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Contaminants, such as polycyclic aromatic hydrocarbons (PAHs), can be absorbed on the particles of indoor dust, which may pose potential health risks. In this study, indoor dust samples were collected and sieved into 6 size fractions (i.e., <43 μm, 43–63 μm, 63–100 μm, 100–150 μm, 150–200 μm, and 200–2000 μm). Ingestion bioaccessibility of PAHs was measured by physiologically based extraction test. Bioaccessibility in fractions of 200–2000 μm was generally higher than those in other particle sizes. Daily uptake doses based on benzo(a)pyrene toxic equivalency quantity were 1.09–15.0 ng/d/kg, and peaked at fractions of <43 μm, while doses considering bioaccessibility ranged from 0.02 to 0.21 ng/d/kg, and peaked at fractions with relatively larger particle size. Cell toxicity was also investigated by human normal liver cell line viability through exposure to organic extracts of indoor dust fractions with various particle sizes. Our results indicated that it is crucial to consider dust particle size and bioaccessibility during risk assessment. [ABSTRACT FROM AUTHOR]

Wide application of nanoparticles (NPs) in consumer products over the last decade has increased their flux in the environment. This paper provides comprehensive review on the biocatalytic production pathways, transformations, and toxicity to human and other organisms of important NPs. Plants, algae, fungi, and bacteria have been used for energy-efficient and nontoxic biocatalytic production of NPs. The process is simple, serving as an alternative to the more popular physicochemical methods. NPs go through significant physicochemical transformation in the environment. Ionic strength, pH, and NPs’ surface potential strongly influence their stability and aggregation. Their transformations are linked to their bioavailability and aging including surface coatings and dissolved organic carbon effects. In addition, nanotoxicity has been a major global concern as NPs are toxic to organisms due to their cytotoxicity and genotoxicity. The stability and transformation of NPs in environment influence their short- and long-term toxicity. Release of free metal ions, dissolution-enhanced toxicity, and direct intercalation with biological targets are studied the most. Their toxicity to ecological receptors and organisms are linked to oxidative stress by generation of reactive oxygen species. Moreover, NPs toxicity depends on their physicochemical alterations. Inherent and acquired properties have potential to alter toxicity of NPs. Thus achieving safe nanotechnology and minimizing their adverse impact is important to protect the health of humans as well as the environment. [ABSTRACT FROM AUTHOR]

Abstract: Antimony (Sb) accumulation in rice is a potential threat to human health, but its uptake mechanisms are unclear. A hydroponic experiment was conducted to investigate uptake, translocation, speciation and subcellular distribution of Sb in rice plants exposed to antimonite (SbIII) and antimonate (SbV) at 0.2, 1.0 or 5.0mg/L for 4h. More Sb was accumulated in iron plaque than in the plant, with both the roots (~10–12 times) and Fe plaque (~28–54 times) sequestering more SbIII than SbV. The presence of iron plaque decreased uptake of both SbV and SbIII. SbIII uptake kinetics fitted better to the Michaelis–Menten function than SbV. Antimonate (56 to 98%) was the predominant form in rice plant with little methylated species being detected using HPLC–ICP-MS. Cell walls accumulated more Sb than organelles and cytosol, which were considered as the first barrier against Sb entering into cells. Sb transformation and subcellular distribution can help to understand the metabolic mechanisms of Sb in rice. [Copyright &y& Elsevier]

Highlights: [•] Biochar-derived dissolved organic matter (DOM) effectively reduced Cr(VI) and oxidized As(III). [•] Cr(VI) and As(III) could serve as a redox couple. [•] Cr(VI) and As(III) redox conversion was more effective in the ice phase than aqueous phase. [•] FTIR and ESR showed that biochar DOM served as both electron donor and acceptor. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hg concentrations were 2–4 times greater in colloids than in soils. [•] Hg in organic matter bound fraction was the most abundant in contaminated soils. [•] Ionic strength reduction and flow interruption enhanced colloidal Hg release from soils. [•] Hg was primarily associated with organic matter bound fraction in released colloids. [Copyright &y& Elsevier]

Highlights: [•] Quartz sand effectively sorbed ciprofloxacin (CIP) with Fe/Al oxides on surface being important. [•] Aqueous Ca and Cu significantly promoted CIP transport in clean sand. [•] Neither Cu nor Ca was effective in mobilizing pre-sorbed CIP from native sand. [•] Mathematical model successfully simulated CIP transport in sand media. [Copyright &y& Elsevier]

We investigated the mechanisms of Hg sorption onto biochars produced from Brazilian pepper (BP; Schinus terebinthifolius) at 300, 450, and 600 °C using different analytical techniques. The Hg sorption capacity of BP300, BP450, and BP600 was 24.2, 18.8, and 15.1 mg g–1 based on Langmuir isotherm. FTIR data suggested the participation of phenolic hydroxyl and carboxylic groups in Hg sorption by biochars. XPS analysis showed that 23–31% and 77–69% of sorbed Hg was associated with carboxylic and phenolic hydroxyl groups in biochars BP300–450, whereas 91% of sorbed Hg was associated with a graphite-like domain on an aromatic structure in BP600 biochar, which were consistent with flow calorimetry data. Based on flow calorimetry, sorption of K and Ca onto biochar was exchangeable with the molar heat of sorption of 3.1 kJ mol–1. By comparison, Hg sorption was via complexation with functional groups as it was not exchangeable by K or Ca with molar heat of sorption of −19.7, −18.3, and −25.4 kJ mol–1 for BP300, BP450, and BP600. Our research suggested that Hg was irreversibly sorbed via complexation with phenolic hydroxyl and carboxylic groups in low temperature biochars (BP300 and BP450) and graphite-like structure in high temperature biochar (BP600). [ABSTRACT FROM AUTHOR]

