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

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.

Release mechanism and interactions of cadmium and arsenic co-contaminated ferrihydrite by simulated in-vitro digestion assays

Cadmium (Cd) and arsenic (As) co-contamination is widespread and threatens human health, therefore it is important to investigate the bioavailability of Cd and As co-exposure. Currently, the interactions of Cd and As by in vitro assays are unknown. In this work, we studied the concurrent Cd-As release behaviors and interactions with in vitro simulated gastric bio-fluid assays. The studies demonstrated that As bioaccessibility (2.04 to 0.18 ± 0.03%) decreased with Cd addition compared to the As(V) single system, while Cd bioaccessibility (11.02 to 39.08 ± 1.91%) increased with As addition compared to the Cd single system. Release of Cd and As is coupled to proton-promoted and reductive dissolution of ferrihydrite. The As(V) is released and reduced to As(Ⅲ) by pepsin. Pepsin formed soluble complexes with Cd and As. X-ray photoelectron spectroscopy showed that Cd and As formed Fe-As-Cd ternary complexes on ferrihydrite surfaces. The coordination intensity of As-O-Cd is lower than that of As-O-Fe, resulting in more Cd release from Fe-As-Cd ternary complexes. Our study deepens the understanding of health risks from Cd and As interactions during environmental co-exposure of multiple metal(loid)s.

Foliar spraying of lanthanum activates endocytosis in lettuce (Lactuca sativa L.) root cells, increasing Cd and Pb accumulation and their bioaccessibility

Cadmium (Cd) and lead (Pb) accumulate easily in leafy vegetables and can harm human health. Lanthanum (La) have been used to improve agricultural yield and quality, but the effect of La application on Cd/Pb enrichment in leafy vegetables remains incomplete currently. A previous study reported that the endocytosis in lettuce leaf cells can be activated by La, leading to an increase in Pb accumulation in lettuce leaves. However, it has not been investigated whether foliar application of La enhances root cellular endocytosis and promotes its uptake of Cd and Pb. In this study, the influence of La on the uptake of Cd and Pb, Cd bioaccessibility, and the safety risks of cultivating lettuce under Cd and Pb stress were explored. It was found that La increased Cd (16-30 % in shoot, 16-34 % in root) and Pb (25-29 % in shoot, 17-23 % in root) accumulation in lettuce. The increased accumulation of Cd and Pb could be attributed to La-enhanced endocytosis. Meanwhile, La enhanced the toxicity of both Cd and Pb, inhibited lettuce growth, and aggravated the damage to the photosynthetic and antioxidant systems. Finally, gastrointestinal simulation experiments showed that La increased the Cd bioaccessibility in both gastric and intestinal phase by 7-108 % and 9-87 %, respectively. These results offer valuable insights into the safety of REEs for agricultural applications.

Sex-dependent effects of rice cadmium exposure on body weight, gut microflora, and kidney metabolomics based on a mouse model

Consumption of cadmium (Cd) contaminated rice is the main dietary source of Cd exposure and toxicity. To protect humans from Cd toxicity, it is pivotal to fully understand the sex-dependent toxicity of subchronic rice-Cd exposure. However, the sex-dependent effects of subchronic rice-Cd exposure on body weight gain, gut microflora, and kidney metabolomics are still unclear. In this study, a Cd-free and a Cd-contaminated rice (0.005 and 0.74 mg Cd kg-1) were fed to both female and male mice for one month, with changes in body weight gain, Cd accumulation in tissue, bone mineral concentration, expression of intestinal channels involving in Cd and calcium (Ca) absorption, gut microbiota, and kidney metabolites assessed for both genders. Results showed that female mice had normal body weight gain after rice-Cd exposure, while body weight of male mice was decreased from 19.8 to 17.5 g over the one-month consumption of the Cd-contaminated rice (0.74 mg kg-1), suggesting specific toxicity on growth of male mice. Rice-Cd exposure had limited effects on gut microbiota for both genders. However, higher Cd accumulation in liver and femur was observed in male mice than in females, which may be due to higher intestinal expression of Ca channels involving in intestinal Cd absorption in male mice with rice-Cd exposure. Greater risk of osteoporosis was also observed in male mice. In addition, kidney metabolomic profiling showed special disruption of adrenocortical hormone homeostasis for male mice with rice-Cd exposure. Particularly, expression of cortisol in kidneys of male mice was elevated 37.1-fold with rice-Cd exposure, likely resulting in Cushing's syndrome and contributing to growth retardation. This study advances our understanding of the sex-dependent toxicity of rice-Cd exposure, and highlights the priority of protecting males from the adrenocortical hormone disrupting effects of rice-Cd exposure.

Mixed effects and co-transfer of CeO2 NPs and arsenic in the pakchoi-snail food chain

Nanomaterial application in agriculture offers novel solutions for soil arsenic (As) pollution control, yet safety along the food chain is of concern. We comprehensively assessed CeO2 nanoparticles (NPs) foliar application effects on As uptake by pakchoi and their presence in the pakchoi-snail food chain. CeO2 NPs reduced As transfer from pakchoi roots to shoots by 37.9%, lowered As in snail foot by 39%, and halved human As exposure risk. The NPs alleviated pakchoi shoot As toxicity by regulating antioxidants, enhancing water use efficiency, and photosynthesis. CeO2 +As treatment raised GSH/GSSG ratios by 38.92%- 167.54%, leading to an increased AsIII/AsV ratio and inorganic As detoxification compared to As alone. Metabolomics revealed CeO2's rapid As response via phosphatidylinositol signaling. The enzyme-like activity of CeO2 NPs may drive these effects. While CeO2 foliar application accumulated Ce on pakchoi leaves, > 99% of Ce was excreted following snail consumption. Ce transfer from pakchoi leaves to snail foot was minimal (trophic transfer factor ∼0.00007) due to limited bioavailability. The target hazard quotient of Ce in pakchoi shoot (1.21 ± 0.18) and snails (0.0016 ± 0.0004) indicated low exposure risk, suggesting a 'risk filter' effect for CeO2. Our results contribute to the safe and sustainable application of CeO2 NPs in the future implication.

Chromium contents, distribution and bioaccessibility in cultivated mushrooms from market: Health implications for human consumption

Mushrooms are consumed worldwide as they constitute a part of traditional cuisine culture in many countries. However, chromium (Cr) accumulation in mushrooms may constitute a potential pathway for its chronical exposure to humans. In this work, the Cr contents, distribution and bioaccessibility in 140 cultivated mushrooms from 14 species in 10 top-producing provinces in China were examined. Total Cr contents were 0.09-4.71 mg·kg-1 dw (mean 0.74 mg kg-1), with 59% exceeding the 0.5 mg kg-1standard. Additionally, less Cr was accumulated in the caps than stipes, with Cr ratio in caps/stipes being 0.28-2.6, averaging 0.91. Based on the Solubility Bioaccessibility Research Consortium (SBRC) assay, the mean Cr bioaccessibility in the mushrooms was 24.8% and 50.1% in the gastric phase (GP) and intestinal phase (IP). However, samples from Guizhou show the lowest Cr bioaccessibility at 12.5% in GP and 24.8% in IP. Further, a negative correlation between total Cr contents and Cr bioaccessibility suggests that Cr bioaccessibility is critical for accurate assessment of Cr exposure. In addition, drying mushrooms increased their bioaccessibility in the gastric phase. This study shows a high Cr exceeding rate of cultivated mushrooms, which may indicate a potential exposure risk, with Cr contents and bioaccessibility showing species and regional variation.

