Arsenic-enhanced plant growth in As-hyperaccumulator Pteris vittata: Metabolomic investigations and molecular mechanisms

The first-known As-hyperaccumulator Pteris vittata is efficient in As uptake and translocation, which can be used for phytoremediation of As-contaminated soils. However, the underlying mechanisms of As-enhanced plant growth are unknown. We used untargeted metabolomics to investigate the potential metabolites and associated metabolic pathways regulating As-enhanced plant growth in P. vittata. After 60 days of growth in an MS-agar medium containing 15 mg kg-1 As, P. vittata biomass was 33-34 % greater than the no-As control. Similarly, the As contents in P. vittata roots and fronds were 272 and 1300 mg kg-1, considerably greater than the no-As control. Univariate and multivariate analyses based on electrospray ionization indicate that As exposure changed the expression of 1604 and 1248 metabolites in positive and negative modes. By comparing with the no-As control, As exposure significantly changed the expression of 14 metabolites including abscisic acid, d-glucose, raffinose, stachyose, chitobiose, xylitol, gibberellic acids, castasterone, citric acid, riboflavin-5-phosphate, ubiquinone, ubiquinol, UDP-glucose, and GDP-glucose. These metabolites are involved in phytohormone synthesis, energy metabolism, and sugar metabolism and may all potentially contribute to regulating As-enhanced plant growth in P. vittata. Our data provide clues to understanding the metabolic regulations of As-enhanced plant growth in P. vittata, which helps to enhance its phytoremediation efficiency of As-contaminated soils.

Novel Phosphate Transporter-B PvPTB1;1/1;2 Contribute to Efficient Phosphate Uptake and Arsenic Accumulation in As-Hyperaccumulator Pteris vittata

Arsenic (As) contamination in soil poses a potential threat to human health via crop uptake. As-hyperaccumulator Pteris vittata serves as a model plant to study As uptake and associated mechanisms. This study focuses on a novel P/AsV transport system mediated by low-affinity phosphate transporter-B 1 family (PTB1) in P. vittata. Here, we identified two plasma-membrane-localized PTB1 genes, PvPTB1;1/1;2, in vascular plants for the first time, which were 4.4-40-fold greater in expression in P. vittata than in other Pteris ferns. Functional complementation of a yeast P-uptake mutant and enhanced P accumulation in transgenic Arabidopsis thaliana confirmed their role in P uptake. Moreover, the expression of PvPTB1;1/1;2 facilitated the transport and accumulation of As in both yeast and A. thaliana shoots, demonstrating a comparable AsV uptake capacity. Microdissection-qPCR analysis and single-cell transcriptome analysis collectively suggest that PvPTB1;1/1;2 are specifically expressed in the epidermal cells of P. vittata roots. PTB1 may play a pivotal role in efficient P recycling during phytate secretion and hydrolysis in P. vittata roots. In summary, the dual P transport mechanisms consisting of high-affinity Pht1 and low-affinity PTB1 may have contributed to the efficient P/As uptake in P. vittata, thereby contributing to efficient phytoremediation for As-contaminated soils.

Insight into the availability and desorption kinetics of Se and Cd in naturally-rich soils using diffusive gradients in thin-films technique

Cadmium (Cd) contamination of selenium (Se)-rich soils may jeopardize the nutritional benefits of Se-biofortified crops. This study employed diffusive gradients in thin-films (DGT) technique and DIFS (DGT-induced fluxes in soils) model to understand the interdependency and driving factors of Se and Cd distribution and desorption kinetics across 50 soils from south China with naturally elevated levels. DGT-labile Se was the highest (up to 2.66 μg L-1) in non-carbonate/shale-derived soils, while Cd was maximal (5.53 μg L-1) in carbonate-based soils, reflecting soil background concentrations and soil characteristics. Over one-third of the soils showed labile Se:Cd molar ratio below 0.7, suggesting Cd phytotoxicity risks. The DIFS-derived response times (Tc) and desorption rate constants (k-1) suggested that Se was resupplied to the soil solution faster than Cd in soils with higher pH and SOM level, but Se resupply was still restricted due to the rapid depletion of its labile pool. As the first study of Se and Cd release kinetics in soils, our results reveal dependence on soil parent materials, with low labile Se:Cd soils presenting greater Cd hazards. By elucidating Se and Cd lability and interactions in soils, our findings help to inform management strategies to balance reduced Cd risk with adequate Se availability.

Insoluble-Phytate Improves Plant Growth and Arsenic Accumulation in As-Hyperaccumulator Pteris vittata: Phytase Activity, Nutrient Uptake, and As-Metabolism

Phytate, the principal P storage in plant seeds, is also an important organic P in soils, but it is unavailable for plant uptake. However, the As-hyperaccumulator Pteris vittata can effectively utilize soluble Na-phytate, while its ability to utilize insoluble Ca/Fe-phytate is unclear. Here, we investigated phytate uptake and the underlying mechanisms based on the phytase activity, nutrient uptake, and expression of genes involved in As metabolisms. P. vittata plants were cultivated hydroponically in 0.2-strength Hoagland nutrient solution containing 50 μM As and 0.2 mM Na/Ca/Fe-phytate, with 0.2 mM soluble-P as the control. As the sole P source, all three phytates supported P. vittata growth, with its biomass being 3.2-4.1 g plant-1 and Ca/Fe-phytate being 19-29% more effective than Na-phytate. Phytate supplied soluble P to P. vittata probably via phytase hydrolysis, which was supported by 0.4-0.7 nmol P min-1 g-1 root fresh weight day-1 phytase activity in its root exudates, with 29-545 μM phytate-P being released into the growth media. Besides, compared to Na-phytate, Ca/Fe-phytate enhanced the As contents by 102-140% to 657-781 mg kg-1 in P. vittata roots and by 43-86% to 1109-1447 mg kg-1 in the fronds, which was accompanied by 21-108% increase in Ca and Fe uptake. The increased plant As is probably attributed to 1.3-2.6 fold upregulation of P transporters PvPht1;3/4 for root As uptake, and 1.8-4.3 fold upregulation of arsenite antiporters PvACR3/3;1/3;3 for As translocation to and As sequestration into the fronds. This is the first report to show that, besides soluble Na-phytate, P. vittata can also effectively utilize insoluble Ca/Fe-phytate as the sole P source, which sheds light onto improving its application in phytoremediation of As-contaminated sites.

Total contents, fractionation and bioaccessibility of nine heavy metals in household dust from 14 cities in China

The potential health risk caused by long-term exposure to heavy metals in household dust is not only depended on their total content, but also bioaccessibility. In this study, twenty-one dust samples were collected from residential buildings, schools, and laboratories in 14 provincial-capital/industrial cities of China, aiming to evaluate the total contents, fractionation, bioaccessibility and health risks of nine heavy metals (As, Cd, Cr, Ni, Pb, Mn, Zn, Fe, and Cu). Results showed that the highest levels of Cd, Cr, Ni and Zn were found in laboratory dust, As, Pb and Mn in school dust, and Fe and Cu in residential dust, indicating different source profiles of the heavy metals. The mean bioaccessibility of the heavy metals across all samples as evaluated using SBRC (Solubility Bioavailability Research Consortium), IVG (In Vitro Gastrointestinal), and PBET (Physiologically Based Extraction Test) assays was 58.4%, 32.4% and 17.2% in gastric phase (GP), and 24.9%, 21.9% and 9.39% in intestinal phase (IP), respectively. Cadmium had the highest content in the fractions of E1+C2 (43.7%), as determined by sequential extraction, and Pb, Mn, and Zn had a higher content in E1+C2+F3 (64.2%, 67.2%, 78.8%), resulting in a higher bioaccessibility of these heavy metals than others. Moreover, the bioaccessibility of most heavy metals was inversely related to dust pH (R = -0.18 in GP; -0.18 in IP; P < 0.01) and particle size, while a positive correlation was observed with total organic carbon (R = 0.40 in GP; 0.38 in IP; P < 0.01). The exposure risk calculated by the highest bioaccessibility was generally lower than that calculated by the total content. However, Pb in one school dust sample had an unacceptable carcinogenic risk (adult risk = 1.19 × 10-4; child risk = 1.08 × 10-4). This study suggests that bioaccessibility of heavy metals in household dust is likely related to geochemical fractions and physical/chemical properties. Further research is needed to explore the sources of bioaccessible heavy metals in household dust.

