Heavy metal immobilization and radish growth improvement using Ca(OH)2-treated cypress biochar in contaminated soil.

Heavy metal contamination poses a significant threat to soil quality, plant growth, and food safety, and directly affects multiple UN SDGs. Addressing this issue and offering a remediation solution are vital for human health. One effective approach for immobilizing heavy metals involves impregnating cypress chips with calcium hydroxide (Ca(OH)2) to enhance the chemical adsorption capacity of the resulting woody charcoal. In the present study, un-treated cypress biochar (UCBC) and calcium-treated cypress biochar (TCBC), were introduced into pristine and contaminated soil, at rates of 3, 6, and 9% (w/w). Both BCs were alkaline (UCBC pH: 8.9, TCBC pH: 9.7) with high specific surface area, which improved the soil properties (pH, EC, and OM). Radish (Raphanus sativus) cultivated in pots revealed that both UCBC and TCBC demonstrated significant improvements in growth attributes and heavy metal immobilization compared to the control, with TCBC exhibiting superior effects. The TCBC surface showed highly active nanosized precipitated calcium carbonate particles that were active in immobilizing heavy metals. The application of TCBC at a rate of 9% resulted in a substantial reduction in Zn and Cu uptake by radish roots and shoots. In contaminated soil, Zn uptake by radish roots decreased by 55% (68.3-31.0 mg kg-1), and shoots by 37% (49.3-31.0 mg kg-1); Cu uptake decreased by 40% (38.6-23.2 mg kg-1) in roots and 39% (58.2-35.2 mg kg-1) in shoots. Uptake of Pb was undetectable after TCBC application. Principal component analysis (PCA) highlighted the potential of TCBC over UCBC in reducing heavy metal concentrations and promoting radish growth. Future research should consider the long-term effects and microbial interactions of TCBC application.

Relationship between nitrate, heavy metal, and sterols contents in Japanese agricultural soils with risk of groundwater pollution.

In Japanese agricultural lands, nitrate-nitrogen contamination of soil and groundwater often occurs due to the application of livestock excrements and compost. Therefore, rural soils in Japan were sampled and analyzed for nitrate-nitrogen leaching, heavy metal content, and sterols associated with livestock excrement and compost to calculate contamination risk indicators. The results were analyzed using self-organizing maps and cluster analysis. Nitrate-nitrogen content using water extraction was detected in most of the sampled soils. In addition, many samples from areas that were already severely contaminated with nitrate-nitrogen showed particularly high concentrations. Coprostanol, an indicator of fecal contamination, was detected in more than half of the samples. The main source of nitrate-nitrogen contamination in these areas is livestock excrement and compost. Self-organization maps showed that areas with high nitrate-nitrogen contamination also corresponded to areas with high copper and zinc soil contents. The self-organization maps and cluster analysis resulted in five clusters: a nitrate-contaminated group mainly originating from livestock excrement and compost, a heavy metal-contaminated group, a general group, a nitrate-contaminated group mainly originating from chemical fertilizers, and a contaminated group with potentially hazardous substances requiring attention. Authorities and decision-makers can use the results to prioritize areas requiring remediation.