Assessment of heavy metal contamination and its effect on earthworms in different types of soils

Earthworms encourage the mineralization of soil organic matter, the production of nutrients and the growth of plants through their feeding habits in the soil. But unsustainable development along with rapid urbanization and industrialization degrades the soils at an alarming rate which increases the level of different contaminants, i.e., heavy metals in the soil. The present study was conducted to assess the heavy metals, pH and organic carbon in agricultural, non-agricultural and industrial soils and their effects on the earthworm community structures. A total of seven earthworm species belonging to two families (Megascolecidae and Octochaetidae) were reported in this study. The earthworm species Metaphire posthuma was the most abundant in all collected soils, i.e., agricultural, non-agricultural and industrial soil with a relative abundance of 76.56%, 77.19% and 78.85%, respectively. The abundance and biomass of M. posthuma were in the order of agricultural soil > non-agricultural soil > industrial soil. It was also reported that the abundance of both anecic and endogeic species was higher in agricultural soils followed by non-agricultural and industrial soil. The findings of heavy metals indicated that industrial soil has the highest concentration of heavy metals followed by non-agricultural and agricultural soils. The contamination factor, enrichment factor, geoaccumulation index, pollution index and modified pollution index showed high, moderate and less pollution levels at industrial, non-agricultural and agricultural soil, respectively. The present study also indicated that Cd and As showed severe contamination in all studied soil types.

Automated summary

Earthworms play a crucial role in soil health by promoting mineralization of soil organic matter, nutrient production, and plant growth through their feeding habits. However, unsustainable development has led to soil degradation and increased levels of heavy metal contaminants, with industrial soils showing the highest concentrations. The study found varying levels of heavy metals in agricultural, non-agricultural, and industrial soils, as well as differences in earthworm species abundance and diversity across different soil types.