Rice Husk Ash as a Soil Amendment: Ecotoxicological Impacts on Copper-Contaminated Soils

Rice husk ash (RHA) is a by-product generated from the controlled combustion of rice husks, offering potential applications in agriculture as a soil amendment. This study evaluates the ecotoxicological effects of RHA on copper-contaminated soils, particularly vineyard soil, which presents high levels of copper accumulation due to fungicide use. Three soil types—vineyard soil (V), native field soil (NF), and tropical artificial soil (TAS)—were analyzed under different RHA concentrations (5%, 15%, 25%, 50%, and 100%). Two model plant species, lettuce (Lactuca sativa) and arugula (Eruca sativa), were used in germination assays to assess toxicity levels. The vineyard soil presented 34.19 mg/kg of copper (Cu), exceeding the quality reference value (11 mg/kg) established by environmental regulations, while Native Field soil contained only 0.81 mg/kg of Cu. Germination index (GI) and normalized residual germination percentage index (NGI) indicated a moderate toxicity (-0.34%) for lettuce at 5% RHA, while toxicity levels were lower at 25% and 50% RHA. Root growth inhibition was observed in lettuce at 6.16% and 6.03% for 25% and 50% RHA, respectively. Arugula showed higher sensitivity to RHA concentrations, with root growth inhibition reaching 72.89% in vineyard soil and 60.78%, 63.04%, and 72.38% at 5%, 15%, and 25% RHA, respectively. The findings highlight the potential of RHA for soil remediation but emphasize the need for controlled applications to prevent adverse. Sustainable application of RHA may contribute to soil rehabilitation strategies and agro-industrial residue management, but further studies are needed to optimize its use in contaminated environments.