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

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

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

Bioaccessibility of lead and cadmium in soils around typical lead-acid power plants and their effect on gut microorganisms

Potentially toxic elements (Pb and Cd) contamination of soil can adversely affect human health. Moreover, these metal ions interact with the gut microbiota after entering the human digestive system. Based on the physiologically based extraction test and the simulator of human intestinal microbial ecosystem, the bioaccessibility of Pb and Cd in soils contaminated with lead-acid power plants was assessed. The gastric stage exhibited the greatest average bioaccessibility of lead and cadmium (63.39% and 57.22%), followed by the small intestinal stage (6.86% and 36.29%); due to gut microorganisms, the bioaccessibility of lead and cadmium was further reduced in the colon stage (1.86% and 4.22%). Furthermore, to investigate soil contamination's effects on gut microbes, 16S rRNA high-throughput sequencing was used to identify the gut microbial species after the colon period. Due to Pb and Cd exposure, the relative abundance of Firmicutes and unidentified_Bacteria decreased, while the relative abundance of Proteobacteria, Synergistota, and Bacteroidota increased. The relationship between environmental factors and the number of microbial species in the gut was also examined using Spearman correlation analysis. Pb and Cd exposure has been found to affect the composition and structure of the gut microbiota.

Effects of Intestinal Microbiota on the Biological Transformation of Arsenic in Zebrafish: Contribution and Mechanism

Both the gut microbiome and their host participate in arsenic (As) biotransformation, while their exact roles and mechanisms in vivo remain unclear and unquantified. In this study, as3mt-/- zebrafish were treated with tetracycline (TET, 100 mg/L) and arsenite (iAsIII) exposure for 30 days and treated with probiotic Lactobacillus rhamnosus GG (LGG, 1 × 108 cfu/g) and iAsIII exposure for 15 days, respectively. Structural equation modeling analysis revealed that the contribution rates of the intestinal microbiome to the total arsenic (tAs) and inorganic As (iAs) metabolism approached 44.0 and 18.4%, respectively. Compared with wild-type, in as3mt-/- zebrafish, microbial richness and structure were more significantly correlated with tAs and iAs, and more differential microbes and microbial metabolic pathways significantly correlated with arsenic metabolites (P < 0.05). LGG supplement influenced the microbial communities, significantly up-regulated the expressions of genes related to As biotransformation (gss and gst) in the liver, down-regulated the expressions of oxidative stress genes (sod1, sod2, and cat) in the intestine, and increased arsenobetaine concentration (P < 0.05). Therefore, gut microbiome promotes As transformation and relieves As accumulation, playing more active roles under iAs stress when the host lacks key arsenic detoxification enzymes. LGG can promote As biotransformation and relieve oxidative stress under As exposure.

Study on arsenic speciation, bioaccessibility, and gut microbiota in realgar-containing medicines by DGT technique and artificial gastrointestinal extraction (PBET) combine with simulated human intestinal microbial ecosystem (SHIME)

It is well-known that several Chinese patent medicines use realgar as a specific component. People are more aware of the health dangers associated with realgar since it includes arsenic. Previous research overstated the arsenic toxicity of realgar-containing Chinese prescription medications because little thought was given to the influence of arsenic bioaccessibility by gut microbiota. In light of this, this study examined the total content, bioaccessibility and speciation of targeted medications while also examining intestinal epithelial transit utilizing the diffusive gradients in thin-films (DGT). All samples contained arsenic, and the bioaccessibilities of the colon, intestine and gastric regions ranged from 0.19% to 1.73%, 0.25-1.88% and 0.21-1.70% respectively. The range of DGT-bioaccessibility is 0.01-0.0018%. Three steps of analysis were conducted on inorganic As(III) and As(V). In health risk assessment, the ADDs and HQs of DGT-bioaccessibility were below the threshold levels when compared to computing average daily intake dose (ADD) and hazard quotient (HQ) by bioaccessibility of gastric, intestinal and colon. Additionally, Proteobacteria and Firmicutes were discovered to be the two predominant kinds of gut microbes in this study. Under arsenic exposure, the abundance of Christensenellaceae, Desulfovibrionaceae and Akkermansiaceae increased, but the quantity of Rikenellaceae decreased. These findings revealed that alterations in gut microbiota had an impact on host metabolism.

