Taurine (TAU) has recently been found to have an impactful role in regulating plant responses under abiotic stresses. This study presented the comparative effects of TAU seed priming and foliar spray application on chickpea plants exposed to hexavalent chromium. Taurine priming and foliar applications (1.6 and 2.4 mM) notably modulated morpho-physiological and biochemical responses of plants under Cr(VI) stress. Plants subjected to 25 mg kg-1 soil Cr in the form of potassium dichromate (K2Cr2O7) displayed a significant reduction in growth, chlorophyll, and uptake of essential nutrients (N, K, P, and Ca). Cr(VI) toxicity also resulted in a notable increase in osmolyte accumulation, lipid peroxidation, relative membrane permeability, ROS generation, antioxidant enzyme activities, antioxidant compounds, endogenous Cr levels, and aerial Cr translocation. Taurine abridged lipoxygenase activity to diminish lipid peroxidation owing to the overproduction of ROS initiated by a higher Cr content. The acquisition and assimilation of essential nutrients were augmented by the TAU-related decrease in leaf and root Cr levels. Consequently, TAU enhanced growth by mitigating oxidative damage, reducing Cr content in the aerial parts, and reinforcing the activities of antioxidant enzymes. Compared to foliar spray, TAU seed priming has demonstrated superior efficacy in mitigating Cr phytotoxicity in plants.

A novel iron-based phosphate cement (IPC), derived from iron-rich smelting slag (ISS), was developed as a sustainable and efficient binder for the stabilization/solidification of trivalent chromium (Cr3+). The mechanical properties, hydration behavior, microstructure, leaching toxicity, chromium chemical forms, and environmental safety of chromium-stabilized iron phosphate cement (CIPC) were thoroughly evaluated. The results showed that, with a mass ratio of ISS to ammonium dihydrogen phosphate (ADP) of 2.0, and even with the addition of 20 % chromium nitrate nonahydrate (CN), the compressive strength of CIPC reached 4.2 MPa after curing for 28 d. Furthermore, chromium leaching was well below 1 mg/L, significantly lower than the GB 5085.3-2007 standard limit of 15 mg/L, demonstrating the effective encapsulation of Cr3+ due to IPC's high early strength. In the IPC system, Cr3+ was primarily stabilized by forming CrPO4 and CrxFe1-x(OH)3 co-precipitates, which were further solidified through the physical encapsulation of IPC hydration products, such as (NH4)2Fe(PO3OH)2 center dot 4H2O, (NH4) (Mg,Ca)PO4 center dot H2O, and FePO4. This process resulted in a solidification efficiency of up to 99 %. BCR analysis confirmed that more than 98 % of the chromium in the CIPC remained in a stable residual form. Finally, the ecological risk index (PERT) was found to be 23.52, far below the safety threshold of 150, indicating the solidified material's long-term environmental safety. This study provides an innovative approach for the reutilization of ISS while effectively stabilizing/solidifying chromium.

Chromium is a heavy metal used in tanneries, leather industries, electroplating, and metallurgical operations, but improper disposal of waste from these industries leads to environmental contamination. Chromium exists primarily in trivalent and hexavalent forms, with hexavalent chromium (Cr (VI)) being highly toxic. Cr (VI) is carcinogenic, damages fish gills, and negatively impacts crops. Considering these negative impacts of Cr (VI), several physical, chemical, and biological remediation methods have been implemented at contaminated sites, but in most instances, these methods could be uneconomical, highly labor-intensive, and not sustainable. Therefore, a crucial goal is to implement an effective and sustainable remediation technique with consideration of actual site conditions. The aim is to develop a sustainable remediation strategy for a hexavalent chromiumcontaminated site in Ranipet, Tamil Nadu. The comprehensive risk assessment for the site has depicted hazard quotients greater than 1 for both onsite and offsite conditions, indicating the necessity of remediation. To address this, it is suggested to build permeable reactive filters (PRFs) packed with scrap iron filings to reduce Cr (VI) to Cr (III), and succeeding filters with locally produced waste coconut shell biochar to aid in adsorption. The use of waste here aims to eliminate the need to procure any commercially available materials for remediation, completely cutting down the environmental impact of raw material extraction or processing. A continuous chambered set-up packed with contaminated soil and PRFs with biochar and iron filings aided in the decrease of the peak concentration of Cr (VI) by 61 % as compared to a set-up without intervention. Moreover, the outlet concentration after 7 days reduced to 0.08 mg/L, which was 97.6 % less than that in the set-up without intervention.