Contamination and Carcinogenic Risks of Lead in Lip Cosmetics in China

There are growing concerns about elevated lead (Pb) levels in lip cosmetics, yet in China, the largest lip cosmetic market, recent Pb contamination in lip cosmetics and associated Pb exposure remain unclear. Here, we measured Pb levels of 29 popular lip cosmetics in China and conducted the bioaccessibility-corrected carcinogenic risk assessments and sensitivity analysis regarding Pb exposure for consumers using Monte Carlo simulation. The Pb concentrations of collected samples ranged from undetectable (< 0.05 µg/kg) to 0.21 mg/kg, all of which were well below the Pb concentration limit set for cosmetics in China (10 mg/kg). The 50th percentile incremental lifetime cancer risk (ILCR) of Pb in Chinese cosmetics (1.20E-07) was below the acceptable level (1E-06), indicating that the application of lip cosmetics and subsequent Pb exposure does not pose carcinogenic risks to consumers in most cases. The results of this study provide new insights into understanding the Pb risk in lip cosmetics.

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.

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.

Copper enhanced arsenic-accumulation in As-hyperaccumulator Pteris vittata by upregulating its gene expression for As uptake, translocation, and sequestration

In contaminated soils, arsenic (As) often co-exists with copper (Cu). However, its effects on As accumulation and the related mechanisms in As-hyperaccumulator Pteris vittata remain unclear. In this study, P. vittata plants were exposed to 50 µM As and/or 50 µM Cu under hydroponics to investigate the effects of Cu on plant growth and As accumulation, as well as gene expression related to arsenic uptake (P transporters), reduction (arsenate reductases), and translocation and sequestration (arsenite antiporters). After 14 d of growth and compared to the As treatment, the As concentration in P. vittata fronds increased by 1.4-times from 793 to 1131 mg·kg-1 and its biomass increased by 1.2-fold from 18.0 to 21.1 g·plant-1 in the As+Cu treatment. Copper-enhanced As accumulation was probably due to upregulated gene expressions related to As-metabolisms including As uptake (1.9-fold in P transporter PvPht1;3), translocation (2.1-2.4 fold in arsenite antiporters PvACR3/3;2) and sequestration (1.5-2.0 fold in arsenite antiporters PvACR3;1/3;3). Our results suggest that moderate amount of Cu can help to increase the As accumulation efficiency in P. vittata, which has implication in its application in phytoremedation in As and Cu co-contaminated soils.

Refining health risk assessment of arsenic in wild edible boletus from typical high geochemical background areas: The role of As species, bioavailability, and enterotoxicity

Arsenic (As) is easily accumulated in wild Boletus. However, the accurate health risks and adverse effects of As on humans were largely unknown. In this study, we analyzed the total concentration, bioavailability, and speciation of As in dried wild boletus from some typical high geochemical background areas using an in vitro digestion/Caco-2 model. The health risk assessment, enterotoxicity, and risk prevention strategy after consumption of As-contaminated wild Boletus were further investigated. The results showed that the average concentration of As was 3.41-95.87 mg/kg dw, being 1.29-56.3 folds of the Chinese food safety standard limit. DMA and MMA were the dominant chemical forms in raw and cooked boletus, while their total (3.76-281 mg/kg) and bioaccessible (0.69-153 mg/kg) concentrations decreased to 0.05-9.27 mg/kg and 0.01-2.38 mg/kg after cooking. The EDI value of total As was higher than the WHO/FAO limit value, while the bioaccessible or bioavailable EDI suggested no health risks. However, the intestinal extracts of raw wild boletus triggered cytotoxicity, inflammation, cell apoptosis, and DNA damage in Caco-2 cells, indicating existing health risk assessment models based on total, bioaccessible, or bioavailable As may be not accurate enough. Given that, the bioavailability, species, and cytotoxicity should be systematically considered in accurate risk assessment. In addition, cooking mitigated the enterotoxicity along with decreasing the total and bioavailable DMA and MMA in wild boletus, suggesting that cooking could be a simple and effective way to decrease the health risks of consumption of As-contaminated wild boletus.

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.

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.

As-hyperaccumulator Pteris vittata and non-hyperaccumulator Pteris ensiformis under low As-exposure: Transcriptome analysis and implication for As hyperaccumulation

Soil contamination by arsenic (As) poses potential health risks to humans. As-hyperaccumulator P. vittata has been used in As-contaminated soils for phytoremediation. Clarifying the mechanisms of its As-hyperaccumulation is critical to enhance its efficiency in phytoremediation. Here, based on transcriptome analysis, we determined the concentration-dependent patterns of As-related gene families by comparing As-hyperaccumulator P. vittata and non-hyperaccumulator P. ensiformis after exposing to 20 µM arsenate (AsV). As expected, arsenic induced more stress in P. ensiformis than P. vittata. Based on gene ontology, differences in transporter activity are probably responsible for their differential As accumulation. Though As exposure induced expression of phosphate transporter PvPht1;4 for AsV absorption in both plants, stronger AsV reduction, AsIII transport, and AsIII-GSH complexation were found in P. ensiformis roots. Unlike P. ensiformis, As metabolism processes occurred mainly in P. vittata fronds. Notably, tonoplast-localized ACR3s were only present in P. vittata, making it more effective in sequestrating AsIII into frond vacuoles. Further, vesicle As transformation via PvGAPC1 (glyceraldehyde 3-phosphate dehydrogenase), PvOCT4 (organic cation transporter 4), and PvGSTF1 (glutathione S-transferase) contributed little to As-hyperaccumulation. This study provides information on critical genes responsible for As-hyperaccumulation by P. vittata, which can be applied to construct As-hyperaccumulating plants by genetic engineering to enhance their phytoremediation efficiency in As-contaminated soils.

Using Fe biofortification strategies to reduce both Ni concentration and oral bioavailability for rice with high Ni

Due to naturally high Ni or soil Ni contamination, high Ni concentrations are reported in rice, raising a need to reduce rice Ni exposure risk. Here, reduction in rice Ni concentration and Ni oral bioavailability with rice Fe biofortification and dietary Fe supplementation was assessed using rice cultivation and mouse bioassays. Results showed that for rice grown in a high geogenic Ni soil, increases in rice Fe concentration from ∼10.0 to ∼30.0 μg g^-1 with foliar EDTA-FeNa application led to decreases in Ni concentration from ∼4.0 to ∼1.0 μg g^-1 due to inhibited Ni transport from shoot to grains via down-regulated Fe transporters. When fed to mice, Fe-biofortified rice was significantly (p < 0.01) lower in Ni oral bioavailability (59.9 ± 11.9% vs. 77.8 ± 15.1%; 42.4 ± 9.81% vs. 70.4 ± 6.81%). Dietary amendment of exogenous Fe supplements to two Ni-contaminated rice samples at 10-40 μg Fe g^-1 also significantly (p < 0.05) reduced Ni RBA from 91.7% to 61.0-69.5% and from 77.4% to 29.2-55.2% due to down-regulation of duodenal Fe transporter expression. Results suggest that the Fe-based strategies not only reduced rice Ni concentration but also lowered rice Ni oral bioavailability, playing dual roles in reducing rice-Ni exposure.