Bioaccessibility assessment of arsenic and cadmium in polished and unpolished rice: Comparison of three in vitro methods

INFOGEST is a standardized in vitro digestion method suitable for foods, but rarely used to study the bioaccessibility of heavy metals in food. This study aimed to explore the differences between INFOGEST and the extensively used Physiologically Based Extraction Test (PBET) and Unified Bioaccessibility Research Group of Europe Method (UBM) methods for determining the bioaccessibility of As and Cd in rice. Intestinal As (79.3 ± 8.5 %, 75.8 ± 12.7 %, and 72.3 ± 12.2 % for INFOGEST, PBET, and UBM, respectively) and Cd (47.0 ± 6.4 %, 40.7 ± 13.8 %, and 38.1 ± 15.7 % for INFOGEST, PBET, and UBM, respectively) bioaccessibilities in the rice samples determined by the three methods were generally similar (p > 0.1, except for As bioaccessibility between INFOGEST and UBM). Furthermore, PBET was significantly correlated with INFOGEST for As bioaccessibility (R2 = 0.416) and with UBM for Cd bioaccessibility (R2 = 0.879). Additionally, PBET indicated that the bioaccessibilities of As and Cd in the polished rice were 17.0 % and 19.8 % higher, respectively, than that in the unpolished rice. This study highlights the influence of in vitro methods and rice matrices on heavy metal bioaccessibility values, necessitating a more accurate assessment of health risks associated with rice consumption.

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

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

Heavy metal(loid)s in agricultural soil from main grain production regions of China: Bioaccessibility and health risks to humans

Unintentional ingestion of metal-contaminated soils may pose a great threat to human health. To accurately evaluate the health risks of heavy metal(loid)s in soils, their bioaccessibility has been widely determined by in vitro assays and increasingly employed to optimize the assessment parameters. Given that, using meta-analysis, we analyzed the literature on farmland heavy metal(loid)s (As, Cd, Cr, Cu, Hg, Pb, Ni, and Zn) in Chinese main grain production regions, and collected their total and bioaccessibility data to accurately assess their human health risks. Monte Carlo simulation was used to reduce the uncertainty in metal concentration, intake rate, toxicity coefficient, and body weight. We found that the mean concentration (0.47 mg/kg) and geological accumulation index (I_geo, 0-5.24) of Cd were the priority position of controlling metals. Moreover, children are more vulnerable to carcinogenic risks than adults. Soil mineralogy, physicochemical properties, Fe, and the types of in vitro assays are the influencing factors of bioaccessibility discrepancy. Furthermore, appropriate bioaccessibility determination methods can be adapted according to the differences in ecological receptors for the risk assessment, like developing a "personalized assessment" scheme for polluted farmland soil management. Collectively, bioaccessibility-based models may provide an accurate and effective approach to human health risk assessment.

The fecal arsenic excretion, tissue arsenic accumulation, and metabolomics analysis in sub-chronic arsenic-exposed mice after in situ arsenic-induced fecal microbiota transplantation