Dietary Galactooligosaccharides Supplementation as a Gut Microbiota-Regulating Approach to Lower Early Life Arsenic Exposure

Prebiotics may stimulate beneficial gut microorganisms. However, it remains unclear whether they can lower the oral bioavailability of early life arsenic (As) exposure via regulating gut microbiota and altering As biotransformation along the gastrointestinal (GI) tract. In this study, weanling mice were exposed to arsenate (iAsV) via diet (7.5 μg As g-1) amended with fructooligosaccharides (FOS), galactooligosaccharides (GOS), and inulin individually at 1% and 5% (w/w). Compared to As exposure control mice, As concentrations in mouse blood, liver, and kidneys and As urinary excretion factor (UEF) were reduced by 43.7%-74.1% when treated with 5% GOS. The decrease corresponded to a significant proliferation of Akkermansia and Psychrobacter, reduced percentage of inorganic arsenite (iAsIII) and iAsV by 47.4% and 65.4%, and increased proportion of DMAV in intestinal contents by 101% in the guts of mice treated with 5% GOS compared to the As control group. In contrast, FOS and inulin either at l% or 5% did not reduce As concentration in mouse blood, liver, and kidneys or As UEF. These results suggest that GOS supplementation may be a gut microbiota-regulating approach to lower early life As exposure via stimulating the growth of Akkermansia and Psychrobacter and enhancing As methylation in the GI tract.

Effect of soluble phosphate and bentonite amendments on lead and cadmium bioavailability and bioaccessibility in a contaminated soil

Effect of commonly used heavy metal immobilizing agents on risks of soil heavy metals has not been well investigated. In this work, a contaminated acidic soil (total Cd = 8.05, total Pb = 261 mg kg-1) was amended with soluble phosphate (P: 160 mg kg-1) and bentonite (3 g kg-1) and incubated for 360 d. The soil was then added to mouse feed at 1:9 soil: feed ratio (weight) and fed to mouse for 10 days, after which the liver, kidney and bone Pb and Cd concentrations were measured. The amended soils were extracted with SBRC and PBET to assay bioaccessibility, and extracted with DTPA to assess the environmental availability. The amendments did not affect the DTPA-Pb/Cd significantly (p > 0.05), while the Cd bioaccessibility in the gastric phase of the SBRC assay was reduced from 90.0 to 20.4 % for the bentonite amended treatment (p < 0.05). Kidney Pb and Cd concentrations of the mice fed with feed containing phosphate spiked soil was 80.2 and 66.0 % lower than the control mice fed with unamended soil (CK), respectively. Significant linear correlations were found between DTPA-extractable concentration and kidney concentrations for Pb/Cd. The effect of amendment on Pb/Cd bioavailability differed between the results calculated with different endpoints. The phosphate amendment resulted in 82.7 and 34.3 % lower Pb RBA compared with the unamended soil calculated with kidney and kidney+liver+bone Pb concentrations, respectively, and 68.8 and 49.7 % lower Cd RBA than the control with kidney and kidney+liver concentrations, respectively. However, no significant effect was observed with both amendments when the RBA was calculated with liver or bone Pb/Cd concentrations, or on Pb RBA with kidney, liver or bone metal concentrations. Results indicate the complex effect of amendments on organ, tissue and overall health risk of soil Pb/Cd to animal/human.

Lowered oral bioaccessibility of cadmium and selenium and associated health risk by co-digestion of rice and vegetables

Since foods are not ingested individually, co-digestion, in accordance with human daily diet conditions, should be stressed when assessing elements bioaccessibility and associated health risks. The oral bioaccessibility of cadmium (Cd) and selenium (Se) in 11 types of crops (rice, maize, pakchoi, eggplant, red pepper, towel gourd, kidney bean, soybean, cowpea, sweet potato, and taro) were determined, and the effects of co-digestion of 7 types of rice and vegetables on the bioaccessibility of Cd and Se were evaluated and validated with in vitro PBET method. The underlying mechanism was revealed by observing the surface morphological characteristics of digested substrates, and the exposure risk of Cd and Se were assessed. The results showed that the average bioaccessibility of Cd and Se in 11 types of crops varied from 58.7 % to 39.1 % and 48.4 % to 62.6 % from the gastric phase (GP) to the intestinal phase (IP). Interestingly, co-digestion of rice and vegetables reduced the bioaccessibility of Cd and Se to varying degrees compared to theoretical values. Great reduction in the bioaccessibility of Cd and Se in the GP (16.9-36.4 % and 9.9-23.2 %) than that in the IP (0.2-6.62 % and 0.23-12.3 %) were detected, which was attributed to the rice-vegetable aggregates formed during co-digestion. Rice-vegetable aggregates inhibited the release of Cd and Se, which was more pronounced in the GP than in the IP. Consequently, co-digestion of rice and vegetables reduced the oral exposure to Cd by 35.8 % and to Se by 19.6 %. The areas with higher non-carcinogenic risk of Cd and Se in the study region were reduced by 17 % and 10 %, respectively. Therefore, the role of co-digestion in assessing Cd and Se bioaccessibility and associated health risk cannot be neglected. This study has significant implications for investigating elements bioaccessibility and optimizing associated health risk assessment from a novel perspective.

Target-Controlled Redox Reaction and Ru(II) Release of a Smart Metal-Organic Framework Nanomaterial for Highly Sensitive Ratiometric Homogeneous Electroanalysis of Cadmium(II)

In this work, a highly sensitive ratiometric homogeneous electroanalysis (HEA) strategy of cadmium(II) (Cd2+) was proposed via a Cd2+-controlled redox reaction and Ru(bpy)32+ (Ru(II)) release from a smart metal-organic framework (MOF) nanomaterial. For achieving this purpose, Ru(II) was entrapped ingeniously into the pores of an MOF material (UiO-66-NH2) and subsequently gated by the double-strand hybrids of a Cd2+-aptamer (Apt) and its complementary sequences (CP) to form a novel smart nanomaterial (denoted as Ru@UiO-66-NH2); meanwhile, Fe(III) was selected as an additional probe present in electrolyte to facilitate the Ru(II) redox reaction: Fe(III) + Ru(II) → Fe(II) + Ru(III). Owing to the strong binding effect of the Cd2+ target to the specific Apt, the Apt-CP hybridization at Ru@UiO-66-NH2 would be destroyed in the presence of Cd2+, and the related Apt was further induced away from the smart nanomaterial, leading to the opening of the gate and release of Ru(II). Meanwhile, the released Ru(II) was quickly oxidized chemically by Fe(III) to Ru(III). On the basis of the generated Ru(III) and consumed Fe(III), the ratio of the reduction currents between Ru(III) and Fe(III) exhibits an enhancement and it is dependent on the level of Cd2+; thus, a novel HEA strategy of Cd2+ was then designed. Under the optimal conditions, the HEA sensor shows a wide linearity ranging from 10.0 pM to 500.0 nM, and the achieved detection limit of Cd2+ is 3.3 pM. The as-designed ratiometric HEA strategy not only offers a unique idea to realize a simple and sensitive assay for Cd2+ but also possesses significant potential as an effective tool to be introduced for other target analysis just via altering the specific Apt.

Health risk assessment of trace metal(loid)s in agricultural soil using an integrated model combining soil-related and plants-accumulation exposures: A case study on Hainan Island, South China

Traditional health risk assessment of trace metal(loid)s (TMs) in agricultural soil exclusively considers direct soil-related exposure and may underestimate the health risks they pose. In this study, the health risks of TMs were evaluated using an integrated model that combined soil-related and plant-accumulating exposures. A detailed investigation of common TMs (Cr, Pb, Cd, As, and Hg) coupled with probability risk analysis based on a Monte Carlo simulation was conducted on Hainan Island. Our results showed that, except for As, the non-carcinogenic risk (HI) and carcinogenic risk (CR) of the TMs were all within the acceptable ranges (HI < 1.0, and CR < 1E-06) for direct soil-related exposure to bio-accessible fractions and indirect exposure via plant accumulation (CR substantially lower than the warning threshold 1E-04). We identified crop food ingestion as the essential pathway for TM exposure and As as the critical toxic element in terms of risk control. Moreover, we determined that RfDo and SFo are the most suitable parameters for assessing As health risk severity. Our study demonstrated that the proposed integrated model combining soil-related and plant-accumulating exposures can avoid major health risk assessment deviations. The results obtained and the integrated model proposed in this study can facilitate future multi-pathway exposure research and could be the basis for determining agricultural soil quality criteria in tropical areas.

