Remediation materials for the immobilization of hexavalent chromium in contaminated soil: Preparation, applications, and mechanisms

Chromium dynamics in soil and detoxification of chromite belts using rhizospheric soil-plant interface

The chromium-contaminated soil expresses its severe eco-toxicity on living organisms of the locality and adjoining regions. This review has focused on the chemical interactions of chromium variants in soil and the sequestration of chromium using the soil-plant interface in the rhizosphere. The application of plant hyper-accumulators on chromium-contaminated soil for chromium sequestration is an attempt to minimize chromium toxicity of mining and industrial belts. This review utilized the PRISMA 2009 systematic review methodology. The literature screening was conducted by searching databases such as Scopus, Google Scholar, and Web of Science up to 2025 using specific keywords. In countries like Kazakhstan, South Africa, and India, more than 90% of world shipping-grade mine reserves of chromium are present. The mining and metallurgy of chromium can threaten the environmental quality and the region's public health. The Sukinda chromite mines in India are globally known for their rich chromite mining, metallurgy, and eco-toxicity. The present article analyzes the ecological challenges and searches for possible interactions of chromium variants in soil. The solution to mitigate chromium toxicity is possible using the rhizospheric soil-plant interface. This article's findings and discussion section help solve ecological challenges and strive for healthy soil at chromium-polluted sites. This review article can contribute to sustainable soil quality improvement at mining and industrial belts. Further research on the isotopic tracer technique is recommended to enhance the understanding of chromium dynamics in soil.

Bioaccumulation of Cr by the Buddleja Species and Schinus molle L. Grown with and Without Compost in a Sandy Soil Contaminated by Leather Industrial Effluents

This research aimed to assess the bioaccumulation capacity of the Buddleja species and Schinus molle L. using organic amendments to the phytoremediation of total chromium in the mid-zone of the Añashuayco Ravine, Uchumayo, Arequipa, impacted by tanneries from the Rio Seco Industrial Park. Additionally, it analyzed total chromium concentrations, soil physicochemical properties, and morphological changes in plants with and without organic matter. Samples of the Buddleja species and Schinus molle L. were distributed into groups with and without compost, along with control groups. They were monitored over 6 months, every 60 days, showing significant morphological variations. The results highlight an important finding: the remarkable bioaccumulation capacity of the species studied all exceeded 30%. The samples without compost showed a lower percentage of total chromium bioaccumulation in plants compared to the samples with the organic amendment. The Buddleja species demonstrated a 39.01% chromium bioaccumulation with compost compared to 37.99% without it. Likewise, Schinus molle L. achieved 33.99% chromium accumulation with compost and 31.84% without it. These findings emphasize the superior ability of these species to bioaccumulate heavy metals, highlighting that the Buddleja species has mayor bioaccumulation capacity and more remotion of total chromium in the soil.

Human and environmental risk assessment and plausible sources of toxic heavy metals at beach placers in southeast Sri Lanka

Beach placers are typically rich in heavy minerals, which are crucial for a wide range of industrial applications. This study investigates the human and environmental risks posed by toxic heavy metals (As, Pb, Zn, Cu, Cr, Fe, V and Mn) in beach placers of southeastern Sri Lanka using 42 X-ray fluorescence data. Risk indicators (EF, Igeo, CF and PLI) indicate the polluted nature of the placers. Correlation analysis (correlation matrix and HCA) identified pollution sources as heavy mineral-rich rocks, agricultural fertilizers, pesticides and municipal wastes. The environmental impact caused by toxic metals is less in placers. The highest non-carcinogenic risks (HI) resulted by Cr (1.69E+00), V (4.29E+00) and Fe (2.06E+00) to children. The total cancer risk of As and Cr in placers is unacceptable (children: 2.60E-04, 2.48E-03, and adults: 3.14E-05, 2.87E-04, respectively). Different strategies are introduced to mitigate the identified risks in source areas and the coastal environment.

