Novel synthesis and application of biochar for controlling release and exposure of mercury in the farmland: From human health risk perspective

Mercury (Hg)-contaminated farmlands have received wide attention because of the adverse risks posed to food security and human health. In addition, climate change altered the mobility of Hg in the soil, limiting soil productivity and nutrient bioavailability, hence elevating health risks. To adapt to these risks, pot experiments were employed to showcase the impacts of single-pyrolytic synthesized biochar with nitrogen and phosphorus impregnation (NPBC) on the nutrient accessibility, Hg immobilization, and human health risks, compared to pristine and control groups. Results revealed that, with increased surface area and abundant function groups, impregnation amplified bulk nitrogen, phosphorus, and oxygen content from 0.47, 0.25, and 9.47 % to 3.01, 4.50, and 21.4 %, respectively. The pot experiments indicated the effectiveness of NPBC900 in immobilizing soil Hg, hence reducing Brassica rapa chinensis’ Hg uptake by 88 %. Notably, NPBC transformed ∼93 % of water soluble and exchangeable Hg species to stable fractions, enhancing the residue concentration three-fold higher than the control. Additionally, NPBC700-900 showcased characteristic phosphorus and nitrogen slow-release (best at NPBC900 and NPBC500, respectively; 5 %) contributing to controlled soil available nutrients. Hg bioaccessible fraction exhibited a notably higher level (1.7 mg kg⁻¹) in the control group measured against BC (0.8 mg kg⁻¹) and NPBC treatments (∼0.1 mg kg⁻¹). Through dietary and soil ingestion pathways, NPBC900 treatment demonstrated the best health risk reduction for farmers and the public by ∼93 and 69 %, respectively. With versatile capabilities, NPBC emerges as a practical, green, and sustainable alternative in Hg remedy technologies, a breakthrough for climate change adaptation.