure to anthropogenic metal(loids). Environmental quality of outdoor playgrounds is mainly assessed through direct geochemical monitoring, which is time-consuming and expensive. In this study we adapted a multidisciplinary approach combining magnetic measurements, geochemical analyses, particle-based techniques and bioaccessibility data so as to evaluate the applicability of magnetic methods as a low-cost and easy-to-use technology to monitor pollution level in public playgrounds. Playground sands were collected and their magnetic characteristics were studied in detail aiming to gain helpful additional details in relation to the type, concentration and particle-size distribution of the sand-bound magnetic particles. The obtained χ_lf values indicated an enhanced level of sand-bound magnetic components, while the dominant control of SSD grains on the magnetic load of playground-PG sands was revealed. Hysteresis parameters and thermomagnetic curves indicated low-coercivity ferrimagnetic minerals, such as magnetite and/or maghemite, as the predominant magnetic carriers. Ratios of χ_ARM/χ_lf and χ_ARM/SIRM indicated the dominance of coarser anthropogenic magnetic grains in the sampled PG sands compared to other recreational areas. Correlation analysis among magnetic variables and reported metal(loid) contents designated χ_ARM as a more effective indicator for the detection of anthropogenic load in PG sand samples than χ_lf or SIRM. Simultaneously, through geochemical analyses in magnetic extracts separated from PG sands, metal(loid) contents were notably enriched in the magnetic fraction validating their strong affinity with sand-bound magnetic particles. Finally, bioaccessibility tests revealed lower UBM-extracted fractions for the magnetic extracts of PG sands compared to bulk samples. However, arsenic (As) was more bioaccessible in the sand-bound magnetic particles raising serious concerns for the children exposed to playground sands.

Role of climate and geography in arsenic mobility and risk at an artisanal mining site in an urbanized semi-arid environment

Ultra-enriched arsenic (As) concentrations >30% occur at an abandoned artisanal mine in an urban park in San Diego, California, presenting a complex risk to the public. This study uses geochemistry in consideration with climate and geography to evaluate As transport away from the mine. Sediment As concentrations reach 2320 mg/kg (483 times background crustal concentrations; n = 73) along drainage pathways and sequential extraction experiments indicate As overwhelmingly partitions into the least mobile phase (mean 83% As in residual fraction; n = 30); there is little redistribution of As from primary minerals into secondary or dissolved phases - a potentially positive outcome for managing the risk - despite the sediments being exposed to a century of weathering. Dissolved As transport does occur, with intermittent rain events producing As up to 272 μg/L in runoff. Both sediment and water As decrease to background concentrations within 1,000 m of the mines, influenced by the encroaching urbanization, and the semi-arid climate which limits weathering and transport. Similar patterns of As migration downgradient of abandoned mines occur at other mining sites in arid and semi-arid regions; however, off-site As transport at other sites extends far greater distances. This study indicates that a combination of geochemistry, geomorphology, climate, and urbanization can work together to retard the surface transport of As from artisanal and un-remediated mine sites; and helps inform environmental management at this site and others like it.

Tracking changes in rhodium nanoparticles in the environment, including their mobility and bioavailability in soil

The goals of the undertaken studies included assessment of the mobility of Rh nanoparticles (Rh NPs) and ionic forms (Rh(III)) in soil, optimization of the digestion procedure of environmental samples containing Rh NPs, and comparison of Rh NPs and Rh(III) uptake and bioaccumulation by hydroponically cultivated plants. Mass spectrometry with inductively coupled plasma (ICP MS) was used to determine the total content of Rh in solutions obtained after the processes of digestion and extraction. Transmission Electron Microscopy (TEM) supported the investigation of Rh NPs decomposition and proved the presence of uptaken nano forms in plant tissues. Adsorptive stripping voltammetry (AdSV) allowed to distinguish ionic and metallic forms of Rh, based on the fact that Rh NPs are electrochemically inactive. A two-step digestion procedure with H₂SO₄ and HNO₃ was proposed for efficient decomposition of Rh NPs. Based on single extractions with selected extractants, it was found that independently of its chemical form Rh is substantially immobilized in soil. The mobility of Rh(III) and Rh NPs was below 38% and 0.02%, and the accumulation factor in leaves equaled 0.2 and 4.4, respectively.