Prenatal exposure to 209 PCBs in mother-infant pairs from two cities in China: Levels, congener profiles, and transplacental transfer

Prenatal exposure to polychlorinated biphenyls (PCBs) has been well researched, but studies covering all 209 congeners are limited. Recent literature suggests a shift in the dominant congeners and increasing levels of unintentionally-produced PCBs (UP-PCBs) in environmental samples in China. To investigate the exposure levels and profiles of PCBs in pregnant women and newborns, as well as the characteristics of transplacental transfer, we measured 209 PCBs in 80 pairs of maternal serum (MS) and cord serum (CS) from Hangzhou and Mianyang, China. The levels of ∑PCBs of participants in this study were lower than those in developed countries and followed the order of (ng/g lw): Hangzhou-MS (148) > Hangzhou-CS (107) > Mianyang-MS (63.8) > Mianyang-CS (57.9). UP-PCBs (mainly PCB-11) contributed around 50% of ∑PCBs in serum, which is consistent with the environmental samples. Environmental burden and dietary intake may account for the differences in the exposure levels, while the historical production and release may have impacted the homologue profiles. Prenatal exposure to PCB-126 was associated with increased birth weight (n = 80, adjusted β = 0.270, p = 0.030). The body burden of dioxin-like PCBs of newborns in Hangzhou was 82.4 pg TEQ/kg bw, suggesting certain health risks under WHO tolerable daily intake of 1-4 pg TEQ/kg bw. Log₁₀ K_OW was negatively correlated with log₁₀-transformed transplacental transfer efficiency (R² = 0.36, p < 0.001), serving its importance for PCBs' transplacental transfer. This study is the first to investigate maternal and fetal exposure to PCBs in China based on their levels, congener and homologue profiles, and potential adverse effects. Our findings help to provide insights into the processes and factors influencing the transplacental transfer of PCBs.

Antimony uptake and speciation, and associated mechanisms in two As-hyperaccumulators Pteris vittata and Pteris cretica

The behaviors of antimony (Sb) and arsenic (As) in plants are different, though they are chemical analogs. Here, we examined the Sb uptake and speciation in two As-hyperaccumulators P. vittata and P. cretica, which were exposed to 0.5 or 5 mg L^-1 antimonate (SbV) or antimonite (SbIII) under hydroponics for 7 d. Both plants grew better under Sb exposure, especially for P. cretica. The biomass of P. cretica roots increased by 29-46% after exposing to SbV, possibly due to increased S. Further, the Sb content in P. vittata was 17-93% greater than P. cretica, with 2-3 times more SbIII than SbV in both plants and > 92% Sb being concentrated in the roots, showing limited translocation. Under SbV exposure, SbV was dominant in P. vittata roots at 86-94%, while SbIII was predominant in P. cretica roots at 36-95%. P. cretica's stronger reducing ability than P. vittata may be due to arsenate reductases HAC1 and ACR2, which were upregulated in both plants. In short, while effective in Sb accumulation, it is mostly concentrated in the roots for both plants. The differences in their accumulation and speciation may help to better understand Sb behaviors in other plants.

Plasma-Membrane-Localized Transporter NREET1 is Responsible for Rare Earth Element Uptake in Hyperaccumulator Dicranopteris linearis

Rare earth elements (REEs) are critical for numerous modern technologies, and demand is increasing globally; however, production steps are resource-intensive and environmentally damaging. Some plant species are able to hyperaccumulate REEs, and understanding the biology behind this phenomenon could play a pivotal role in developing more environmentally friendly REE recovery technologies. Here, we identified a REE transporter NRAMP REE Transporter 1 (NREET1) from the REE hyperaccumulator fern Dicranopteris linearis. Although NREET1 belongs to the natural resistance-associated macrophage protein (NRAMP) family, it shares a low similarity with other NRAMP members. When expressed in yeast, NREET1 exhibited REE transport capacity, but it could not transport divalent metals, such as zinc, nickel, manganese, or iron. NREET1 is mainly expressed in D. linearis roots and predominantly localized in the plasma membrane. Expression studies in Arabidopsis thaliana revealed that NREET1 functions as a transporter mediating REE uptake and transfer from root cell walls into the cytoplasm. Moreover, NREET1 has a higher affinity for transporting light REEs compared to heavy REEs, which is consistent to the preferential enrichment of light REEs in field-grown D. linearis. We therefore conclude that NREET1 may play an important role in the uptake and consequently hyperaccumulation of REEs in D. linearis. These findings lay the foundation for the use of synthetic biology techniques to design and produce sustainable, plant-based REE recovery systems.

Reduced dietary Ca, Cu, Zn, Mn, and Mg bioavailability but increased Fe bioavailability with polyethylene microplastic ingestion in a mouse model: Changes in intestinal permeability and gut metabolites

Microplastics emerge as a new environmental and human health crisis. Minimal research exists on effects of microplastic ingestion on the oral bioavailability of minerals (Fe, Ca, Cu, Zn, Mn, and Mg) in the gastrointestinal tract via impacting intestinal permeability, mineral transcellular transporters, and gut metabolites. Here, mice were exposed to polyethylene spheres of 30 and 200 μm (PE-30 and PE-200) in diet (2, 20, and 200 μg PE g^-1) for 35 d to determine the microplastic effects on mineral oral bioavailability. Results showed that for mice fed diet amended with PE-30 and PE-200 at 2-200 μg g^-1, Ca, Cu, Zn, Mn, and Mg concentrations in the small intestine tissue were 43.3-68.8 %, 28.6-52.4 %, 19.3-27.1 %, 12.9-29.9 %, and 10.2-22.4 % lower compared to control mice, suggesting hampered bioavailability of these minerals. In addition, Ca and Mg concentrations in mouse femur were 10.6 % and 11.0 % lower with PE-200 at 200 μg g^-1. In contrast, Fe bioavailability was elevated, as suggested by significantly (p < 0.05) higher Fe concentration in the intestine tissue of mice exposed to PE-200 than control mice (157-180 vs. 115 ± 7.58 μg Fe g^-1) and significantly (p < 0.05) higher Fe concentrations in liver and kidney with PE-30 and PE-200 at 200 μg g^-1. Following PE-200 exposure at 200 μg g^-1, genes coding for duodenal expression of tight junction proteins (e.g., claudin 4, occludin, zona occludins 1, and cingulin) were significantly up-regulated, possibility weakening intestinal permeability to Ca, Cu, Zn, Mn, and Mg ions. The elevated Fe bioavailability was possibly related to microplastic-induced greater abundances of small peptides in the intestinal tract, which inhibited Fe precipitation and elevated Fe solubility. Results showed that microplastic ingestion may cause Ca, Cu, Zn, Mn, and Mg deficiency but Fe overload via altering intestinal permeability and gut metabolites, posing a threat to human nutrition health.

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.