Arsenic can be specifically enriched by rice, and the health hazards caused by high arsenic rice are gradually attracting attention. This study aimed to explore the potential of microbial detoxification via gut microbiome in the treatment of sub-chronic arsenic poisoning. We first exposed mice to high-dose arsenic feed (30 mg/kg, rice arsenic composition) for 60 days to promote arsenic-induced microbes in situ in the gastrointestinal tract, then transplanted their fecal microbiota (FMT) into another batch of healthy recipient mice, and dynamically monitored the microbial colonization by 16S rRNA sequencing and ITS sequencing. The results showed that in situ arsenic-induced fecal microbiome can stably colonized and interact with indigenous microbes in the recipient mice in two weeks, and established a more stable network of gut microbiome. Then, the recipient mice continued to receive high-dose arsenic exposure for 52 days. After above sub-chronic arsenic exposure, compared with the non-FMT group, fecal arsenic excretion, liver and plasma arsenic accumulation were significantly lower (P < 0.05), and that in kidney, hair, and thighbone present no significant differences. Metabolomics of feces- plasma-brain axis were also disturbed, some up-regulated metabolites in feces, plasma, and cerebral cortex may play positive roles for the host. Therefore, microbial detoxification has potential in the treatment of sub-chronic arsenic poisoning. However, gut flora is an extremely complex community with different microorganisms have different arsenic metabolizing abilities, and various microbial metabolites. Coupled with the matrix effects, these factors will have various effects on the efflux and accumulation of arsenic. The definite effects (detoxification or non-detoxification) could be not assured based on the current study, and more systematic and rigorous studies are needed in the future.

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

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

Assessment of intestinal injury of hexavalent chromium using a modified in vitro gastrointestinal digestion model

Intestinal injury assessment of hexavalent chromium (Cr-VI) in humans is crucial for quantifying assessment of adverse health risk posed by the intake of Cr (VI)-contaminated water. To overcome the deficiency in simulating human gastric reduction and intestinal absorption, we modified the constituents of simulated gastric fluid in in vitro digestion method by adding reductants glutathione (18 μM) and ascorbic acid (180 μM), which incorporated with human intestinal epithelial model to construct an in vitro gastrointestinal digestion (IVGD) model for intestinal injury assessment. Cr-VI bioaccessibility results from IVGD model showed that weak gastric acidity significantly increased the intestinal accessible Cr-VI dose by 22.41-38.43 folds. The time-course intestinal absorption indicated prolongation of intestinal exposure destroyed the intestinal epithelium, and 24 h after Cr-VI treatment was a good time point to perform intestinal absorption and toxicity assessment. A series of cell-based bioassays provided initial warning of adverse effect, suggesting that epithelial integrity exhibited greatest sensitivity to Cr-VI exposure and might be used as a sensitive marker for the toxicity assessment of oral exposure to Cr-VI. Notably, this study provides a feasible strategy for delineation of Cr-VI biotransformation and intestinal injury following ingestion exposure, which contributes to address the toxicity data gap of low-dose exposure in humans and puts forward a reference for intestinal toxicity assessment of other chemicals.

The Need to Unravel Arsenolipid Transformations in Humans

The main source of arsenic exposure to humans worldwide is the diet, in particular, drinking water, rice, and seafood. Although arsenic is often considered toxic, it can exist in food as more than 300 chemical species with different toxicities. This diversity makes it difficult for food safety and health authorities to regulate arsenic levels in food, which are currently based on a few arsenic species. Of particular interest are arsenolipids, a type of arsenic species widely found in seafood. Emerging evidence indicates that there are risks associated with human exposure to arsenolipids (e.g., accumulation in breast milk, ability to cross the blood-brain barrier and accumulate in the brain, and potential development of neurodegenerative disorders). Still, more research is needed to fully understand the impact of arsenolipid exposure, which requires establishing interdisciplinary collaborations.

Improving the predictive value of bioaccessibility assays and their use to provide mechanistic insights into bioavailability for toxic metals/metalloids - A research prospectus

Widespread contamination of soil, dust, and food with toxic metal(loid)s pose a significant public health concern. Only a portion of orally ingested metal(loid) contaminants are bioavailable, which is defined as the fraction of ingested metal(loid)s absorbed across the gastrointestinal barrier and into systemic circulation. Bioaccessibility tools are a class of in vitro assays used as a surrogate to estimate risk of oral exposure and bioavailability. Although development and use of bioaccessibility tools have contributed to our understanding of the factors influencing oral bioavailability of metal(loid)s, some of these assays may lack data that support their use in decisions concerning adverse health risks and soil remediation. This review discusses the factors known to influence bioaccessibility of metal(loid) contaminants and evaluates experimental approaches and key findings of SW-846 Test Method 1340, Unified BARGE Method, Simulated Human Intestinal Microbial Ecosystem, Solubility Bioaccessibility Research Consortium assay, In Vitro Gastrointestinal model, TNO-Gastrointestinal Model, and Dutch National Institute for Public Health and the Environment bioaccessibility models which are used to assess oral absolute bioavailability and relative bioavailability in solid matrices. The aim of this review was to identify emerging knowledge gaps and research needs with an emphasis on research required to evaluate these models on (1) standardization of assay techniques and methodology, and (2) use of common criteria for assessing the performance of bioaccessibility models.

