Remediation Of Cr Contaminated Soil Research Articles

Synergistic Effects of Unmodified Tea Leaves and Tea Biochar Application on Remediation of Cr-Contaminated Soil

Hexavalent chromium (Cr(VI)) contamination in soil presents significant risks due to its high toxicity to both the environment and human health. Renewable, low-cost natural materials offer promising solutions for Cr(VI) reduction and soil remediation. However, the effects of unmodified tea leaves and tea-derived biochar on chromium-contaminated soils remain inadequately understood. In this study, tea tree pruning waste was converted into biochar at various temperatures, and the impacts of both unmodified tea leaves and tea biochar on soil Cr(VI) content, chromium fractionation, and soil biochemical properties were assessed using a soil incubation experiment. The results showed that the combined treatment of tea and tea biochar produced at 500 °C reduced Cr(VI) content by up to 49.30% compared to the control. Chromium fractionation analysis revealed a significant increase in the residual chromium fraction, accounting for 32.97% of total chromium, substantially reducing its bioavailability and mobility. Soil properties were markedly improved, with notable increases in pH (14.89%), cation exchange capacity (CEC; up to 100.24%), and organic matter content (up to 167.12%) under the combined treatments. Correlation analysis confirmed that Cr(VI) content reductions were positively correlated with increases in pH, nutrient retention, and enzyme activities, highlighting their role in chromium stabilization. This study underscores the synergistic potential of unmodified tea leaves and tea biochar as an innovative, eco-friendly strategy for Cr(VI) remediation, enhancing both soil quality and heavy metal stabilization.

Characterization of the composition, structure, and functional potential of bamboo rhizosphere archaeal communities along a chromium gradient.

Bamboo can be used in the phytoremediation of heavy metal pollution. However, the characteristics of the bamboo rhizosphere archaeal community in Cr-contaminated soil under field conditions remain unclear. In this study, high-throughput sequencing was used to examine the rhizosphere soil archaeal communities of Lei bamboo (Phyllostachys precox) plantations along a Cr pollution gradient. The results revealed U-shaped relationships between Cr [total Cr (TCr) or HCl-extractable Cr (ACr)] and two alpha indices (Chao1 and Shannon) of archaea. We also established that high Cr concentrations were associated with a significant increase in the abundance of Thaumarchaeota and significant reductions in the abundances of Crenarchaeota and Euryarchaeota. The archaeal co-occurrence networks reduced in complexity with Cr pollution, decreasing the community's resistance to environmental disturbance. Candidatus nitrosotalea and Nitrososphaeraceae_unclassified (two genera of Thaumarchaeota) were identified as keystone taxa. The community structure of soil archaeal communities was also found to be affected by TCr, ACr, pH, total organic C, and available nutrient (N, P, and K) concentrations, with pH being identified as the most reliable predictor of the archaeal community in assessed soils. These findings enhance our understanding of microbial responses to Cr pollution and provide a basis for developing more refined approaches for the use of bamboo in the remediation of Cr-contaminated soils.

Monitoring localized changes of Cr(VI) bioavailability related to root-induced changes around rice roots

Transformation between Cr(III) and Cr(VI) occurs in Cr-contaminated soils. Although redox conditions and biotic/microbial activity are known to be important factors in determining Cr transformation and accumulation in soil-rice systems, how spatial trends and specific soil processes regulate Cr behaviour around lowland/flooded rice roots are poorly understood. In this study, the Cr(VI) bioavailability was evaluated using the diffusive gradients in thin film (DGT) technology. Root activity reduced Cr(VI) bioavailability. The Cr(VI) flux near rice roots was 1.27–3.92 times lower than that in bulk soil (0.94 ng cm−2 h−1). The radial extension of the strong influence zone (R1) in the rhizosphere of C-LYZ was smaller than that in Hui-LY985. Although Fe(II) and S2− were involved in Cr(VI) reduction, they were not the primary influence, especially for the rhizosphere region. The high phosphate concentration in the C-LYZ rhizosphere hindered Cr(VI) uptake. The DGT technique overcomes the limitations of traditional research methods, revealing the spatial variability in Cr(VI) and its interactions with other elements in the rhizosphere, thereby providing theoretical basis for bioavailability evaluation and remediation of Cr-contaminated soils.

Thermophysical and molecular mechanisms of a novel and cost-efficient Cr-contaminated soil stabilization by steam flash heating

Chemical stabilization is a frequently used method to stabilize heavy metals in soils, however suffering from the reagent overdosage and exorbitant cost due to the insufficient reactions between chemical stabilizers and heavy metals. In this work, we innovated an economy and energy efficient stabilization technique, namely steam flash heating (SFH), and investigated its stabilization performance and mechanisms for hexavalent chromium [Cr(VI)]. SFH can efficiently promote Cr(VI) reduction by both soil organic matter and chemical stabilizers. From thermophysical analysis, SFH efficiently enhanced the molecular contact and accelerated mass transfer in porous soils, resulting in the promoted transformation of Cr(VI) into OM-Cr(III), Fh-Cr(III), and Cr(OH)3 from Cr/Fe/S/C XANES results. By replacing partial chemical stabilizers with soil organic matter in Cr(VI) reduction, SFH decreased nearly 70.7% of cost and 38.1% of CO2 emission. Besides, Mn XANES results unraveled that MnOx was reduced by soil organic matter and chemical stabilizers with the aid of SFH, and this process decreased the risk of Cr(III) re-oxidation and benefited long-term Cr stability. These results proved that SFH could efficiently immobilize Cr with low energy consumption, low economic cost, high stabilizer efficiency, and low re-mobility risk, exhibiting applicable potential in the remediation of Cr-contaminated soils. This study revolutionized chemical stabilization by SFH and unraveled the underlying mechanisms of Cr immobilization in contaminated soils.