Heavy metal(loid)s in agriculture soils, rice, and wheat across China: Status assessment and spatiotemporal analysis

Heavy metal(loid)s (HMs) accumulation in agricultural soils, rice, and wheat is of particular concern in China, while the status and spatio-temporal distribution of HMs in the soil-crops system have been rarely reported at the national scale. This study aimed to summarize the overall pollution status, spatiotemporal patterns, and drivers of HMs in agricultural soil, rice, and wheat nationwide. The metal-polluted data from 1030 agricultural soils, rice, and wheat in China were collected from the literature published from 2000 to 2022. The results showed that Cd was the most prevailing contaminant in soils based on its spatiotemporal distribution and accumulation. The pollution cases and severe pollution percentage of Cd (103 %) and Hg (128 %) show an increasing trend pattern. Mining activities are the main anthropogenic sources of agricultural soil HMs in China. Cd and Pb had the highest exceedance rate in rice (33.5 and 32.2 %) and wheat (25.8 and 30.3 %). The rice from Hunan, Fujian, and Guangxi showed the highest average concentration of Cd and Pb, respectively, while wheat samples from Hubei had the greatest exceedance rate of Pb. Besides, HMs in crops was not usually corresponding to soil HMs but increased gradually from north to south areas. Several mitigation strategies and accurate health risk assessments model of HMs based on bioavailability were also proposed and recommended. Collectively, this review provides valuable information to improve the management of farmland nationwide, optimize the accurate risk assessment, and reduce HMs pollution.

Arsenic induced plant growth by increasing its nutrient uptake in As-hyperaccumulator Pteris vittata: Comparison of arsenate and arsenite

Arsenic-hyperaccumulator Pteris vittata is efficient in taking up arsenate (AsV) and arsenite (AsIII), however, their impacts on P. vittata growth and nutrient uptake remain unclear. The uptake of AsV and AsIII, their influences on nutrient uptake and plant biomass, and As speciation were investigated in P. vittata after exposing to 5 or 50 μM AsV or AsIII for 12 d under hydroponics. The results show that AsV uptake in P. vittata was 1.2 times more efficient than AsIII, corresponding to 1.7-2.1 fold greater biomass than the control at 50 μM As. While AsV was dominant in the roots at ∼60%, AsIII was more dominant in the fronds at ∼70% in all treatments. Macronutrients P, K, Ca, and S were increased by 118-185% at 50 μM As, with greater uptake of micronutrients Fe, Mn, Cu, and Zn at 5 μM As. Further, positive correlations between P. vittata biomass and its As contents (r = 0.97), and P. vittata biomass and its S, Mg, P, or Ca contents (r = 0.70-0.98) were observed. Our results suggest that its increased nutrient uptake probably enhanced P. vittata growth under As exposure.

Bacterial coculture enhanced Cd sorption and As bioreduction in co-contaminated systems

The bacterial interactions that regulate Cd sorption and As bioreduction in co-contaminated systems are poorly understood. We isolated two bacterial strains, i.e., Pseudomonas aeruginosa and Bacillus licheniformis from a Cd and As co-contaminated soil and compared the effects of monoculture and coculture on microbial Cd sorption and As bioreduction efficiency in the media with different Cd (0, 0.5, 5, 10, 50, 100 mg/L) and As(Ⅴ) (0, 90 mg/L) concentrations. Compared with monoculture, the bacterial coculture increased the Cd sorption efficiency by up to 32% and the As bioreduction (As(Ⅴ) to As(Ⅲ)) efficiency by up to 28%, associated with the increased abundance of As reduction gene arsB. Based on SEM-TEM and metabolomics, the enhanced efficiency was attributed to bacterial interactions, supported by the differential secretion of extracellular polymeric substances. Notably, the differential lipids and lipid-like molecules, and organoheterocyclic compounds resulted from bacterial interactions compared to monoculture exhibited the highest Cd sorption and As bioreduction. The increased efficiencies by bacterial coculture were verified by soil incubation experiments. These results provide insight on applying specific bacterial coculture and their metabolites to enhance Cd sorption and As bioreduction in effective and sustainable remediation of co-contaminated environments.

Sporadic Pb accumulation by plants: Influence of soil biogeochemistry, microbial community and physiological mechanisms

Recent results revealed that considerable Pb accumulation in plants is possible under specific soil conditions that make Pb phytoavailable. In this review, the sources and transformations of Pb in soils, the interaction of Pb with bacteria and specifically the microbiota in the soil, factors and mechanisms of Pb uptake, translocation and accumulation in plants and Pb toxicity in living organisms are comprehensively elaborated. Specific adsorption and post-adsorption transformations of Pb in soil are the main mechanisms affecting the mobility, bioavailability, and toxicity of Pb. The adsorption ability of Pb largely depends on the composition and properties of soils and environmental conditions. Microbial impact on Pb mobility in soil and bioavailability as well as bacterial resistance to Pb are considered. Specific mechanisms conferring Pb-resistance, including Pb-efflux, siderophores, and EPS, have been identified. Pathways of Pb entry into plants as well as mechanisms of in planta Pb transport are poorly understood. Available evidence suggests the involvement of Ca transporters, organic acids and the phytochelatin pathway in Pb transport, mobility and detoxification, respectively.

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.

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.

Phytate and Arsenic Enhance Each Other's Uptake in As-hyperaccumulator Pteris vittata: Root Exudation of Phytate and Phytase, and Plant Uptake of Phytate-P

Phytate as a root exudate is rare in plants as it mainly serves as a P storage in the seeds; however, As-hyperaccumulator Pteris vittata effectively secretes phytate and utilizes phytate-P, especially under As exposure. This study investigated the effects of As on its phytate and phytase exudation and the impacts of As and/or phytate on each other's uptake in P. vittata through two hydroponic experiments. Under 10-100 μM arsenate (AsV), the exudation of phytate and phytase by P. vittata was increased by 50-72% to 20.4-23.4 μmol h^-1 g^-1 and by 28-104% to 18.6-29.5 nmol h^-1 plant^-1, but they were undetected in non-hyperaccumulator Pteris ensiformis at 10 μM AsV. Furthermore, compared to 500 μM phytate, the phytate concentration in the growth media was reduced by 69% to 155 μM, whereas the P and As contents in P. vittata fronds and roots were enhanced by 68-134% and 44-81% to 2423-2954 and 82-407 mg kg^-1 under 500 μM phytate plus 50 μM AsV. The increased P/As uptake in P. vittata was probably attributed to 3.0-4.5-fold increase in expressions of P transporters PvPht1;3-1;4. Besides, under As exposure, plant P may be converted to phytate in P. vittata roots, thereby increasing phytate's contents by 84% to 840 mg kg^-1. Overall, our results suggest that As-induced phytate/phytase exudation and phytate-P uptake stimulate its growth and As hyperaccumulation by P. vittata.

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.