Mechanistic Insights into Effects of Different Dietary Polyphenol Supplements on Arsenic Bioavailability, Biotransformation, and Toxicity Based on a Mouse Model

Arsenic (As) exposure has been related to many diseases, including cancers. Given the antioxidant and anti-inflammatory properties, the dietary supplementation of polyphenols may alleviate As toxicity. Based on a mouse bioassay, this study investigated the effects of chlorogenic acid (CA), quercetin (QC), tannic acid (TA), resveratrol (Res), and epigallocatechin gallate (EGCG) on As bioavailability, biotransformation, and toxicity. Intake of CA, QC, and EGCG significantly (p < 0.05) increased total As concentrations in liver (0.48-0.58 vs 0.27 mg kg-1) and kidneys (0.72-0.93 vs 0.59 mg kg-1) compared to control mice. Upregulated intestinal expression of phosphate transporters with QC and EGCG and proliferation of Lactobacillus in the gut of mice treated with CA and QC were observed, facilitating iAsV absorption via phosphate transporters and intestinal As solubility via organic acid metabolites. Although As bioavailability was elevated, serum levels of alpha fetoprotein and carcinoembryonic antigen of mice treated with all five polyphenols were reduced by 13.1-16.1% and 9.83-17.5%, suggesting reduced cancer risk. This was mainly due to higher DMAV (52.1-67.6% vs 31.4%) and lower iAsV contribution (4.95-10.7% vs 27.9%) in liver of mice treated with polyphenols. This study helps us develop dietary strategies to lower As toxicity.

Chronic Exposure to Drinking Water As, Pb, and Cd at Provisional Guideline Values Reduces Weight Gain in Male Mice via Gut Microflora Alterations and Intestinal Inflammation

Few studies have investigated the long-term effect of exposure to arsenic (As), lead (Pb), and cadmium (Cd) via drinking water at the provisional guideline values on gut microflora. In this study, male and female mice were exposed to water As, Pb, or Cd at 10, 10, or 5 μg L-1 for 6 months. At the end of the exposure, the net weight gain of male mice exposed to As and Pb (9.91 ± 1.35 and 11.2 ± 1.50 g) was significantly (p < 0.05) lower compared to unexposed control mice (14.1 ± 3.24 g), while this was not observed for female mice. Relative abundance of Akkermansia, a protective gut bacterium against intestinal inflammation, was reduced from 29.7% to 3.20%, 4.83%, and 17.0% after As, Pb, and Cd exposure in male mice, which likely caused chronic intestinal inflammation, as suggested by 2.81- to 9.60-fold higher mRNA levels of pro-inflammatory factors in ileal enterocytes of male mice. These results indicate that long-term exposure to drinking water As, Pb, and Cd at concentrations equivalent to the China provisional guideline values can cause loss of protective bacteria and lead to chronic intestinal inflammation, thereby affecting body weight gain in male mice.

Evaluation of the oral bioaccessibility of legacy and emerging brominated flame retardants in indoor dust

Indoor dust is the main source of human exposure to brominated flame retardants (BFRs). In this study, in vitro colon-extended physiologically-based extraction test (CE-PBET) with Tenax as a sorptive sink was applied to evaluate the oral bioaccessibility of twenty-two polybrominated diphenyl ethers (PBDEs) and seven novel BFRs (NBFRs) via indoor dust ingestion. The mean bioaccessibilities of two NBFRs pentabromotoluene (PBT) and 1,2-Bis(2,4,6-tribromophenoxy) ethane (BTBPE) were first proposed, reaching 36.0% and 26.7%, respectively. In order to maintain homeostasis of the gastrointestinal tract, 0.4 g Tenax was added in CE-PEBT, which increased BFRs bioaccessibility by up to a factor of 1.4-1.9. The highest bioaccessibility of legacy PBDEs was tri-BDEs (73.3%), while 2-ethylhexyl-tetrabromo-benzoate (EHTBB), one of penta-BDE alternatives, showed the highest (62.2%) among NBFRs. The influence of food nutrients, liquid to solid (L/S) ratio, and octanol-water partition coefficient (Kow) on bioaccessibility was assessed. The oral bioaccessibility of BFRs increased with existence of protein or carbohydrate while lipid did the opposite. The bioaccessibilities of PBDEs and NBFRs were relatively higher with 200:1 L/S ratio. PBDEs bioaccessibility generally decreased with increasing LogKow. No significant correlation was observed between NBFRs bioaccessibility and LogKow. This study comprehensively evaluated the bioaccessibilities of legacy and emerging BFRs via dust ingestion using Tenax-assisted CE-PBET, and highlighted the significance to fully consider potential influencing factors on BFRs bioaccessibility in further human exposure estimation.

Alcohol consumption promotes arsenic absorption but reduces tissue arsenic accumulation in mice

Alcohol consumption alters gut microflora and damages intestinal tight junction barriers, which may affect arsenic (As) oral bioavailability. In this study, mice were exposed to arsenate in the diet (6 μg/g) over a 3-week period and gavaged daily with Chinese liquor (0.05 or 0.10 mL per mouse per day). Following ingestion, 78.0% and 72.9% of the total As intake was absorbed and excreted via urine when co-exposed with liquor at daily doses of 0.05 or 0.10 mL, significantly greater than when As was supplied alone (44.7%). Alcohol co-exposure significantly altered gut microbiota but did not significantly alter As biotransformation in the intestinal tract or tissue. Significantly lower relative mRNA expression was observed for genes encoding for tight junctions in the ileum of liquor co-exposed mice, contributing to greater As bioavailability attributable to enhanced As absorption via the intestinal paracellular pathway. However, As concentration in the liver, kidney, and intestinal tissue of liquor-treated mice was decreased by 24.4%-42.6%, 27.5%-38.1%, and 28.1%-48.9% compared to control mice. This was likely due to greater renal glomerular filtration rate induced by alcohol, as suggested by significantly lower expression of genes encoding for renal tight junctions. In addition, in mice gavaged daily with 0.05 mL liquor, the serum antidiuretic hormone level was significantly lower than control mice (2.83 ± 0.59 vs. 5.40 ± 1.10 pg/mL), suggesting the diuretic function of alcohol consumption, which may facilitate As elimination via urine. These results highlight that alcohol consumption has a significant impact on the bioavailability and accumulation of As.

Effects of calcium supplements on oral bioavailability of fluoride in soil based on In Vivo and In Vitro methods

Dietary calcium (Ca) intake can alleviate fluoride (F) induced fluorosis to maintain bone health. However, it is unclear whether calcium supplements can reduce the oral bioavailability of F present in contaminated soils. Here we evaluated the effects of Ca supplements on F bioavailability in three soils using an in vitro method (Physiologically Based Extraction Test) and an in vivo mouse model. Seven Ca salts, commonly used in calcium supplements, significantly reduced the F bioaccessibility in the gastric and small intestinal phases. Particularly for Ca phosphate at 150 mg Ca supplementation, F bioaccessibility in the small intestinal phase was reduced from 35.1-38.8% to 0.7-1.9% where soluble F concentrations were less than 1 mg/L. Overall, the eight Ca tablets tested in this study showed greater efficiency at decreasing F solubility. The in vitro bioaccessibility after Ca supplementation was consistent with the relative bioavailability of F. As supported by X-ray photoelectron spectroscopy, a possible mechanism is that freed F can be bound by Ca to form insoluble CaF2 and exchanged with OH groups from Al/Fe hydroxide to strongly adsorb F. These findings provide evidence of Ca supplementation in reducing health risks associated soil F exposure.

