The main intent of the current research was to appraise if combined application of hydrogen sulfide (H₂S, 0.2 mM) and silicon (Si 2.0 mM) could improve tolerance of tomato plants to arsenic (As as sodium hydrogen arsenate heptahydrate, 0.2 mM) stress. Plant growth, chlorophylls (Chl), PSII maximum efficiency (Fv/Fm), H₂S concentration and L-cysteine desulfhydrase activity were found to be suppressed, but leaf and root As, leaf proline content, phytochelatins, malondialdehyde (MDA) and H₂O₂ as well as the activity of lipoxygenase (LOX) increased under As stress. H₂S and Si supplied together or alone enhanced the concentrations of key antioxidant biomolecules such as ascorbic acid, and reduced glutathione and the activities of key antioxidant system enzymes including catalase (CAT), superoxide dismutase (SOD), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and glutathione S-transferase (GST). In comparison with individual application of H₂S or Si, the joint supplementation of both had better effect in improving growth and key biochemical processes, and reducing tissue As content, suggesting a putative collaborative role of both molecules in improving tolerance to As-toxicity in tomato plants.

Bacteria play crucial roles in the biogeochemical cycle of arsenic (As) and selenium (Se) as these elements are metabolized via detoxification, energy generation (anaerobic respiration) and biosynthesis (e.g. selenocysteine) strategies. To date, arsenic and selenium biomineralization in bacteria were studied separately. In this study, the anaerobic metabolism of As and Se in Shewanella sp. O23S was investigated separately and mixed, with an emphasis put on the biomineralization products of this process. Multiple analytical techniques including ICP-MS, TEM-EDS, XRD, Micro-Raman, spectrophotometry and surface charge (zeta potential) were employed. Shewanella sp. O23S is capable of reducing selenate (SeO₄²⁻) and selenite (SeO₃²⁻) to red Se(-S)⁰, and arsenate (AsO₄³⁻) to arsenite (AsO₃³⁻). The release of H₂S from cysteine led to the precipitation of AsS minerals: nanorod AsS and granular As₂S₃. When As and Se oxyanions were mixed, both As–S and Se(-S)⁰ biominerals were synthesized. All biominerals were extracellular, amorphous and presented a negative surface charge (−24 to −38 mV). Kinetic analysis indicated the following reduction yields: SeO₃²⁻ (90%), AsO₄³⁻ (60%), and SeO₄²⁻ (<10%). The mix of SeO₃²⁻ with AsO₄³⁻ led to a decrease in As removal to 30%, while Se reduction yield was unaffected (88%). Interestingly, SeO₄²⁻ incubated with AsO₄³⁻ boosted the Se removal (71%). The exclusive extracellular formation of As and Se biominerals might indicate an extracellular respiratory process characteristic of various Shewanella species and strains. This is the first study documenting a complex interplay between As and Se oxyanions: selenite decreased arsenate reduction, whereas arsenate stimulated selenate reduction. Further investigation needs to clarify whether Shewanella sp. O23S employs multi-substrate respiratory enzymes or separate, high affinity enzymes for As and Se oxyanion respiration.

Research over the last three decades showed that chromium, particularly the oxyanion chromate Cr(VI) behaves as a toxic environmental pollutant that strongly damages plants due to oxidative stress, disruption of nutrient uptake, photosynthesis and metabolism, and ultimately, represses growth and development. However, mild Cr(VI) concentrations promote growth, induce adventitious root formation, reinforce the root cap, and produce twin roots from single root meristems under conditions that compromise cell viability, indicating its important role as a driver for root organogenesis. In recent years, considerable advance has been made towards deciphering the molecular mechanisms for root sensing of chromate, including the identification of regulatory proteins such as SOLITARY ROOT and MEDIATOR 18 that orchestrate the multilevel dynamics of the oxyanion. Cr(VI) decreases the expression of several glutamate receptors, whereas amino acids such as glutamate, cysteine and proline confer protection to plants from hexavalent chromium stress. The crosstalk between plant hormones, including auxin, ethylene, and jasmonic acid enables tissues to balance growth and defense under Cr(VI)-induced oxidative damage, which may be useful to better adapt crops to biotic and abiotic challenges. The highly contrasting responses of plants manifested at the transcriptional and translational levels depend on the concentration of chromate in the media, and fit well with the concept of hormesis, an adaptive mechanism that primes plants for resistance to environmental challenges, toxins or pollutants. Here, we review the contrasting facets of Cr(VI) in plants including the cellular, hormonal and molecular aspects that mechanistically separate its toxic effects from biostimulant outputs.

