Chromium contamination and effect on environmental health and its remediation: A sustainable approaches

Hexavalent chromium and cellular senescence: A comprehensive analysis from chromate-exposed occupational population and chromate-inhaled mouse model

Cellular senescence may predominantly drive the progression of early subclinical injury under conditions of low-dose, long-term occupational exposure. However, previous research has largely overlooked the cellular senescence induced by hexavalent chromium [Cr(VI)]. To bridge the gap, 304 workers from a chromate facility were enrolled, and a mouse model was used to confirm the effects of Cr(VI) on cellular senescence. A 2.7-fold increase in blood Cr was related to the changes of p53 [23.19 (13.06, 34.23)%], serum α-Klotho [11.45 (6.13, 17.04)%], adipsin [-14.11(-22.16, -5.24)%], leptin [-4.32(-6.99, -1.58)%] and resistin [-3.29(-5.54, -0.98)%]. There were significant correlations of blood Cr with DNA methylation of ELOVL2 and hTERT genes. Furthermore, methylation at hTERT Pos1, Pos2, Pos6, and Pos8 significantly mediated the relationship between blood Cr and p53. In the mouse model, we observed significantly higher mRNA expression levels of key genes in the p53/p21 and Rb/p16 pathways and senescence-associated β-galactosidase positive cell ratio in the exposed group. In conclusion, we found that p53 in human peripheral blood cells serves as a Cr(VI)-induced senescence biomarker, with α-Klotho upregulation and adipokines (adipsin, leptin, and resistin) downregulation indicating compensatory responses, as well as hTERT methylation partially mediating Cr(VI)-senescence association.

Adsorption and ecotoxicology studies with aqueous solution of Cr(VI) ions using adsorbent materials derived from Inga edulis

Adsorbents derived from the bark of Inga edulis were developed for the removal of Cr(VI) ions. Chemical activation with sulfuric acid led to significant changes in the physicochemical properties of the biomass. The adsorbent materials denoted IB (inga biomass) and AIB (activated inga biomass) showed higher removal efficiencies at pH 2.0 and dosages of 1.0 and 0.25 g L-1, respectively. The adsorption kinetics could be fitted using the Elovich model, indicating that the adsorption occurred on heterogeneous surfaces. The maximum adsorption capacities were 46.0 mg g-1 for IB and 356.6 mg g-1 for AIB, with behaviors that could be described by the Langmuir (monolayer) and Freundlich (multilayer) models, respectively. XPS analyses confirmed the reduction of Cr(VI) to Cr(III), due to interactions with oxygenated functional groups. Thermodynamic evaluation indicated that the adsorption was spontaneous, with exothermic character for IB and endothermic character for AIB. Ecotoxicological assays using Daphnia similis showed that a Cr(VI) concentration of 4.34 μg L-1 caused 50.0 % immobility, while adsorption by the materials eliminated the toxicity, demonstrating the effectiveness of the adsorbents in reducing environmental impacts. Additionally, an electrode derived from the adsorption of Cr(VI) on AIB, denoted CPEAIB-Cr-ads-active, presented good performance in the hydrogen evolution reaction (HER), with high current density and low overpotential. The structure of the electrode, with high surface area and the presence of pores and cavities, was favorable for electrochemical catalysis, evidencing its potential for use in applications concerning renewable energy and environmental detoxification.

Metals in the coastal systems of Abaco Island, The Bahamas following Hurricane Dorian

Hurricanes can introduce metals into coastal systems. Unfortunately, metal concentrations are unknown in many hurricane prone locations. Here we measured vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, arsenic, molybdenum, cadmium, antimony, barium, lead, and uranium in surface water, sediments, and seagrass (Thalassia testudinum) collected in seagrass beds and marinas around The Abacos, The Bahamas in November 2019, May 2020, and June and December 2021 to establish a post-Hurricane Dorian baseline, assess changes post-storm, and understand bioconcentration in seagrass. Metal concentrations were higher in marinas and several increased over time. Also, metal profiles in sediments became more similar over time. Together, these suggest that metals were impacted by Hurricane Dorian and are either returning to pre-storm conditions or increasing due to recovery-related activities. Thalassia testudinum uptakes most metals more readily from surface water than sediments. Therefore, seagrasses may phytoremediate metals, but also transfer metals to higher trophic levels.

Exploring the potential of biologically synthesized nano-adsorbents in removal of hexavalent chromium (Cr (VI)): Mechanistic studies and circular economy integration

Heavy metals, particularly chromium (VI), cause severe environmental and health risks due to its toxicity and persistence in environment. Thus, it is essential to remediate such metals from the environment owing to its detrimental effects. A key promising method for removing environmental pollutants from such contamination is adsorption. However, conventional adsorbents often face limitations in efficiency and reusability, necessitating synthesizing methods for nanoparticles. Nanotechnology has demonstrated superior capabilities in this regard, particularly through the modification and functionalization of nanoparticles to enhance adsorption capacity and regeneration potential. These nanoparticles fabricated using various biological sources offer an eco-friendly and cost-effective alternative methods. Furthermore, biologically synthesized nanoparticles demonstrate high adsorption efficiency, with removal rates for Cr (VI) ranging up to 99 % with multiple regeneration cycles. The adsorption process has predominantly followed pseudo second-order kinetics, with maximum adsorption capacities reaching up to 459 mg g-1 and the best fitted isotherm model for these nanoparticles is the Langmuir isotherm, which depends on the nano-adsorbent type and operating conditions. Taking an extensive literature review method, this review looks into the importance of surface modification of nano-adsorbents and highlighting the role of biologically synthesized nanoparticles as effective adsorbents. Additionally, it provides the management of spent adsorbents with a focused on circular economy to address sustainability. Moreover, it covers computational analyses to optimize nanoparticle design and predict adsorption performance and addresses the challenges of scalability, suggesting future research directions to ensure sustainable and effective heavy metal remediation.

Plastic dispersion in Northeast Brazil beaches and plastic contaminant detection in Brazilian coast fishing nets

This study investigates the dispersion of floating plastic from Recife-PE harbor using a particle tracking model and examines contaminants in fishing nets collected from Brazilian beaches. Simulations were conducted for both dry and rainy seasons. Fishing nets were collected from eight beaches for analysis. The plastic movement simulation showed particles dispersed 0.41 km southward during the dry season and 177.50 km northward during the rainy season. Most particles (90 %) beached within the first week, indicating localized litter distribution. The study identified 14 pesticide residues in the collected nets, along with heavy metals such as arsenic, cadmium, chromium, copper, nickel, zinc, and iron, detected via Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The pesticide and metal data were used to calculate the toxicological priority index (ToxPi), showing the sample from Joaquina-SC had the highest toxicity, while the sample from Sancho-PE had the lowest. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) revealed pollution patterns, with potential associations between pesticides and metals. These findings raise concerns about the contaminants' impact on marine organisms and human health, highlighting the importance of understanding plastic pollution dynamics and associated risks. Also, the outcomes emphasize the need to reevaluate environmental regulations to better protect ecosystems and species from harmful pollutants, including plastics.

Heavy metal contamination in wastewater-irrigated vegetables: assessing food safety challenges in developing Asian countries

Vegetables are crucial for human nutrition, providing essential micronutrients and beneficial compounds. Heavy metal contamination of vegetables irrigated with wastewater poses a significant public health risk in developing Asian countries. This review analyses recent research on heavy metal accumulation in vegetables across India, Bangladesh, Pakistan, and China. Studies consistently report concerning levels of cadmium, lead, chromium, arsenic, nickel, and mercury in vegetables, often exceeding international safety standards. Leafy vegetables consistently show higher heavy metal accumulation compared to fruit and root vegetables. Within plant structures, roots generally contain higher heavy metal concentrations than edible parts, though this varies depending on the metal and plant species. Many studies report health risk indices exceeding safe limits, indicating potential non-carcinogenic and carcinogenic risks from chronic dietary exposure, with children at higher risk. The review highlights inadequate regulatory frameworks and enforcement mechanisms. A multi-faceted approach is urgently needed, encompassing improved wastewater treatment, best agricultural practices, rigorous monitoring, and public awareness campaigns. Future research directions are identified, including long-term health impact studies, development of cost-effective remediation techniques, and exploration of sustainable alternatives to wastewater irrigation. While wastewater irrigation addresses immediate water scarcity, it poses significant long-term food safety and public health risks. Integrated policies balancing water scarcity, agricultural productivity, and health risks are essential. This review underscores the pressing need for coordinated efforts from policymakers, researchers, and health officials to safeguard public health and ensure sustainable agriculture in developing Asian countries facing increasing urbanization and water scarcity.

