Vermiremediation of Heavy Metals Using Native Earthworm Species of Assam, India

Abstract

Rapid urbanization and changing consumption patterns have intensified municipal solid waste (MSW) generation, posing a significant global management challenge. Traditional disposal techniques like landfilling and incineration present serious environmental hazards, such as greenhouse gas emissions and contamination of soil and water. An environmentally beneficial substitute that improves soil fertility and controls heavy metal contamination is vermicomposting. The effectiveness of four native earthworm species of Assam—Amynthas diffringens, Perionyx excavatus, Perionyx annulatus, and Drawida nepalensis—in breaking down MSW was evaluated in this study, which was carried out in Guwahati, Assam during 2023–2024. The experiment followed a completely randomized design with five treatments, each replicated five times, comprising four native earthworm species and an unamended control. The results showed that vermicomposting increased vital nutrients like phosphorus (0.48–0.70%), potassium (0.61–0.92%), calcium (0.34–0.96%), magnesium (0.02–0.15%), and sulfur (0.32–0.81%) while significantly lowering organic carbon to 181.47–250.62 g/kg and the C:N ratio to 14.9–23.08 from 38.6 in control. In addition, the process elevated the heavy metal concentrations of cadmium (0.66±0.04 mg/kg), chromium (46.00±6.2 mg/kg), lead (38.32±7.1 mg/kg), and nickel (29.00±6.3 mg/kg), but also diminished their mobility relative to the control treatment lacking earthworms. All vermicomposting treatments resulted in lower available cadmium (not detectable), chromium (16.61 mg/kg), and lead (3.91 mg/kg), thereby reducing their environmental mobility and phytotoxic potential. Amynthas diffringens demonstrated the highest efficacy among the tested species, with superior nutrient transformation and maximum reduction of heavy metal bioavailability. The study demonstrated the capacity of earthworms to reduce heavy metal bioavailability through concurrent bioaccumulation and metal-organic complex formation. This enables the use of vermicompost produced from MSW in agricultural fields and mitigates the danger posed by heavy metals by increasing their immobilization.