Benefit-risk assessment of metal bioavailability in edible fungi by biomimetic whole digestive tracts with digestion, metabolism, and absorption functions

As worldwide edible fungi, Lentinula edodes and Agaricus bisporus accumulate both essential and harmful metals. Metal bioavailability is important for metal benefit-risk assessment. A full functional model of digestive tracts (including digestion, metabolism, and absorption) is established. Under the digestive tract functions, the bioaccessible and bioavailable metals are released from edible fungi and absorbed by intestinal tract, respectively. Based on bioavailable metal contents in the intestine, safe dosage and maximum consumption are 43.52 g/d and 248.7 g/d for Agaricus bisporu, 20.59/328.9 g/d (for males/ female) and 132.9 g/d for Lentinus edodes; V, Co, Ni, Cu, Zn, Se, Cr, Cd and Pb in Agaricus bisporus and Lentinula edodes are absorbed mainly in the large intestine; Fe is mainly absorbed in small intestine; edible fungi species-specificity in metal bioavailability is observed for As and Mn, which are mainly absorbed by small and large intestine for Agaricus bisporus and Lentinus edodes, respectively; and then metal toxicity on small and large intestine is disclosed. Metal benefit-risk is assessed by the content of monolayer liposome-extracted metal in the chyme from small and large intestine, which is controlled by the gastrointestinal functions, metal and edible fungi species.

In vitro models of gut digestion across childhood: current developments, challenges and future trends

The human digestion is a multi-step and multi-compartment process essential for human health, at the heart of many issues raised by academics, the medical world and industrials from the food, nutrition and pharma fields. In the first years of life, major dietary changes occur and are concomitant with an evolution of the whole child digestive tract anatomy and physiology, including colonization of gut microbiota. All these phenomena are influenced by child exposure to environmental compounds, such as drugs (especially antibiotics) and food pollutants, but also childhood infections. Due to obvious ethical, regulatory and technical limitations, in vivo approaches in animal and human are more and more restricted to favor complementary in vitro approaches. This review summarizes current knowledge on the evolution of child gut physiology from birth to 3 years old regarding physicochemical, mechanical and microbial parameters. Then, all the available in vitro models of the child digestive tract are described, ranging from the simplest static mono-compartmental systems to the most sophisticated dynamic and multi-compartmental models, and mimicking from the oral phase to the colon compartment. Lastly, we detail the main applications of child gut models in nutritional, pharmaceutical and microbiological studies and discuss the limitations and challenges facing this field of research.

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.

Assessment of nutrients effect on the bioaccessibility of Cd and Cu in contaminated soil

Soil is considered as a sink for heavy metals. Human health is severely affected by the continuous intake of toxic heavy metals even in a very low concentration. In the present experiment, we determined the influence of nutritional status including control (fasted condition), glucose (fed state), plant protein (fed state), animal protein (fed state) and calcium (fed state) on soil cadmium (Cd) and copper (Cu) bioaccessibility using physiologically-based extraction test (PBET) method together with simulator of the human intestinal microbial ecosystem (SHIME) model. The bioaccessibility of Cd was 1.06-73.58%, 0.44-54.79% and 0-17.78% and Cu was 3.81-67.32%, 4.98-71.14%, and 0-17.54% in the phase-I, phase-II and Phase-III respectively (in this study gastric phase, small intestinal phase and colon phase were considered as phase-I, phase-II and Phase-III respectively). The outcomes showed that, the average Cd bioaccessibility was higher with animal protein addition compared with other treatments in different phases. So, the effect of animal protein on Cd bioaccessibility was higher than other treatments in the phase-I, phase-II and phase-III. Due to the addition of plant protein, the higher average bioaccessibility of Cu was noticed in phase-I and phase-II in comparison to other treatments. However, in phase-III, the higher average bioaccessibility of Cu was found due to control treatment comparing with other treatments. Therefore, the influence of plant protein was higher than other nutrients on Cu bioaccessibility in the phase-I and phase-II. Moreover, other nutrients showed variable influence on Cd and Cu bioaccessibility. So, nutritional status has a significant effect on bioaccessibility as well as human health risk assessment.