Cadmium and lead bioavailability to poultry fed with contaminated soil-spiked feed

Geophagy is common for free-range chickens, however, the relative bioavailability (RBA) of heavy metals in contaminated soils consumed by chickens has not fully investigated. In this work, chickens were fed diets increasingly spiked with a contaminated soil (Cd = 105, Pb = 4840 mg kg^-1; 3, 5, 10, 20 and 30 % of overall feed by weight), or Cd/Pb reagent spikes (from CdCl₂ or Pb(Ac)₂), for 23 d. After the study period, chicken liver, kidney, femur and gizzard samples were analyzed for Cd and Pb concentrations, and organ/tissue metal concentrations were used to calculate Cd and Pb RBA. Linear dose response curves (DRCs) were established for both Cd/Pb reagents-spiked and soil-spiked treatments. Femur Cd concentrations of soil-spiked treatments were two times of Cd-spiked treatments with similar feed Cd levels, while feed spiked with Cd or Pb also resulted in elevated Pb or Cd concentrations in some organ/tissues. Metal RBA was calculated using three different methods. Most Cd and Pb RBA values were in the range 50-70 %, with the chicken gizzard as a potential endpoint for bioaccessible Cd and Pb. Cadmium and Pb bioavailability values can help with more precise estimation of Cd and Pb accumulation in chicken following heavy metal-contaminated soil ingestion, with overall results helping to protect human health.

Dietary cadmium health risk assessment for the Chinese population

Cadmium (Cd) has high rates of soil-to-plant transference, coupled with its non-biodegradability and persistence; long-term management of Cd in agriculture is thus required to ensure better soil and food security and safety. Identifications of regions with high soil Cd concentration or high dietary Cd intakes are critical public health priorities. Human health risk assessment for dietary Cd intake was thus undertaken by employing three approaches: FCA (food chain approach), TDA (total diet approach), and FQA (food quality approach). The correlation between green/total vegetable consumption rates and dietary Cd intake from vegetables was statistically significant. For consumption, the hazard quotients (HQs) calculated by FCA and TDA were all less than 1 except for Hunan and Sichuan province. For rice consumption, the HQs derived by FCA or TDA approach for eight provinces exceeded 1. Residents in Hubei, Guangxi, Jilin, Zhejiang, Liaoning, Shanghai, Sichuan, and Guangxi were more vulnerable due to their notable higher consumption rates.Weighted rankings of the health risk levels were determined to derive the comparative risk management priority. For Cd intake from vegetables, four provinces/cities have high relative priority; for Cd intake from grains, three provinces have high relative priority. The comparative risk management priority for Hunan and Sichuan was high for dietary intake from vegetables or rice. Weighted average HQs were derived to determine the integrated dietary Cd intake health risk levels for dietary intake from vegetables or grains. The risk levels for Hunan, Guangxi, Sichuan, and Zhejiang are high, so effective measures should be taken to reduce Cd dietary intakes to ensure health protection.It is envisaged that the methodology employed in this study could provide useful insights into how various approaches can be integrated to determine human health risk levels for Cd intake, so more effective and targeted measures can be taken accordingly for the relevant regions.

Microplastics affect arsenic bioavailability by altering gut microbiota and metabolites in a mouse model

Microplastics exposure is a new human health crisis. Although progress in understanding health effects of microplastic exposure has been made, microplastic impacts on absorption of co-exposure toxic pollutants such as arsenic (As), i.e., oral bioavailability, remain unclear. Microplastic ingestion may interfere As biotransformation, gut microbiota, and/or gut metabolites, thereby affecting As oral bioavailability. Here, mice were exposed to arsenate (6 μg As g^-1) alone and in combination with polyethylene particles of 30 and 200 μm (PE-30 and PE-200 having surface area of 2.17 × 10³ and 3.23 × 10² cm² g^-1) in diet (2, 20, and 200 μg PE g^-1) to determine the influence of microplastic co-ingestion on arsenic (As) oral bioavailability. By determining the percentage of cumulative As consumption recovered in urine of mice, As oral bioavailability increased significantly (P < 0.05) from 72.0 ± 5.41% to 89.7 ± 6.33% with PE-30 at 200 μg PE g^-1 rather than with PE-200 at 2, 20, and 200 μg PE g^-1 (58.5 ± 19.0%, 72.3 ± 6.28%, and 69.2 ± 17.8%). Both PE-30 and PE-200 exerted limited effects on pre- and post-absorption As biotransformation in intestinal content, intestine tissue, feces, and urine. They affected gut microbiota dose-dependently, with lower exposure concentrations having more pronounced effects. Consistent with the PE-30-specific As oral bioavailability increase, PE exposure significantly up-regulated gut metabolite expression, and PE-30 exerted greater effects than PE-200, suggesting that gut metabolite changes may contribute to As oral bioavailability increase. This was supported by 1.58-4.07-fold higher As solubility in the presence of up-regulated metabolites (e.g., amino acid derivatives, organic acids, and pyrimidines and purines) in the intestinal tract assessed by an in vitro assay. Our results suggested that microplastic exposure especially smaller particles may exacerbate the oral bioavailability of As, providing a new angle to understand health effects of microplastics.

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

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

Relative Bioavailability of Cadmium in Rice: Assessment, Modeling, and Application for Risk Assessment

Rice consumption is the primary route of cadmium (Cd) exposure to the populations with rice as the staple food. To accurately assess the potential health risks of Cd exposure via rice consumption, determination of Cd relative bioavailability (RBA) in rice is necessary. However, large variations exist in Cd-RBA, hindering the application of source-specific Cd-RBA values to different rice samples. In this study, we collected 14 rice samples from Cd contaminated areas and determined both rice compositions and Cd-RBA using in vivo mouse bioassay. Total Cd concentration varied from 0.19 to 2.54 mg/kg in the 14 rice samples, while Cd-RBA in rice ranged from 42.10% to 76.29%. Cadmium-RBA in rice correlated positively with calcium (Ca) (R = 0.76) and amylose content (R = 0.75) but negatively with the concentrations of sulfur (R = -0.85), phosphorus (R = -0.73), phytic acid (R = -0.68), and crude protein (R = -0.53). Cd-RBA in rice can be predicted by Ca and phytic acid concentrations in a regression model (R² = 0.80). Based on the total and bioavailable Cd concentrations in rice, weekly dietary Cd intake for adults was estimated to be 4.84-64.88 and 2.04-42.29 μg/kg bw/week, respectively. This work demonstrates the possibility of Cd-RBA prediction based on rice compositions and provides valuable suggestions for health risk assessment with consideration of Cd-RBA.

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.

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.

