Bioaccumulation of heavy metals in earthworms collected from abattoir soils in Abeokuta, south-western Nigeria

Abstract

Activities in abattoirs and direct release of its waste into the environment are on the increase due to high protein demand in the country; and there is a need for proper assessment of abattoir soil for pollution. This study evaluated bioaccumulations of heavy metals in indigenous earthworm from abattoir soils as a measure of pollution. Five replicates each of earthworms, soil and cow dung samples were collected from three abattoir sites (Lafenwa, Gbonogun and Madojutimi) in Abeokuta, Ogun State and a control site (Federal University of Agriculture, Abeokuta, Arboretrum) beside an undisturbed stream with no cow dung. Samples were collected at 1m interval from sampling point at each site. Heavy Metal (Cu, Zn, Pb, Cd, Co, Cr, Ni and Mn) concentrations were measured in the earthworm species (Libyodrilus violaceus, Eudrilus eugeniae and Alma millsoni), soil and cow dung samples from the sites using Atomic Absorption Spectrophotometer. Some physico-chemical parameters (pH and percentage organic matter) of the soil and cow dung from the sample sites were also assessed using standard methods. The heavy metals concentrations, pH and the percentage organic matter recorded in the cow dung of all the abattoir locations were significantly higher (p<0.05) than the concentrations in their respective soil samples. Lafenwa abattoir had the highest concentrations of heavy metals and percentage organic matter (4.57 ± 0.06) in its soil. Concentrations of Cu, Zn, Pb, Cd and Mn were highest in the tissue of earthworm species obtained from Lafenwa abattoir. The bioaccumulation factors for the metals analysed were less than unity except for Cd. Libyodrilus violaceus, Eudrilus eugeniae and Alma millsoni bioaccumulate heavy metals from the abattoir soils and the accumulation is directly related to the concentration of such heavy metals in the soil. Indigenous earthworms are a good bioindicator of pollution for heavy metals.

Keywords: heavy metal, bioaccumulation, abattoir soils, earthworms