Gut microbiota influence on oral bioaccessibility and intestinal transport of pesticides in Chaenomeles speciosa

There is limited research focusing on the effects of human gut microbiota on the oral bioaccessibility and intestinal absorption of pesticide residues in food. In the present study, we use a modified setup of the Simulator of the Human Intestinal Microbial Ecosystem for the determination of pesticide residue bioaccessibility in Chaenomeles speciosa, and a Caco-2 cell model of human intestinal absorption. Results showed that gut microbiota played a dual role based their effects on contaminant release and metabolism in the bioaccessibility assay, and Lactobacillus plantarum was one of key bacterial species in the gut microbiota that influenced pesticide stability significantly. The addition of L. plantarum to the system reduced the relative amounts (by 11.40-86.51%) of six pesticides. The interaction between the food matrix and human gut microbiota led to different absorption rates, and the barrier effects increased with an increase in incubation time.

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.

Comparison of arsenic fractions and health risks in PM2.5 before and after coal-gas replacement

Coal-Gas replacement project has been implemented to decrease haze pollution in China in recent years. Airborne arsenic (As) mostly originates from coal burning processes. It is noteworthy to compare the distribution of arsenic fraction in PM_2.5 before and after coal-gas replacement. Eighty PM_2.5 samples were collected in Baoding in December 2016 (coal dominated year) and December 2017 (gas dominated year) at different functional areas including residential area (RA), industrial area (IA), suburb (SB), roadside (ST) and Botanical Garden Park (BG). The fraction, bioavailability and health risk of As in the PM_2.5 samples were investigated and compared between these two years. Arsenic was mainly distributed in the non-specifically sorbed fraction (F1) and the residual fraction (F5). However, the proportion of F1 to the total As in 2017 was higher than that in 2016, while the proportion of As in the amorphous and poorly-crystalline hydrous oxides of Fe and Al fraction (F3) in 2017 was lower. The distributions of fraction and bioavailability showed temporal and spatial characteristics. The total concentration and bioavailability of As in SB and IA were significantly higher than those in RA, ST and BG. The BF (Bioavailability Factor) values of As ranged from 0.30 to 0.61. Health risk assessment indicated that the hazard quotient (HQ) and carcinogenic risk (CR) of As in PM_2.5 significantly decreased after coal-gas replacement.

Arsenic and the gastrointestinal tract microbiome

Arsenic is a toxin, ranking first on the Agency for Toxic Substances and Disease Registry and the Environmental Protection Agency Priority List of Hazardous Substances. Chronic exposure increases the risk of a broad range of human illnesses, most notably cancer; however, there is significant variability in arsenic-induced disease among exposed individuals. Human genetics is a known component, but it alone cannot account for the large inter-individual variability in the presentation of arsenicosis symptoms. Each part of the gastrointestinal tract (GIT) may be considered as a unique environment with characteristic pH, oxygen concentration, and microbiome. Given the well-established arsenic redox transformation activities of microorganisms, it is reasonable to imagine how the GIT microbiome composition variability among individuals could play a significant role in determining the fate, mobility and toxicity of arsenic, whether inhaled or ingested. This is a relatively new field of research that would benefit from early dialogue aimed at summarizing what is known and identifying reasonable research targets and concepts. Herein, we strive to initiate this dialogue by reviewing known aspects of microbe-arsenic interactions and placing it in the context of potential for influencing host exposure and health risks. We finish by considering future experimental approaches that might be of value.