Green synthesis and adsorption performance of Fe3O4/chitosan/polypyrrole composites for efficient removal of chromium ion

In this study, Fe3O4/chitosan/polypyrrole (Fe3O4/CS/PPy) magnetic adsorbents were successfully synthesized using the in situ chemical oxidation polymerization method. These adsorbents were characterized by SEM, FT-IR, TGA, and XPS. The results of batch adsorption experiments showed that the Fe3O4/CS/PPy composite exhibited a maximum adsorption capacity of 193.23 mg g-1 in a 100 mg L-1 Cr(vi) solution at 298 K, with a pH of 2.0. The adsorption behavior of the adsorbent to Cr(vi) was in good agreement with the Langmuir isothermal model and the quasi-second-order kinetic model. Thermodynamic studies indicated that the process of adsorption was spontaneous and endothermic. The mechanism of adsorption may be attributed to electrostatic interactions and chemical reduction. After five cycles, the removal efficiency of the Fe3O4/CS/PPy composite for Cr(vi) has consistently remained at 84.32%. Overall, the Fe3O4/CS/PPy composite exhibits great potential as an adsorbent for effectively removing Cr(vi) from aqueous solutions.

Harnessing native bacterial consortium to boost duckweed biomass and chromium removal from batik industry effluents

Batik industry is one of the largest contributors to chromium hexavalent (Cr(VI)) pollution due to the dying and pigmenting process. Remediation agents such as duckweed and bacteria have been commonly used to treat wastewater (WW)-containing Cr(VI). This study utilized native bacterial consortium from the batik WW environment to enhance duckweed growth and Cr(VI) removal. Among the formulated consortia, consortium G4 showed the highest growth promotion on duckweed in WW by 1.3 to 2-fold, while other consortia showed a contrasting result. Additionally, duckweed chromium uptake in WW reached 74 % after 12 days when applied with G4. Consortium G4 features two plant growth-promoting bacteria, Enterobacter mori TALD 1.2 and Enterobacter cloacae TALA 5, along with two chromium-reducing bacteria, Lysinibacillus fusiformis TALA 1.1 and Bacillus thuringiensis TA1. Several combinations of the G4 members were also tested for chromium reduction activity in an NB medium containing 100 mg L-1 Cr(VI). The original G4 combination showed the fastest Cr(VI) removal, achieving an 81.93 % Cr(VI) reduction within 48 h and a 99 % reduction within 105 h. Interestingly, combining only the chromium-reducing bacteria TALA 1.1 and TA 1 significantly reduced chromium reduction activity and bacterial growth, possibly due to carbon source competition. Thus, the complete members of consortium G4 enhance cross-feeding, with each species playing a vital role in improving interspecies interactions and aiding in chromium reduction. This study underscores the importance of designing a specific and compatible consortium to collaborate with duckweed, offering insights into environmental management practices for other contaminated sites.

Two-dimensional Monte Carlo simulation coupled with multilinear regression modeling of source-specific health risks from groundwater

Effective protection of groundwater requires an accurate health risk assessment of contaminants; however, the diversity of pollution sources, variability, and uncertainties in exposure parameters present significant challenges in this assessment. In this study, groundwater risk estimates associated with NO3-, and F-, along with fourteen heavy metal(loid)s (V, Cr, Mn, Fe, Ni, Cu, As, Co, Cd, Se, Pb, Hg, Zn, and Al) in an agricultural area were optimized by implementing positive matrix factorization (PMF), multilinear regression, and two-dimensional Monte Carlo simulations to characterize source-specific health risks. Groundwater pollution was analyzed considering regional variations, including differences in elevation, land use and land cover, and soil types. Three pollution sources were identified: agricultural practices, traffic, and natural processes. Moreover, the results revealed NO3- from an agricultural source as the primary control contaminant. Additionally, both adults and children in the study area face significant non-carcinogenic health risks. To mitigate these risks, this study recommends maximum consumption levels of 1.44 L/day for adults and 0.35 L/day for children. Furthermore, adults weighing > 68.1 kg and children weighing > 15.9 kg are likely to be at reduced risk of experiencing adverse health effects. Compared to deterministic health risk assessment and one-dimensional Monte Carlo simulation of health risks, two-dimensional Monte Carlo simulation showed improved performance, providing better accuracy and higher precision in health risk assessment results. Thus, this research is expected to enhance the understanding of health risk assessment related to groundwater and to provide valuable guidance for managing groundwater pollution.

Tidal control of heavy metal loading in the nearshore of the northwestern Indian coast

Heavy metals accumulate in the marine food chain and their excessive amounts are hazardous to aquatic and human lives. The current study presents the role of ecosystem variables especially tides in deciding the presence of ten heavy metals (Fe, Zn, Cu, Co, Cr, Mn, Ni, V, Pb, and Cd) in seawater and copepods along the Indian west coast. The Indian northwestern coast is an industrial hub, where thousands of industries release enormous volumes of effluents, while the southwest coast has a far lower number of industries. Multiple surface seawater and zooplankton samples from eight selected marine outfall regions in the nearshore of the Indian west coast showed that Fe/Cd was generally the highest/lowest in seawater (av. 184 ± 12.40 μg L-1/ av. 0.01 ± 0.01 μg L-1) and copepods (av. 41,818 ± 2867 μg. g-1/ av. 0.2 ± 0.02 μg g-1). The heavy metals in seawater/copepods generally showed the order Fe/Fe > Zn/Zn > V/Mn > Cr/Cr > Pb/Cu > Ni/Ni > Cu/Pb > Mn/V > Co/Co > Cd/Cd. Contrary to expectations, despite being loaded with massive amounts of effluent from thousands of industries, most heavy metals in seawater on the northwestern Indian coast were not higher than on the southwestern coast. It is shown here that this feature is the result of the macro-tidal nature of the northwest Indian coast (av. 7 m tide), where tidal currents, sediment resuspension, and flushing are far more intense than in the southwest (av. 1 m tide), which reduce pollution levels. Yet, the marine pollution index and bioaccumulation factor of heavy metals in copepods was found highest along the northwestern Indian coast, which are important indicators to be considered when developing environmental management strategies for the area.

Ecotoxicological evaluation of urban wastewater treatment plants: a Sicilian study

(1) Background: Ecotoxicological screening evaluates the acute toxicity of WWs. The Vibrio fischeri ecotoxicological assay analyses inlet and outlet wastewater samples from two urban wastewater treatment plants in Catania, Sicily, Italy. (2) Methods: The APAT CNR IRSA 8030 Man 29 method was used as method; (3) Results: The results showed toxicity values below the limit of the Italian Legislative Decree 152/06; (4) Conclusions: This monitoring study allows to verify the efficacy, and the outlet quality of WWs discharged to sea water. This ecotoxicological assay is a valuable tool for evaluating the combined toxicity of various pollutants that underline the total damage of the studied matrices detecting the true effect of complex mixtures on the environment and its fauna.

Carboxymethyl cellulose/alginate/chitosan-based polyelectrolyte complex hydrogel with irregularly shaped multi-metallic nanowires for efficient continuous-flow Cr(VI) remediation

The efficient removal of hexavalent chromium (Cr(VI)) from industrial wastewater is a pressing environmental challenge. A natural polyelectrolyte complex (PEC) hydrogel composed of carboxymethyl cellulose, alginate and chitosan, was developed to support Pd/Au/Ag/Pt nanowires for the continuous-flow catalytic reduction of Cr(VI) to the less toxic Cr(III). PEC hydrogels are formed through the association of oppositely charged polyelectrolytes, a process that is primarily driven by entropy gain due to the release of counterions, resulting in highly porous networks with tunable physical and chemical properties. These characteristics make them ideal platforms for nanoparticle stabilization and catalytic applications. Crosslinking with glutaraldehyde, citric acid and calcium ions further improved the stability and porosity of the hydrogels. Pd/Au/Ag/Pt nanowires, synthesised through galvanic replacement and co-reduction of Pd/Au/Ag nanowires formed via an oriented attachment mechanism, exhibit a distinctive, irregular, undulating morphology that enhances their suitability for introduction into hydrogel matrices. These multi-metallic nanowires achieved complete Cr(VI) reduction within 15 min. When incorporated into a nanocomposite hydrogel, the Pd/Au/Ag/Pt nanowires significantly enhanced catalytic activity while maintaining structural integrity and high catalytic efficiency. Notably, the system achieved complete Cr(VI) reduction within 5 h of continuous-flow operation, highlighting its potential as a robust and scalable solution for industrial wastewater remediation.

Augmenting Cr(VI) phytoremediation potential of Ricinus communis through rhizospheric crosstalk with multi stress tolerant plant growth promoting Bacillus altitudinis M1

Plant growth promoting rhizobacteria are cost-effective and eco-friendly alternative for bioremediation of Cr(VI). This study investigated the effects of rhizobacterial strain Bacillus altitudinis M1 on Cr(VI) reduction, plant growth promotion and Cr(VI) stress mitigation in Ricinus communis. Biosorption and bioreduction of Cr(VI) up to 300 mg/l by the strain M1 was confirmed by FTIR, Raman Spectrum and TEM-EDX analysis. Moreover, the strain M1 exhibited high tolerance to temperature (up to 40 °C), pH (up to 8.0), NaCl (up to 6%) and various heavy metals (Pb, Cd, Ni, Cu, Mn and Zn). The strain M1 produced significant IAA, ammonia and EPS under higher concentration of Cr(VI). The strain improved the growth and development of test crop R. communis under higher Cr(VI) concentration. Inoculation of the strain M1 alleviated Cr(VI)-induced oxidative stress in roots and leaves of R. communis by decreasing proline (up to 24 and 33%), H2O2 (up to 56 and 43%), and MDA (up to 42 and 40%) by regulating the activity of antioxidant enzymes. These findings suggest that the strain M1 promotes plant growth under Cr(VI) stress through multiple mechanisms, including phytohormone production, nutrient mobilization, stress metabolite modulation, and antioxidant defense system regulation. Thus the application of the strain M1 potentially reduces Cr(VI) bioavailability, making it a promising candidate for Cr(VI) bioremediation.

