Modeling Lateral Distribution of Heavy Metal and Bio-accumulation in Earthworm in the Varying Acidic Surface Horizon of Waste- Polluted Soil

摘要

Heavy metal concentrations and its distributions in the soil have been a source of concern to soil usage, particularly to agriculture as concentration and distribution of heavy metal determine to a large extent, the soil quality and consequently that of the crops. The ability to quantify the amount of heavy metal in the soil is of immense importance to soil management. The use of accurate model is essential to estimate the actual soil heavy metal values and its distribution for efficient management. In this study, soil and earthworm samples of the battery-waste-polluted site and that of the background site were collected from five different locations(A,B,C,D and E) along the gradient of decreasing pollution .With five replicates each form one sampling location, twenty–five soil and fifty earthworms samples (two earthworms from each replicate) were collected using stratified random sampling technique. Lead(pb), Cadmium(Cd), Chromium(Cr), Nickel(Ni), Manganese(Mn), Arsenic(As), pH and Mercury(Hg) were analyzed using standard methods. The same process was replicated for the background site. Values of the heavy metals in soil and earthworms were natural and typical of Ameki-Nanka-soil formation. The average range of heavy metals concentrations in soil and earthworm samples from the polluted site were; pb(1025-695 mg/kg), Cd(11.34-6.3 mg/kg), Mn(290-81 mg/kg), pH(2.3-6.9mg/kg), Cr(185-3.7 mg/kg), Ni(12.87-1.7 mg/kg), As(72-4.5 mg/kg), Hg(1.7-0.002mg/kg) and pb(193-37.98 mg/kg), Cd(14.04-0.01 mg/kg), Mn(17.34-1.10mg/kg), pH(6.9-2.3mg/kg), Cr(8.45-0.01 mg/kg), Ni(1.41-0.03 mg/kg), As(0.75-0.01 mg/kg) , Hg(0.4-0.009mg/kg) respectively. Concentrations of heavy metals for soil and earthworm samples decreased along the gradient of decreasing pollution of the polluted site. Three models(Linear , Logarithmic and quadratic models) were developed to test their suitability to the data in which Ph was correlated with heavy metals. Inverse correlation was observed with coefficient R2 of between 0.77-0.95 and lowest percentage deviation of the field from the predicted values.