Effects of various Fe compounds on the bioavailability of Pb contained in orally ingested soils in mice: Mechanistic insights and health implications

Reducing lead (Pb) exposure via oral ingestion of contaminated soils is highly relevant for child health. Elevating dietary micronutrient iron (Fe) intake can reduce Pb oral bioavailability while being beneficial for child nutritional health. However, the practical performance of various Fe compounds was not assessed. Here, based on mouse bioassays, ten Fe compounds applied to diets (100-800 mg Fe kg^-1) reduced Pb oral relative bioavailability (RBA) in two soils variedly depending on Fe forms. EDTA-FeNa was most efficient, which reduced Pb-RBA in a soil from 79.5 ± 14.7 % to 23.1 ± 2.72 % (71 % lower) at 100 mg Fe kg^-1 in diet, more effective than other 9 compounds at equivalent or higher doses (3.6-68 % lower). When EDTA-FeNa, ferrous gluconate, ferric citrate, and ferrous bisglycinate were supplemented, Fe-Pb co-precipitation was not observed in the intestinal tract. EDTA-FeNa, ferrous gluconate, ferric citrate, and ferrous sulfate suppressed duodenal divalent metal transporter 1 (DMT1)mRNA relative expression similarly (27-68 % lower). In comparison, among ten compounds, EDTA-FeNa elevated Fe concentrations in mouse liver, kidney, and blood (1.50-2.69-fold higher) most efficiently, suggesting the most efficient Fe absorption that competed with Pb. In addition, EDTA was unique from other organic ligands, ingestion of which caused 12.0-fold higher Pb urinary excretion, decreasing Pb concentrations in mouse liver, kidney, and blood by 68-88 %. The two processes (Fe-Pb absorption competition and Pb urinary excretion with EDTA) interacted synergistically, leading to the lowest Pb absorption with EDTA-FeNa. The results provide evidence of a better inhibition of Pb absorption by EDTA-FeNa, highlighting that EDTA-FeNa may be the most appropriate supplement for intervention on human Pb exposure. Future researches are needed to assess the effectiveness of EDTA-FeNa for intervention on human Pb exposure.

Biochar increases Panax notoginseng's survival under continuous cropping by improving soil properties and microbial diversity

Replant problem is widespread in agricultural production and causes serious economic losses, which has limited sustainable cultivation of Panax notoginseng (PN), a well-known medicinal plant in Asia. Here we conducted a field experiment to investigate the effectiveness and possible mechanisms of biochar to improve its survival under continuous cropping. Biochar from tobacco stems was applied at 4 rates of 9.0, 12, 15, and 18 t/ha to a soil where PN has been continuously cultivated for 10 years. After 18 months, soil properties, 5 allelochemicals, including p-hydroxybenzoic acid, vanillic acid, syringic acid, p-coumaric acid, and ferulic acid, key pathogen Fusarium oxysporum, microbial community, and PN survival rate were investigated. Our results show that 10 years' continuous PN cropping led to soil acidification, accumulation of NH₄⁺-N and F. oxysporum, and low PN survival rate. However, biochar increased its survival rate from 6.0% in the control to 69.5% under 15 t/ha treatment. Moreover, soil pH, available P and K, organic matter content, and microbial diversity were increased while NH₄⁺-N and allelochemicals vanillic acid and syringic acid contents were decreased under biochar treatment (P<0.05). Soil available K increased from 177 to 283 mg·kg^-1 while NH₄⁺-N decreased from 6.73 to 4.79 mg·kg^-1 under 15 t/ha treatment. Further, soil pH, available P and K, and microbial diversity (bacteria and fungi) were positively correlated with PN survival rate, however, NH₄⁺-N content was negatively correlated (P<0.05). Our study indicates that biochar effectively increased the survival rate of Panax notoginseng under continuous cropping by improving soil properties and microbial diversity.

Selenium Increased Arsenic Accumulation by Upregulating the Expression of Genes Responsible for Arsenic Reduction, Translocation, and Sequestration in Arsenic Hyperaccumulator Pteris vittata

Selenate enhances arsenic (As) accumulation in As-hyperaccumulator Pteris vittata, but the associated molecular mechanisms are unclear. Here, we investigated the mechanisms of selenate-induced arsenic accumulation by exposing P. vittata to 50 μM arsenate (AsV₅₀) and 1.25 (Se_1.25) or 5 μM (Se₅) selenate in hydroponics. After 2 weeks, plant biomass, plant As and Se contents, As speciation in plant and growth media, and important genes related to As detoxification in P. vittata were determined. These genes included P transporters PvPht1;3 and PvPht1;4 (AsV uptake), arsenate reductases PvHAC1 and PvHAC2 (AsV reduction), and arsenite (AsIII) antiporters PvACR3 and PvACR3;2 (AsIII translocation) in the roots, and AsIII antiporters PvACR3;1 and PvACR3;3 (AsIII sequestration) in the fronds. The results show that Se_1.25 was more effective than Se₅ in increasing As accumulation in both P. vittata roots and fronds, which increased by 27 and 153% to 353 and 506 mg kg^-1. The As speciation analyses show that selenate increased the AsIII levels in P. vittata, with 124-282% more AsIII being translocated into the fronds. The qPCR analyses indicate that Se_1.25 upregulated the gene expression of PvHAC1 by 1.2-fold, and PvACR3 and PvACR3;2 by 1.0- to 2.5-fold in the roots, and PvACR3;1 and PvACR3;3 by 0.6- to 1.1-fold in the fronds under AsV₅₀ treatment. Though arsenate enhanced gene expression of P transporters PvPht1;3 and PvPht1;4, selenate had little effect. Our results indicate that selenate effectively increased As accumulation in P. vittata, mostly by increasing reduction of AsV to AsIII in the roots, AsIII translocation from the roots to fronds, and AsIII sequestration into the vacuoles in the fronds. The results suggest that selenate may be used to enhance phytoremediation of As-contaminated soils using P. vittata.

Novel Mycorrhiza-Specific P Transporter PvPht1;6 Contributes to As Accumulation at the Symbiotic Interface of As-Hyperaccumulator Pteris vittata

Arsenic (As) is toxic and ubiquitous in the environment, posing a growing threat to human health. As-hyperaccumulator Pteris vittata has been used for phytoremediation of As-contaminated soil. Symbiosis with arbuscular mycorrhizal fungi (AMF) enhances As accumulation by P. vittata, which is different from As inhibition in typical plants. In this study, P. vittata seedlings inoculated with or without AMF were cultivated in As-contaminated soils for 2 months. AMF-root symbiosis enhanced plant growth, with 64.5% greater As contents in the fronds. After exposure to AsV for 2 h, the arsenate (AsV) and arsenite (AsIII) contents in AMF-roots increased by 1.8- and 3.6-fold, suggesting more efficient As uptake by P. vittata with AMF-roots. Plants take up and transport AsV via phosphate transporters (Phts). Here, for the first time, we identified a novel mycorrhiza-specific Pht transporter, PvPht1;6, from P. vittata. The transcripts of PvPht1;6 were strongly induced in AMF-roots, which were localized to the plasma membrane of arbuscule-containing cells. By complementing a yeast mutant lacking 5-Phts, we confirmed PvPht1;6's transport activity for both P and AsV. In contrast to typical AMF-inducible phosphate transporter LePT4 from tomato, PvPht1;6 showed greater AsV transport capacity. The results suggest that PvPht1;6 is probably critical for AsV transport at the periarbuscular membrane of P. vittata root cells, revealing the underlying mechanism of efficient As accumulation in P. vittata with AMF-roots.

Nickel bioaccessibility in soils with high geochemical background and anthropogenic contamination

Abnormally high concentrations of metals including nickel (Ni) in soils result from high geochemical background (HB) or anthropogenic contamination (AC). Metal bioaccessibility in AC-soils has been extensively explored, but studies in HB-soils are limited. This study examined the Ni bioaccessibility in basalt and black shale derived HB-soils, with AC-soils and soils without contamination (CT) being used for comparison. Although HB- and AC-soils had similar Ni levels (123 ± 43.0 vs 155 ± 84.7 mg kg^-1), their Ni bioaccessibility based on the gastric phase of the Solubility Bioaccessibility Research Consortium (SBRC) in vitro assay was different. Nickel bioaccessibility in HB-soils was 6.42 ± 3.78%, 2-times lower than the CT-soils (12.0 ± 9.71%) and 6-times lower than that in AC-soils (42.6 ± 16.3%). Based on the sequential extraction, a much higher residual Ni fractionation in HB-soils than that in CT- and AC-soils was observed (81.9 ± 9.52% vs 68.6 ± 9.46% and 38.7 ± 16.0%). Further, correlation analysis indicate that the available Ni (exchangeable + carbonate-bound + Fe/Mn hydroxide-bound) was highly correlated with Ni bioaccessibility, which was also related to the organic carbon content in soils. The difference in co-localization between Ni and other elements (Fe, Mn and Ca) from high-resolution NanoSIMS analysis provided additional explanation for Ni bioaccessibility. In short, based on the large difference in Ni bioaccessibility in geochemical background and anthropogenic contaminated soils, it is important to base contamination sources for proper risk assessment of Ni-contaminated soils.

