Sensitivity of Earthworm (Eisenia fetida) in Mining Soil from Ijero-Ekiti, Nigeria

Abstract

Excavation and processing of mineral deposits are valuable revenue sources yet they contribute serious environmental problems worldwide. Mining activities are widespread and contribute to heavy metal contamination in rural communities in Ekiti State, Nigeria. Available research failed to establish how mining soil may impact on resident terrestrial organisms. This study assessed the health of soil from active mining site by testing it on earthworms (Eisenia fetida) for 10 weeks. Survival, mobility, morphology and behaviour of worms were assessed while soil was analyzed for selected heavy metals by atomic absorption spectrometry. Worm survival was evident as the proportion of reference soil increased in exposure mixture and improved until 92% in the control. Worms curled up at the bottom of test vessels with varying proportions of mining site soil and appeared discolored and dehydrated when taken out of test soil, with characteristic sluggishness, particularly as the proportion of mining soil increased in exposure mixtures. Though metal levels were within permissible limits, morphology of exposed worms were visibly impacted, which corresponds in severity with increasing proportion of mining soil. On the contrary, worms tested in 100% reference soil appeared healthy and active in upper part of exposure vessels. These results suggest that the tested mining soil had adverse impacts on mobility, morphology, behavior and survival of exposed organisms when compared with the control population. Therefore, food products grown downstream of the mining site may be at risk of heavy metal contamination with consequences on food quality, water quality and food chain.