Biofilm Formation and Detoxification of Hexavalent Chromium by Bacillus subtilis: A Sustainable Approach to Bioremediation

Hexavalent chromium [Cr(VI)] is a toxic environmental pollutant, primarily generated by industrial processes, posing a significant risk to biota. Effective detoxification of Cr(VI) is necessary before environmental discharge. This study focused on the Cr(VI) tolerance and detoxification potential of an isolated Bacillus subtilis strain KCBA07C10, along with the effects of Cr(VI) stress on its biofilm formation, and its potential application in bioremediation. The bacterial strain isolated from treated textile effluent, was subjected to growth studies in Cr(VI)-supplemented media with a low carbon source. Detoxification potential was assessed through Cr(VI) and total Cr removal analyses, while biofilm formation was evaluated using spectrophotometric assays and scanning electron microscopy. Results revealed that B. subtilis KCBA07C10 tolerates high Cr(VI) concentrations (> 16.0 mg/L) and achieves significant detoxification via bioreduction, removing nearly 88% of Cr(VI) even under nutrient-limited conditions. These findings highlight the strain's potential for bioremediation. Furthermore, quantitative assays demonstrated a positive correlation between Cr(VI) exposure and biofilm formation (p = 0.009, α = 0.05), suggesting an adaptive defense mechanism. This study highlights the potential of B. subtilis KCBA07C10 as an eco-friendly agent for Cr(VI) detoxification and bioremediation applications.

Iron oxide-MXene-based composite for the removal of copper ions from wastewater

The present work primarily aims to evaluate the adsorption properties of MXene and its nanocomposite, Fe3O4@MXene, for removing heavy metal ions from industrial wastewater. Two-dimensional (2D) MXene nanosheets were combined with Fe3O4 nanoparticles through a hydrothermal synthesis process to create the Fe3O4@MXene nanocomposite. Characterization revealed that Fe3O4 nanoparticles self-assembled onto MXene sheets, forming a structure that enhanced the 2D structure of MXene, with nanoparticles uniformly distributed throughout the nanosheet network. Performance experiments demonstrated that Fe3O4@MXene nanocomposite significantly outperformed pristine MXene in adsorbing heavy metal ions from wastewater. Notably, Fe3O4@MXene nanocomposite achieved an 83% removal efficiency for Cu ions, highlighting its potential as a highly efficient adsorbent in industrial wastewater treatment. This work underscores the viability of Fe3O4@MXene for heavy metal remediation, marking an important step toward practical environmental applications of MXene-based materials.

Classification and predictive leaching risk assessment of construction and demolition waste using multivariate statistical and machine learning analyses

Managing construction and demolition waste (CDW) poses serious concerns regarding landfilling and recycling because of the potential release of hazardous elements after leaching. Ceramic materials such as bricks, tiles, and porcelain account for more than 70% of CDW. Fourteen samples of different CDW products from Ferrara (Northeast Italy) were subjected to geochemical analyses, including leaching tests, in accordance with UNI EN 12457-2. The interaction between ceramics and concrete was examined, highlighting the influence of mixed environments on the leaching behavior. Results were compared with an extensive database of more than 150 samples collected from the literature on different CDW types worldwide. Multivariate statistical analysis and machine learning were used to classify the CDW compositions based on the bulk chemical data. Various metrics-contaminant factors (Cf and Cd) and hazardous quotients (HQ and HQm)-were introduced to quantify the key environmental hazards of leachates. The results of this study underscore the potential of the proposed approaches in automating CDW classification and predicting Cf and HQ using only the starting bulk chemical composition. The findings enhance CDW management practices and support sustainability efforts in the construction industry.

Bioremediation of chromium (VI) from mining-contaminated soil using Klebsiella sp. (BH-A1): environmental implications

The present investigation aimed to isolate and identify a novel bacterium from chromium (VI)-contaminated soil samples collected from the Gorbi mine area, Singrauli coalfield, evaluates its potential for Cr(VI) reduction to Cr(III) and enhances environmental and operational conditions to apply this in bioremediation of Cr-contaminated soils. A bacterium was newly isolated from contaminated soils of coal mines for chromium (VI) reduction and identified as Klebsiella sp. (BH-A1) using 16S rRNA gene sequencing. Calcium chloride and sodium alginate solutions were used to immobilize the bacterial cells of isolated Klebsiella sp. Bacteria beads (Klebsiella sp. BH-A1) were tailored to reduce 10 µg/g Cr(VI)-contaminated soil under varied environmental factors such as bead biomass (200-1000 mg), pH (5-8), temperature (25-35 °C), and nutrient sources. Beads of Klebsiella sp. (BH-A1) (1000 mg/g) were efficient for 87% reduction of 10 µg/g Cr(VI) present in the soil at pH 7, 30 °C, within a six-hour contact period. Fourier transform infrared spectroscopy analyses reveal varied functional groups like -OH, -NH, and -COOH in Cr-treated bacterial beads. Functional groups corroborate their involvement in Cr(VI) and Cr(III) absorption on the cell surface of bacteria. Chromium-treated Klebsiella sp. (BH-A1) cell size was wider due to chromium absorption than the non-treated bacterial cells after SEM analyses. The energy dispersive X-ray plot has proven the 0.41 weight percent chromium accumulation inside the bacterial cells. Moreover, XPS analyses of Cr-treated bacterial cells indicate reduced Cr(VI) into Cr(III). The finding further suggests that Klebsiella sp. (BH-A1) might be a new prospect for potential application in Cr detoxification from Cr-contaminated soil. The limitations of this research include the accumulation of hazardous metabolic products due to low diffusion rates, the formation of thick biofilms blocking bead pores, and interrupted substrate transport from the bulk liquid to immobilized cells.

Nanomaterials for Removal and Speciation of Chromium

The removal of chromium compounds, particularly its more toxic Cr(VI) form, from industrial wastewater is important as it causes serious environmental and health issues. Adsorption processes have attracted continuous interest for solving these problems due to the diverse range of various adsorbents. Nanomaterials are increasingly employed as novel sorbents as they have a large specific surface area and high chemical stability. Functionalization of their surface by covalent or noncovalent interactions with other components, grafting or doping with heteroatoms can enhance separation and removal efficiency. This paper aims to provide insights into the recent progress in the application of nanomaterials for chromium removal from aqueous solutions and speciation analysis of it.

Magnetite Stoichiometry (Fe(II)/Fe(III)) Controls on Trivalent Chromium Surface Speciation

While the elimination of the most toxic form of chromium (Cr(VI)) by its reduction to Cr(III) at the magnetite (Fe3O4) surface has widely been documented, elucidating the exact mechanism involved in Cr(III) sorption to magnetite has attracted less attention. Indeed, magnetite stoichiometry (R = Fe(II)/Fe(III)) is rarely controlled or monitored in Cr-magnetite interaction studies, although it was shown to affect not only redox transformation but also adsorption mechanisms of several contaminants. This study examined the interaction of 20 μM (∼1 mg L-1) Cr(III) with 10 nm magnetites, whose stoichiometries were carefully defined (0.1 ≤ R ≤ 0.5) and preserved under anaerobic conditions in 10 mM NaCl. X-ray absorption spectroscopy showed the formation of a tridentate trinuclear inner-sphere surface complex, but it occurred only on oxidized magnetite (R0.1) or on stoichiometric magnetite (R0.5) under acidic conditions, where H+-promoted dissolution generated an Fe(II)-depleted surface. When magnetite stoichiometry increased, Cr surface speciation evolved in favor of a [Fe2+Crx3+Fe3+ 1-x]OhFeTd3+O4-like solid solution in which Cr(III) partially substitutes Fe(III) in octahedral sites. This study reveals the joint effects of pH and magnetite stoichiometry on the Cr(III) sorption mechanism, demonstrating that Cr(III)-(hydr)oxide precipitation is not necessarily the driving process of Cr(III) elimination from solutions. These results will help predict the fate and transport of chromium as well as develop magnetite-based chromium remediation processes.

Insight into migration of Cr(VI) in self-hardening slurry materials for trench cutoff wall

The migration and immobilization of heavy metals in soil and groundwater pose significant environmental challenges, particularly in the context of Cr(VI), a highly toxic and mobile contaminant. Self-hardening slurry materials, commonly used for trench cutoff walls, have gained great attention due to their potential for pollutant containment. However, the relationship between their adsorption properties and pollutant diffusion behaviors remains poorly understood. This study investigates the adsorption properties and free-diffusion behaviors of Cr(VI) in two self-hardening slurry materials, SCB (slag-cement-bentonite) and MASB (MgO activated slag-bentonite), to better understand the pollutant migration and immobilization mechanisms. Adsorption experiments reveal that MASB exhibits a higher Cr(VI) adsorption capacity than SCB, resulting in greater retardation factors and longer breakthrough times, improved by 57.6% and 94.9% at Cr(VI) concentrations of 2600 mg/L and 26000 mg/L, respectively. However, free-diffusion tests show that MASB has a larger migration depth and shorter breakthrough times, reduced by 68.2% and 57.9%. Microscopic analysis reveals that the presence of stable and ion-exchangeable hydration products (hydrotalcite-like phases) in MASB enhances its Cr(VI) adsorption capacity but provides favorable conditions for Cr(VI) diffusion. SCB demonstrates superior retardation to Cr(VI) in free-diffusion due to the transformation of AFm phases absorbed with Cr(VI) into stable AFt phases.