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.

Arsenic-induced up-regulation of P transporters PvPht1;3-1;4 enhances both As and P uptake in As-hyperaccumulator Pteris vittata

Plants often up-regulate gene expression of P transporters under P deficiency, but down-regulate them under arsenic stress. Different from other P transporters, PvPht1;3 and PvPht1;4 expressions in As-hyperaccumulator Pteris vittata are up-regulated under P deficiency and As stress, showing strong transport capacity for both As and P. This study examined the mechanisms behind As-induced up-regulation of P transporters in P. vittata after exposing to 10-50 µM arsenate (AsV) for 14 d under hydroponics, with non-hyperaccumulator P. ensiformis as a control. Under As stress, P. vittata was more efficient in taking up both As and P than P. ensiformis, showing 48-84% more P content in the fronds and roots, leading to 18-79% greater biomass. Though As enhanced the P uptake by P. vittata, the inorganic P was reduced by 25-64% from 140-347 to 65-126 mg kg^-1. It is likely that, under As stress, more P was utilized by P. vittata to counter As toxicity, causing reduction in inorganic P. This was supported by As-induced conversion of inorganic P to phytate in P. vittata, with phytate-P being increased by 26-75% from 239-713 to 418-1221 mg kg^-1, maintaining internal low P levels. Under As-induced low inorganic-P conditions, the expressions of P transporters PvPht1;3 and PvPht1;4 were up-regulated by 1.4- and 2.7-fold in the roots, helping greater As and P uptake by P. vittata. Clearly, As-induced overexpression of P transporters in P. vittata roots plays a critical role in taking up both As and P, thereby increasing its efficiency in As-hyperaccumulation from contaminated media.

Arsenic contents, speciation and bioaccessibility in rice grains from China: Regional and variety differences

As the staple food for Asian countries and with its ability in arsenic accumulation, rice consumption becomes a dominant pathway for As exposure to humans. Here, we collected 108 rice samples from local markets and online sources in 13 major rice-producing regions in China, and determined As contents, speciation and bioaccessibility in the samples. Total As contents were 25-327 μg kg^-1 (averaging 120), showing regional differences, with Hunan province being greater than other provinces at 180 vs 110. In rice grains, inorganic As was the dominant species, being 39.9-88.5 (61.1 %), but all being within the Chinese standard at 200 μg kg^-1. Based on the modified physiologically-based extraction test (MPEBT), arsenic bioaccessibility in rice samples was 20.1-82.2 (52.3 %) in the gastric phase and 47.2-113 (81.2 %) in the intestinal phase. Strong positive correlation between total As and bioaccessible As suggested bioaccessible As was content-dependent. Based on the intestinal phase, the rice samples from northern region had lower As bioaccessibility than other regions (59.2 vs 83.2 %), and Japonica variety had lower As bioaccessibility than Indica variety (71.1 vs 83.1 %). This study suggests that rice from markets in China is safe, with their As contents and bioaccessibility showing regional and variety differences.

Uptake, speciation and detoxification of antimonate and antimonite in As-hyperaccumulator Pteris Cretica L

Antimony (Sb) and arsenic (As) are chemical analogs, but their behaviors in plants are different. To investigate the Sb uptake, translocation and speciation in As-hyperaccumulator P. cretica, a hydroponic experiment was conducted. In this study, P. cretica was exposed to 0.2-strength Hoagland nutrient solution, which contained 0.5 or 5 mg/L antimonite (SbIII) or antimonate (SbV). After 14 d exposure, P. cretica took up 1.4-2.8 times more SbIII than SbV. Since P. cretica was unable to translocate Sb, its roots accumulated >97% Sb with the highest at 7965 mg/kg. In both SbIII and SbV treatments, SbIII was the predominant species in P. cretica, with 90-100% and 46-100% SbIII in the roots. As the first barrier against Sb to enter plant cells, more Sb was accumulated in cell wall than cytosol or organelles. The results suggest that P. cretica may detoxify Sb by reducing SbV to SbIII and immobilizing it in root cell walls. Besides, the presence of SbIII significantly reduced the concentrations of dissolved organic C including organic acids in P. cretica root exudates. Further, increasing Sb levels promoted P accumulation in the plant, especially in the fronds, which may help P. cretica growth. The information from this study shed light on metabolic transformation of Sb in As-hyperaccumulators P. cretica, which helps to better understand Sb uptake and detoxification by plants.

Nrf2/Keap1 pathway in countering arsenic-induced oxidative stress in mice after chronic exposure at environmentally-relevant concentrations

Contamination of drinking water by carcinogen arsenic (As) is of worldwide concern as its exposure poses potential threat to human health. As such, it is important to understand the mechanisms associated with As-induced toxicity to humans. The Nrf2/Keap1 signal pathway is one of the most important defense mechanisms in cells to counter oxidative stress; however, limited information is available regarding its role in countering As-induced stress in model animal mouse. In this study, we assessed the responses of Nrf2/keap1 pathway in mice after chronic exposure to As at environmentally-relevant concentrations of 10-200 μg L^-1 for 30 days via drinking water. Our results indicate that chronic As exposure had limited effect on mouse growth. However, As induced oxidative stress to mice as indicated by increased content of malondialdehyde (MDA; 52-90%), an index of lipid peroxidation. Further, arsenic exposure reduced the activity of superoxide dismutase (SOD; 14-18%), an indication of reduced anti-oxidative activity. Besides, arsenic exposure increased MnSOD mRNA transcription by 25-66%, and decreased the mRNA transcriptions of Cu/ZnSOD by 72-83% and metallothionein by 16-75%, a cysteine-rich protein involved in metal detoxification. To counter arsenic toxicity, the expression of transcription factor for Nrf2 and Keap1 was increased by 2.8-8.9 and 0.2-8.1 fold in mice. To effectively reduce As-induced oxidative stress, the Nrf2/Keap1 transcription factor upregulated several downstream anti-oxidative genes, including heme oxygenase-1 (0.9-2.5 fold), glutamate-cysteine ligase catalytic subunit (0.6-1.7 fold), and NADH quinone dehydrogenase 1 (2.1-4.8 fold). This study shows the importance of Nrf2/Keap1 signaling pathway and associated anti-oxidative enzymes in countering As-toxicity in mice, possibly having implication for human health.

