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

Abstract

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.

Ecological Implications and Source Apportionment of Heavy Metal and Hydrocarbon Contaminants in the Soil of a Poorly Crude Oil Remediated Site in Nigeria: A Case of Ikot Ada Udo Community

“…The obtained findings revealed variations in the accumulation of metals and TPH between the sampling points soil (study site), and recorded higher values of metals and TPH for each sampling point compared to the control. This result corroborated with a previous study on the toxic metals pollution in impacted soils using soil invertebrates [Udousoro et al, 2015]. The higher concentration of the studied contaminants in the study site compared to the control could be because crude oil spill contains hydrocarbons and heavy metals, which were potentially released into the environment, thereby increasing the level of the contaminants in the soil [Albers, 1995;Akporido, 2008].…”

“…The difference in the level of heavy metals, TPH, and trend between the present study and the other studies compared could be because the extent of contamination of soil and residual oil impact on soil quality varies depending on the time duration of productivity of oil well [Wang and Feng, 2009]. Furthermore, the extent of environmental pollution [Nakamura et al, 2005], solubility of soil and chemical form precipitation [Udousoro et al, 2015], and distance of the sampling point from the corked Ibibio oil well could also be the reason for the difference. The concentrations of Cd, Cr, Fe, V, and As were above the WHO limit for soil by 1.3, 2.74, 2.49, 2, and 1.8 times.…”