This study investigates the potential of green-fabricated manganese dioxide (MnO2) nanoparticles (NPs) to mitigate chromium (Cr) toxicity in wheat, presenting a novel approach to enhancing ion homeostasis and physiological resilience under Cr stress. Chromium contamination in agricultural soils is a significant concern, severely impacting crop productivity and disrupting the physiological homeostasis of wheat. Chromium exposure compromises nutrient uptake, induces oxidative stress, and impairs plant growth and yield. This study explored the use of green-fabricated MnO2NPs to mitigate Cr-induced oxidative stress in two bread wheat cultivars, Borlaug-16 and SKD-1. Seed nano-priming with MnO2NPs (100, 250, and 500 mg kg-1) was applied, followed by Cr (100 mg kg-1) exposure, and key physiological, biochemical, and ionomic responses were evaluated. Manganese dioxide nanoparticles significantly reduced Cr uptake and improved ion transport. In Borlaug-16, NP250 enhanced seedling height by 74 %, while NP100 reduced H2O2and TBARS by 60.28 % and 50.17 %, respectively, indicating improved oxidative stress tolerance. SKD-1 exhibited greater Cr stress tolerance, with NP250 improving root length by 31.03 % and relative water content by 56.66 %, supporting better water retention. Additionally, MnO2NP treatments boosted antioxidant enzyme activities, increasing APX and GPX by up to 12.47 %, and restored root and leaf anatomy, reversing Cr-induced structural damage. Furthermore, MnO2NPs enhanced the uptake of essential nutrients such as calcium, potassium, and magnesium, while restricting Cr translocation, improving overall nutrient efficiency. These findings emphasize the potential of MnO2NPs as an eco-friendly strategy for enhancing crop resilience and promoting sustainable agriculture in Cr-contaminated soils.

Here, we investigate how the oxidation state of Cr adsorbed to solid surfaces can change during XPS analysis. Experiments are performed to test how Fe(III) solid surfaces, aqueous chemistry, and XPS vacuum conditions affected the measured Cr oxidation state. While oxidized Cr(VI) adsorbs onto nonreducing solid surfaces in the experiments, reduced Cr(III) is primarily measured by XPS. The reduction of adsorbed Cr(VI) occurs under the vacuum conditions of the XPS as CO2, O-2, and H2O are removed from the sample surface. These results suggest that Fe(III) solid surfaces exposed to high-vacuum conditions and/or X-rays can cause the reduction of Cr or other elements with a high redox potential contained on that surface.

Heavy metal contamination in agricultural soils is a growing environmental concern, particularly due to the increasing accumulation of cadmium (Cd) and chromium (Cr) from industrial discharge, wastewater irrigation, and excessive fertilizer use. These toxic metals severely impact crop productivity by disrupting nutrient uptake, damaging root structures, and inducing oxidative stress, which collectively inhibit plant growth and development. Maize (Zea mays L.), a globally important cereal crop, is highly susceptible to heavy metal toxicity, making it essential to develop cost-effective and sustainable mitigation strategies. Spent mushroom substrate (SMS) biochar has emerged as an effective and sustainable method due to its ability to absorb heavy metals. Spent mushroom substrate biochar improves compost quality, soil fertility, and health. Its high porosity and surface area immobilize toxic metals, reducing nutrient losses and oxidative stress in plants. Pyrolysis temperature affects its surface area, nutrient composition, and adsorption abilities. This study aims to address this gap by evaluating the effectiveness of SMS biochar at varying application rates in mitigating Cd and Cr toxicity in maize. By assessing key physiological and agronomic parameters, this research provides novel insights into the potential of SMS biochar as a sustainable soil amendment for heavy metal-contaminated soils. Five treatments, i.e., 0, 50, 100, 150 and 200B were applied under Cd and Cr toxicity in 3 replications following the completely randomized design (CRD). Results exhibited that 200B caused an increase in maize plant height (26.1%), root dry weight (99.7%), grain yield (98.2%), and chlorophyll contents (50%) over control under Cd and Cr stress. In conclusion, 200B can mitigate Cd and Cr stress in maize plants. More investigations are suggested to declare 200B as a promising amendment for mitigation of Cd and Cr stress in other crops.

Most improved strategies for phytoextraction do not achieve a synergistic enhancement of chromium (Cr) accumulation capacity and biomass. This study investigated the impacts of co-addition of garbage enzyme (GE) and microelectrolytic iron-carbon filler (MF) on soil physicochemical properties, as well as form and uptake of Cr during aging and phytoextraction process. The response of rhizosphere microbial community to co-addition and its role in enhancing the remediation performance of ryegrass was further analyzed. Co-addition of GE and MF during the 12-day aging process resulted in an increase of nutrients, a shift from an oxidising to a reducing soil environment, a decrease of Cr(VI) content, and an enhancement of soil microbial community diversity and richness, creating a suitable environment for subsequent phytoextraction. During the 40-day phytoextraction process, co-addition played a crucial role in facilitating the establishment of a complex, efficient and interdependent ecological network among soil microorganisms and contributed to the evolution of microbial community composition and functional pathways. An increase in the relative abundance of Trichococcus, Azospirillum and g_norank_f_JG30-KF-CM45 elevated soil nutrient levels, while a decrease in the relative abundance of TM7a and Brucella reduced pathogen harbouring. Meanwhile, co-addition increased the relative abundance of Bacillus, Arthrobacter and Exiguobacterium, attenuated Cr phytotoxicity and improved soil biochemical activity. These markedly diminished oxidative damage and improved ryegrass growth by reducing malondialdehyde accumulation. In addition, regular additions of GE and the increase in relative abundance of norank_fnorank_o_Microtrichales led to rhizosphere acidification, which inhibited short-term Cr immobilization and contributed to a notable increase in phytoextraction efficiency. This study presents a strategy to enhance phytoremediation efficiency and soil quality during phytoextraction of Cr-contaminated soils.