We evaluated the ability of As-hyperaccumulator Pteris vittata (PV) to remove As from As-contaminated soils over five harvests in 2.5 years in raised beds (162 kg soil/bed). We tested the hypothesis that a P-limiting environment would enhance PV growth and As uptake owing its unique ability to uptake P under As-rich environment. In Dec. 2009, PV was transplanted to three As-contaminated soils (pH of 5.5-7.2) containing 25-129 mg kg-1 As, which was amended with sparingly-soluble phosphate rock (PR-soil) or soluble P fertilizer (P-soil). During the 2.5-year, PV obtained sufficient P (1882 vs 2225 mg kg-1) from PR-soils, with increased root biomass (33%) and root exudation (53%) compared to P-soils. In addition, its frond biomass increased by 20% consecutively with each harvest (six month interval) from 18 to 36 g plant-1. Its frond biomass in PR-soils (52.2 g plant-1 year-1 or ~12 mt ha-1 year-1) averaged 39% more than that in P-soils. To our knowledge, this represented the largest PV frond biomass reported, demonstrating the unique ability of PV in using insoluble P from PR in alkaline soils. In addition to biomass increase, PV from PR-soils had 1.5 times more As in fronds (2540, 780, and 920 mg kg-1) than those from P-soils (1740, 570, and 400 mg kg-1), with soils containing 129, 25, and 30 mg kg-1 As, respectively. The low available P in PR-soils induced substantial plant growth and As uptake by PV. This translated into significantly more As removal from soil, averaging 48% reduction in PR-soils and 36% in P-soils in 2.5 years. With multiple harvests and PR amendments, our results showed As removal by PV from contaminated soils was 7 times faster than published studies. [ABSTRACT FROM AUTHOR]

Highlights: [•] Quartz sand effectively sorbed ciprofloxacin with Fe/Al coating on surface being important. [•] When on solid phase, Cu and Ca enhanced CIP sorption onto quartz sand. [•] When present in solution phase, Cu and Ca inhibited CIP sorption onto quartz sand. [•] CIP sorption onto quartz sand was primarily through surface complexation and cation bridging. [ABSTRACT FROM AUTHOR]

Arsenate interferes with enzymatic processes and inhibits inorganic phosphorus (Pi) uptake in many plants. This study examined the role of phytase and phosphatase in arsenate tolerance and phosphorus (P) acquisition in the arsenic hyperaccumulator Pteris vittata. Enzyme-mediated hydrolysis of phytate in P. vittata extracts was not inhibited by arsenate at 5 mM or by heating at 100 °C for 10 min. Root exudates of P. vittata exhibited the highest phytase activity (18 nmol Pi mg-1 protein min-1) when available P was low, allowing its growth on media amended with phytate as the sole source of P. Phosphorus concentration in P. vittata gametophyte tissue grown on phytate was equivalent to plants grown with inorganic phosphate at 2208 mg kg-1, and arsenic was increased from 1777 to 2630 mg kg-1. After 2 h of mixing with three soils, P. vittata phytase retained more activity, decreasing from 26 to 25 nmol Pi mg-1 protein min-1, whereas those from Pteris ensiformis and wheat decreased from 18 to 1 nmol Pi mg-1 protein min-1. These results suggest P. vittata has a uniquely stable phytase enabling its P acquisition in P-limiting soil environments. Furthermore, the P. vittata phytase has potential use as a soil amendment, a transgenic tool, or as a feed additive supplement, reducing the need for nonrenewable, polluting P fertilizers. [ABSTRACT FROM AUTHOR]

Abstract: To evaluate the potential of Hg release and co-transport by colloids, it is important to understand how Hg, colloids and Hg-loaded colloids migrate in soils. Hg sorption by kaolinite and sand were nonlinear and fit the Langmuir model, with the maximum Hg sorption capacity being 1.2mg/g kaolinite and 0.11mg/g sand. Co-transport of Hg and kaolinite was evaluated using: (1) 1 or 100mg/L Hg or 100mg/L kaolinite, (2) 1 or 100mg/L Hg mixed with 100mg/L kaolinite, (3) 1 or 100mg/L Hg presorbed onto kaolinite, and (4) 250mg/L kaolinite in Hg-loaded sand columns. The presence of kaolinite (100mg/L) reduced Hg''s mobility through sand column by increasing deposition rate of Hg-loaded kaolinite. At 100mg/L Hg, soluble Hg dominated Hg transport; but at 1mg/L Hg, colloidal Hg (Hg sorbed on kaolinite) affected Hg transport. Preloading 100mg/L Hg onto kaolinite (0.43mg/g) reduced kaolinite''s mobility with low recovery rate (78%), with Hg retardation (R =1) in Hg-loaded kaolinite being lower than Hg retardation at 100mg/L Hg (R =1.287). The Hg recovery rate (93%) from Hg-loaded kaolinite at 1mg/L Hg was higher compared to 22% from 1mg/L Hg. Kaolinite can serve as a carrier to enhance Hg transport in porous media, with 250mg/L kaolinite mobilizing ∼2.4% Hg presorbed onto sand media. Correlation analysis revealed that desorbed Hg was significantly correlated with kaolinite (r =0.81, P <0.0001). Hence kaolinite enhanced Hg transport in the sand media serving both as a carrier (Hg was loaded before transport) and as mobile colloids stripping Hg off the sand media (Hg was loaded during transport). [Copyright &y& Elsevier]

Arsenate (AsV) and arsenite (AsIII) are two dominant arsenic species in the environment. While arsenate uptake is via phosphate transporter in plants, including arsenic hyperaccumulator Pteris vittata, AsIII uptake mechanisms by P. vittata are unclear. In this study, we investigated AsIII uptake by P. vittata involving root radial transport from external medium to cortical cells and xylem loading. In the root symplastic solution, AsIII was the predominant species (90-94%) and its concentrations were 1.6-21 times those in the medium. AsIII influx into root symplast followed Michaelis-Menten kinetics with Km of 77.7 μM at external AsIII concentrations of 2.6-650 μM. In the presence of metabolic inhibitor 2,4-dinitrophenol (DNP), arsenic concentrations in the root symplast were reduced to the levels lower than in the medium, indicating that a transporter-mediated active process was mainly responsible for AsIII influx into P. vittata roots. Unlike radial transport, AsIII loading into xylem involved both high- and low-affinity systems with Km of 8.8 μM and 70.4 μM, respectively. As indicated by the effect of 2,4-DNP, passive diffusion became more important in arsenic loading into xylem at higher external AsIII. The unique AsIII uptake system in P. vittata makes it a valuable model to understand the mechanisms of arsenic hyperaccumulation in the plant kingdom. [ABSTRACT FROM AUTHOR]

Abstract: Removal of Cr(VI) from aqueous solutions using biochar from sugar beet tailing (SBT) was investigated as a function of pH, contact time, and biochar mass via batch experiments. The surface characteristics of SBT biochar before and after Cr(VI) sorption was investigated with scanning electron microscopy equipped with energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. Desorption and X-ray photoelectron spectroscopy studies showed that most of the Cr bound to SBT biochar was Cr(III). These results indicated that the electrostatic attraction of Cr(VI) to positively charged biochar surface, reduction of Cr(VI) to Cr(III) ion, and complexation between Cr(III) ion and SBT''s function groups were probably responsible for Cr(VI) removal by SBT biochar. An initial solution with a pH of 2.0 was most favorable for Cr(VI) removal. The sorption process can be described by the pseudo-second order equation and Langmuir isotherm. The maximum sorption capacity for Cr(VI) was 123mg/g under an acidic medium, which was comparable to other low-cost sorbents. [Copyright &y& Elsevier]