Bioaccessibility of arsenic, lead, and cadmium in contaminated mining/smelting soils: Assessment, modeling, and application for soil environment criteria derivation

Soil environment criteria (SEC) are commonly derived from the total concentration of pollutants in soils, resulting in overly stringent values. Herein, we examined the feasibility of deriving the SEC by using the bioaccessibility of pollutants. In this regard, soil samples from 33 locations at 12 mining/smelting sites in China were collected and examined in terms of soil properties, chemical fraction distributions, and bioaccessibilities of cadmium (Cd), lead (Pb), and arsenic (As). The gastric (GP) and intestinal phases (IP) of the potentially hazardous trace elements (PHEs) were measured by in vitro assays, showing that these values varied from 11 % to 72 %, 1-79 %, and 2-27 % for Cd, Pb and As, respectively. Pearson analysis showed that the GP and IP bioaccessibilities of these PHEs were mainly influenced by soil pH, CEC, and clay fraction and positively correlated with the sequential extraction form. The random forest regression (RF) model showed excellent performance in predicting the gastric phase (GP) bioaccessibilities of Cd, Pb, and As, with a mean R2 and RMSE of 0.86 and 0.31, respectively. Both the measured and predicted bioaccessibilities were feasible to be used to derive SEC. This work will contribute to the development of regional soil environmental standards based on bioaccessibility for Cd-, Pb-, and As-contaminated mining/smelting soils.

Contribution and Effects of PM2.5-Bound Lead to the Cardiovascular Risk of Workers in a Non-Ferrous Metal Smelting Area Considering Chemical Speciation and Bioavailability

Lead is known to have toxic effects on the cardiovascular system. Owing to its high concentration, transmission range, and absorption efficiency in organisms, inhalation of fine particulate matter (PM2.5)-bound lead (PM2.5-Pb) may cause significant cardiovascular damage. However, the contribution and adverse effects of PM2.5-Pb on workers and residents in non-ferrous metal smelting areas are not fully understood. In this work, the concentration and chemical speciation of PM2.5-Pb were analyzed to determine its pollution characteristics at a typical non-ferrous metal smelting site. A panel study conducted among factory workers revealed that PM2.5-Pb exposure makes an important contribution to the human absorption of Pb. Although the chemical speciation of PM2.5-Pb suggested poor water solubility, a high bioavailability was observed in mice (tissue average value: 50.1%, range: 31.1-71.1%) subjected to inhalation exposure for 8 weeks. Based on the bioavailability data, the relationship between PM2.5-Pb exposure and cardiovascular damage was evaluated in animal simulation experiments. Finally, a damage threshold and cardiovascular-specific risk assessment model were established for the non-ferrous metal smelting area. Our project not only accurately estimates the risk of PM2.5-bound heavy metals on the cardiovascular system but also offers a scientific basis for future prevention and therapy of PM2.5-Pb-related diseases.

Arsenic Ingested Early in Life Is More Readily Absorbed: Mechanistic Insights from Gut Microbiota, Gut Metabolites, and Intestinal Morphology and Functions

Early-life arsenic (As) exposure is a particular health concern. However, it is unknown if As ingested early in life is more readily absorbed from the gastrointestinal (GI) tract, i.e., higher in oral bioavailability. Here, weanling (3-week) and adult (6-week-old) female mice were exposed to arsenate in the diet (10 μg g^-1) over a 3-week period with As oral bioavailability estimated using As urinary excretion as the bioavailability endpoint. The As urinary excretion factor was 1.54-fold higher in weanling mice compared to adult mice (82.2 ± 7.29 versus 53.1 ± 3.73%), while weanling mice also showed 2.28-, 1.50-, 1.48-, and 1.89-fold higher As concentration in small intestine tissue, blood, liver, and kidneys, demonstrating significantly higher As oral bioavailability of early-life exposure. Compared to adult mice, weanling mice significantly differed in gut microbiota, but the difference did not lead to remarkable differences in As biotransformation in the GI tract or tissue and in overall gut metabolite composition. Although the expression of several metabolites (e.g., atrolactic acid, hydroxyphenyllactic acid, and xanthine) was up-regulated in weanling mice, they had limited ability to elevate As solubility in the intestinal tract. Compared to adult mice, the intestinal barrier function and intestinal expression of phosphate transporters responsible for arsenate absorption were similar in weanling mice. However, the small intestine of weanling mice was characterized by more defined intestinal villi with greater length and smaller width, providing a greater surface area for As to be absorbed across the GI barrier. The results highlight that early-life As exposure can be more readily absorbed, advancing the understanding of its health risk.

Variation of lead bioaccessibility in soil reference materials: Intra- and inter-laboratory assessments

Standard reference materials (SRMs) have been commonly used to perform quality assurance and quality control (QA/QC) in soil total metal concentration analyses or bioaccessibility assessment. In this study, 10 experimenters from 4 laboratories determined bioaccessibility of lead (Pb) in 4 widely-used SRMs (NIST 2710a, NIST 2587, BGS 102, and GBW 07405). Based on the gastric phase (GP) of the unified BARGE bioaccessibility method (UBM) and the Solubility Bioavailability Research Consortium procedure (SBRC), Pb bioaccessibility in SRMs was compared within and between laboratories to assess their intra-laboratory repeatability and inter-laboratory reproducibility. Lead bioaccessibility was 14.1 ± 2.44%-101 ± 2.48% in the 4 SRMs. The values were in vivo validated based on a mouse model in previous studies (R² = 0.97-0.98), suggesting the reliability of Pb bioaccessibility data. Strong correlations were observed for Pb bioaccessibility among 7 experimenters (R² = 0.94-0.99) at the Nanjing University (NJU) laboratory and similar strong correlations were also found between each two of the 4 laboratories (R² = 0.94-0.98), illustrating consistency in intra- and inter-laboratory performance. The intra-laboratory repeatability and inter-laboratory reproducibility were generally acceptable with relative standard deviations (RSDs) of Pb bioaccessibility being ≤10% within laboratory and ≤20% between laboratories, except in a soil with low bioaccessible Pb (BSG 102). Our study suggested that measurements of Pb bioaccessibility in SRMs based on the two in vivo validated methods were repeatable and reproducible within and between laboratories, further verified their reliability being used as QA/QC samples during Pb bioaccessibility assessment.

Detection of microplastics in domestic and fetal pigs' lung tissue in natural environment: A preliminary study

Microplastics (MPs) are ubiquitous in the environment. However, it is unclear whether MPs are present in mammalian lungs through inhalation, and if so, could be possibly found in fetal tissues. In this study, we aim to determine the presence and characteristics of particles in domestic and fetal pig lung tissue in the natural environment. Specimens from the lungs of domestic pigs (n = 10) and fetal pigs that already died in matrix during vaginal birth from the non-contaminated area (n = 10) were obtained from farmers' nearby sludge treatment plant. These specimens were compressed between two glass microscope slides, which were examined under polarized light microscopy. In addition, Agilent 8700 LDIR Chemical imaging system (LDIR) was used to determine the quantitative and qualitative characteristics of MPs. According to the polarized light microscope survey of domestic pig lungs, we observed an average of 12 particles/g, which was more than the 6 particles/g observed in fetal pig lungs, which ranged in size from 115.14 μm to 1370.43 μm. All the observed MP particles were fiber in shape. LDIR indicated an average of 180 particles/g of domestic pig lungs, ranging in size from 20.34 μm to 916.36 μm, which was twice as many MPs observed in fetal pig lungs. Furthermore, the compositions of MPs were different between them. LDIR indicated that polyamide (PA) was the most common polymer identified in domestic pig lungs (46.11%), while polycarbonate (PC) was the most common polymer in fetal pig lungs (32.99%). These findings confirmed the presence of MPs in the lung tissue of both domestic and fetal pigs in the natural environment, but the main characteristics differed. This fact indicated the increasing risk of MPs to human respiratory tract is increasing. Further research should be conducted to entirely estimate the specific exposure level on humans and offspring.

Bioaccessibility and Intestinal Transport of Tebuconazole in Table Grape by Using In Vitro Digestion Models

In this study, the effects of various digestive models, influencing factors and dietary supplements on the bioaccessibility of tebuconazole in table grapes were compared. The Caco-2 cell model was employed to reveal the transfer behavior of tebuconazole. The results indicated that digestion time is the main factor affecting bioaccessibility. With an increase in time, the tebuconazole in grapes was almost completely dissolved, with bioaccessibility reaching 98.5%, whereas dietary fiber reduced bioaccessibility. Tebuconazole undergoes carrier-free passive transport in permeable cells in the Caco-2 cell model. These findings have practical application value for correctly evaluating the harmful level of pollutants in the matrix to human body.