Chromium is a widespread toxic trace metal in cultivated lands owing to human actions, insufficient treatment, and unregulated disposal. Chromium toxicity is facilitated by the production of reactive oxygen species, which induce lipid peroxidation and damage the cellular membranes and nuclei. This study evaluated the preparation and characterization of Pterospermum-derived biochar based on a set of test categories from the International Biochar Initiative. The aim of this study was to assess the effectiveness of Pterospermum-derived biochar and salicylic acid (SA) in promoting the growth and biochemical attributes of tomato plants grown in Crcontaminated soils. The results showed that Cr toxicity reduced root (42.86 %) and shoot (23.26 %) lengths, which subsequently increased (65 % root and 39.94 % shoot lengths) under SA and biochar treatments. Increased levels of superoxide anions (O2 center dot-) (104.43 %), malondialdehyde (MDA) (115.53 %), and H2O2 (72.35 %) were observed in the Cr-treated tomato plantlets. The combined treatment of SA and biochar effectively reduced MDA, H2O2, and O2 center dot- levels by 51.17%, 36.89%, and 45.53%, respectively, under Cr toxicity conditions. In addition, the combined treatment with SA and biochar enhanced the activity and gene expression of dehydrogenase (7.06fold), guaiacol peroxidase (6.51-fold), superoxide dismutase (7.90-fold), polyphenol oxidase (1.89-fold), glutathione-s-transferase (2.55-fold), ascorbate peroxidase (1.26-fold), and glutathione peroxidase (8.75-fold) under Cr toxicity conditions. The results highlight the combined treatment of biochar and SA as an effective amendment that offers an environment-friendly method for alleviating Cr toxicity and promoting growth and the antioxidative defense system in tomato plantlets.

Increased anthropogenic activities over the last decades have led to a gradual increase in chromium (Cr) content in the soil, which, due to its high mobility in soil, makes Cr accumulation in plants a serious threat to the health of animals and humans. The present study investigated the ameliorative effect of foliar-applied Si nanoparticles (SiF) and soil-applied SiNPs enriched biochar (SiBc) on the growth of wheat in Cr-polluted soil (CPS). Two levels of CPS were prepared, including 12.5 % and 25 % by adding Cr-polluted wastewater in the soil as soil 1 (S1) and soil 2 (S2), respectively for the pot experiment with a duration of 40 days. Cr stress significantly reduced wheat growth, however, combined application of SiF and SiBc improved root and shoot biomass production under Cr stress by (i) reducing Cr accumulation, (ii) increasing activities of antioxidant enzymes (ascorbate peroxidase and catalase), and (iii) increasing protein and total phenolic contents in both root and shoot respectively. Nonetheless, separate applications of SiF and SiBc effectively reduced Cr toxicity in shoot and root respectively, indicating a tissue-specific regulation of wheat growth under Cr. Later, the Langmuir and Freundlich adsorption isotherm analysis showed a maximum soil Cr adsorption capacity similar to Q((max)) of 40.6 mg g(-1) and 59 mg g(-1) at S1 and S2 respectively, while the life cycle impact assessment showed scores of -1 mg kg(-1) and -211 mg kg(-1) for Cr in agricultural soil and - 0.184 and - 38.7 for human health at S1 and S2 respectively in response to combined SiF + SiBC application, thus indicating the environment implication of Si nanoparticles and its biochar in ameliorating Cr toxicity in different environmental perspectives.

Frequent and severe wildfires have led to increased application of fire suppression products (long-term fire retardants, water enhancers, and Class A foams) in the American West. While fire suppressing products used on wildfires must be approved by the U.S. Forest Service, portions of their formulations are trade secrets. Increased metals content in soils and surface waters at the wildland-urban interface has been observed after wildfires but has primarily been attributed to ash deposition or anthropogenic impact from nearby urban areas. In this study, metal concentrations in several fire suppression products (some approved by the U.S. Forest Service, and some marketed for consumer use) were quantified to evaluate whether these products could contribute to increased metal concentrations observed in the environment postfire. Long-term fire retardants contained concentrations of toxic metals (V, Cr, Mn, Cu, As, Cd, Sb, Ba, Tl, and Pb) 4-2,880 times greater than drinking water regulatory limits, and potentially greater than some aquatic toxicity thresholds when released into the environment. Water enhancers and Class A foams contained some metals, but at lower concentrations than fire retardants. Based on these concentrations and retardant application records, we estimate fire retardant application in the U.S. contributed approximately 380,000 kg of toxic metals to the environment between 2009 and 2021.