Determination of Heavy Metal Contamination in Lagos Dumpsites Using Earthworms as Bio-indicators

In an attempt to determine the level of heavy metals contamination and factors affecting their adsorption in living organisms, soil and earthworms (Eudrilus eugeniae) were used at four registered dumpsites within Lagos metropolis. Three of the dumpsites were active; Abule Egba, Olusosun and Soluos while the fourth Oke Afa was inactive. Soil and earthworms used were sampled during the wet season (July 2006), digested using concentrated HNO3, and analysed with an atomic absorption spectrophotometer. Concentrations of Pb(364µg/g), Cu(428µg/g), Cd(4.2µg/g), Ni(19.3µg/g) and Zn(2110µg/g) were highest at Oke Afa while Cr(14.5µg/g) was highest at Abule Egba. Correlation between earthworms and soil was positive in all the dumpsites with the least (R2=0.59) reported at Oke Afa. The relation between metals in soil and earthworms in all the dumpsites was greatly influenced by soil organic matter, pH and metal concentrations in the soil. Our findings show that most of the metals in the dumpsites exceeded the Canadian environmental guideline and Toronto public health guide for soil. This could lead to possible heavy metal poisoning of residents living close to the dumpsite through ground water contamination by leachate.