Ca Minerals and Oral Bioavailability of Pb, Cd, and As from Indoor Dust in Mice: Mechanisms and Health Implications

BACKGROUND

Elevating dietary calcium (Ca) intake can reduce metal(loid)oral bioavailability. However, the ability of a range of Ca minerals to reduce oral bioavailability of lead (Pb), cadmium (Cd), and arsenic (As) from indoor dust remains unclear.

OBJECTIVES

This study evaluated the ability of Ca minerals to reduce Pb, Cd, and As oral bioavailability from indoor dust and associated mechanisms.

METHODS

A mouse bioassay was conducted to assess Pb, Cd, and As relative bioavailability (RBA) in three indoor dust samples, which were amended into mouse chow without and with addition of CaHPO4,  CaCO3, Ca gluconate, Ca lactate, Ca aspartate, and Ca citrate at 200-5,000μg/g Ca. The mRNA expression of Ca and phosphate (P) transporters involved in transcellular Pb, Cd and As transport in the duodenum of mice was quantified using real-time polymerase chain reaction. Serum 1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], parathyroid hormone (PTH), and renal CYP27B1 activity controlling 1,25(OH)2D3 synthesis were measured using ELISA kits. Metal(loid) speciation in the feces of mice was characterized using X-ray absorption near-edge structure (XANES) spectroscopy.

RESULTS

In general, mice exposed to each of the Ca minerals exhibited lower Pb-, Cd-, and As-RBA for three dusts. However, RBAs with the different Ca minerals varied. Among minerals, mice fed dietary CaHPO4 did not exhibit lower duodenal mRNA expression of Ca transporters but did have the lowest Pb and Cd oral bioavailability at the highest Ca concentration (5,000μg/g Ca; 51%-95% and 52%-74% lower in comparison with the control). Lead phosphate precipitates (e.g., chloropyromorphite) were observed in feces of mice fed dietary CaHPO4. In comparison, mice fed organic Ca minerals (Ca gluconate, Ca lactate, Ca aspartate, and Ca citrate) had lower duodenal mRNA expression of Ca transporters, but Pb and Cd oral bioavailability was higher than in mice fed CaHPO4. In terms of As, mice fed Ca aspartate exhibited the lowest As oral bioavailability at the highest Ca concentration (5,000μg/g Ca; 41%-72% lower) and the lowest duodenal expression of P transporter (88% lower). The presence of aspartate was not associated with higher As solubility in the intestine.

DISCUSSION

Our study used a mouse model of exposure to household dust with various concentrations and species of Ca to determine whether different Ca minerals can reduce bioavailability of Pb, Cd, and As in mice and elucidate the mechanism(s) involved. This study can contribute to the practical application of optimal Ca minerals to protect humans from Pb, Cd, and As coexposure in the environment. https://doi.org/10.1289/EHP11730.

Bioaccessibility, source and human health risk of Pb, Cd, Cu and Zn in windowsill dusts from an area affected by long-term Pb smelting

Non-ferrous metal smelting results in heterogenous spatial distribution of potentially toxic metals (PTM) near smelters. In this work, windowsill dusts were collected from smelting (SA) and urban (UJ) sub-areas of Jiyuan (a city affected by >70 years of Pb smelting) to investigate PTM source and bioaccessibility. The <10 μm fraction of dusts were analyzed for total and bioaccessible Pb, Cd, Cu and Zn concentrations; bioaccessibility was analyzed by a three-stage assay (i.e., lung phase, gastric phase and gastrointestinal phase) using artificial lysosomal fluid (ALF, L phase) followed by simulated gastric and gastrointestinal fluids (G and GI phases). This assay mimicked the movement of particles phagocytosed by alveolar macrophages in the respiratory system, then transported up the oropharynx and subsequently swallowed and transported into the digestive system. Zinc had greater bioaccessible concentrations in L and GI phases than other metals, and the mean L phase bioaccessible PTM concentrations in SA were greater than in UJ. The mean L + GI phase bioaccessible concentrations of Pb, Cd, Cu and Zn in SA were 280, 79, 124 and 1458 mg kg^-1, while those in UJ were 215, 54, 116 and 598 mg kg^-1, respectively. The L phase extracted 87.7 to 98.8 % of PTM within the L + GI assay. Lead had a lower L + GI bioaccessibility than Cd, Cu and Zn (70-76 % vs. 82-92 %). Higher tolerable Cd carcinogenic risks based on bioaccessibility were found in SA sub-area than in UJ while no carcinogenic or non-carcinogenic risk was found for other metals. Lead isotopic ratios indicated that both Pb ore and smelting bottom ash contributed to dust Pb accumulation in SA, while coal burning, lead ore, Pb smelting bottom ash and diesel engine exhaust contributed to dust Pb accumulation in UJ. Overall, results indicated heterogenous distribution of PTM source and bioaccessibility in the vicinity of Pb smelters.

Nickel oral bioavailability in contaminated soils using a mouse urinary excretion bioassay: Variation with bioaccessibility

To assess the health risk of nickel (Ni) in contaminated soils, studies rarely evaluated Ni bioavailability in the gastrointestinal (GI) tract, limiting the accurate regulation of contaminated sites. Here, for 15 soil samples contaminated by Ni-electroplating, Ni oral relative bioavailability (RBA, relative to NiSO₄) was measured using a mouse urinary excretion bioassay. Nickel-RBA varied from 7.89% to 33.8% at an average of 19.1 ± 18.6%. The variation was not explained well by variation in soil properties including Ni speciation and co-contamination of other metals, which showed weak correlation with Ni-BRA (R² < 0.36). In comparison, the Ni-RBA variation was explained well by the variation of soil-Ni solubility in simulated human gastric or gastrointestinal fluids, i.e., Ni bioaccessibility. Determined using the gastric (GP) and intestinal phases (IP) of solubility bioaccessibility research consortium (SBRC), physiologically based extraction test methods (PBET), and unified BARGE method (UBM), Ni bioaccessibility explained 54-71% variation of the Ni-RBA, suggesting that Ni oral bioavailability was predominantly controlled by Ni solubility in the GI tract. The results highlight the suitability of using simple, fast, and cost-effective bioaccessbility assays to predict site-specific Ni oral bioavailability.

Effect of vitamin C supplement on lead bioaccessibility in contaminated soils using multiple in vitro gastrointestinal assays: Mechanisms and health risks

Effects of vitamin C supplementation on the oral bioaccessibility of lead (Pb) present in contaminated soils were examined using a number of in vitro assays (PBET, SBRC, UBM and IVG). In the presence of vitamin C, an increase in Pb bioaccessibility was observed in the gastric phase by 1.3-fold (30.5%-85.5%) and in the intestinal phase by 3.1-fold (0.9%-58.9%). Lead mobilization was regulated by reductive dissolution of Fe(III) and sequestration of Pb on secondary Fe minerals. Sequential extraction by the Bureau Community of Reference (BCR) provided more evidence that reducible fraction and residual fraction were major contributor of gastric Pb bioaccessibility, as well as reduced fractions in intestinal Pb bioaccessibility. In addition, higher non-carcinogenic risks may occur based on target hazard quotient (THQ ≥ 1). For people exposed to Pb present in soil, the management of vitamin C supplements is of serious concern.

