Comparative Assessment of Levels of Heavy Metals in Earthworm Casts and Soils at Contaminated Sites

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Author(s) Iorungwa, M.S. | Wuana, R.A. | Yiase, S.G.
Pages 320-325
Volume 2
Issue 4
Date April, 2013
Keywords Earthworm, metals, bio-monitoring, soil contamination

In this study, the levels of some metals in earthworm casts (EWC), surface organic matter (SOM) and the parent soil (PS) were compared to assess the bio-monitoring potential of earthworm casts. Samples of earthworm casts, surface organic matter (SOM) and the actual soil were collected from each of the randomly selected points (16) around an active dumpsite located at the North Bank Area of the River Benue in Makurdi, north-central Nigeria. The samples were assayed for Cd, Cu, Fe, Pb, Mn and Zn by flame atomic absorption spectrophotometry after aqua regia digestion. Results revealed that in the casts, metal concentrations (mg/kg) ranged as: Cd(0.20 – 2.93), Cu(5.00 – 20.00), Fe(0.52 – 1.90), Pb(26.00 – 83.00), Mn(52 – 130) and Zn(44.00 – 80.00). In SOM, the concentrations were Cd(0.30 – 2.00), Cu(95.00 – 15.00), Fe(0.30 – 1.50), Pb(31.00 – 88.00), Mn(63.00 – 122.00) and Zn(42.00 – 98.00). In the actual soil samples, metal concentrations were Cd(0.12 – 3.00), Cu(3.50 – 28.00), Fe(0.25 – 4.10), Pb(38.00 – 120.00), Mn(69.00 – 202.00) and Zn(35.00 – 112.00). Depending on the sample matrix, even though metal concentrations varied as parent soil > earthworm cast > SOM; on a whole they were well correlated indicating that earthworm cast may be adopted as surrogate in the bio-monitoring of soil contamination.

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