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.

Pollution evaluation and children's multimedia exposure of atmospheric arsenic deposition in the Pearl River Delta, China

The populous Pearl River Delta (PRD) region in China suffers from serious air arsenic (As) pollution. The objective of this study was to explore the pollution situation of atmospheric arsenic deposition in the PRD region, and to evaluate the associated multimedia daily intake in children. The average deposition flux was 3921.7 μg/m²/year during the 2016-2017, and the pollution situation was even worse than that in 2015. A continuously increasing trend of arsenic atmospheric deposition was found. The bioaccessibility of As in the settled dust was determined as about 22% by a physiologically based extraction test (PBET). After corrected with the bioaccessibilities of As in the settled dust and food items, the geometry means (GM) value of daily uptake through multimedia ingestion of produce (dust and diet) originated from arsenic atmospheric deposition was 0.23 μg/kg/day for 1- to 6-year-old children. The contribution of the non-dietary oral exposure (settled dust) was negligible and just accounted for only 0.01% of the daily uptake. This estimated value was much lower than those in the literatures, in which the bioaccessibility of As was not taken into account, concluding that the role of the settled dust in the total daily intake may have been overestimated previously. Milk, eggs and freshwater fish were the dominant pathways for children to intake the products derived from atmospheric arsenic deposition. There still be a concern about the high non-carcinogenic and carcinogenic risk by long-term multimedia ingestion. Special care should be considered toward the emission sources of air arsenic, including the coal combustion from industries and construction dust, etc., to reduce the negative effect of air arsenic in children.

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.

In vitro model insights into the role of human gut microbiota on arsenic bioaccessibility and its speciation in soils

The bioaccessibility of arsenic and its speciation are two important factors in assessing human health risks exposure to contaminated soils. However, the effects of human gut microbiota on arsenic bioaccessibility and its speciation are not well characterized. In this study, an improved in vitro model was utilized to investigate the bioaccessibility of arsenic in the digestive tract and the role of human gut microbiota in the regulation of arsenic speciation. For all soils, arsenic bioaccessibility from the combined in vitro model showed that it was <40% in the gastric, small intestinal and colon phases. This finding demonstrated that the common bioaccessibility approach assuming 100% bioaccessibility would overestimate the human health risks posed by contaminated soils. Further to this, the study showed that arsenic bioaccessibility was 22% higher in the active colon phase than that in the sterile colon phase indicating that human colon microorganisms could induce arsenic release from the solid phase. Only inorganic arsenic was detected in the gastric and small intestinal phases, with arsenate [As(V)] being the dominant arsenic species (74%-87% of total arsenic). Arsenic speciation was significantly altered by the active colon microbiota, which resulted in the formation of methylated arsenic species, including monomethylarsonic acid [MMA(V)] and dimethylarsinic acid [DMA(V)] with low toxicity, and a highly toxic arsenic species monomethylarsonous acid [MMA(III)]. Additionally, a high level of monomethylmonothioarsonic acid [MMMTA(V)] (up to 17% of total arsenic in the extraction solution) with unknown toxicological properties was also detected in the active colon phase. The formation of various organic arsenic species demonstrated that human colon microorganisms could actively metabolize inorganic arsenic into methylated arsenicals and methylated thioarsenicals. Such transformation should be considered when assessing the human health risks associated with oral exposure to soil.