Assessment of heavy metal levels in bee pollen (Apis mellifera L) from urban and rural areas of Egypt: implications for bioindication and food safety

This study examined pollen samples from several parts of Egypt to assess the heavy metal levels present. Assessment of the performance of bee pollen (Apis mellifera L) as a bioindicator for the presence of Zn, Cd, Fe, Cu, Ni, Pb, Mo, and Cr in municipal and countryside areas was the main objective of this research and concurrently the study's central premise. Four places were in rural areas, and one was near the city center, giving five locations for three honeybee colonies. In order to compare pollen samples from urban and rural locations, heavy metal (Zn, Cd, Fe, Cu, Ni, Pb, Mo, and Cr) levels were measured in those gathered from these colonies. The study found that there were no significant differences in the levels of Cd in the pollen samples collected from different sites. Compared to urban areas, pollen sample heavy metal values in countryside regions generally decreased (P <0.05). It was determined that the concentrations of Cr, Fe, Cu, Ni, Mn, and Zn in pollen specimens varied significantly (P< 0.05) across the localities. Consistent with International Food Standards, the levels of heavy metals in pollen specimens collected from diverse areas were determined to be acceptable.

Influence of Miscanthus floridulus on Heavy Metal Distribution and Phytoremediation in Coal Gangue Dump Soils: Implications for Ecological Risk Mitigation

Coal gangue dumps, a byproduct of coal mining, contribute significantly to heavy metal contamination, impacting soil and water quality. In order to assess the levels of heavy metal contamination in soils at different stages of abandonment, this study investigated the role of Miscanthus floridulus (M. floridulus) in the spatial distribution and remediation of six heavy metals (Cd, Cr, Mn, Ni, Cu, and Pb) in coal gangue dump soils abandoned for 0, 8, and 12 years in Pingxiang City, Jiangxi Province, China. Fieldwork was conducted at three sites operated by the Pingxiang Mining Group: Anyuan (active, barren), Gaokeng (8 years, natural vegetation), and Qingshan (12 years, partially remediated). Anyuan remains largely barren, while Gaokeng supports natural vegetation without formal remediation. In contrast, Qingshan supports diverse plant species, including M. floridulus, due to partial remediation. Using a randomized design, root exudates, heavy metal concentrations, and soil properties were analyzed. The results showed that Cd poses the highest ecological risk, with concentrations of 64.56 mg kg-1 at the active site, 25.57 mg kg-1 at the 8-year site, and 39.13 mg kg-1 at the 12-year site. Cu and Pb showed accumulation, while Cr and Mn decreased over time. Root exudates from M. floridulus enhanced metal bioavailability, influencing Cd, Cr, and Ni concentrations. These findings highlight the importance of rhizosphere processes in metal mobility and inform sustainable remediation strategies for post-mining landscapes.

Evaluating Heavy Metals in Human Breast Milk: a Cross-Sectional Study from Mining and Agricultural Areas in Northwestern Iran

This study aimed to assess the levels of heavy metals in the breast milk of women residing in the mining and agricultural areas of East Azerbaijan province in Iran. This cross-sectional study analyzed 68 lactating mothers from mining (n = 28) and agricultural (n = 40) areas of East Azerbaijan province in Iran between June 2022 and March 2023. The study used an Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) to measure the concentrations of heavy metals, including arsenic (As), chromium (Cr), copper (Cu), and iron (Fe). A semi-quantitative food frequency questionnaire (SQ-FFQ) was used to collect data on the dietary and sociodemographic characteristics of the mothers. Although the concentration of arsenic (As) was below the limit of detection (LOD), the mean concentrations of chromium (Cr), copper (Cu), and iron (Fe) were 1.11, 0.87, and 13.25 mg/L in agricultural areas and 0.83, 0.93, and 11.35 mg/L in mining areas, respectively. The concentrations of Cr (p < 0.001) and Fe (p = 0.019) were significantly higher in the breast milk of women residing in agricultural areas. However, the concentration of Cu was significantly higher (p = 0.085) in the breast milk of women living in mining areas. Additionally, lactation age had a significant effect on Cu levels (p = 0.015), with a negative coefficient of -0.011. The study indicates that the levels of heavy metals in breast milk can be influenced by the exposure to pesticides, fertilizers, volcanic soil, and disparities in access to post-natal care and iron supplements.

Ultrahigh and rapid removal of Ni2+ using a novel polymer-zeolite-biochar tri-composite through one-pot synthesis route

In this work, a novel adsorbent from alginate, zeolite and biochar has been made through one-pot synthesis route with highly compatible Sodium Dodecyl Sulphate (SDS) modification. This gave ultra-high Ni2+ removal of 1205 mg/g in batch mode while treating almost 200 L of solution in column mode with 1171 mg/g capacity, which are the one of the highest reported values. The Point of Zero Charge (pHzpc) for Ni2+ removal was determined to be 5, with optimal removal efficiency being observed at pH 7, indicating a negative surface charge of the ABPC beads, which aligns with the anionic charge provided by SDS enhancement. Mechanistic studies have been done to show the most prominent mechanisms of metal removal besides demonstrating stability up to 20 cylces with desorption efficiency as high as 97%. The adsorbent is found to be highly cost effective at 1.87USD per kg.

Highly Dense TiO2 Nanorods as Potential Electrode Material for Electrochemical Detection of Multiple Heavy Metal Ions in Aqueous Medium

This study describes the direct deposition of extremely dense TiO2 nanorods (NRs) on an ITO substrate for the improved detection of heavy metal ions (HMIs). A facile hydrothermal method was employed to synthesize TiO2 NRs on the ITO substrate at ~130 °C. Synthesized TiO2 NRs were analyzed for morphological, structural, and electrochemical properties. As an electrode material, TiO2 NRs were used for the simultaneous detection of three HMIs (i.e., Cr3+, Cu2+, and Hg2+), which showed a remarkably high sensitivity of ~92.2 µA.mM-1.cm-2 for the Cu2+ ion. Relatively low sensitivities of ~15.6 µA.mM-1.cm-2 and ~19.67 µA.mM-1.cm-2 were recorded for the Cr3+ and Hg2+ ions, respectively. The fabricated TiO2 NR-based HMI sensor showed an effective dynamic linear detection range with low LOD values of ~21.7 mM, 37 mM, and ~ 28.5 mM for Cr3+, Cu2+, and Hg2+, respectively. The TiO2 NR-based HMI sensor exhibited efficient charge transfer over the electrode toward the trace detection of Cr3+, Cu2+, and Hg2+. Moreover, the reliability of the TiO2 NR-based HMI sensor was assessed, which exhibited a promising stability of 30 days. The obtained results indicate that TiO2 NRs grown on an ITO substrate are a promising electrode material for detecting hazardous Cr3+, Cu2+, and Hg2+ and might eventually be commercialized in the near future.

Assessment of forest soil contamination by heavy metals in the Polish National Park near Warsaw

The forest ecosystems are essential for human well-being development and reduction of the risk of natural disasters. Maintaining forest growth and ecosystem services is dependent on soil sustainability. The content of heavy metals is the main parameter determining the degree of soil contamination and degradation. The objective of the study was to assess the extent of soil contamination and identify the sources of potential anomalies. The content of the cadmium, lead, manganese and chromium (using atomic emission spectroscopy with induction-coupled plasma), as well as granulometric composition, pH value and nitrogen and total carbon content, were conducted on soil samples taken from the surface layer (0-10 cm) in the protected area of the Kampinos National Park in Poland. The soil quality assessment was conducted by calculating indicators of contamination including the geo-accumulation index, contamination factor, degree of contamination, ecological risk of individual heavy metals and potential ecological risk index. The results exhibited that the tested soils were very acidic or acidic sands. The content of the determined elements did not exceed the permissible limits as outlined in Polish standards, which are 2 mg/kg, 100 mg/kg and 150 mg/kg for cadmium, lead and chromium, respectively. The indicators show differences in the degree of contamination of the surface soil layer in the studied area, which is predominantly uncontaminated by heavy metals. However, the geochemical index values equal 0.42, 0.71 and 0.98 for certain samples suggesting the anthropogenic impact on the soils of the Kampinos National Park. The pollution appears to have been generated by the metallurgical industry, heating and power plants in the Warsaw agglomeration and transport.

