Evaluating the impact of vermicomposted products on tomato and forecasting risks from metal-contaminated tannery sludge through innovative machine learning insights

The extensive production and improper disposal of tannery waste sludge (TWS) worldwide is an urgent concern due to the presence of hazardous heavy metals, which severely limit its reutilization. Vermitechnology transforms TWS into an eco-friendly product, but the use of vermiprocessed TWS as an organic manure remains poorly understood. Addressing this gap, the present study assessed the effectiveness of vermiprocessed TWS as an organic supplement for Solanum lycopersicum L., considering heavy metal bioavailability, human health risks, and fruit production. According to findings, compared to crude sludge amended treatments T8 (100% sludge) and T9 (50% sludge + 50% fertilizer), the treatment T3 (1:1 tannery sludge vermicompost 50% + 50% fertilizer), had prolific microbial activity, abundant soil nutrient (potassium and phosphorus), and low heavy metal bioavailability post-harvest. Plant metal uptake was significantly subsided in TWS vermicompost application ensuring a safer consumption, which was further supported by Free ion activity model– Hazard Quotient (FIAM-HQ) and Severity adjusted margin of exposure– Target cancer risk (SAMOE-TCR) assessment. Fuzzy-Topsis identified T8 and T9 as the most toxic treatments, raising a class 5 (< 0.01) category risk specifically through Cr (T8: 0.002; T9: 0.004) and Ni (T8: 0.006, T9: 0.013), denoted by SAMOE risk-thermometer indices. Artificial neural network (ANN) regarded Cr as the most influential metal for posing sensitivity to soil microbial activity and accumulation in different plant parts. Correlational and Sobol analysis further indicated both soil enzyme and microbial activity to be highly sensitive to metal bioavailability. Inclusively, vermiprocessed TWS proved to be a successful substitute to synthetic fertilizer in terms of crop yield and soil fertility.