Effect of biochar on the uptake, translocation and phytotoxicity of chromium in a soil-barley pot system

Remediation of Cr-contaminated soils with biochar is an effective method, but its effect on plant detoxification has not been clarified, and the translocation pathways of different chemical forms of Cr in the soil–plant system have not been quantitatively evaluated. This study investigated the effects of magnetically modified Enteromorpha prolifera biochar (FBC) on Cr uptake, translocation and phytotoxicity in the soil and barley (Hordeum vulgare L.). When the FBC dosage increased to 30 g·kg−1, the content of bioavailable Cr in the soil decreased by 56.82%. Additionally, the contents of Cr in H. vulgare decreased by 53.22%, and growth recovered to the normal level. Partial least squares path modelling (PLS-PM) was applied to establish two influence paths to explain how FBC impacted the whole system of soil and plants upon Cr exposure. The phytotoxic effect path of Cr suggested that FBC decreased the contents of Cr in soil and H. vulgare and then recovered growth by alleviating oxidative stress (β = −0.45) and promoting chlorophyll synthesis (β = 0.53) in shoots. The translocation and conversion path of Cr further indicated that Cr in the shoots was converted into low-migration forms and mainly trapped in cell walls and vacuoles rather than in organelles, consequently decreasing the phytotoxicity of Cr (β = −0.73). These two soil–plant paths offer new insights into the application of biochar and plants in Cr-contaminated soils.

Assessing Chromium Contamination in Red Soil: Monitoring the Migration of Fractions and the Change of Related Microorganisms.

The improper stacking of chromium (Cr) slag poses a great threat to the environment and human health. The toxicity of Cr in soil is not only related to its total amount, but also to its fractions. A simulated experiment was conducted in laboratory to assess the environmental risk of Cr fractions migration and distribution in red soil. The results showed the content of acid-soluble and reducible Cr significantly decreased (P < 0.05) in top layer but increased in middle and substratum layers over time. This indicated that acid-soluble and reducible Cr migrated downward with time and the relative mobility of acid-soluble Cr (0.038 mg/kg·d·m) was higher than that of reducible Cr (0.028 mg/kg·d·m). Furthermore, correlation analysis between microbial community and chromium fraction showed the relative abundance of Lysobacter, Flavihumibacter, Flavisolbacter, and Altererythrobacter was significantly (P < 0.05) correlated with acid-soluble and reducible fractions. Thus, these microorganisms might be evaluators to assess the migration of acid-soluble and reducible fractions in red soil. In summary, this study provided a new comprehension on remediation of Cr-contaminated soil by monitoring the migration of acid-soluble and reducible fractions and the changes of related microbial groups.

Phyto-management of Cr-contaminated soils by sunflower hybrids: physiological and biochemical response and metal extractability under Cr stress.

Chromium (Cr) is a biologically non-essential, carcinogenic and toxic heavy metal. The cultivation of Cr-tolerant genotypes seems the most favorable and environment friendly strategy for rehabilitation and remediation of Cr-contaminated soils. To prove this hypothesis and identify the Cr tolerance, the present study was performed to assess the physiological and biochemical response of sunflower genotypes to Cr stress. The seeds of six sunflower hybrids, namely FH-425, FH-600, FH-612, FH-614, FH-619, and FH-620, were grown in spiked soil for 12weeks under increasing concentrations of Cr (0, 5, 10, and 20mgkg-1). A seed germination test was also run under different concentrations of Cr (0, 5, 10, 200 mM) in petri dishes. Plants were harvested after 12 weeks of germination. Different plant attributes such as growth; biomass; photosynthesis; gas exchange; activity of antioxidant enzymes, i.e., superoxide dismutase (SOD), guaiacol peroxidase (POD), ascorbate (APX), and catalases (CAT); reactive oxygen species (ROS); lipid peroxidation; electrolyte leakage; and Cr concentration as well as accumulations in all plant parts were studied for the selection of the most Cr-tolerant genotype. Increasing concentration of Cr in soil triggered the reduction of all plant parameters in sunflower. Cr stress increased electrolyte leakage and production of reactive oxygen species which stimulated the activities of antioxidant enzymes and gas exchange attributes of sunflower. Chromium accumulation in the root and shoot increased gradually with increasing Cr treatments and caused reduction in overall plant growth. The accumulation of Cr was recorded in the order of FH-614 > FH-620 > FH-600 > FH-619 > FH-612 > FH-425. The differential uptake and accumulation of Cr by sunflower hybrids may be useful in selection and breeding for Cr-tolerant genotypes.