NaCl-mediated strategies for the trade-off between Cd bioconcentration and translocation in Solanum nigrum L

Regulation strategies of microplastics with different particle sizes on cadmium migration processes and toxicity in soil-pakchoi system

It is still unclear whether there are differences in the effects of microplastics with different particle sizes on the environmental behavior of cadmium (Cd) in the soil-crop system. By introducing the polystyrene microplastics (PS-MPs) with 0.2, 2, and 20 μm, this study explored the regulation strategies of different-sized MPs on the migration and toxicity of Cd in the soil-pakchoi system. Compared to the Cd treatment, the mobility factor of Cd in the soil decreased by 12.97 %, 34.73 %, and 40.12 % with increasing particle sizes of PS-MPs, while the relative binding intensity increased significantly. The 0.2 μm PS-MPs had no effect on Cd content in pakchoi, however, 2 and 20 μm PS-MPs significantly reduced the Cd content in shoots and roots of pakchoi by 47.40 %-29.67 % and 44.56 %-20.92 %, respectively. Additionally, 20 μm PS-MPs reduced the enrichment of the heavy Cd isotope in pakchoi. The results of principal component analysis (PCA) and structural equation modeling (SEM) indicated that 2 and 20 μm PS-MPs may promote the growth of pakchoi by regulating soil properties, nutrient uptake, Cd accumulation, and antioxidant system activity. This study provides evidence for the importance of particle size of MPs in regulating the environmental behavior of heavy metals.

Trade-offs between Cd bioconcentration and translocation and underlying physiological and rhizobacterial mechanisms in Phragmites australis

Cadmium (Cd) pollution poses a significant threat to wetland ecosystems. Phragmites australis, a species with intraspecific ploidy diversity, is commonly used in constructed wetlands for pollution remediation. However, little is known about how the ploidy variation of P. australis influences the phytoremediation processes via physiological and rhizosphere regulations. Here, we used P. australis from two major lineages in China (i.e., tetraploid lineage O and octoploid lineage P) and applied three Cd treatments (control, low Cd concentration, and high Cd concentration). We found that the lineage O had a bioconcentration factor of Cd approximately 40% higher than that of the lineage P. The translocation factor of the lineage P was about 300% higher than that of the lineage O. These suggest that the lower ploidy lineage exhibited a greater capacity to absorb Cd from the environment into the underground part compared to the higher ploidy lineage, and the higher ploidy lineage demonstrated a superior ability in transferring Cd from the underground to the aboveground part. The advanced transpiration system in the higher ploidy lineage can contribute to its enhanced ability to translocate Cd, as the translocation factor of Cd was significantly correlated with the base shoot diameter and the transpiration rate, both notably higher in the lineage P. The rhizobacterial community associated with the lineage P displayed a more intense response to Cd, characterized by an increase in both the diversity of the community and the number of varied bacterial functions following the addition of Cd. Our study offers profound insights into the ecological consequences of intraspecific polyploidization and the application of intraspecific ploidy variation in environmental management and wetland restoration.

Reclamation of co-pyrolyzed dredging sediment as soil cadmium and arsenic immobilization material: Immobilization efficiency, application safety, and underlying mechanisms

The safe management of toxic metal-polluted dredging sediment (DS) is imperative owing to its potential secondary hazards. Herein, the co-pyrolysis product (DS@BC) of polluted DS was creatively applied to immobilize soil Cd and As to achieve DS resource utilization, and the efficiency, safety, and mechanism were investigated. The results revealed that the DS@BC was more effective at reducing soil Cd bioavailability than the DS was (58.9-73.2% vs. 21.8-27.4%), except for the dilution effect, whereas the opposite phenomenon occurred for soil As (25.5-35.7% vs. 35.7-42.8%). The DS@BC immobilization efficiency was dose-dependent for both Cd and As. Soil labile Cd and As were transformed to more stable fractions after DS@BC immobilization. DS@BC immobilization inhibited the transfer of soil Cd and As to Brassica chinensis L. and did not cause excessive accumulation of other toxic metals in the plants. The appropriate addition of the DS@BC (8%) sufficiently alleviated the oxidative stress response of the plants and enhanced their growth. These findings indicate that the DS@BC was safe and effective for soil Cd and As immobilization. DS@BC immobilization decreased the diversity and richness of the rhizosphere soil bacterial community because of the dilution effect. The DS@BC immobilized soil Cd and As via direct adsorption, and indirect increasing soil pH, and regulating the abundance of specific beneficial bacteria (e.g., Bacillus). Therefore, the use of co-pyrolyzed DS as a soil Cd and As immobilization material is a promising resource utilization method for DS. Notably, to verify the long-term effects and safety of DS@BC immobilization, field trials should be conducted to explore the effectiveness and risk of harmful metal release from DS@BC immobilization under real-world conditions.

Cadmium biosorption and mechanism investigation using two cadmium-tolerant microorganisms isolated from rhizosphere soil of rice

Microbial remediation of cadmium-contaminated soil offers advantages like environmental friendliness, cost-effectiveness, and simple operation. However, the efficacy of this remediation process relies on obtaining dominant strains and a comprehensive understanding of their Cd adsorption mechanisms. This study identified two Cd-resistant bacteria, Burkholderia sp. 1-22 and Bacillus sp. 6-6, with significant growth-promoting effects from rice rhizosphere soil. The strains showed remarkable Cd resistance up to ∼200 mg/L and alleviated Cd toxicity by regulating pH and facilitating bacterial adsorption of Cd. FTIR analysis showed crucial surface functional groups, like carboxyl and amino groups, on bacteria played significant roles in Cd adsorption. The strains could induce CdCO3 formation via a microbially induced calcium precipitation (MICP) mechanism, confirmed by SEM-EDS, X-ray analysis, and elemental mapping. Pot experiments showed these strains significantly increased organic matter and enzyme activity (e.g., urease, sucrase, peroxidase) in the rhizosphere soil versus the control group. These changes are crucial for restricting Cd mobility. Furthermore, strains 6-6 and 1-22 significantly enhance plant root detoxification of Cd, alleviating toxicity. Notably, increased pH likely plays a vital role in enhancing Cd precipitation and adsorption by strains, converting free Cd into non-bioavailable forms.