Enhancing Phytate Availability in Soils and Phytate-P Acquisition by Plants: A Review

Phytate (myo-inositol hexakisphosphate salts) can constitute a large fraction of the organic P in soils. As a more recalcitrant form of soil organic P, up to 51 million metric tons of phytate accumulate in soils annually, corresponding to ∼65% of the P fertilizer application. However, the availability of phytate is limited due to its strong binding to soils via its highly-phosphorylated inositol structure, with sorption capacity being ∼4 times that of orthophosphate in soils. Phosphorus (P) is one of the most limiting macronutrients for agricultural productivity. Given that phosphate rock is a finite resource, coupled with the increasing difficulty in its extraction and geopolitical fragility in supply, it is anticipated that both economic and environmental costs of P fertilizer will greatly increase. Therefore, optimizing the use of soil phytate-P can potentially enhance the economic and environmental sustainability of agriculture production. To increase phytate-P availability in the rhizosphere, plants and microbes have developed strategies to improve phytate solubility and mineralization by secreting mobilizing agents including organic acids and hydrolyzing enzymes including various phytases. Though we have some understanding of phytate availability and phytase activity in soils, the limiting steps for phytate-P acquisition by plants proposed two decades ago remain elusive. Besides, the relative contribution of plant- and microbe-derived phytases, including those from mycorrhizas, in improving phytate-P utilization is poorly understood. Hence, it is important to understand the processes that influence phytate-P acquisition by plants, thereby developing effective molecular biotechnologies to enhance the dynamics of phytate in soil. However, from a practical view, phytate-P acquisition by plants competes with soil P fixation, so the ability of plants to access stable phytate must be evaluated from both a plant and soil perspective. Here, we summarize information on phytate availability in soils and phytate-P acquisition by plants. In addition, agronomic approaches and biotechnological strategies to improve soil phytate-P utilization by plants are discussed, and questions that need further investigation are raised. The information helps to better improve phytate-P utilization by plants, thereby reducing P resource inputs and pollution risks to the wider environment.

Effects of copper and arsenic on their uptake and distribution in As-hyperaccumulator Pteris vittata

Arsenic (As) and copper (Cu) are common co-contaminates in soils. However, their interactive effects on their accumulation and distribution in As-hyperaccumulator Pteris vittata are poorly understood. A hydroponic experiment was conducted with As being 0, 5, or 50 μM and Cu being 0.32, 3.2, or 32 μM to evaluate their phytotoxicity, accumulation, and distribution in P. vittata. In addition, As and Cu uptake kinetics were examined using the Michaelis-Menten kinetics model. Total As and Cu concentrations in P. vittata were up to 487 and 1355 mg kg^-1. About 39-81% of the As was in the fronds compared to 0.6-18% for Cu. At 50 μM As, increasing Cu concentration from 0.32 to 32 μM increased root As while decreasing frond As concentrations, with the translocation factor (ratio of As in fronds to roots) being reduced from 4.0 to 0.31. In contrast, As did not affect Cu accumulation in P. vittata. Michaelis constant K_m value for As was higher than that of Cu (6.49-24.9 vs. 0.43-3.36), consistent with higher Cu uptake than As. Besides, Cu reduced root K but increased P levels in the roots, whereas As increased the K and P concentrations in the fronds. Our results suggest that P. vittata accumulated more Cu than As in the roots, contributing to its low As translocation. As such, high levels of Cu are likely to reduce As uptake by P. vittata during phytoremediation of As-contaminated sites.

Effects of soil-extractable metals Cd and Ni from an e-waste dismantling site on human colonic epithelial cells Caco-2: Mechanisms and implications

E-wastes release toxic metals including Cd, Cu, Ni, Pb and Zn into nearby soils during dismantling process. However, their adverse effects and the associated mechanisms on human intestinal epithelium are poorly understood. In this study, their toxic effects on human colonic epithelial cells Caco-2 and the underlying mechanisms were assessed basing on three soils from Wenling e-waste dismantling site. Since soil-extractable metals are more available for gastrointestinal absorption, we used phosphate buffer saline solution to extract metals at solid to liquid ratio of 1:2. Among metals, total Cd and Ni exceeded the risk screening values in three soils, being 3.8-8.8 and 42.4-155 mg/kg. Furthermore, high extractable-metals at 5.9, 1.9, and 0.87 mg/kg Cd (20-67%) and 4.6, 6.4, and 12.4 mg/kg Ni (3.6-29%) were observed for Soil-1, -2 and -3, respectively. All three extracts triggered cytotoxicity, with Soil-2 showing the strongest inhibition of cell viability. Higher production of reactive oxygen species and stronger inhibition of antioxidant enzymes SOD1 and CAT were observed in Soil-2 and -3. Upregulation of proinflammatory mediators (IL-1β, IL-8 and TNF-α) and apoptosis-regulatory genes (GADD45α, Caspase-3, and Caspase-8) were observed. Our data suggest that soil extracts induced cytotoxicity, oxidative damage, inflammatory response, and cell apoptosis in Caco-2 cells, indicating soil ingestion from e-waste dismantling site may adversely impact human health.

Prenatal and postnatal exposure to emerging and legacy per-/polyfluoroalkyl substances: Levels and transfer in maternal serum, cord serum, and breast milk

Gestation and lactation are critical and vulnerable stages for fetuses and newborns. During these periods, per-/polyfluoroalkyl substances (PFASs) accumulated in mothers can be transferred to newborns through placenta and/or breastfeeding, causing potential health risks. To investigate the pre- and postnatal PFAS exposure of newborns, we analyzed 21 emerging and legacy PFASs in 60 sets of matched maternal serum, cord serum, and breast milk samples. In serum, perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and 6:2 chlorinated polyfluorinated ether sulfonates (6:2 Cl-PFESA) were the most predominant PFASs, while PFOA, PFOS and 6:2 fluorotelomer phosphate diester (6:2 diPAP) contributed most to breast milk. For most PFASs, the levels followed the order of maternal serum > cord serum > breast milk. The 6:2 Cl-PFESA was positively associated with birth weight and ponderal index (p < 0.05). The breastfeeding transfer efficiencies (R_BM, median: 0.02-0.10) of most PFASs were 1-2 orders of magnitude lower than transplacental transfer efficiencies (R_CM, median: 0.40-1.45), except for perfluorobutanesulfonic acid (PFBS) showing high transfer efficiency both through placenta (median at 0.89) and breastfeeding (median at 0.86). The one-month postnatal exposure to PFASs via breastfeeding was much higher than prenatal exposure in utero. This study enhances the understanding of transplacental and breastfeeding transfer of PFASs and provides assessments of prenatal and postnatal exposure of newborns to emerging and legacy PFASs.

Amine- and thiol-bifunctionalized mesoporous silica material for immobilization of Pb and Cd: Characterization, efficiency, and mechanism

In this study, a two-step functionalizing strategy by combining co-condensation with grafting procedures was employed to synthesize well-ordered Amino- and Thiol-Bifunctionalized SBA-15 (ATBS) mesoporous silica. Its physicochemical properties, performance, and mechanisms in immobilization of toxic metals Pb and Cd in water and soil were investigated. After bi-functionalization, X-ray diffractometer, transmission electron microscope, and N₂ adsorption-desorption measurements confirmed that the ATBS maintained a highly-ordered mesoporous structure, large surface area and pore volume. The elemental analysis, Fourier transform infrared spectroscopy and X-ray Photoelectron Spectroscopy (XPS) evidenced the successful incorporation of amine and thiol groups into ATBS. These structure and functional characteristics of ATBS benefited Pb and Cd sorption. Sorption isotherms of Pb and Cd were better fit with Sips and Redlich-Peterson models. Sorption kinetics suggested that Pb sorption was mainly regulated by chemical reactions, whereas both diffusion process and chemical reactions were rate-regulating steps in Cd sorption. ATBS showed the maximum sorption capacities for Pb and Cd at 120 and 38 mg g^-1, respectively. The sorption mechanisms revealed by XPS measurements suggested that Cd sorption was mainly attributed to thiol groups while Pb was efficiently bond to both thiol and amino groups. High and stable sorption efficiencies were attained in the pH range of 4-6, with a higher affinity towards Pb than Cd. Furthermore, its ability to immobilize Pb and Cd in soils was examined with an incubation experiment, which showed that ATBS reduced 30-56% of MgCl₂-extractable Pb and Cd in a contaminated soil. The synthesized sorbent via the two-step functionalizing strategy shows high sorption efficiency towards Pb and Cd, and thus it has potential application in remediating Pb and Cd contaminated water and soils.