Abstract: This experiment investigated the Zn accumulation and tolerance, and responses of non-protein thiols in Zn hyperaccumulator Arabis paniculata under different Zn stress (0, 100, 250, 500, 1000 and 2000μM Zn). No obvious phytotoxicity or biomass reduction was observed in the plants during a 3-w of growth. Compared to the control, addition of 100–500μM Zn increased plant biomass by 18–38%. The high Zn concentrations in the roots (9025–12,892mgkg−1) and the shoots (777–6030mgkg−1) did not impair the membrane stability or increase the lipid peroxidation except for the roots treated with 2000μM Zn. Substantial amounts of Zn accumulated in the plant were water-soluble, with 58–73% in the shoots and 30–53% in the roots. Low Zn translocation from the shoots to the roots was observed in all treatments. This phenomenon was consistent with the XRD analysis, which showed the presence of ZnO and ZnS in the ashed-roots. No phytochelatin was detected in the shoots and only PC4 was eluted in the roots, suggesting their limited role in Zn tolerance in A. paniculata. While glutathione did not correspond to Zn loading in plants, cysteine had significant positive correlation with Zn concentration in plants. Our data suggested that A. paniculata exhibited high Zn tolerance and cysteine may be involved in its Zn tolerance. [ABSTRACT FROM AUTHOR]

Abstract: This study determined the role of plant and microbes in arsenite (AsIII) oxidation in the growth media and the location of AsIII oxidation and arsenate (AsV) reduction in Pteris vittata tissues. P. vittata grew in 0.10–0.27mM AsV or AsIII solution under aerated or sterile condition for 1h to 14d. Arsenic speciation was conducted in the growth media, biomass (roots, rhizomes, rachis, pinnae, and fronds), and sap (rhizomes and fronds). Arsenite was rapidly oxidized in the growth media by microbes (18–67% AsV after 1d) and was then further oxidized in the roots of P. vittata (35% AsV in the roots growing in AsIII media). While limited reduction occurred in the roots (7–8% as AsIII), AsV reduction mostly occurred in the rhizomes (68–71% as AsIII) and pinnae (>90% as AsIII) of P. vittata. Regardless AsIII or AsV was supplied, AsV dominated in the roots while AsIII dominated in the rhizomes and fronds. AsIII translocation from the roots to the fronds was more rapid than AsV. This study shed new insights into arsenic transformation in the growth media and P. vittata biomass and raise new question into the tissue distribution of arsenic reducing and oxidizing enzymes in P. vittata. [Copyright &y& Elsevier]

Abstract: To better understand arsenite (AsIII) uptake via aquaporin channels by arsenic hyperaccumulator Pteris vittata, the effects of silicic and boric acid (AsIII analogues) and HgCl2 (aquaporin inhibitor) on plant arsenic uptake and translocation were investigated. P. vittata was grown in 0.2-strength Hoagland solution containing (1) 15μM AsIII or arsenate (AsV) for 1d with or without 0.5mM silicic acid (Si experiment) or 0.3mM boric acid (B experiment), or (2) 15μM AsIII for 2d with or without 10μM HgCl2 (Hg experiment). Silicic acid and boric acid had no effect on AsIII and AsV uptake by P. vittata, nor did HgCl2. It is possible that AsIII was taken up by different aquaporins in P. vittata or those aquaporins in P. vittata had high capacity and they were insensitive to Hg. While AsV was stable in the growth media, substantial amount of AsIII was oxidized to AsV, i.e., 16–76%. In the presence of 210μM P at pH 6, P. vittata was more efficient in taking up and translocating AsIII than AsV as demonstrated by greater arsenic concentrations in the fronds and roots (6.6 and 46mgkg−1) in the AsIII treatment than those in the AsV treatment (2.3 and 8.2mgkg−1). However, at 15μM AsIII, its AsIII translocation rate from the roots to the fronds was slower than its AsIII uptake rate by the roots since the arsenic concentration in the fronds was only ∼14% of that in the roots. Our data also demonstrated that both AsIII oxidation and AsV reduction occurred in the roots of P. vittata. However, how and if AsIII uptake by P. vittata is via aquaporins still need further investigation. [Copyright &y& Elsevier]

Abstract: We investigated the responses of phytochelatins (PCs), glutathione (GSH) and other non-protein thiols in Cd hyperaccumulator Arabis paniculata after Cd exposure. Applying γ-glutamylcysteine synthetase (γ-ECS) inhibitor, l-buthionine-sulfoximine (BSO), the roles of PCs in Cd tolerance and Cd accumulation in A. paniculata were evaluated. Plants were exposed to four Cd concentrations (0, 50, 100 and 250μM) for different times (2w or 3w) with and without BSO. Overall, Cd exposure had little impact on plant biomass after 2w or 3w of growth except at the highest Cd level. A. paniculata tolerated ≤100μM Cd with up to 1127mgkg−1 Cd in the shoots and 5624mgkg−1 Cd in the roots after 3w of Cd exposure. Cd exposure induced formation of PCs and three unknown thiols in the roots, but none were detected in the shoots. BSO had no significant effect on Cd sensitivity in plants though it reduced Cd accumulation in the roots. In addition, the molar ratio of PCs:Cd, which ranged from 0.7 to 1.3 after exposing to 50–100μM Cd without BSO in the roots, was close to the value expected for PC-mediated Cd sequestration in plants. Those data indicate that GSH and PCs did not contribute to Cd tolerance in the shoots and Cd transport from the root to shoot in A. paniculata, but they may play an important role in Cd accumulation and Cd complexation in the roots of A. paniculata. [Copyright &y& Elsevier]

Arsenic hyperaccumulation by Pteris vittata L. (Chinese brake fern) may serve as a defense mechanism against herbivore attack. This study examined the effects of arsenic exposure (0, 5, 15 and 30mgkg−1) on scale insect (Saissetia neglecta) infestation of P. vittata. Scale insects were counted as a percentage fallen from the plant to the total number of insects after 1 week of As-treatment. The arsenic concentrations in the fronds ranged from 5.40 to 812mgkg−1. Greater arsenic concentrations resulted in higher percentage of fallen-scale insects (17.2–55.0%). Lower arsenic concentrations (≤5mgkg−1) showed significantly lower effect on the population compared to 15–30mgkg−1 (p <0.05). Arsenic content in the fallen-scale insects was as high as 194mgkg−1, which indicated that arsenic has been ingested by the scale insects via plant sap. This study is consistent with the hypothesis that arsenic may help P. vittata defend against herbivore''s attack. [Copyright &y& Elsevier]