Disturbance of trace element and gut microbiota profiles as indicators of autism spectrum disorder: A pilot study of Chinese children

Autism spectrum disorder (ASD) is a neuro-developmental disorder that is characterized by impairments of reciprocal social interaction and restricted stereotyped repetitive behavior. The goal of the present study was to investigate the trace element and gut microbiota profiles of Chinese autistic children and screen out potential metallic or microbial indicators of the disease. One hundred and thirty-six children (78 with ASD and 58 healthy controls) aged from 3 to 7 years were enrolled. The levels of lead, cadmium, arsenic, copper, zinc, iron, mercury, calcium and magnesium in hair samples from the children were analyzed. Fecal samples were also collected and the children's gut microbiota profiles were characterized by 16s rRNA sequencing. Concentrations of lead, arsenic, copper, zinc, mercury, calcium and magnesium were significantly higher in the ASD group than in the control group. Linear discriminant analysis effect size analysis indicated that the relative abundance of nine genera was increased in the autistic children. Redundancy analysis showed that arsenic and mercury were significantly associated with Parabacteroides and Oscillospira in the gut. A random forest model was trained with high accuracy (84.00%) and the metallic and microbial biomarkers of ASD were established. Our results indicate significant alterations in the trace element and gut microbiota profiles of Chinese children with ASD and reveal the potential pathogenesis of this disease in terms of metal metabolism and gut microecology.

Salivary and Gut Microbiomes Play a Significant Role in in Vitro Oral Bioaccessibility, Biotransformation, and Intestinal Absorption of Arsenic from Food

The release of a toxicant from a food matrix during the gastrointestinal digestion is a crucial determinant of the toxicant's oral bioavailability. We present a modified setup of the human simulator of the gut microbial ecosystem (SHIME), with four sequential gastrointestinal reactors (oral, stomach, small intestine, and colon), including the salivary and colonic microbiomes. Naturally arsenic-containing rice, mussels, and nori seaweed were digested in the presence of microorganisms and in vitro oral bioaccessibility, bioavailability, and metabolism of arsenic species were evaluated following analysis by using HPLC/mass spectrometry. When food matrices were digested with salivary bacteria, the soluble arsenic in the gastric digestion stage increased for mussel and nori samples, but no coincidence impact was found in the small intestinal and colonic digestion stages. However, the simulated small intestinal absorption of arsenic was increased in all food matrices (1.2-2.7 fold higher) following digestion with salivary microorganisms. No significant transformation of the arsenic species occurred except for the arsenosugars present in mussels and nori. In those samples, conversions between the oxo arsenosugars were observed in the small intestinal digestion stage whereupon the thioxo analogs became major metabolites. These results expand our knowledge on the likely metabolism and oral bioavailabiltiy of arsenic during human digestion, and provide valuable information for future risk assessments of dietary arsenic.

Nutritional status affects the bioaccessibility and speciation of arsenic from soils in a simulator of the human intestinal microbial ecosystem

Arsenic (As) is a highly toxic contaminant in food and soil. In this study, we investigated the effects of four nutritional states (including a fed state with vitamin C, a fed state with protein powder, a fed state with glucose and a fasted state) on the variability of soil As bioaccessibility and biotransformation using the physiologically based extraction test (PBET) combined with a simulator of the human intestinal microbial ecosystem model (SHIME). The results indicated that the vitamin C and protein powder increased As bioaccessibility in gastric digests. In the colon phase, As bioaccessibility was observably enhanced by protein powder, and it varied under the vitamin C and glucose conditions. Additionally, the order of As methylation percentages in the four nutritional states was protein powder > vitamin C > fasted state > glucose (except S2); As bioaccessibility increased 1.3-13.7% and 15.8-35.4% in treatments of the vitamin C and protein powder, respectively. Meanwhile, large amounts of monomethylarsonic acid (MMA^V) were observed in the colon digest in the protein powder condition. In contrast, As methylation was significantly decreased with the addition of glucose, with a decline of 25.9-45.5%. Additionally, glucose enhanced the reduction of As(V). Therefore, nutritional status is a crucial parameter for the prediction of bioaccessibility and speciation of As when assessing health risks from As following oral exposure.