Evaluation of the dynamics of nutrients and potentially toxic elements along a major river in Ethiopia using multivariate statistical techniques: Implications of possible co-occurrences

This study utilized established field and laboratory methods and multivariate statistical tools to evaluate the nutrient and potentially toxic elements (PTEs) distribution, identify possible sources, and determine potential co-existence in the Awash River. The levels of soluble reactive phosphorus (SRP), total phosphorus (TP), NO3-N, Mn, Ni, Cr, and Cu generally increased downstream in the upper Awash, with the highest respective values of 0.70, 1.34, 1.19, 1.58, 1.03, 0.85, and 0.11 mg L-1 at the inlet to Lake Koka. Sites found downstream of the inflow of Lake Beseka and Metehara town showed the highest levels of Fe, B, Zn, and dissolved silica. Principal components and correlation analysis findings revealed strong associations (r ≥ 0.80, p < 0.05) between nutrient parameters (SRP, TP, and NO3-N) and PTEs (Cu, Ni, Mn, and Cr), implying common origins and potential co-occurrences. The potential co-occurrences of these parameters may strengthen their potential individual impacts due to complex interactions.

Foliar spraying melatonin reduces the threat of chromium-contaminated water to wheat production by improving photosynthesis, limiting Cr translocation and reducing oxidative stress

Chromium (Cr)-contaminated in irrigation water poses a significant threat to the safety of wheat (Triticum aestivum L.) production safety. Recent studies suggest that melatonin (MT) could enhance crop tolerance to Cr pollution. This study aimed to investigate the effects of foliar spraying MT on alleviating Cr toxicity and accumulation in wheat irrigated with K2Cr2O7 solution at concentrations of 5, 10, and 20 mg/kg Cr in the soil. Our results showed that Cr-contaminated water irrigation significantly reduced dry weight, grain numbers, grain weight, yield, harvest index, net photosynthetic rate (Pn), maximum and actual photochemical efficiency of photosystem II (Fv/Fm and ΦPSII), chlorophyll contents, and the a/b ratio. It also increased PSII photodamage and oxidative stress in wheat leaves, resulting in high Cr accumulation in roots, leaves, and grains. Foliar spraying of MT alleviated Cr toxicity by improving Pn, Fv/Fm, and ΦPSII, enhancing chlorophyll content, promoting dry matter accumulation and yield, and reducing oxidative stress and Cr translocation. Furthermore, MT application enhanced transcriptional regulation, alleviated oxidative stress by boosting antioxidant enzyme activities, and restricted Cr translocation from roots to leaves and grains by increasing the accumulation of secondary metabolites, such as lignin and metallothionein. These findings suggest that MT application could serve as a viable strategy for reducing Cr contamination in cereals and supporting phytoremediation efforts.

Loading of anionic surfactant on eco-friendly biochar and its applications in Cr(VI) removal: adsorption, kinetics, and reusability studies

Surfactant-modified biochar is a viable adsorbent for eliminating Cr(VI) from synthetic wastewater. The biochar obtained from the zea mays plant (BC) was tailored with sodium dodecyl sulfate (SDS) as an anionic surfactant forming SDS-BC adsorbent. Different controlling conditions have been evaluated including pH of the solution, biomass concentration, primary Cr(VI) concentration, time of adsorption, and temperature. Under the best controlling circumstances, the percentage of removal has attained 99%. The pseudo-second-order kinetic model best described the removal process, according to the kinetic data, while the Temkin model, one of the applicable adsorption isotherm models, well expressed the adsorption process. The thermodynamic parameters were computed, which disclosed the spontaneity and exothermic character of the Cr(VI) elimination. According to the regeneration cycles, SDS-BC was cost-effective and had a good removal capability.

Assessment of heavy metals, PAHs, and pesticide levels in yerba mate on the European market

Although yerba mate has been known and used for hundreds of years, not all of its properties have been fully understood yet. Yerba mate is a source of many desirable substances, but it may also contain toxic metals and other substances that are harmful to health. Fifteen samples of yerba mate tea from three South American countries were analyzed. The content of Cr, Ni, and Cd was determined using the AAS technique, while the PHA's content was determined with the gas chromatography method. Our studies show that some of the analyzed substances present in Ilex paraguariensis may exceed their acceptable levels specified in European standards established for the given substances. All analyzed samples contained the determined metals, where the concentrations of individual elements ranged from 1.92 ± 0.38 to 0.12 ± 0.05 µg/g (for Cr), from 4.86 ± 0.28 to 1.72 ± 0.14 µg/g (for Ni), and from 0.0008 ± 0.000 to 0.0695 ± 0.0745 µg/g (for Cd). The total PAH content ranged from 0.064 to 0.585 mg/kg. Yerba mate samples from Brazil were characterized by a lower PAH content (0.064-0.254 mg/kg), compared with mate from Argentina and Paraguay (0.084-0.374 and 0.197-0.585 mg/kg, respectively). Pesticide residues were found only in samples from Argentina and Paraguay, while samples from Brazil did not contain those compounds. Only four active substances belonging to the group of herbicides, fungicides, and insecticides were detected, two of them not approved for use in the EU: chlorpyrifos and fenbuconazole. The most frequently detected compounds in yerba mate samples were pendimethalin (in four samples), fluazifop-p-butyl and fenbuconazole (detected in two samples), and chlorpyrifos (in one sample).

A convenient colorimetric assay for Cr(VI) detection based on homogeneous Cu(II)-GMP system with oxidoreductase-like activity

Hexavalent chromium (Cr(VI)) is an environmental pollutant and recognized as a human carcinogen. Therefore, it is necessary to develop a simple and sensitive detection technique for Cr(VI). Herein, it is found that Cu2+ interacts with guanosine 5'-monophosphate (GMP) to form a homogeneous Cu(II)-GMP complex (Cu2+·GMP) that efficiently displays the oxidoreductase-like catalytic activity. Cu2+·GMP can catalyze the oxidation between Cr(VI) and substrate 3,3',5,5'- tetramethylbenzidine (TMB), resulting in color change recognized by the naked eyes. Base on this, a convenient colorimetric assay for Cr(VI) detection was developed. The detection limit (3σ/s) of this sensor for Cr(VI) was 23 nM with a linear range of 0.1-25 μM. Moreover, the proposed assay was successfully applied to detect Cr(VI) in different environmental water samples with satisfactory recoveries. Our method is simple, efficient, rapid and cost-effective for Cr(VI) detection without the need for complicated material preparation or special separation, which shows great potential in environmental monitoring.

New Schiff base covalently bonded graphene oxide for removing chromium(VI) from surface runoff

Hexavalent chromium (Cr(VI)) poses severe health and environmental risk, especially in industrial vicinities where runoff concentrations are elevated by evaporation and sedimentation dynamics. This study investigates the utilization of modified graphene oxide (GO) with abundant active groups as an adsorbent. The novel adsorbent, GO/ATA, was synthesized by covalently attaching a Schiff base (ATA) to GO via a coupling reaction, enhancing its adsorptive properties. The physicochemical properties of GO/ATA were meticulously characterized to ascertain structural and morphological attributes. GO/ATA exhibit exceptional adsorptive capabilities, surpassing the performance parameters of other adsorbents with a maximum of 243.3 mg g-1 at 298 K. The electrostatic attraction between the N-containing functional groups in the graphene oxide and Schiff base composite (GO/ATA) and Cr(VI) is the main mechanism behind the adsorption process; Subsequently, a reduction reaction occurs, facilitated by the thiol and N-containing functional groups in GO/ATA composite, resulting in the transformation of Cr(VI) into Cr(III). This transformation is essential for the following chelation process occurring on the surface of the adsorbent material. Evaluations of recyclability indicated that GO/ATA retains substantial adsorption efficacy, with a reduction from 91.2% to 72.7% over five cycles, thus affirming its recyclability and practical application in the remediation of Cr(VI)-contaminated waterborne environment. Additionally, GO/ATA's effectiveness in removing Cr(VI) from surface runoff was specifically tested, emphasizing its economic and environmental viability.

SbSeI for high-efficient photocatalytic degradation of multiple pollutants

Photocatalytic degradation is an effective technology for degrading water pollution that plays a significant role in environmental remediation. Ternary 2D ternary V-VI-VIIA semiconductors are ideal candidates for photocatalytic degradation of pollutants due to effective light absorption and high charge carrier mobility. In this work, high-quality SbSeI crystals were prepared using the chemical vapor transport (CVT) method and their photocatalytic degradation performance for multiple pollutants was studied. SbSeI exhibits excellent photocatalytic performance in the degradation of potassium dichromate (Cr (VI)), rhodamine B (RhB), tetracycline hydrochloride (TC-HCl) and methyl orange (MO). More than 98% of Cr (VI) and RhB can be removed after irradiation with an Xe lamp for 10 min and 40 min, respectively. The capture experiments and electron spin resonance results indicated that ·O2- plays a major role in reducing Cr (VI), while h+ plays a primary role in the degradation of MO, RhB and TC-HCl. Interestingly, the degradation rate of Cr (VI) is 1.3 times higher than that of a single pollutant system, and the degradation rate of RhB is 1.6 times higher, due to the enhanced separation and utilization of holes and electrons. The results demonstrate that SbSeI is a potential photocatalytic degradation material.