Innovative isotopic method to evaluate bioaccumulation of As and MTEs in Vitis vinifera

The transfer of metal and metalloid trace elements (MTEs) from contaminated soil to grapevines is a major issue for grape consumption and for the associated health risks. Based on an isotopic approach, we shed light on the concept of MTE bioavailability. The bioavailable fractions are identified by using the Sr-isotope ratio as a proxy for MTEs. This allows us to differentiate three soil reservoirs: the 'current available fraction' in soil water, the 'reserve available fraction' stored in mineral phases of the soil fractions, and the 'non-available fraction'. The reserve available fraction, representing 10 to 60% of bulk soil depending on the MTE, includes the exchangeable, carbonates, humic substance and oxides fractions. The ⁸⁷Sr/⁸⁶Sr isotopic signatures of grape berries and vine leaves show an additional source of MTEs, which is imported by foliar uptake and can contribute up to 10% of the MTEs in leaves. In addition, root-uptake and translocation rates show high accumulation rates of Co, Sn and Cu, and low ones for As, Sb, Zn and Cd. A daily intake between 1 and 3 kg of (dry grapes) would reach the benchmark dose level for a 0.5% (BMDL_0.5). While such a daily intake of grapes is unreasonable, consumption of other local vegetables and fruit would contribute to the daily intake. Hence, a chronic arsenic exposure is of great concern for human health in mining areas. We outline the importance of geochemical tracers, such as Sr isotopes, when determining the transfer and translocation of MTEs in plants. Our method presents a high-precision evaluation of the bioavailability and bioaccumulation of MTEs, and a better understanding of these processes in plants, thus leading to a better assessment of the environmental risk on human health.

Linking oral bioaccessibility and solid phase distribution of potentially toxic elements in extractive waste and soil from an abandoned mine site: Case study in Campello Monti, NW Italy

Oral bioaccessibility and solid phase distribution of potentially toxic elements (PTE) from extractive waste streams were investigated to assess the potential human health risk posed by abandoned mines. The solid phase distribution along with micro-X-ray fluorescence (micro-XRF) and scanning electron microscopy (SEM) analysis were also performed. The results showed that the total concentrations of PTE were higher in <250 μm size fractions of waste rock and soil samples in comparison to the <2 mm size fractions. Mean value of total concentrations of chromium(Cr), copper (Cu), and nickel (Ni) in waste rocks (size fractions <250 μm) were found to be 1299, 1570, and 4010 mg/kg respectively due to the parent material. However, only 11% of Ni in this sample was orally bioaccessible. Detailed analysis of the oral bioaccessible fraction (BAF, reported as the ratio of highest bioaccessible concentration compared with the total concentration from the 250 μm fraction) across all samples showed that Cr, Cu, and Ni varied from 1 to 6%, 14 to 47%, and 5 to 21%, respectively. The variation can be attributed to the difference in pH, organic matter content and mineralogical composition of the samples. Non-specific sequential extraction showed that the non-mobile forms of PTE were associated with the clay and Fe oxide components of the environmental matrices. The present study demonstrates how oral bioaccessibility, solid phase distribution and mineralogical analysis can provide insights into the distribution, fate and behaviour of PTE in waste streams from abandoned mine sites and inform human health risk posed by such sites .

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).

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.

Fate of arsenic before and after chemical-enhanced washing of an arsenic-containing soil in Hong Kong

This study evaluated the feasibility of 2-h chemical-enhanced washing of As-containing soil resulting from geogenic sources in Hong Kong and the fate of As before and after remediation. The soil morphology and As speciation in soil was elucidated by scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Integrated analysis of the results suggests that the As (>90%) resides predominantly as arsenate bound to ferric iron oxides, with a minor contribution (<10%) from an As^III-sulphide phase. This accounts for the marginal leachability, mobility, and bioaccessibility of geogenic As in the untreated soil despite its high concentration. Among the five types of reagents (organic ligands, reductants, alkaline solvents, inorganic acids, and chelants), only dithionite-citrate-bicarbonate method and alkaline solvents (NaOH and Na₂CO₃) extracted 37-78% and 26-42% of the As by mineral dissolution. However, these extraction methods notably increased the leachability, mobility, and bioaccessibility of remaining As after soil washing, suggesting that a significant proportion of newly released As is prone to re-adsorption onto the soil surface and becomes highly mobile and bioaccessible. While inorganic acids and chelating agents had marginal effects on the fate of remaining As, organic ligands (citrate, oxalate, or pyrophosphate) probably destabilized the bonding of geogenic As and increased its mobility/bioaccessibility despite marginal extraction. The applicability of chemical extraction of geogenic As is questionable regardless of chemical agents, thus proper management of the As-containing soil by containment or physical encapsulation may be considered before land development.