Nephrotoxic Biomarkers with Specific Indications for Metallic Pollutants: Implications for Environmental Health

Environmental and occupational exposure to heavy metals and metalloids is a major global health risk. The kidney is often a site of early damage. Nephrotoxicity is both a major consequence of heavy metal exposure and potentially an early warning of greater damage. A paradigm shift occurred at the beginning of the 21st century in the field of renal medicine. The medical model of kidney failure and treatment began to give way to a social model of risk factors and prevention with important implications for environmental health. This development threw into focus the need for better biomarkers: markers of exposure to known nephrotoxins; markers of early damage for diagnosis and prevention; markers of disease development for intervention and choice of therapy. Constituents of electronic waste, e-waste or e-pollution, such as cadmium (Cd), lead (Pb), mercury (HG), arsenic (As) and silica (SiO₂) are all potential nephrotoxins; they target the renal proximal tubules through distinct pathways. Different nephrotoxic biomarkers offer the possibility of identifying exposure to individual pollutants. In this review, a selection of prominent urinary markers of tubule damage is considered as potential tools for identifying environmental exposure to some key metallic pollutants.

Incorporating Tenax into the in vitro method to improve the predictive capability of bioaccessibility of triazole fungicides in grape

In vitro bioaccessibility assays have been developed for high-throughput prediction of relative bioavailability (RBA). However, methods to reliably and efficiently assess pesticide residues remain limited, hindering the precise estimation of pesticide exposure risk. The inclusion of a sorption sink material to simulate intestinal sorption could be a promising approach to optimize in vitro bioaccessibility methods. The current study aimed to explore the feasibility of incorporating Tenax into the Rijksinstituut voor Volksgezondheid en Milieu (RIVM) method for accurate evaluation of the bioaccessibility of triazole fungicides. The use of 1.0 g of Tenax enabled the valid trapping of triazole fungicides released from grape, resulting in a significant increase of 23.59-38.51 % in the value of bioaccessibility. A strong in vivo-in vitro correlation was observed between pesticide RBA and bioaccessibility, suggesting that the Tenax-assisted RIVM method is a suitable replacement for time-consuming and laborious in vivo alternatives. In addition, the exposure assessment indicated that the hazard quotients for triazole fungicides in grape may be overestimated by 5.79-27.34 % without considering bioaccessibility based on the Tenax-assisted RIVM method. These results provide further insights into the assessment of bioaccessibility-based human exposure to pesticides as well as dietary exposure and related risk for human health.

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.

Cadmium oral bioavailability is affected by calcium and phytate contents in food: Evidence from leafy vegetables in mice

To test high cadmium (Cd) concentration may not be high in health risk when considering Cd bioavailability, we assessed variation of Cd relative bioavailability (RBA, relative to CdCl₂) using a mouse assay for 14 vegetables of water spinach, amaranth, and pakchoi. Cadmium concentration varied from 0.13 ± 0.01-0.37 ± 0.00 μg g^-1 fw. Cadmium-RBA also varied significantly from 22.9 ± 2.12-77.2 ± 4.46%, however, the variation was overall opposite to that of Cd concentration, as indicated by a strong negative correlation between Cd-RBA and Cd concentration (R² = 0.43). Based on both Cd concentration and bioavailability, the identified high-Cd pakchoi variety resulted in significantly lower Cd intake than the high-Cd varieties of water spinach and amaranth (4.74 ± 0.05 vs. 10.1 ± 0.54 and 8.03 ± 0.04 μg kg^-1 bw week^-1) due to significantly lower Cd-RBA (22.9 ± 2.12 vs. 77.2 ± 4.46 and 51.3 ± 2.93%). The lower Cd-RBA in pakchoi was due to its significantly higher Ca and lower phytate concentrations, which facilitated the role of Ca in inhibiting intestinal Cd absorption. This was ascertained by observation of decreased Cd-RBA (90.5 ± 12.0% to 63.5 ± 5.53%) for a water spinach when elevating its Ca concentration by 30% with foliar Ca application. Our results suggest that to assess food Cd risk, both total Cd and Cd bioavailability should be considered.

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

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

Lead content in soil, plants, rodents, and amphibians in the vicinity of a heating plant's ash waste

This study supplements previous research focused on environmental condition in the vicinity of waste ash material. The main aim of our study was the comparative analysis of lead levels in soil, plant, and animal organisms in the area of the tailings pond and surroundings, using x-ray. Findings confirm that the level of Pb in the top layer of soil is in the range of 20-135 ppm. Lead content in Calamagrostis plant tissues was confirmed only at the tailings pond area, with the highest lead concentrations measured in above-ground components; stems with blooms followed by roots and ground floor sheats. The livers, kidneys, and hearts of Apodemus flavicollis were examined, with findings of higher values in the tailings pond area than in the reference site, and average values of 14.5 ppm for livers, 16.0 ppm for kidneys, and 16.6 ppm for hearts. No significant differences were discovered based on sex and body length/body weight of A. flavicollis individuals. Values for Bombina variegata liver tissue reached an average of 12.3 ppm for individuals caught in a water reservoir without ash sediments, versus 15.7 ppm in those trapped by the edge of then tailings pond area. Females had lower concentrations of lead than males, but with no statistically significant differences found. Despite lower lead levels in soil and ash than expected, concentrations in mammalian and amphibian organs suggest a possible transition of this element into the food chain, and therefore further research in this area is recommended.

Leaching and In Vivo Bioavailability of Antimony in PET Bottled Beverages

Antimony (Sb) may leach from polyethylene terephthalate (PET) materials into bottled water under improper storage conditions, particularly at high temperatures, leading to potential Sb chronic exposure and adverse health effects. However, Sb leaching may be promoted by various beverage constituents, which has received limited attention to date. In addition, few studies have considered Sb bioavailability in beverages and the influence of the beverage matrix on Sb bioavailability. In this study, PET-bottled beverages (n = 50) covering six categories (namely, carbonated, fruit juices, tea, sports, protein, and coffee beverages) were explored. Antimony leaching was assessed following the incubation of beverages at 60 °C for 7 days, which resulted in Sb concentrations 1.10-10.9 times greater than concentrations observed pre-incubation. Although regulatory standards vary internationally, a total of 21 beverages exceeded the Japanese Sb drinking water standard of 2 μg/L (up to 4.08 ± 0.11 μg/L) following incubation at 60 °C. pH significantly influenced Sb leaching (r = -0.38, p = 0.007) with beverages displaying lower pH (e.g., carbonated drinks) exhibiting higher Sb concentrations. An in vivo mouse model, using the liver as the biological endpoint, was adopted to assess Sb relative bioavailability (RBA) in bottled beverages. Sb RBA ranged from 1.97-58.7% with coffee beverages exhibiting the lowest Sb RBA (1.97-13.7%) and protein drinks the highest (41.1-58.7%). Linear regression revealed that Sb RBA in beverages was negatively influenced by Fe (r = -0.69, p = 0.02) and P (r = -0.73, p = 0.01) concentrations but positively correlated with tartaric acid (r = 0.59, p = 0.02). When an exposure assessment was undertaken using data generated in this study, carbonated and protein-rich beverages exhibited a higher exposure risk due to elevated Sb leaching and high Sb RBA compared to other beverage categories.