A Biorefinery Approach Integrating Lipid and EPS Augmentation Along with Cr (III) Mitigation by Chlorella minutissima

The quest for cleaner and sustainable energy sources is crucial, considering the current scenario of a steep rise in energy consumption and the fuel crisis, exacerbated by diminishing fossil fuel reserves and rising pollutants. In particular, the bioaccumulation of hazardous substances like trivalent chromium has not only disrupted the fragile equilibrium of the ecological system but also poses significant health hazards to humans. Microalgae emerged as a promising solution for achieving sustainability due to their ability to remediate contaminants and produce greener alternatives such as biofuels. This integrated approach provides an ambitious strategy to address global concerns pertaining to economic stability, environmental degradation, and the energy crisis. This study investigates the intricate defense mechanisms deployed by freshwater microalgae Chlorella minutissima in response to Cr (III) toxicity. The microalga achieved an impressive 92% removal efficiency with an IC50 value of 200 ppm, illustrating its extraordinary resilience towards chromium-induced stress. Furthermore, this research embarked on thorough explorations encompassing morphological, pigment-centric, and biochemical analyses, aimed at revealing the adaptive strategies associated with Cr (III) resilience, as well as the dynamics of carbon pool flow that contribute to enhanced lipid and extracellular polysaccharide (EPS) synthesis. The FAME profile of the biodiesel produced complies with the benchmark established by American and European fuel regulations, emphasizing its suitability as a high-quality vehicular fuel. Elevated levels of ROS, TBARS, and osmolytes (such as glycine-betaine), along with the increased activity of antioxidant enzymes (CAT, GR, and SOD), reveal the activation of robust defense mechanisms against oxidative stress caused by Cr (III). The finding of this investigation presents an effective framework for an algal-based biorefinery approach, integrating pollutant detoxification with the generation of vehicular-quality biodiesel and additional value-added compounds vital for achieving sustainability under the concept of a circular economy.

Assessment of drinking water quality and identifying pollution sources in a chromite mining region

Water sources near mining regions are often susceptible to contamination from toxic elements. This study employs machine learning (ML) techniques to evaluate drinking water quality and identify pollution sources near a chromite mine in Iran. Human health risks were assessed using both deterministic and probabilistic approaches. Findings revealed that concentrations of calcium (Ca), chromium (Cr), lithium (Li), magnesium (Mg), and sodium (Na) in the water samples exceeded international safety standards. The Unweighted Root Mean Square water quality index (RMS-WQI) and Weighted Quadratic Mean (WQM-WQI) categorized all water samples as 'Fair', with average scores of 67.95 and 67.19, respectively. Of the ML models tested, the Extra Trees (ET) algorithm emerged as the top predictor of WQI, with Mg and strontium (Sr) as key variables influencing the scores. Principal component analysis (PCA) identified three distinct clusters of water quality parameters, highlighting influences from both local geology and anthropogenic activities. The highest average hazard quotient (HQ) for Cr was 1.71 for children, 1.27 for adolescents, and 1.05 for adults. Monte Carlo simulation for health risk assessment indicated median hazard index (HI) of 4.48 for children, 3.58 for teenagers, and 2.98 for adults, all exceeding the acceptable threshold of 1. Total carcinogenic risk (TCR) exceeded the EPA's acceptable level for 99.38 % of children, 98.24 % of teenagers, and 100 % of adults, with arsenic (As) and Cr identified as the main contributors. The study highlights the need for urgent mitigation measures, recommending a 99 % reduction in concentrations of key contaminants to lower both carcinogenic and non-carcinogenic risks to acceptable levels.

Remediation of Cr(VI) Polluted Groundwater Using Zero-Valent Iron Composites: Preparation, Modification, Mechanisms, and Environmental Implications

The extensive application of chromium (Cr) in many industries has inevitably resulted in the release of Cr(VI) into the groundwater environment, thus posing damage to the ecosystem and human health. Nano zero-valent iron (nZVI) has been widely studied and applied in the remediation of Cr(VI)-contaminated water as an ideal material with high reductive capacity, which enables the transformation of teratogenic and carcinogenic Cr(VI) into less toxic Cr(III). This review comprehensively summarizes the preparation and modification methods of nZVI Cr(VI) removal performance and mechanisms by nZVI and modified nZVI materials. The field applications of nZVI-based materials, such as combining the injection well and the permeable reactive barrier (PRB) to remove Cr(VI) in groundwater, have been reported. Subsequently, the potential toxicity of nZVI-based materials to organisms during environmental application has been highlighted in the current study. Finally, the review outlines potential improvements and explores future directions for the use of nZVI-based materials in groundwater contamination remediation.

Human health risk assessment of heavy metals in beer brands from Tanzania market

Heavy metal contamination in the environment, often resulting from industrial activities, mining, and improper waste disposal, leads to the accumulation of heavy metals in soil, water, air, drinks and food. Prolonged exposure to these metals can cause serious health issues in humans, including neurological damage, kidney failure, respiratory problems, and an increased risk of cancer. High levels of heavy metals in food are hazardous to human health. Heavy metals can find their way into beer at different stages, including through raw materials, the brewing process, equipment, bottling, and storage. This study examined the presence of Cu, Cd, Pb, Cr, Fe, and Zn in ten of the most consumed beer brands in Tanzania using an atomic absorption spectrometer (AAS). The results showed that the concentration of heavy metals in the beer samples increased in the order of Zn < Cu < Fe < Cr. Cd and Pb were not detected in any beer samples. Compared to WHO guidelines, the levels of Zn and Cu were below the limit, while Fe and Cr exceeded it. Estimated daily intake (CDI), hazard quotient (HQ), hazard index (HI), and incremental lifetime cancer risk (ILCR) were used to evaluate the potential human health risks. The EDI values of Fe and Zn were lower than the provisional maximum tolerable daily intake (PMTDI) set by the FAO/WHO. However, the mean EDI for Cr surpassed the recommended value, posing a potential risk for moderate and high beer consumers. The HQ and HI values for Zn and Fe were below 1, signifying no non-carcinogenic health concerns. In contrast, Cr had HQ and HI values greater than 1, indicating a notable non-carcinogenic health risk through beers consumption. ILCR due to Cr ranged from 0.029 to 0.695. These ILCR values for Cr in all beer samples are above range of10 - 6 - 10 - 4 recommended by USEPA, suggesting a potential carcinogenic risk linked to this toxic metal and, consequently, a possible cancer risk for beer consumers. Therefore, beer manufacturers should continuously work to minimize public health risks. Additionally, further research involving a larger variety of beer brands and the implementation of policy interventions is needed.

Highland barley ELNs and physiological responses to different concentrations of Cr (VI) stress

This study is the first to use highland barley (HB) to study the toxic effects of Cr (VI) on seedlings and the response mechanism of HELNs to Cr (VI) stress. The outcomes indicated that the germination rate of HB seeds, plant height, root length, water content, and levels of proline (PRO) and soluble sugar in both leaves and roots were all impacted by varying concentrations of Cr (VI) treatments. Differential changes in the activities of antioxidant enzymes (SOD, POD, CAT) were observed in leaves and roots of HB. We also extracted HB-derived ELNs (HELNs) and characterized and sequenced HELNs. The average particle size of CK-HELNs was 79.0 nm, and the concentration of HELNs was 4.56 E+10 (particles/mL). As the concentration of Cr (VI) increased, the particle size of HELNs in HB seedlings also increased, while the concentration decreased. A total of 29 miRNA species were identified in CK-HELNs, Cr10-HELNs, and Cr40-HELNs. Out of these, 25 were newly predicted miRNAs, and the remaining four were known miRNAs. A total of 2 known miRNAs and 11 novel miRNAs were upregulated under different concentrations of Cr (VI) stress. 1 known and 5 novel miRNAs were downregulated under different concentrations of Cr (VI) stress. Enrichment of the GO and KEGG pathways revealed that the differential gene functions were mainly focused on binding and catalytic activities. This study reveals for the first time the changes of HELNs under different concentrations of Cr (VI) stress and the toxic effects of Cr (VI) on HB seedlings. This study provides a new perspective to explore the function and utilisation of ELNs.

"Efficient novel fungal-enriched biochar formulation for hexavalent chromium bioremediation"

Chromium (Cr), a key element in industrial processes such as leather tanning, poses severe environmental hazards, particularly its hexavalent form, Cr(VI), which is highly toxic and prevalent in tannery effluents/sludge. The persistence and toxicity of Cr(VI) necessitate the development of effective remediation strategies to mitigate its environmental impact. This study investigated the potential of Trichoderma yunnanense (NBRICRF_97) and its combination with 0.5% sugarcane bagasse biochar (SBC) for the reduction of Cr(VI). The results demonstrated that T. yunnanense alone achieved a 91.04% reduction of 50 mg L-1 Cr(VI) within 72 h. Combined with 0.5% SBC, the reduction efficiency increased to 99.65% within 48 h. However, the efficiency decreased at higher concentrations (200 mg L-1). The combination also improved fungal growth and increased extracellular ChrR enzyme activity (13.07 U mg-1 protein compared to the control). Total glutathione activity was boosted by 161.07% at 100 mg L-1 Cr(VI). Antioxidant enzymes (SOD, POD, CAT) and proline mitigated oxidative stress and FTIR analysis revealed changes in fungal cell wall functional groups (-OH and -NH) upon Cr(VI) exposure. SEM-EDX confirmed chromium deposition on fungal surfaces. These results underscore the Cr(VI) detoxification capabilities of T. yunnanense and the synergistic benefits of SBC, suggesting a promising bioremediation strategy for Cr(VI)-contaminated environments. The integration of T. yunnanense with SBC offers a sustainable and cost-effective approach for the bioremediation of Cr(VI)-contaminated sites, with potential for implementation in large-scale environmental cleanup efforts.