Inorganic arsenic (iAs) is a naturally occurring metalloid present in drinking water and polluted air exposing millions of people globally. Epidemiological studies have linked iAs exposure to the development of numerous diseases including cognitive impairment, cardiovascular failure and cancer. Despite intense research, an effective therapy for chronic arsenicosis has yet to be developed. Laboratory studies have been of great benefit in establishing the pathways involved in iAs toxicity and providing insights into its mechanism of action. However, the in vivo analysis of arsenic toxicity mechanisms has been difficult by the lack of reliable in vivo biomarkers of iAs’s effects. To address this issue we have applied the use of our recently developed stress reporter models to study iAs toxicity. The reporter mice Hmox1 (oxidative stress/inflammation; HOTT) and p21 (DNA damage) were exposed to iAs at acute and chronic, environmentally relevant, doses. We observed induction of the oxidative stress reporters in several cell types and tissues, which was largely dependent on the activation of transcription factor NRF2. We propose that our HOTT reporter model can be used as a surrogate biomarker of iAs-induced oxidative stress, and it constitutes a first-in-class platform to develop treatments aimed to counteract the role of oxidative stress in arsenicosis. Indeed, in a proof of concept experiment, the HOTT reporter mice were able to predict the therapeutic utility of the antioxidant N-acetyl cysteine in the prevention of iAs associated toxicity.

Inoculation of soil or seeds with plant growth promoting bacteria ameliorates metal toxicity to plants by changing metal speciation in plant tissues but the exact location of these changes remains unknown. Knowing where the changes occur is a critical first step to establish whether metal speciation changes are driven by microbial metabolism or by plant responses. Since bacteria concentrate in the rhizosphere, we hypothesised steep changes in metal speciation across the rhizosphere. We tested this by comparing speciation of zinc (Zn) in roots of Brassica juncea plants grown in soil contaminated with 600 mg kg⁻¹ of Zn with that of bulk and rhizospheric soil using synchrotron X-ray absorption spectroscopy (XAS). Seeds were either uninoculated or inoculated with Rhizobium leguminosarum bv. trifolii and Zn was supplied in the form of sulfide (ZnS nanoparticles) and sulfate (ZnSO₄). Consistent with previous studies, Zn toxicity, as assessed by plant growth parameters, was alleviated in B. juncea inoculated with Rhizobium leguminosarum. XAS results showed that in both ZnS and ZnSO₄ treatments, the most significant changes in speciation occurred between the rhizosphere and the root, and involved an increase in the proportion of organic acids and thiol complexes. In ZnS treatments, Zn phytate and Zn citrate were the dominant organic acid complexes, whilst Zn histidine also appeared in roots exposed to ZnSO₄. Inoculation with bacteria was associated with the appearance of Zn cysteine and Zn formate in roots, suggesting that these two forms are driven by bacterial metabolism. In contrast, Zn complexation with phytate, citrate and histidine is attributed to plant responses, perhaps in the form of exudates, some with long range influence into the bulk soil, leading to shallower speciation gradients.

Ionic liquids (ILs), also known as green solvents, are widely acknowledged in several fields, such as chemical separation, synthesis, and electrochemistry, owing to their excellent physiochemical properties. However, their poor biodegradability may lead to environmental and health risks, posing a severe threat to humans, thus requiring further research. In this study, the biotoxicities of the imidazolium-based ILs were evaluated in Tetrahymena pyriformis. Moreover, IL detoxification was investigated by addition of glutathione (GSH), cysteine, and nicotinamide adenine dinucleotide (NADH). Reactive oxygen species (ROS) initiated by different IL types caused damage to Tetrahymena, while glutathione, cysteine, and NADH eliminated ROS, achieving the detoxification purposes. Detoxification results showed that NADH exhibited the best detoxification ability, followed by glutathione and cysteine. Finally, RT-PCR results suggested that metallothionein might have participated in IL detoxification.

In freshwater ecosystems with frequent cyanobacterial blooms, the cyanobacteria toxin pollution is becoming increasingly serious. Nodularin (NOD), which has strong biological toxicity, has emerged as a new pollutant and affects the normal growth, development and reproduction of aquatic organisms. However, little information is available regarding this toxin. In this study, a graphene oxide material modified by L-cysteine was synthesized and used to immobilize microcystin-LR (MC-LR)-degrading enzyme (MlrA) to form an immobilized enzyme nanocomposite, CysGO-MlrA. Free-MlrA was used as a control. The efficiency of NOD removal by CysGO-MlrA was investigated. Additionally, the effects of CysGO-MlrA and the NOD degradation product on zebrafish lymphocytes were detected to determine the biological toxicity of these two substances. The results showed the following: (1) There was no significant difference in the degradation efficiency of NOD between CysGO-MlrA and free-MlrA; the degradation rate of both was greater than 80% at 1 h (2) The degradation efficiency of the enzyme could retain greater than 81% of the initial degradation efficiency after the CysGO-MlrA had been reused 7 times. (3) CysGO-MlrA retained greater than 50% of its activity on the 8th day when preserved at 0 °C, while free-MlrA lost 50% of its activity on the 4th day. (4) CysGO-MlrA and the degradation product of NOD showed no obvious cytotoxicity to zebrafish lymphocytes. Therefore, CysGO-MlrA might be used as an efficient and ecologically safe degradation material for NOD.