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.

Selenate increased plant growth and arsenic uptake in As-hyperaccumulator Pteris vittata via glutathione-enhanced arsenic reduction and translocation

The beneficial effects of selenium on As uptake and plant growth in As-hyperaccumulator Pteris vittata are known, but the associated mechanisms remain unclear. Here, we investigated the effects of selenate on arsenic accumulation by P. vittata under two arsenate levels. P. vittata plants were exposed to 13 (As₁₃) or 133 µM (As₁₃₃) arsenate and 5 µM selenate in 0.2-strength Hoagland solution. After 14 d of growth, plant biomass, Se and As content, As speciation, and malondialdehyde (MDA), glutathione reductase (GR), glutathione peroxidase (GPX), and glutathione (GSH and GSSG) levels were determined. The results show that selenate promoted P. vittata growth and increased As concentrations in the roots and fronds by 256% from 97 to 346 mg kg^-1 and 142% from 213 to 514 mg kg^-1 under As₁₃ treatment, and by 166% from 500 to 1332 mg kg^-1 and 534% from 777 to 4928 mg kg^-1 under As₁₃₃ treatment. In addition, selenate increased the glutathione content in P. vittata roots and fronds by 75-86% under As₁₃ treatment and 44-45% under As₁₃₃ treatment. Selenate also increased the GPX activity by 161-173%, and GR activity by 72-79% in P. vittata under As₁₃ and As₁₃₃ treatments. The HPLC-ICP-MS analysis indicated that selenate increased both AsIII and AsV levels in P. vittata, with AsIII/AsV ratio being lower in the roots and higher in the fronds, i.e., more AsIII was being translocated to the fronds. Taken together, our results suggest that, via GPX-GR mediated enhancement of GSH-GSSG cycle, selenate effectively increases plant growth and As uptake in P. vittata by improving AsV reduction in the roots and AsIII translocation from the roots to the fronds.

Novel phytase PvPHY1 from the As-hyperaccumulator Pteris vittata enhances P uptake and phytate hydrolysis, and inhibits As translocation in Plant

Developing P-efficient plants helps improve P uptake from soils with low-available P and reduce environmental damage by P runoff. Here, we investigated a novel root-specific phytase PvPHY1 from As-hyperaccumulator Pteris vittata, which can efficiently utilize phytate, a recalcitrant organic phosphorus in soil. Unlike other plants, expression of PvPHY1 in P. vittata was greater in the roots than the fronds. A pure phytase with considerable activity was obtained via prokaryotic expression. Expressing PvPHY1 in tobacco (PvPHY1-Ex) enhanced its growth (2.8 to 3.5-3.9 g per plant) and increased its P accumulation by 10-50% under low- and adequate-P conditions. Further, PvPHY1-Ex tobacco showed 25-32% lower intracellular phytate and 30-56% higher inorganic P in the roots, likely due to phytase-mediated hydrolysis of phytate. Decrease of phytate levels up-regulated phosphate transporter genes (NbPht1;1, NbPht1;2 and NbPht1;6), leading to greater P and As uptake. However, As translocation to the shoots was low, probably due to competition from increased inorganic P via phytate hydrolysis. As such, PvPHY1 facilitated P uptake from soils and phytate hydrolysis in plants, thereby promoting tobacco growth. Overall, PvPHY1 from P. vittata helps better understand the novel phytase to increase soil P utilization efficiency, thereby reducing P fertilizer requirements for crop production.

Coupling in vitro assays with sequential extraction to investigate cadmium bioaccessibility in contaminated soils

To understand how Cd in different fractions contributes to Cd bioaccessibility by in vitro assays, Cd bioaccessibility in 12 contaminated soils was determined by four assays (UBM, SBRC, IVG, and PBET) and correlated with different Cd fractions based on a sequential extraction scheme. The Cd bioaccessibility in the gastric phase (GP) was high (35-107%, averaging at 77%), implicating high risk to human health, while it decreased to 19-88% averaging at 47% in the intestinal phased (IP). From the GP to IP, the reduction of extractable Cd (0.45-48 mg kg^-1) and Fe (118-3884 mg kg^-1) showed significant correlation (R = 0.54-0.74) via UBM, SBRC, and IVG, suggesting co-precipitation with Fe and/or sorption onto Fe oxides maybe responsible for decrease in Cd bioaccessibility. Although Cd bioaccessibility varied among assays, their results show some consistency based on their correlation in the GP (R = 0.56-0.90) and IP (0.34-0.73, excluding UBM-IP and PBET-IP). Sequential extraction data show that Cd was primarily associated with the exchangeable fraction (E1; 7.05-72.9%, averaging 39.4%). The carbonate (C2; 6.86-44.8%, 21.9%) and Fe/Mn oxides fraction (F3; 12.5-53.6%, 28.2%) were similar, while organic (O4; 0.62-25.0%, 7.91%) and residual fraction (R5; 0.22-8.54%, 2.62%) were the lowest. Significant correlation (R = 0.59-0.88) between the first two fractions (E1+C2) and bioaccessible Cd suggest they were the main sources of bioaccessible Cd in those contaminated soils.

Geographical distribution of As-hyperaccumulator Pteris vittata in China: Environmental factors and climate changes

Understanding the distribution of hyperaccumulators helps to implement more efficient phytoremediation strategies of contaminated sites, however, limited information is available. Here, we investigated the geographical distribution of the first-known arsenic-hyperaccumulator Pteris vittata in China and the key factors under two climate change scenarios (SSP 1-2.6 and SSP 5-8.5) at two time points (2030 and 2070). Species distribution model (MaxEnt) was applied to examine P. vittata distribution based on 399 samples from field surveys and existing specimen records. Further, among 23 environmental factors, 11 variables were used in the MaxEnt model, including temperature, precipitation, elevation, soil property, and UV-B radiation. The results show that P. vittata can grow in ~23% of the regions in China. Specifically, it is mainly distributed in 11 provinces of southern China, including Hainan, Guangdong, Guangxi, Yunnan, Guizhou, Hunan, Hubei, Jiangxi, Fujian, Zhejiang, and Jiangsu. Besides, eastern Sichuan, and southern Henan, Shaanxi, and Anhui are suitable for P. vittata growth. Under two climate change scenarios, P. vittata distribution in China would decrease by ~5.76-7.46 × 10⁴ km² in 2030 and ~3.22-4.68 × 10⁴ km² in 2070, with southern Henan and most Jiangsu being unsuitable for P. vittata growth. Among the 11 environmental variables, the minimum temperature of coldest month (bio6) and temperature annual range (bio7) are the two key factors limiting P. vittata distribution. At bio6 <-5 °C and/or bio7 >33 °C, the regions are unsuitable for P. vittata growth. Based on the MaxEnt model, precipitation had limited effects, so P. vittata can probably survive under both dry and moist environments. This study helps guide phytoremediation of As-polluted soils using P. vittata and provides an example to evaluate habitat suitability of hyperaccumulators at international scales.