Soil Invertebrates As Bio-Monitors of Toxic Metals Pollution in Impacted Soils

The bio-indicator potentials of two invertebrate species, Eudrilus eugeniae (earthworm) and Pachybolus ligulatus (millipede) in toxic metals impacted soils in Akwa Ibom State, in the Niger Delta region of Nigeria were assessed. The study involved collection of Eudrilus eugeniae and Pachybolus ligulatus, and their site soil samples from different impacted and non-impacted soils in ten locations spread over four Local Government Areas. Toxic metals (Pb, Fe, Zn, Ni and Cd) in soils and in the bio-indicator organisms were analysed using Atomic Absorption Spectrometry, after acid digestion. Geo-accumulation Index (Igeo) was used to measure the extent of soil pollution; Bio-Accumulation Factor (BAF) to compute the metal uptake from soil by bio-indicators; and multivariate statistics to identify interrelationships among metals and the pollution sources. Metals in all soils were higher than the background levels, and were classified as unpolluted to very strongly polluted. Pb, Fe, Zn and Cd were higher in Eudrilus eugeniae, and Ni in Pachybolus ligulatus at 0.05 level. The organisms absorbed all metals (BAF<1), but Eudrilus eugeniae accumulated Cd and Fe and Pachybolus ligulatus, Ni and Fe (BAF>1). Metals were clustered into three (Eudrilus eugeniae) and two (Pachybolus ligulatus) dissimilar groups. Two principal components extracted, each for Eudrilus eugeniae and Pachybolus ligulatus accounted for 64% and 72% of total variations, respectively. The invertebrates exhibited varying levels of affinity in metals uptake. Eudrilus eugeniae appeared to accumulate Pb, Fe and Cd more, and could serve as a better bio-indicator for monitoring these metals. Pachybolus ligulatus accumulated 3-folds more Ni, and could provide a monitoring tool especially in agriculture, in the Niger Delta Region of Nigeria, plagued by crude oil pollution of its land and water bodies. key words: Soil bio-indicators, Pollution, Multivariate analysis, Atomic Spectroscopy.