Selenium (Se) is a non-metallic element, which has the capability to increase the antioxidative capacity and stress tolerance of plants to heavy metals. Plants vary considerably in their physiological response to Se. The reported research investigated the effects of Se on arsenic (As) uptake by As hyperaccumulator Pteris vittata L. and determined possible mechanisms of interaction. Pteris vittata plants were exposed hydroponically to 0, 150 or 300μM of Na2HAsO4 in the presence of 0, 5 or 10μM of Na2SeO4 for 5 or 10d. Application of 5μM Se enhanced As concentration by P. vittata fronds by 7–45%. At 5μM, Se acted as an antioxidant, inhibiting lipid peroxidation (reduced by 26–42% in the fronds) via increased levels of thiols and glutathione (increased by 24% in the fronds). The results suggest that Se is either an antioxidant or it activates plant protective mechanisms, thereby alleviating oxidative stress and improving arsenic uptake in P. vittata. [Copyright &y& Elsevier]

Abstract: Phytoremediation, an emerging, plant-based technology for the removal of toxic contaminants from soil and water, has been receiving increased attention. The prerequisite for successful phytoremediation is the existence of hyperaccumulator plants. Designed to search for new arsenic (As) hyperaccumulators, an experiment was conducted under greenhouse conditions in a completely randomized design with four replications. This experiment identified Pteris biaurita L., P. quadriaurita Retz and P. ryukyuensis Tagawa as new hyperaccumulators of As and re-confirmed Pteris cretica as a hyperaccumulator. The average As concentration ranged from 1770 to 3650 mg kg−1 DW in the fronds and 182 to 507 mg kg−1 DW in the roots of P. cretica, P. biaurita, P. quadriaurita and P. ryukyuensis after having been grown in 100 mg As kg−1 soil. There was a greater percentage of As(III) as compared to As (V) in the fronds of these plants. Based on our study, P. ryukyuensis is the most promising candidate to phytoremediate As contaminated soils compared to the other three species. The nutrient requirements or distributions within the Pteris species were altered distinctly when the plants were exposed to As. [Copyright &y& Elsevier]

Abstract: This greenhouse experiment evaluated the effects of phosphate rock (PR) on arsenic and metal uptake by the arsenic hyperaccumulator Pteris vittata in a soil spiked with arsenic and heavy metals Cd, Pb and Zn. Five soil treatments were used, 1) control with no arsenic, 2) spiked with 50 mg kg−1 As (As) as Na2H AsO4, 3) spiked with 50 mg kg−1 As and P as PR (AsP), 4) spiked with 50 mg kg−1 As, Pb, Cd, and Zn (AsM), and 5) spiked with 50 mg kg−1 As, Pb, Cd, Zn and P (AsMP). The plants were harvested after growing in the soil for five weeks. Compared to the As treatment, the presence of heavy metals (AsM) reduced arsenic concentrations in the fronds from 1631 to 608 mg kg−1. However, this effect was mitigated by PR (AsMP), with arsenic concentrations in the fronds increased from 608 to 1046 mg kg−1. Phosphate rock also significantly reduced Pb (13.5 to 4.10 mg kg−1) and Cd (13.0 to 3.45 mg kg−1) concentrations in the fronds. Most of the arsenic in P. vittata was accumulated in the fronds (89–93%). Compared to the control, P was more concentrated in the roots along with less P being translocated to the fronds in the treatments with arsenic. While in those same treatments higher Ca concentrations in both the fronds and roots were observed. This research shows that PR was effective in increasing arsenic uptake and decreasing metal uptake by P. vittata and thus can be used as a cost-effective amendment for phytoremediation of arsenic and metal polluted soils. [Copyright &y& Elsevier]

Abstract: This study examined the metabolic adaptations of Pteris vittata L, an arsenic hyperaccumulator, under arsenic stress as compared to Pteris ensiformis, a non-arsenic hyperaccumulator. Both plants were grown hydroponically in 20% Hoagland medium in controlled conditions and were treated with 0, 133 or 267μM arsenic as sodium arsenate for 1, 5 or 10d. The fern fronds were analysed for differences in oxidative stress and antioxidant capacities after arsenic exposure. Upon exposure to 133μM arsenic, concentrations of chlorophyll, protein and carotenoids increased in P. vittata whereas they decreased in P. ensiformis. The H2O2 and TBARs concentrations were greater in P. ensiformis than P. vittata in all treatments, indicating greater production of reactive oxygen species (ROS) by P. ensiformis. The levels of ascorbate and glutathione, and their reduced/oxidized ratios in the fronds of P. vittata of the control was much greater than P. ensiformis indicating that P. vittata has an inherently greater antioxidant potential than P. ensiformis. The lower levels of antioxidant compounds (ascorbate, carotenoids and glutathione) in P. ensiformis than P. vittata are consistent with its greater exposure to ROS and lower scavenging ability. The results together indicate that protection from oxidative damage by a greater level of ascorbate–glutathione pool is involved in the arsenic-tolerance in arsenic-hyperaccumulator P. vittata. [Copyright &y& Elsevier]

Plant species capable of hyper-accumulating heavy metals are of considerable interest for phytoremediation, and differ in their ability to accumulate metals from the environment. This work aims to examine (i) arsenic accumulation in three fern species [Chinese brake fern (Pteris vittata L.), slender brake fern (Pteris ensiformis Burm. f.), and Boston fern (Nephrolepis exaltata L.)], which were exposed to 0, 150, or 300 μM of arsenic (Na2HAsO4.7H2O), and (ii) the role of anti-oxidative metabolism in arsenic tolerance in these fern species. Arsenic accumulation increased with an increase in arsenic concentration in the growth medium, the most being found in P. vittata fronds showing no toxicity symptoms. In addition, accumulation was highest in the fronds, followed by the rhizome, and finally the roots, in all three fern species. Thiobarbituric acid-reacting substances, indicators of stress in plants, were found to be lowest in P. vittata, which corresponds with its observed tolerance to arsenic. All three ferns responded differentially to arsenic exposure in terms of anti-oxidative defence. Higher levels of superoxide dismutase, catalase, and ascorbate peroxidase were observed in P. vittata than in P. ensiformis and N. exaltata, showing their active involvement in the arsenic detoxification mechanism. However, no significant increase was observed in either guaiacol peroxides or glutathione reductase in arsenic-treated P. vittata. Higher activity of anti-oxidative enzymes and lower thiobarbituric acid-reacting substances in arsenic-treated P. vittata correspond with its arsenic hyper-accumulation and no symptoms of toxicity. [ABSTRACT FROM PUBLISHER]

