Açaí Seed Biochar-Based Phosphate Fertilizers for Improving Soil Fertility and Mitigating Arsenic-Related Impacts from Gold Mining Tailings: Synthesis, Characterization, and Lettuce Growth Assessment

Biochar represents a promising alternative for enhancing substrates and remediating contaminants in mining areas. Given that arsenic (As) and phosphorus (P) share similar chemical forms, the combination of biochar and P fertilizers may reduce As uptake, thereby mitigating As-related impacts. This study aimed to evaluate the potential of biochar-based P fertilizers in improving soil fertility and mitigating human health risks from gold mining tailings in the eastern Brazilian Amazon. Biochar from açaí palm (Euterpe oleracea Mart.) seeds was produced through enrichment with single and triple superphosphate at a ratio of 1:4, at 400 ${}^{\circ }$C, and applied to mining tailings at 0.5%, 1%, and 2%. After one year of incubation, lettuce plants were grown for 70 days. Biochar reduced As absorption by lettuce and improved biomass and nutrient accumulation, resulting in improved vegetation indices. Biochar was effective in reducing non-carcinogenic As risks via ingestion of soil and plants to acceptable levels. Regression equations explained the As absorption behavior as affected by the biochar and the importance of biochar-related nutrients in reducing As stress. This study demonstrates the potential of P-enriched biochar as an amendment for As-contaminated soils, reducing As absorption, increasing P availability, and improving plant growth.