Assessing chromium toxicity across aquatic and terrestrial environments: a cross-species review

Chromium (Cr) toxicity, even at low concentrations, poses a significant health threat to various environmental species. Cr is found in the environment in two oxidation states that differ in their bioavailability and toxicity. While Cr(III) is essential for glucose metabolism, the oxyanion chromate Cr(VI) is mostly of anthropogenic origin, toxic, and carcinogenic. The sources of Cr in the environment are multiple, including geochemical processes, disposal of industrial waste, and industrial wastewater. Cr pollution may consequently impact the health of numerous plant and animal species. Despite that, the number of published studies on Cr toxicity across environmental species remained mainly unchanged over the past two decades. The presence of Cr in the environment affects several plant physiological processes, including germination or photosynthesis, and consequently impacts growth, and lowers agricultural production and quality. Recent research has also reported the toxic effects of Cr in different aquatic and terrestrial organisms. Whereas some species showed sensitivity, others exhibited tolerance. Hence, this review discusses the understanding of the ecotoxicological effect of Cr on different plant and animal groups and serves as a concise source of consolidated information and a valuable reference for researchers and policymakers in an understanding of Cr toxicity. Future directions should focus on expanding research efforts to understand the mechanisms underlying species-specific responses to Cr pollution.

Experimental investigation of Cd (II) ion adsorption on surface-modified mixed seaweed Biosorbent: A study on analytical interpretation and thermodynamics

Despite advancements in wastewater treatment technologies, heavy metal contamination, especially cadmium (Cd), severely threatens human health and ecosystems. The purpose of this work is to compare the removal of Cd (II) ions from aqueous solutions by chemically modified mixed seaweed biosorbent (CMSB) and physically modified mixed seaweed biosorbent (PMSB). BET, SEM, EDAX, FTIR, and XRD techniques characterized the mixed seaweed biosorbents before and after adsorption. They are well-known for their sustainability, affordability, and biodegradability. The BET study revealed that CMSB had a surface area of 19.682 m2/g, while PMSB had a lower surface area of 14.803 m2/g. The optimum adsorption conditions were a temperature of 303 K, pH of 6.0, and biosorbent dosages of 1 g/L for CMSB and 2.5 g/L for PMSB. For CMSB and PMSB, the most efficient contact times were 40 and 80 min, respectively. The Langmuir model was demonstrated to be the best fit for the experimental data when compared to other isotherm models, with a coefficient of determination, or R2, of 0.9713 and a maximum monolayer capacity of 151.2 mg/g and 181.6 mg/g for physical and chemical activated mixed seaweed biomass. There was a significant relationship between the R2 values of chemically modified and physically modified biomass. The findings demonstrate that pseudo-second-order kinetics more accurately represent the adsorption process than pseudo-first-order and Elovich models. Thermodynamic experiments validated the endothermic, spontaneous and favourable characteristics of the removal process. According to the results of the current study, PMSB and CMSB may be used as effective adsorbents to remove Cd (II) from aqueous solutions.

Up-regulation of nitrogen metabolism and chlorophyll biosynthesis by hydrogen sulfide improved photosystem photochemistry and gas exchange in chromium-contaminated bean (Phaseolus vulgaris L.) plants

Hydrogen sulfide (H₂S) is considered as plant growth promoter under heavy metal stress, though its specific effects on photosynthesis are rarely explored. This study investigates the protective effects of exogenous H2S donor sodium hydrosulfide (NaHS) on chlorophyll metabolism and photosystem II (PSII) function in 24-day-old bean plants exposed to 10 μM chromium (Cr) stress. Sodium hydrosulfide (100 μM) reduced Cr accumulation in both roots and leaves, leading to restored plant growth. Concomitantly, H₂S mitigated Cr-induced oxidative damages by decreasing reactive oxygen species levels and further enhancing antioxidant scavenging activities. This resulted in significant reductions in Cr-elevated leaf pheophytin and chlorophyllide levels by 59% and 67%, respectively. Furthermore, NaHS application increased levels of porphyrin and its precursor, 5-aminolevulinic acid (5-ALA), in Cr-stressed bean. The up-regulation in chlorophyll biosynthesis was associated with enhanced activities of glutamine synthetase and glutamate synthase, essential for glutamate (precursor of 5-ALA) production, as well as nitrate and nitrite reductase, leading to increased nitric oxide generation. Under Cr stress, H₂S significantly improved the electron transport rate, effective quantum yield of PSII, and photochemical quenching by 112%, 53%, and 38%, respectively, while reducing non-photochemical quenching by 50%. Furthermore, H₂S promoted net CO₂ assimilation and photosynthesis at saturating light, respectively, while reducing stomatal conductance and transpiration to maintain water balance. Exogenous H₂S restored respiration, as indicated by increased light saturation and compensation points in Cr-treated plants. Overall, these findings indicate that H₂S regulates photosynthesis in Cr-stressed bean by modulating nitrogen and chlorophyll metabolism, thereby optimizing PSII efficiency and gas exchange.

Hydrogeochemical evolution and heavy metal characterization of groundwater from southwestern, Nigeria: An integrated assessment using spatial, indexical, irrigation, chemometric, and health risk models

This study examines the hydrogeochemical and heavy metal parameters of groundwater in Ojo District to determine its suitability for use, potential sources, and human health implications. Ten groundwater samples were assessed, and hydrogeochemical modelling was performed via the Aquachem software. The chemical ions were in the following order: EC > (107.78-448.65 μS/cm) > TDS (182.02-320.77 mg/l) > TH (46.22-182.45 mg/l) > pH (5.55-6.35); HCO3 - (64.13-125.82 mg/l) > Na+ (36.87-96.49 mg/l) > Ca2+ (47.65-58.88 mg/l) > SO4 2- (19.94-53.67) > NO3 - (15.55-44.25 mg/l) > Cl- (20.43-27.16 mg/l) > Mg2+ (11.09-16.87 mg/l) and K+ (2.55-7.86 mg/l). The concentrations of heavy metals in groundwater were in the range of: Fe (0.11-0.27 mg/l) > Mn (0.003-0.16 mg/l) > Ni (0.05-0.12 mg/l) > Zn (0.003-0.05 mg/l) > Pb (0.001-0.03 mg/l) > As (0.001-0.005 mg/l) > Cr (0.002-0.005 mg/l) > Cd (0.001-0.003 mg/l) and Cu (0.001-0.0002 mg/l), with Pb, Mn, and Ni exceeding their allowable limits. The Schoeller and Gibbs plots revealed that the major mechanisms controlling the aquifer groundwater in Ojo region are geological rock weathering and mineralization, with a minimal influence of saltwater intrusion. The piper trilinear diagram also revealed that none of the cation was dominant while the anions were strongly dominated by HCO3 - (weak acids). The hydrogeochemical facies which describes the geochemical characteristics of the groundwater were classified into 3 types; "Ca2+-Mg+-HCO3 - (65 %)", "mixing zones (30 %)", and "Na+-K+-Cl--HCO3 - (5 %)". The hydrogeochemical modelling revealed that the groundwater is characterized by forward cation exchange, while rock-water interactions (silicate dissolution) were heavily involved in the geochemical processes. The single pollution index showed that Pb, Ni, and Mn contributed significantly to contamination, and the multi-pollution indices showed that the groundwater was slightly-moderately polluted. The integrated groundwater quality index revealed that only 10 % were clean, 50 % were poor or moderately unclean, 30 % were highly unclean, and only 10 % were extremely unclean (unfit for utilization). The water pollution index showed that 70 % of the groundwater was good. The irrigation indices suggest that the groundwater would enhance soil quality and support plant growth. Multivariate analysis revealed that the groundwater is being influenced by geogenic factors and anthropogenic activities. The health risk assessment (Hazard Quotient and Hazard Index) showed that exposure of adults to the investigated groundwaters could result in noncarcinogenic adverse effects. The cancer risk values also exceeded the minimum limit (1.0 x 10-6) and thresholds (1.0 x 10-4) for adults, indicating the carcinogenic potential of the groundwater.