Contamination of shooting range soils from the use of Pb bullets is under increasing scrutiny. Past research on Pb contamination of shooting ranges has focused on weathering reactions of Pb bullets in soil. The objective of this study was to determine the significance of abrasion of Pb bullets in contributing to soil Pb contamination. This was accomplished by firing a known mass of bullets into sand and analyzing for total Pb after removing bullets, through field sampling of a newly opened shooting range, and a laboratory weathering study. Forty-one mg of Pb were abraded per bullet as it passed through the sand, which accounted for 1.5% of the bullet mass being physically removed. At a shooting range that had been open for 3 months, the highest Pb concentration from the pistol range berm soil was 193 mg/kg at 0.5 m height, and from the rifle range berm soil was 1142 mg/kg at 1.0 m height. Most soils from the field abrasion experiment as well as soil collected from the rifle range had SPLP-Pb >15 μg/l (Synthetic Precipitation Leaching Procedure). Typically, Pb concentration in the rifle range was greater than that of the pistol range. Based on a laboratory weathering study, virtually all metallic Pb was converted to hydrocerussite (Pb3(CO3)2(OH)2), as well as to a lesser extent cerussite (PbCO3) and massicot (PbO) within one week. Our study demonstrated that abrasion of lead bullets and their subsequent weathering can be a significant source of lead contamination in soils of a newly opened shooting range. [Copyright &y& Elsevier]

Measurement of cation selectivity in soils provides important information about the affinity and binding strength of a particular cation on soil surfaces. Gaines-Thomas (K[sub GT]) selectivity coefficients were determined for a variety of K/Ca and K/Pb ratios on an Oxisol and Ultisol soil from Puerto Rico. The calculated K[sub GT] values indicated a preference for K[sup +] over Ca[sup 2+] or Pb[sup 2+]. The selectivity for Pb[sup 2+] was significanfiy greater than that for Ca[sup 2+] due to Pb[sup 2+]'s larger hydrated charge density relative to that of Ca[sup 2+]. The patterns of selectivity were independent of metal type. The selectivity of the Oxisol for Ca[sup 2+] or Pb[sup 2+] exhibited no trend and changed little with changes in divalent metal surface coverage. The Ultisol displayed a decrease in selectivity for Ca[sup 2+] and Pb[sup 2+] with increasing surface coverage of these ions. This was attributed to the presence of smectite in the Ultisol, which was able to partially collapse when K[sup +] saturated. Some of the Pb sorption in the soils was due to chemisorption. The Oxisol chemisorbed ≈3000 mg Pb kg[sup -1] while that value for the Ultisol was ≈1900 mg kg[sup -1]. The differences were due to the greater quantities of Fe/Al oxides and organic matter in the Oxisol relative to the Ultisol. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX) spectroscopy detected discrete Pb-C phase in both soils. The C was from organic matter. Under experimental conditions, any Pb-carbonate phase would not have been stable. It was possible Pb was associated with organic sulfhydral groups. The selectivity exhibited by soil systems for various nutrient and heavy metals is important in elucidating how available these metals will be for plant/animal uptake as well as their mobility and stability in the soil environment. [ABSTRACT FROM AUTHOR]

Arsenic contamination is of great environmental concern due to its toxic effects as a carcinogen. Knowledge of arsenic background concentrations is important for land application of wastes and for making remediation decisions. The soil clean-up target level for arsenic in Florida (0.8 and 3.7 mg kg−1 for residential and commercial areas, respectively) lies within the range of both background and analytical quantification limits. The objective of this study was to compare arsenic distribution in urban and non-urban areas of Florida. Approximately 440 urban and 448 non-urban Florida soil samples were compared. For urban areas, soil samples were collected from three land-use classes (residential, commercial and public land) in two cities, Gainesville and Miami. For the non-urban areas, samples were collected from relatively undisturbed non-inhabited areas. Arsenic concentrations varied greatly in Gainesville, ranging from 0.21 to approximately 660 mg kg−1 with a geometric mean (GM) of 0.40 mg kg−1, which were lower than Miami samples (ranging from 0.32 to 112 mg kg−1; GM=2.81 mg kg−1). Arsenic background concentrations in urban soils were significantly greater and showed greater variation than those from relatively undisturbed non-urban soils (GM=0.27 mg kg−1) in general. [Copyright &y& Elsevier]

A long-term field-scale demonstration project on the feasibility of using P to immobilize Pb in a Pb-contaminated urban soil was conducted. Phosphate was applied at an average rate of 3040 mg P/kg soil based on a P/Pb molar ration of 4.0, with four treatments: T0, no P application; T1, H3PO4 only; T2, 1/2 H3PO4+1/2 CaH2PO4; and T3, 1/2 H3PO4+1/2 phosphate rock. Soil samples were collected and analyzed 220 days after the P applications. For all P treatments, toxicity characteristic leaching procedure (TCLP) extractable Pb levels in surface soils (0–10 cm) were reduced to below 5.0 mg Pb/l, with T2 also effective in reducing the TCLP Pb level in subsurface soils (10–30 cm, <4.63 mg/l). Sequential extraction analysis indicates that P was effective in transforming soil Pb from non-residual fractions to a residual fraction. Such a transformation was mainly through dissolution of Pb associated with carbonate fraction and precipitation of pyromorphite-like minerals, which were confirmed using X-ray diffraction (XRD). Among these three treatments, T3 was the most effective in reducing Pb mobility and minimizing P and Pb leaching in the soil. Our research clearly demonstrates that P amendments were effective in immobilizing Pb in contaminated soil. [Copyright &y& Elsevier]