Feasibility and mechanism of adsorption and bioreduction of hexavalent chromium using Rhodopseudomonas palustris immobilized on multiple materials

Rhodopseudomonas palustris immobilized on multiple materials was used to invistigate Cr(VI) adsorption and bioreduction. The highest Cr(VI) removal (97.5%) was achieved at 276h under the opitimed conditions of 2.5% SA, 8% PVA, and 50% filling degree. The highest adsorption capacity was obtained at 11.75 mg g-1 under 300 mg L-1 Cr(VI). Results from adsorption kinetics and isotherms indicated that Cr(VI) adsorption of immobilized photosynthetic bacteria (IPSB) was consistent with the Freundich model and the pseudo-second-order kinetic model (qe = 14.00 mg g-1). SEM and FTIR analyses verified that the porous multilayer network structure of IPSB provided more adsorption sites and functional groups for the removal of Cr(VI). Furthermore, the maximum Cr(VI) reduction efficiency of IPSB was achieved at 10.80 mg g-1, which correlated with the up-regulation of chrR gene expressions at 100 mg L-1 Cr(VI). This study demonstrated the dual mechanisms of Cr(VI) removal in IPSB-treated Cr wastewater, involving both chemisorption and bioreduction working synergistically.

Electrokinetic bioremediation of trichloroethylene and Cr/As co-contaminated soils with elevated sulfate

Co-contaminants and complex subsurface conditions pose great challenges to site remediation. This study demonstrates the potential of electrokinetic bioremediation (EK-BIO) in treating co-contaminants of chlorinated solvents and heavy metals in low-permeability soils with elevated sulfate. EK-BIO columns were filled with field soils, and were fed by the electrolyte containing 20 mg/L trichloroethylene (TCE), 250 μM Cr(VI), 25 μM As(III), 10 mM lactate, and 10 mM sulfate. A dechlorinating consortium containing Dehalococcoides (Dhc) was injected several times during a 199-d treatment at ∼1 V/cm. Sulfate reduction, Cr/As immobilization, and complete TCE biodechlorination were observed sequentially. EK-BIO facilitated the delivery of lactate, Cr(VI)/As(III), and sulfate to the soils, creating favorable reductive conditions for contaminant removal. Supplementary batch experiments and metagenomic/transcriptomic analysis suggested that sulfate promoted the reductive immobilization of Cr(VI) by generating sulfide species, which subsequently enhanced TCE biodechlorination by alleviating Cr(VI) toxicity. The dechlorinating community displayed a high As(III) tolerance. Metagenomic binning analysis revealed the dechlorinating activity of Dhc and the potential synergistic effects from other bacteria in mitigating heavy metal toxicity. This study justified the feasibility of EK-BIO for co-contaminant treatment and provided mechanistic insights into EK-BIO treatment.

The effects of iron-based nanomaterials (Fe NMs) on plants under stressful environments: Machine learning-assisted meta-analysis

Mitigating the adverse effects of stressful environments on crops and promoting plant recovery in contaminated sites are critical to agricultural development and environmental remediation. Iron-based nanomaterials (Fe NMs) can be used as environmentally friendly nano-fertilizer and as a means of ecological remediation. A meta-analysis was conducted on 58 independent studies from around the world to evaluate the effects of Fe NMs on plant development and antioxidant defense systems in stressful environments. The application of Fe NMs significantly enhanced plant biomass (mean = 25%, CI = 20%-30%), while promoting antioxidant enzyme activity (mean = 14%, CI = 10%-18%) and increasing antioxidant metabolite content (mean = 10%, CI = 6%-14%), reducing plant oxidative stress (mean = -15%, CI = -20%∼-10%), and alleviating the toxic effects of stressful environments. The observed response was dependent on a number of factors, which were ranked in terms of a Random Forest Importance Analysis. Plant species was the most significant factor, followed by Fe NM particle size, duration of application, dose level, and Fe NM type. The meta-analysis has demonstrated the potential of Fe NMs in achieving sustainable agriculture and the future development of phytoremediation.