Public health and economic burden of heavy metals in Ethiopia: Review

Heavy metals pose a significant threat to public health and economic stability in Ethiopia, contaminating various environmental media, including water, soil, and air. This paper aimed to provide an overview of the public health and economic burden of heavy metals in Ethiopia. Exposure to heavy metals such as lead, mercury, cadmium, and arsenic has been linked to numerous adverse health effects, including neurological disorders, renal failure, cardiovascular diseases, and cancer. In Ethiopia, populations are particularly vulnerable to heavy metal exposure due to various factors, such as artisanal mining, industrial activities, agricultural practices, and inadequate waste management systems. The economic burden of heavy metal contamination manifests through increased healthcare costs, loss of productivity, and environmental remediation expenses. Furthermore, the impact extends to sectors such as agriculture and tourism, affecting national development goals and exacerbating poverty levels. Efforts to mitigate the public health and economic burdens of heavy metals in Ethiopia require multidisciplinary approaches, including policy interventions, regulatory enforcement, public awareness campaigns, and investment in sustainable development practices. Strengthening monitoring systems, implementing pollution control measures, and promoting research on alternative technologies for waste management are essential steps toward addressing this pressing issue. In conclusion, addressing the public health and economic challenges posed by heavy metal contamination in Ethiopia necessitates concerted efforts from the government, industry, academia, and civil society to safeguard human health, preserve the environment, and promote sustainable development.

Impacts of chloride ions on the electrochemical decomplexation and degradation of Cr(III)-EDTA: Reaction mechanisms of HO• and RCS

The removal of Cr(III)-organic complexes, encompassing both decomplexation and ligand degradation, presents significant challenges in industrial wastewater treatment. As one of the most common anions in wastewater, Cl- significantly improves the efficiency of electrochemically removing Cr(III)-organic complexes through generated reactive chlorine species (RCS). In the electrochemical chlorine (EC/Cl2) process, extensive experimentation revealed that ClO• plays a dominant role in the degradation of Cr(III)-EDTA, surpassing the effects of free chlorine, direct electrooxidation, HO•, and other RCS. Density functional theory calculations indicated that RCS, primarily Cl• and ClO•, preferentially oxidize the ligand in Cr(III)-EDTA via H-abstraction, whereas HO• trends to attack the Cr atom through electron transfer. The influential factors on the degradation efficiency of Cr(III)-EDTA, Cr(VI) yield, and total organic carbon removal in EC/Cl2 were also assessed, including Cl- concentration, current density, and pH. Real industrial wastewater was employed as a reaction matrix to evaluate the application of the EC/Cl2 process for treating Cr(III)-EDTA, accompanied by energy efficiency calculations. Additionally, a two-chamber reactor was established to simultaneously oxidize Cr(III)-EDTA at the anode and reduce Cr(VI) at the cathode. This study provided insight into developing RCS-dominated AOPs to effectively decomplex and decompose organic Cr(III)-complexes in Cl--containing industrial wastewater.

Challenges and Applications of Supramolecular Metalate Chemistry

While the supramolecular chemistry of simple anions is ubiquitous, the targeting and exploitation of their metal-containing relatives, the metalates, is less well understood. This mini review highlights the latest advances in this emergent area by discussing the supramolecular chemistry of metalates thematically, with a focus on the exploitation of metalates in a diversity of applications, including medical imaging and therapy, environmental remediation, molecular magnetism, catalysis, perovskite materials, and metal separations. The unifying features of these systems are identified with a view to allow the supramolecular chemist to target the unique material properties of the metalates, even in areas that are currently relatively immature.

Chromium uptake and its impact on antioxidant level, photosynthetic machinery, and related gene expression in Brassica napus cultivars

The development of heavy metals, particularly chromium (Cr)-tolerant crop cultivars, is hampered due to lack of understanding of the mechanisms behind Cr stress tolerance. In this study, two Brassica napus cultivars, ZS758 and ZD622, were compared for Cr stress resistance by using the chlorophyll a fluorescence technique and biochemical characteristics. In both cultivars, Cr stress dramatically decreased PSII and PSI efficiency, biomass accumulation, and antioxidant enzyme levels. Although, cultivar ZS758 showed reduction in oxidative stress by decreasing the production of reactive oxygen species (ROS) in terms of reduced H2O2 and MDA content and increased enzymatic activities of key antioxidants enzymes including SOD, APX, CAT, and POD activities that play a crucial role in the regulation of numerous transcriptional pathways involved in oxidative stress responses. Higher non-photochemical quenching (NPQ) and QY were found in tolerant ZS758 cultivar under Cr stress, indicating that tolerant cultivar had a greater capacity to preserve PSII activity under Cr stress by enhancing heat dissipation as a photo-protective component of NPQ. Lower PSI activity and electron transfer from PSII were confirmed by lower PSI efficiency and higher donor end limitation of PSI in both rapeseed cultivars. The Cr concentration was greater in the ZD622 as compared to ZS758, which affected the mineral nutrients profile and damaged the cellular ultrastructure and related gene expression levels. However, current study suggest that cultivar ZS758 is more resistant to Cr stress than ZD622 due to improved metabolism and structural integrity and Cr stress tolerance that is linked with the increased PSII activity, NPQ, and antioxidant potential; these physiological characteristics can be exploited to select cultivars for Cr stress tolerance.

Enhanced aqueous phosphorus removal and mechanism by water spinach (Ipomoea aquatica Forsk) pretreated with lanthanum nitrate

Excess nutrients such as phosphate (PO43-) entering surface waters promote eutrophication, and phosphorous (P) removal is important to clear the water. Phytoremediation efforts have been used to improve water quality by varieties of P removal plants, such as water spinach (Ipomoea aquatica Forsk). Water spinach can reduce both internal and external resources of phosphorus from waterbody. The ion of lanthanum (La), one rare earth element (REE), is an immobilization substance for aqueous phosphate and also a fertilizer for plants. Therefore, lanthanum nitrate La (NO3)3 was used further to improve the phytoextraction of P from the polluted water. This study investigated the effects of La on the aqueous P removal by two genotypes of water spinach, green stem large leaves (GSLL) and green stem willow leaves (GSWL). The low concentration La (NO3)3 helped the plant to remove more phosphorous from eutrophic water, but La at high concentration lowered the removal of P. Under La (NO3)3 treatments, the optimum concentration for maximum P removal in GSLL is 3 mg/L, and for GSWL, it is 10 mg/L and P removal rates were enhanced to 95% and 96%, respectively. When the concentration of La (NO3)3 is 100 mg/L, the removal percentage of P was only 10% for both genotypes. The very high concentration of La will impose toxicity and even cause the death of the water spinach and produce secondary pollution; for example, under some specific circumstances, the bond between lanthanum and nitrates dissociates into lanthanum ions (La3⁺) and nitrate ions (NO₃⁻). If the concentration is high, then it accumulates in the aquatic water organisms and plants and causes toxicity in their bodies. If humans eat up these plants and fish, it causes toxic effects in humans. The La (NO3)3 positively affects different parameters of plants. La (NO3)3 increases the growth, pigments, enzyme activity, and malondialdehyde (MDA) of plants which were also discussed in this study. The biological mechanism should be responsible for the enhanced aqueous phosphorus removal by water spinach using lanthanum nitrate.

Reduction of Cr(VI) by Bacillus toyonensis LBA36 and its effect on radish seedlings under Cr(VI) stress

Chromium, being among the most toxic heavy metals, continues to demand immediate attention in the remediation of Cr-contaminated environments. In this study, a strain of LBA36 (Bacillus toyonensis) was isolated from heavy metal contaminated soil in Luanchuan County, Luoyang City, China. The reduction and adsorption rates of LBA36 in 30 mg·L-1 Cr-containing medium were 97.95% and 8.8%, respectively. The reduction mechanism was confirmed by Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy (XPS). Cr(VI) reduction by this strain predominantly occurred outside the cell, with hydroxyl, amide, carboxyl, C-N group, carbonyl, and sulfur carbonyl as the main reaction sites. XPS analysis revealed the presence of Cr2p1/2 and Cr2p3/2. Furthermore, the hydroponic experiment showed that the fresh weight and plant height of radish seedlings increased by 87.87% and 37.07%, respectively, after inoculation with LBA36 strain under 7 mg·L-1 Cr(VI) stress. The levels of chlorophyll, total protein, malondialdehyde, superoxide dismutase and catalase were also affected to different degrees. In conclusion, this study demonstrated the potential of microbial and phytoremediation in the treatment of heavy metal toxicity, and laid the foundation for the development of effective bioremediation methods for Cr(VI) pollution.

Construction of Stable 2D Cationic Breathing Ni-MOF for Cr(VI) Trapping and Electrochemical Sensing

Pollution of surface water by heavy metal hexavalent chromium ions poses a serious threat to human health; herein, a two-dimensional (2D) cationic breathing Ni-MOF with free nitrate ions between the layers was designed and synthesized according to the characteristics of hexavalent chromium ions, {[Ni(L)2](NO3)2·5H2O}n (L = 1,3,5-tris[4-(imidazol-1-yl)phenyl]benzene). The flexible layer spacing of the 2D breathing Ni-MOF allows the exchange of NO3- by CrO42- without destroying the original structure. Electrostatic and hydrogen bonding interactions between CrO42- and Ni-MOF facilitate its exchange with NO3-. Moreover, CrO42- exhibits a higher binding energy with Ni-MOF compared to NO3-, and the hydrophobic channels of Ni-MOF favor CrO42- trapping due to its lower hydration energy. Consequently, Ni-MOF demonstrates both effective sorption and electrochemical sensing of Cr(VI), achieving a sensitivity of 2.091 μA μM-1 and a detection limit of 0.07 μM.