The use of lead bullets and shot at shooting ranges is under increasing scrutiny as a potentially significant source of Pb pollution. This study assessed Pb contamination in the soils of two shooting ranges (TRR and MPR) in Florida. Soil samples were collected from the two ranges and analyzed for total Pb to determine Pb contamination. Selected spent bullets and berm soil samples were mineralogically characterized to identify Pb transformation. Total Pb in the range soils was significantly elevated with the highest (up to 4.84% by weight) in the berm soils. Most soils failed the synthetic precipitation leaching procedure (SPLP) test. Also, at the MPR shooting range, a substantial amount of Pb migrated down in the subsurface soil, possibly due to the enhanced solubilization of organic Pb complexes at alkaline pH, whereas high cation exchange capacity of the profile soil may be responsible for Pb retention in the subsoil. The weathering products on the surface of the spent bullets were predominantly hydrocerussite [Pb3(CO3)2(OH)2] and cerussite (PbCO3). Hydrocerussite was mainly found in the MPR range soils, whereas Pb was transformed into hydroxypyromorphite [Pb5(PO4)3OH] in the TRR range soils because of the presence of more P. Sequential extraction and lead activity ratio modeling showed that the soil Pb solubility was controlled by Pb carbonate minerals in the MPR shooting range, and by less soluble Pb phosphate minerals in the TRR shooting range. This research suggests that it is important to develop and implement efficient management practices to minimize adverse impacts of Pb at shooting ranges. Phosphate-induced Pb immobilization may be an effective alternative for reducing Pb mobility in the shooting range soils. [Copyright &y& Elsevier]

Points of zero charge were determined on two highly weathered surface soils from Puerto Rico, an Oxisol and Ultisol, as well as mineral-standard kaolinite and synthetic goethite using three methods: (1) potentiometric titration measuring the adsorption of H+ and OH− on amphoteric surfaces in solutions of varying ionic strength (I) (point of zero salt effect), (2) direct assessment of surface charges via non-specific ion adsorption as a function of pH and I (point of zero net charge), and (3) electroacoustic mobility of reversible particles as it varies with pH and I (isoelectric point). The first two methods yielded points of zero charge for kaolinite (2.7–3.2) and synthetic goethite (7.4–8.2) comparable to those reported previously, indicating the reliability of these analyses. The soil values ranged from 3.9 to 4.4 for the Oxisol and 2.3 to 3.7 for the Ultisol. Electroacoustic mobility, as measured by the AcoustoSizer™, is a parameter that has yet to be thoroughly tested for mineral or soil systems as a viable alternative to PZC assessment. The points of zero charge from electroacoustic mobility of kaolinite (3.8–4.1) and synthetic goethite (8.1–8.2) were similar to values obtained by electrophoretic mobility. Furthermore, the values found for the Oxisol (3.4–3.5) and Ultisol (2.6–2.7) were in the range expected for these soils. [Copyright &y& Elsevier]

Arsenate and phosphate interactions are important for better understanding their uptake and accumulation by plant due to their similarities in chemical behaviors. The present study examined the effects of arsenate and phosphate on plant biomass and uptake of arsenate and phosphate by Chinese brake (Pteris vittata L.), a newly-discovered arsenic hyperaccumulator. The plants were grown for 20 weeks in a soil, which received the combinations of 670, 2670, or 5340 μmol kg-1 arsenate and 800, 1600, or 3200 μmol kg-1 phosphate, respectively. Interactions between arsenate and phosphate influenced their availability in the soil, and thus plant growth and uptake of arsenate and phosphate. At low and medium arsenate levels (670 and 2670 μmol kg-1), phosphate had slight effects on arsenate uptake by and growth of Chinese brake. However, phosphate substantially increased plant biomass and arsenate accumulation by alleviating arsenate phytotoxicity at high arsenate levels (5340 μmol kg-1). Moderate doses of arsenate increased plant phosphate uptake, but decreased phosphate concentrations at high doses because of its phytotoxicity. Based on our results, the minimum P/As molar ratios should be at least 1.2 in soil solution or 1.0 in fern fronds for the growth of Chinese brake. Our findings suggest that phosphate application may be an important strategy for efficient use of Chinese brake to phytoremediate arsenic contaminated soils. Further study is needed on the mechanisms of interactive effects of arsenate and phosphate on Chinese brake in hydroponic systems. [ABSTRACT FROM AUTHOR]

Studies impacts of phosphate amendments on lead biogeochemistry at a contaminated site. Effects of phosphate amendments on sandy soil; Mineralogical analysis for the phosphate-treated soils; Lead distribution in phosphate-treated soils; Lead activity controlling minerals.

Forest application of boiler ash is fast becoming a popular alternative to landfilling. Boiler ash is a good source of calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), manganese (Mn), and zinc (Zn), but it may potentially increase soil pH and electrical conductivity. A monitoring study was conducted to determine the changes in soil properties and the availability and leachability of nutrients following the application of large quantities of boiler ash in a sandy soil (with a spodic horizon). Two application rates (900 and 1800 Mg ha- 1) and two application methods (surface and subsurface) were used in a three-hectare area, which was divided into 15 subplots. Soil samples from different depths were collected over a period of 21 months. Soil pH increased from 5.6 to above 9 and the electrical conductivity increased by up to 2 orders in all plots compared to the controls. The high alkalinity from the ash in the 1800 Mg ha- 1 rate depleted the spodic layer, and this was more pronounced in the subsurface treatments. Plant-available water was doubled to 12% in the 1800 Mg ha- 1 treatment and soil bulk density was reduced from 1500 kg m- 3 to 1200–1360 kg m- 3. Total and plant available macronutrients (Ca, Mg, K, and P) and micronutrients [iron (Fe), Mn, copper (Cu), and Zn)] increased substantially after ash application. Based on our study, it is highly recommended that ash application rates be lowered to agronomic rates, e.g., ∼10 Mg ha- 1, based on liming equivalence, to maximize the beneficial effects of boiler ash on soil. [ABSTRACT FROM AUTHOR]

Investigates taxonomic and geographic distribution of total phosphorus (P) in Florida surface soils. Distribution characteristics of P concentration; Taxonomic distribution of total P concentrations in disturbed and undisturbed soils; Impact of anthropogenic input of total P concentrations in soils.