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.

Study of Factors Influencing the Bioaccessibility of Triazolone in Cherry Tomatoes Using a Static SHIME Model

Estimating the influence of bioaccessibility of pesticide residues in fruits and vegetables on dietary exposure is a challenge for human health risk assessment. This study investigated the bioaccessibility of pesticide residues in cherry tomatoes and contributing factors (digestion time, pH, solid/liquid ratio, and dietary nutrition) using an in vitro test simulating the human gastrointestinal tract. pH had the largest effect on triazolone precipitation in the simulated gastric intestinal juice, which had a significant impact on the bioaccessibility. The bioaccessibility of triazolone in the intestinal stage was slightly higher than that in the stomach stage, owing to bile salts and pancreatic enzymes present in the intestinal juice. The bioaccessibility of triazolone did not change significantly with digestion time. In the gastric stage, there was a logarithmic relationship between the bioaccessibility and solid/liquid ratio (R² = 0.9941). The addition of oil significantly changed the bioaccessibility in the gastrointestinal stage. Protein and dietary fiber only affected bioaccessibility in the stomach stage. Dietary nutrition can reduce the release of pesticides from fruits and vegetables into the stomach, sharply reducing the bioaccessibility, and the dietary exposure of pesticide residues in fruits and vegetables can be properly evaluated.

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

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

Interindividual variability of soil arsenic metabolism by human gut microbiota using SHIME model

Arsenic (As) metabolism by human gut microbiota has been evidenced with in vitro experiments from contaminated soils. In this study, the variability in the metabolic potency toward As-contaminated soils and gut microbial diversity were investigated between healthy individuals (Adult versus Child). Arsenic bioaccessibility in the colon phase increased by 1.4-6.8 and 1.2-8.7 folds for adult and child, respectively. We found a high degree of As methylation for the colon digests of the adult (mean 2 μg methylarsenicals/hr/g biomass), 3-folds higher than that of the child. Besides, arsenite [As(III)] concentration (1.5-391.3 μg/L) for the child was 2-18 times for the adult. 16S rRNA gene sequencing revealed that human gut microbiota from 20 various genera potentially had resistance genes to reduce and methylate As under conservative statistics. Our results indicated that As metabolism by gut microbiota from adult and child was significantly different. The adult gut microbiota had a great ability of As methylation; the child gut microbiota exhibited high As(III) level, which could encounter high health risk. The identity and activity of arsenic-metabolizing bacteria isolated from human gut and its homologous role in As metabolism need be further explored. This study provides a better understanding of health risk assessment to adults and children upon soil As exposures.

In vitro study of soil arsenic release by human gut microbiota and its intestinal absorption by Caco-2 cells

Arsenic (As) speciation is essential in assessing health risks from As-contaminated soil. Release of soil-bound arsenic, As transformation by human gut microbiota, and the subsequent intestinal absorption of soil As metabolites were evaluated. A colon microbial community in a dynamic human gut model and the intestinal epithelial cell line Caco-2 were cultured. Arsenic speciation analysis and absorption of different As species were undertaken. In this study, soil As release (3.7-581.2 mg kg^-1) was observed in the colon. Arsenic in the colon digests was transformed more quickly than that in the soil solid phase. X-ray absorption near-edge spectroscopy (XANES) analysis showed that 44.2-97.6% of arsenite [As(III)] generated due to arsenate [As(V)] reduction was in the soil solid phase after the colon phase. We observed a high degree of cellular absorption of soil As metabolites, exhibiting that the intestinal absorption of monomethylarsonic acid and As(III) (33.6% and 30.2% resp.) was slightly higher than that of dimethylarsinic acid and As(V) (25.1% and 21.7% resp.). Our findings demonstrate that human gut microbiota can directly release soil-bound arsenic, particularly As-bearing amorphous Fe/Al-oxides. Determining As transformation and intestinal absorption simultaneously will result in an accurate risk assessment of human health with soil As exposures.