Mitigating potential of Melissa officinale against As3+-induced cytotoxicity and transcriptional alterations of Hsp70 and Hsp27 in fish, Channa punctatus (Bloch)

The mitigating potential of Melissa officinale (MO) (Lamiaceae) against arsenite (As³⁺)-induced oxidative stress, cytogenotoxicity, and expression of stress genes in fish, Channa punctatus (Bloch), teleost, was explored. After confirming the composition of MO extract, caffeic acid (0.96%), hesperidin (1.73%), naringenin (7.70%), lutenolin (3.29%), kaempferol (11.46%) and hesperetin (6.24%), by HPLC-PDA analysis, the experiment was set up in six groups (G1-G6), each containing 10 specimens. Blood, muscle, gills and liver tissues of control and treated fishes were excised at an interval of 24 till 96 h. Ameliorative potential of MO was confirmed by satisfactory restoration of altered activities of malondialdehyde, hydrogen peroxide, superoxide dismutase, catalase, glutathione peroxidise, glutathione reductase, reduced glutathione and ascorbate peroxidase in G4, G5 and G6, co-exposed with 96 h-LC₅₀/10 As³⁺ with MO. A significant (p < 0.05) recovery in the frequencies of cytogenotoxic markers, micronuclei, disintegrated nucleus and echinocytes, which were expressed significantly (p < 0.05) in G3 exposed to sub-lethal concentration of ATO alone, was recorded in fish groups (G4, G5 and G6) together treated with 96 h-LC₅₀/10 of ATO and 2, 4 and 8 ppm of MO, respectively. Moreover, the expression of Hsp70 gene was downregulated (2.29-fold); whereas, Hsp27 gene was upregulated (1.16-fold) in G6, the group co-exposed with 96 h-LC₅₀/10 As³⁺ with 8 ppm of MO in comparison with G3 (3.11-fold for Hsp70; 0.51-fold for Hsp27) after 96 h of exposure period. Thus, it can be inferred that the MO at its tested concentration can be effectively used to mitigate As³⁺ generated toxicities in C. punctatus.

Importance of chemical binding type between As and iron-oxide on bioaccessibility in soil: Test with synthesized two line ferrihydrite

Bioaccessible concentrations of As associated with Fe oxide as different chemical binding types were determined in soils using the in vitro Physiologically Based Extraction Test (PBET). When compared to the five-step sequential extraction data, most of the As extracted by in vitro PBET originated from the amorphous Fe oxide-bound fraction, and more importantly, the bioaccessibility of As ranged from 0 to 58.8% in 24 soil samples. Two batches of ferrihydrite were synthesized separately. For one batch, As was adsorbed onto the ferrihydrite after synthesis; for the other one, As was added while synthesizing ferrihydrite to co-precipitate. The bioaccessible concentration of As determined by in vitro PBET of the former was 415mg of As/kg of ferrihydrite and that of the latter was 67mg of As/kg of ferrihydrite. X-ray photoelectron spectra (XPS) analysis indicated that As-O-Fe bonds were evident in As-associated ferrihydrite sample and especially, As was found within the Fe oxide lattice in the co-precipitated sample. Our data suggest that binding type between As and Fe oxide should be considered when determining the bioaccessibility of As in soil, which, in turn, greatly influences the realistic risk of As present in soil.

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

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