Mercury (Hg) and methylmercury (CH3Hg) bind strongly to micro and nano (NP) particles and this partitioning impacts their fate and bioaccumulation into food webs, and, as a result, potential human exposure. This partitioning has been shown to influence the bioavailability of inorganic Hg to methylating bacteria, with NP-bound Hg being more bioavailable than particulate HgS, or organic particulate-bound Hg. In this study we set out to investigate whether the potential interactions between dissolved ionic Hg (HgII) and CH3Hg and NPs was due to incorporation of Hg into the core of the cadmium selenide and sulfide (CdSe; CdS) nanoparticles (metal exchange or surface precipitation), or due purely to surface interactions. The interaction was assessed based on the quenching of the fluorescence intensity and lifetime observed during HgII or CH3Hg titration experiments of these NP solutions. Additional analysis using inductively coupled plasma mass spectrometry of CdSe NPs and the separated solution, obtained after HgII additions, showed that there was no metal exchange, and X-ray photoelectron spectroscopy confirmed this and further indicated that the Hg was bound to cysteine, the NP capping agent. Our study suggests that Hg and CH3Hg adsorbed to the surfaces of NPs would have different bioavailability for release into water or to (de)methylating organisms or for bioaccumulation, and provides insights into the behavior of Hg in the environment in the presence of natural or manufactured NPs.

Fine dust (FD) is a form of air pollution and is responsible for a wide range of diseases. Specially, FD is associated with several cardiovascular diseases (CVDs); long-term exposure to FD was shown to decrease endothelial function, but the underlying mechanism remains unclear. We investigated whether exposure to FD causes premature senescence-associated endothelial dysfunction in endothelial cells (ECs) isolated from porcine coronary arteries. The cells were treated with different concentrations of FD and senescence associated-beta galactosidase (SA-β-gal) activity, cell cycle progression, expression of endothelial nitric oxide synthase (eNOS), oxidative stress level, and vascular function were evaluated. We found that FD increased SA-β-gal activity, caused cell cycle arrest, and increased oxidative stress, suggesting the premature induction of senescence; on the other hand, eNOS expression was downregulated and platelet aggregation was enhanced. FD exposure impaired vasorelaxation in response to bradykinin and activated the local angiotensin system (LAS), which was inhibited by treatment with the antioxidant N-acetyl cysteine (NAC) and angiotensin II receptor type 1 (AT₁) antagonist losartan (LOS). NAC and LOS also suppressed FD-induced SA-β-gal activity, increased EC proliferation and eNOS expression, and improved endothelial function. These results demonstrate that FD induces premature senescence of ECs and is associated with increased oxidative stress and activation of LAS. This study can serve as a pharmacological target for prevention and/or treatment of air pollution-associated CVD.

Ozone (O₃) and nitrogen dioxide (NO₂) are thought to play primary roles in aggravating air pollution-induced health problems. However, the effects of joint O₃/NO₂ on the allergenicity of pollen allergens are unclear. Humulus japonicus pollen allergen 1 (Hum j1) is a profilin protein that causes widespread pollinosis in eastern Asia. In order to study the effects of combined O₃/NO₂ on the allergenicity of Hum j1, tandem six-histidine peptide tag (His6)-fused recombinant Hum j1 (rHum j1) was expressed in a prokaryotic system and purified through His6 affinity chromatography. The purified rHum j1 was used to immunize SD rats. Rat sera with high titers of IgG and IgE antibodies against rHum j1 were used for allergenicity quantification. The rHum j1 was exposed to O₃/NO₂, and changes in allergenicity of the exposed rHum j1 were assayed using the immunized rat antibodies. Tandem LC-MS/LC (liquid chromatography-mass spectrometer/liquid chromatography spectrometer) chromatography and UV and circular dichroism (CD) spectroscopy were used to study the structural changes in rHum j1. Our data demonstrated that a novel disulfide bond between the sulfhydryl groups of two neighboring cysteine molecules was formed after the rHum j1 exposure to joint O₃/NO₂, and therefore IgE-binding affinity was increased and the allergenicity was reinforced. Our results provided clues to elucidate the mechanism behind air pollution-induced increase in pollinosis prevalence.