The objective of this research was to detect the presence of heavy metals (HMs) in soils polluted with sludge from an industrial wastewater treatment plant and then use Eisenia fetida earthworms to reduce the contamination levels in the soil. The sludge was added to the soil at varying rates of 0, 10, 20, 30, 40, and 50 ton/ha. To examine the impact of organic amendment, 12 Eisenia fetida earthworms were added to all samples for every 500 g of the contaminated soil. After 42 days, the overall concentration and categorization of HMs in the soil, along with the changes in weight and mortality of the earthworms, were determined. The addition of sludge to the soil resulted in an elevation of HM levels, including copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and cadmium (Cd). Notably, with the exception of Cd, the concentration of HMs decreased after the 42-day period following the introduction of earthworms. The highest absorption of metals by the earthworms occurred when 20 ton/ha of sludge was applied. This suggests that the earthworm species Eisenia fetida possesses the capability to bioaccumulate Zn and Cd, as indicated by a bioaccumulation factor exceeding 1 for these metals. In conclusion, the utilization of earthworms in this study not only resulted in the storage of HMs within the worms’ bodies but also contributed to the improvement of the physicochemical properties of the soil.