Effect of Soil Properties and Aging Time on Oral and Inhalation Bioaccessibility of Copper Oxide Nanoparticles in Soils

In this study, soils spiked with copper oxide nanoparticles (CuO NPs) or Cu(NO₃)₂ and aged as long as 90 days were utilized to investigate effect of soil properties and aging on oral and inhalation bioaccessibility of CuO NPs. Results showed that oral bioaccessibility of CuO NPs in gastric phase (GP) ranged from 70% to 84%, it significantly decreased to 50%-70% in intestinal phase (IP). The inhalation bioaccessibility of CuO NPs in artificial lysosomal fluid (ALF) ranged from 66% to 85%, and much higher than that in Gamble's solution (GS, 3.3%-23%). By comparing CuO NPs to Cu(NO₃)₂ bioaccessibility, insignificant difference was found. The aging time (D15 and D90) had limited effect on their oral and inhalation bioaccessibility. CEC and free Al were positively and clay content was negatively correlated with CuO NPs inhalation bioaccessibility, while Cu(NO₃)₂ inhalation bioaccessibility decreased with increasing soil clay content and pH. Our findings provide an essential basis to evaluate the human health risks of CuO NPs.

In Vivo-In Vitro Correlations for the Assessment of Cadmium Bioavailability in Vegetables

The correlation of in vitro and in vivo assays for determining bioavailable Cd amounts in vegetables is limited. Herein, the correlations between Cd relative bioavailability (Cd-RBA) in rat models and Cd bioaccessibility in four in vitro assays were examined in vegetables. Results showed that the combined liver plus kidney data provided the appropriate endpoint and was used as a biomarker to estimate Cd-RBA. The Cd-RBA was negatively correlated with the mole ratio of Ca/Cd and Fe/Cd in vegetables. Strong in vivo-in vitro correlations were found from physiologically based extraction test (PBET) and in vitro gastrointestinal (IVG) (R² = 0.66-0.69). We concluded that PBET and IVG were optimal models for Cd-RBA determination in vegetables. The nutritional elements in the vegetables could affect Cd absorption. Furthermore, the Cd bioavailability in vegetables should be considered because risk estimates solely based on the total Cd concentration in vegetables would overestimate Cd intake.

Nitrogen fertilizer affects rhizosphere Cd re-mobilization by mediating gene AmALM2 and AmALMT7 expression in edible amaranth roots

In-situ stabilization of Cd-contaminated farmland is a commonly used remediation technology. Yet, rhizosphere metabolites (e.g., organic acids) during crop cultivation may cause Cd re-mobilization and over-accumulation. Here, we identified four pivotal cytomembrane-localized genes underlying Cd accumulation difference between two contrasting edible amaranth cultivars based on root gene expression profile, studied their subcellular localization and functional characteristics, and then investigated effects of nitrogen fertilizer on their expression and rhizosphere Cd re-mobilization. Results showed that more Cd accumulated by edible amaranth was due to rhizosphere Cd mobilization by mediating high expression of AmALMT2 and AmALMT7 genes, not Cd transporters in roots. This was confirmed by heterologous expression of AmALMT2 and AmALMT7 genes in Arabidopsis thaliana, since they mediated malic, fumaric, succinic, and aspartic acids efflux. Furthermore, nitrogen influencing rhizosphere acidification might be closely associated with organic acids efflux genes. Compared with N-NO₃^- application, N-NH₄⁺ was massively assimilated into glutamates and oxaloacetates through up-regulating glutamine synthetase and alanine-aspartate-glutamate metabolic pathways, thereby enhancing TCA cycle and organic acids efflux dominated by binary carboxylic acids via up-regulating AmALMT2 and AmALMT7 genes, which finally caused Cd re-mobilization. Therefore, N-NO₃^--dominated nitrogen retarded rhizosphere Cd re-mobilization via inhibiting organic acids efflux function of AmALMT2 and AmALMT7 proteins.

Human health risk assessment in aluminium smelting site: Soil fluoride bioaccessibility and relevant mechanism in simulated gastrointestinal tract

Incidental oral ingestion is considered to be an important exposure route for humans to soil contaminants, such as fluoride (F). For 25 soil samples containing 4000 mg F/kg from aluminium smelting site in southwestern China, this study investigated F bioaccessibility in the human gastrointestinal tract in vitro. Fluoride bioaccessibility (2.4-48.8%) in the gastric phase was primarily caused by the dissolution of F-Ca and F-Al compounds (assigned to residual phase), identified by X-ray photoelectron spectroscopy and sequential extraction. Following modification to the small intestinal phase, the variation in F bioaccessibility (2.5-38.8%) should be the result of concurrent processes, including the formation of F complexes and competitive adsorption, and inversely the precipitation of fluorite and surface adsorption of formed F-Al complexes. The colon incubation with human gut microbiota yielded a 1.3-fold increase in F bioaccessibility (3.9-45.7%), probably due to the dissolution of F bound to Fe (hydr)oxides. Bioaccessibility adjustment can reduce hazard quotient of fluoride, and non-carcinogenic risk for children should be noted that soil F intake contributed 21.7% on average, up to 76.6% of oral reference dose. This will result in better understanding of human health risk assessment associated with F exposures.

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.

Arsenic bioaccessibility in rice grains via modified physiologically-based extraction test (MPBET): Correlation with mineral elements and comparison with As relative bioavailability

Rice consumption is a major dietary source of human exposure to arsenic (As), with As bioavailability being an important factor influencing its health risk. In this study, the As bioaccessibility was measured in 11 rice grains (140-335 μg As kg^-1), which were compared to As relative bioavailability previously measured based on a mouse bioassay (Li et al., 2017). Using modified physiologically-based extraction test for rice (MPBET), As bioaccessibility in raw rice samples (44-88% in the gastric phase and 47-102% in the intestinal phase) was similar to those in cooked rice (42-73% and 43-99%). Arsenic bioaccessibility in rice was generally higher in the intestinal phase than in the gastric phase, with Fe and Ca concentrations in rice being negatively correlated with As bioaccessibility in the gastric phase (R² = 0.47-0.49). In addition, for cooked rice, strong positive correlation was observed between bioaccessible As and inorganic As (R² = 0.63-0.72), suggesting inorganic As in rice was easier to dissolve than organic As in gastrointestinal digestive fluids. Due to limited variation in As bioaccessibility and As bioavailability among the 11 samples, a weak correlation was observed between them (R² = 0.01-0.03); however, As bioaccessibility values measured by the gastric phase (GP) of the MPBET agreed with As bioavailability values based on a mouse bioassay, suggesting the potential of the MPBET_GP to predict As bioavailability in rice. Future work is needed to ascertain the robustness of the MPBET_GP in predicting As bioavailability in rice using additional samples.

Effect of gut microbiota on in vitro bioaccessibility of heavy metals and human health risk assessment from ingestion of contaminated soils

To identify the role of gut microbiota in human health risk assessment, the bioaccessibility of heavy metals in 14 soil samples were determined in simulated gastrointestinal fluids. Compared to the small intestinal phase, the bioaccessibility values of the colon phase varied, either increased by 3.5-fold for As, by 2.2-fold for Cr, and by 1.6-fold for Ni, or reduced by 4.4-fold for Cu, respectively. The colon incubation with adult gut microbiota yielded higher bioaccessibility value of As (1.3 times) and Fe (3.4 times) than that of the child in most soil samples. Colon bioaccessibility was about 60% greater of Cd for the adult and 30% higher of Cr for the child. Congruent data on the bioaccessibility of Cu and Ni was observed. In addition, correlation analysis indicated that in vitro bioaccessibility was primarily related to total concentrations of heavy metals in soils, followed by soil pH and active Fe/Mn oxide. Significantly, risk assessment calculated based on colon bioaccessibility indicated that the target hazard quotient (THQ > 1) of As was presented in 3 soil samples for the adult (1.05-3.35) and in 9 soil samples for the child (1.06-26.93). The hazard index (HI) of the child was 4.00 on average, greater than that of the adult (0.62), primarily due to the contribution of As and Cd. It suggested non-carcinogenic risks are likely to occur in children through typical hand-to-mouth behavior. The adjustment of colon bioaccessibility will result in more accurate risk assessment of human exposure to heavy metals from oral ingestion of contaminated soils.

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.