Background concentrations of soil arsenic have been used as an alternative soil cleanup criterion in many states in the U.S. This research addresses issues related to the interpretation of background concentrations of arsenic in near pristine soils in Florida. Total arsenic was measured in 448 taxonomic and geographic representative surface soil samples using USEPA Method 3052 (HCl-HNO 3 -HF, microwave digestion) and graphite furnace atomic absorption spectrophotometry analysis procedure. Values were log-normally distributed, with geometric mean and baseline concentration (defined as 95% of the expected range of background concentrations) providing the most satisfactory statistical results. An upper baseline concentration of 6.21 mg As/kg was estimated for undisturbed soils (n=267) compared to 7.63 mg As/kg for disturbed soils (n=181). Temporal trend of total soil arsenic concentrations from 1967 to 1989 paralleled decreased usage of arsenic in U.S. agriculture. Soil arsenic background concentrations were generally higher in south Florida than in north and central Florida, and associated with wet soils. Individual high arsenic sites were scattered throughout the state, but the most highly concentrated of these occurred in the Leon-Lee belt along the Ocala uplift district extending to the southwestern flatwoods district. Extrapolation of the data using a single arsenic value regardless of the taxonomic and geographical differences in soil arsenic distribution would underestimate potential arsenic contamination in upland soils. [ABSTRACT FROM AUTHOR]

Compares the accuracy and precision of three aqua regia digestion methods in determining concentrations of different elements found in 20 Florida soils using the National Institute of Standards and Technology's standard reference materials. Variations in properties of soil samples; Spectrophotometric analysis of elemental concentration in the digestion solution; Disadvantage of conventional aqua regia digestion procedures.

Arsenic (As), a toxic metalloid and human carcinogen, has caused severe soil pollution around the world. Pteris vittata is the first known As hyperaccumulator and has been widely and successfully used to remediate As-contaminated soils. Mineral nutrients are crucial for As transfer in soil and As uptake, translocation, detoxification and accumulation in P. vittata. In addition, rhizosphere microbes also play a role in As mobilization, transformation, and plant As uptake. This review summarizes the effects of water status, nutrient elements (phosphorus, sulfur, selenium and calcium), and rhizosphere microbes on the efficiency of phytoextraction of As by P. vittata, providing insights into improvement of phytoremediation in future. [ABSTRACT FROM AUTHOR]

Organic pollutants are potential hazards for human health and are pivotal contributors to ecological imbalances. The spectrum of chemicals in research on organic pollutants has continually evolved, which is influenced by industrial advancements, scientific breakthroughs, and regulatory frameworks. A comprehensive analysis of 30 review articles on organic pollutants published during 2019-2023 in Critical Reviews in Environmental Science and Technology (CREST) provides good perspectives on the trajectory of organic pollutants in the environment. This synthesis delineates the recent advancements in two domains: (1) innovative monitoring technologies (sensor, extraction method, bio-indicator, and radioactive tracer); and (2) fate and transport, and risk assessment of organic pollutants. However, research on organic pollutants needs better monitoring techniques, matrix-related transformation methodologies, and realistic risk assessment tools. The development of novel strategies to monitor and manage organic pollutants, coupled with evaluations of ecosystem impacts under field conditions, is paramount. [ABSTRACT FROM AUTHOR]

Abstract In this study, 46 PM 2.5 samples collected from Nanjing, China were analyzed for total PAH concentration, with 14 samples assessed for PAH inhalation bioaccessibility and dioxin toxicity. The concentration of 19 PAH compounds in PM 2.5 ranged from 4.03 to 102 ng m−3. When PAH inhalation bioaccessibility was assessed using simulated epithelial lung fluid, mean bioaccessibility values ranged from 3.21% (Benzo(c)fluorene) to 44.2% (Acenaphthylene). Benzo(a)pyrene concentration in 50% of the PM 2.5 samples exceeded the Chinese air quality standard of 2.5 ng m−3, however, when bioaccessibility was considered, all samples were below the criterion. Similarly, the cancer risk probability for all PM 2.5 samples was >10−4 incidences on the basis of total PAH concentration, while only 37% of samples posed a risk >10−4 after incorporation of bioaccessibility. Dioxin toxicity of PM 2.5 -bound PAHs was also investigated by characterizing mRNA expression of cytochrome P450 superfamily members in human lung cells (A549 cell). Compared to total PAH concentration, the use of bioaccessible concentration was better at predicting dioxin toxicity of PM 2.5 -associated PAHs (correlation coefficient R 2 = 0.40–0.83 with p < 0.05). This study indicates that PAH inhalation bioaccessibility is an important consideration when assessing and predicting the risk posed by PM 2.5 particles, which is particularly important for countries with deteriorating air quality. Graphical abstract Unlabelled Image Highlights • Inhalation bioaccessibility of PM 2.5 -associated PAHs was measured by simulated epithelial lung fluid. • Life time cancer risk posed by PM 2.5 -associated PAHs was calculated with PAH inhalation bioaccessibility. • Bioaccessible concentration of PAHs can better predict toxicity posed by PM 2.5 -associated PAHs. [ABSTRACT FROM AUTHOR]

Phytohormones, including auxin, abscisic acid, gibberellic acid, ethylene, cytokinin, brassinosteroids, salicylic acid, and jasmonic acid, provide beneficial effects for plants against metal(loid) toxicity. However, their mechanisms in alleviating metal(loid) toxicity in plants have not been fully understood. Here, we summarize phytohormone-mediated detoxification mechanisms of metal(loid)s in plants, including As, Cd, Cr, Hg, and Pb. First, we discussed the functions of phytohormones on plant growth and nutrient uptake, and the effects of metal(loid)s on plant growth and hormone contents. We then discussed the underlying mechanisms of selected phytohormones in alleviating metal(loid) toxicity in plants. Those phytohormones protect plants against metal(loid) toxicity mainly by enhancing plant growth, increasing antioxidant capacity, promoting cell wall synthesis and nutrient uptake, and decreasing metal(loid) accumulation. This review highlights the beneficial roles of phytohormones in reducing plant metal(loid) uptake and in enhancing crop yields, which helps to improve crop production and food safety. [ABSTRACT FROM AUTHOR]

Biological remediation including bioremediation and phytoremediation has been used to remediate contaminated sites due to their cost-effectiveness, energy conservation, and environmental friendliness. There are 24 articles in Critical Reviews in Environmental Science and Technology (CREST) from 2018 to 2022 focusing on this topic. Bioremediation employs microorganisms to modify and/or degrade contaminants, while phytoremediation uses plants to remove, contain, and/or change contaminants. They cover different contaminants including traditional (nutrients, petroleum hydrocarbons, organo-pesticides, plastics, and heavy metals such as Cd, Cr, Pb and U) and emerging contaminants (pharmaceutical and personal care products, and perfluoroalkyl and polyfluoroalkyl substances). However, these remediation technologies have limitations in applications including lengthy periods, environmental sensitivity, nutrient deficiency and contaminant toxicity. Therefore, improvement strategies including immobilization of microbial/microalgal cells, construction of microbial/microalgal consortia, and use of amendments have been employed to overcome its drawbacks. Further studies should focus on cost-effective strategies to enhance the efficiency of biological remediation and their environmental adaptability, especially under extreme environments and with emerging contaminants. Microbes, microalgae and plants with good contaminant removal capability should be coupled with engineering practices based on their interactive mechanisms among bio-association and contaminants at molecular levels. [ABSTRACT FROM AUTHOR]

Announces the discovery that the fern Pteris vittata (brake fern) is extremely efficient in extracting arsenic from soils and translocating it into its above-ground biomass. Importance of its role as an arsenic hyperaccumulator, and as the first fern found to function as a hyperaccumulator; Study of brake fern growing on a site in central Florida contaminated with chromated copper arsenate; Implications for the remediation of arsenic-contaminated soils and for the study of arsenic in plants.

