Bioconcentrations of metals (Fe, Cu, Zn, Pb) in earthworms (Eisenia fetida), inoculated in municipal sewage sludge: do earthworms pose a possible risk of terrestrial food chain contamination?

Efforts have been made to evaluate the possible risks of metal bioaccumulation in composting earthworms during vermicomposting of hazardous wastes, e.g., sewage sludge. The sewage sludge was diluted by mixing cow dung in different proportions, and vermicomposted sludge as well as inoculated earthworms were analyzed for metal (Fe, Cu, Zn, Pb) contents. The sludge processed by worms showed a significant reduction in concentration of metals, Cu (29.4-51.6%), Fe (13.1-19.9%), Zn (15.2-25.8%), and Pb (4.6-46.9%), at the end. A considerable concentration of metals, total Cu (16.7-27.6 mg kg(-1)), total Fe (42.9-89.8 mg kg(-1)), total Zn (5.85-75.0 mg kg(-1)), and total Pb (1.79-12.4 mg kg(-1)), in composting earthworms was also recorded. The greater values of bioconcentration factors for metals suggested the possible risk of entering contaminants in higher food chains; since, earthworms are near to the terrestrial food chain, they can potentially mediate metal transfer from soil to a range of predators, including birds. Therefore, feasibility of vermitechnology in hazardous waste recycling needs close attention in respect to possible risk of environmental contamination.