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 200–5,000 μg/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 (5,000 μg/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 (5,000 μg/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. [ABSTRACT FROM AUTHOR]

Arsenic-hyperaccumulator Pteris vittata exhibits remarkable absorption ability for chromium (Cr) while beneficial element selenium (Se) helps to reduce Cr-induced stress in plants. However, the effects of Se on the Cr uptake and the associated mechanisms in P. vittata are unclear, which were investigated in this study. P. vittata plants were grown for 14 days in 0.2-strength Hoagland solution containing 10 (Cr 10) or 100 μM (Cr 100) chromate (CrVI) and 1 μM selenate (Se 1). The plant biomass, malondialdehyde contents, total Cr and Se contents, Cr speciation, expression of genes associated with Cr uptake, and Cr subcellular distribution in P. vittata were determined. P. vittata effectively accumulated Cr by concentrating 96–99% in the roots under Cr 100 treatment. Further, Se substantially increased its Cr contents by 98% to 11,596 mg kg−1 in the roots, which may result from Se's role in reducing its oxidative stress as supported by 27–62% reduction in the malondialdehyde contents. Though supplied with CrVI, up to 98% of the Cr in the roots was reduced to insoluble chromite (CrIII), with 83–89% being distributed on root cell walls. Neither Cr nor Se upregulated the expression of sulfate transporters PvSultr1;1 − 1;2 or phosphate transporter PvPht1;4 , indicating their limited role in Cr uptake. P. vittata effectively accumulates Cr in the roots mainly as CrIII on cell walls and Se effectively enhances its Cr uptake by reducing its oxidative stress. Our study suggests that Se can be used to enhance P. vittata Cr uptake and reduce its oxidative stress, which may have application in phytostabilization of Cr-contaminated soils. [Display omitted] • P. vittata effectively accumulates Cr by concentrating 96–99 % in the roots at 100 μM CrVI. • Selenate promotes Cr uptake by 98% to 11,596 mg kg-1 in the roots at 100 μM CrVI. • Selenate reduces its oxidative stress as evidenced by 27–62% decrease in its MDA. • 94–99% CrVI is reduced to CrIII in the roots, with 83–89% on cell walls. [ABSTRACT FROM AUTHOR]

Rice cadmium (Cd) and microplastics are prevalent contaminants, posing a co-exposure threat to humans by means of dietary intake. To assess whether co-exposure of microplastics affects the bioavailability of rice Cd, mice were exposed to Cd-contaminated rice with microplastic co-exposure. We found that polyethylene (PE), polystyrene (PS), polypropylene (PP), and polyamide (PA) microplastic co-exposure via diet consumption (2 μg g–1) caused 1.17–1.38-fold higher Cd accumulation in tissue of mice fed by Cd-rice. For mice with co-exposure of PE microplastics, the higher rice-Cd bioavailability corresponded to colonization of Lactobacillus reuteri (38.9 % vs 17.5 %) in the gut compared to control mice, which caused higher production of gut metabolites particularly peptides, likely causing a 'side effect' of elevating Cd solubility in the intestinal lumen. In addition, abundance of sphingosine 1-phosphate in the gut of mice was reduced under PE microplastic exposure, which may reduce intracellular calcium ions (Ca2+) in enterocytes and form a weaker competition in pumping of intracellular Ca2+ and Cd2+ across the basolateral membrane of enterocytes, leading to higher Cd2+ transport efficiency. The results suggest elevated Cd exposure risk from rice consumption with microplastic co-exposure at environmentally relevant low concentrations. [Display omitted] • Microplastic co-exposure caused 1.17–1.38-fold higher Cd accumulation in mouse tissue. • Gut microbiota and gut metabolites were altered with microplastic co-exposure. • There was a correlation between Lactobacillus and elevated rice-Cd bioavailability. [ABSTRACT FROM AUTHOR]

It is known that selenium (Se) enhances plant growth and arsenic (As) accumulation in As-hyperaccumulator Pteris vittata, but the associated mechanisms are unclear. In this study, P. vittata was exposed to 50 μM arsenate (AsV) under hydroponics plus 25 or 50 μM foliar selenate. After 3-weeks of growth, the plant biomass, As and Se contents, As speciation, malondialdehyde (MDA) and glutathione (GSH and GSSG) levels, and important genes related to As-metabolism in P. vittata were determined. Foliar-Se increased plant biomass by 17 − 30 %, possibly due to 9.1 − 19 % reduction in MDA content compared to the As control. Further, foliar-Se enhanced the As contents by 1.9–3.5 folds and increased arsenite (AsIII) contents by 64 − 136 % in the fronds. The increased AsV reduction to AsIII was attributed to 60 − 131 % increase in glutathione peroxidase activity, which mediates GSH oxidation to GSSG (8.8 −29 % increase) in the fronds. Further, foliar-Se increased the expression of AsIII antiporters PvACR3;1–3;3 by 1.6 − 2.1 folds but had no impact on phosphate transporters PvPht1 or arsenate reductases PvHAC1/2. Our results indicate that foliar-Se effectively enhances plant growth and arsenic accumulation by promoting the GSH-GSSG cycle and upregulating gene expression of AsIII antiporters, which are responsible for AsIII translocation from the roots to fronds and AsIII sequestration into the fronds. The data indicate that foliar-Se can effectively improve phytoremediation efficiency of P. vittata in As-contaminated soils. [Display omitted] • Foliar-Se promoted plant growth by 17 − 30 % via decreasing MDA in the fronds. • Foliar-Se enhanced the As accumulation by 1.9–3.5 folds in the fronds. • Foliar-Se increased the glutathione oxidation from GSH to GSSG in the fronds. • Foliar-Se upregulated PvACR3;1-3;3 by 2-fold for As translocation & sequestration. [ABSTRACT FROM AUTHOR]