The optimized BCR sequential extraction procedure (proposed by the Standards, Measurements and Testing Programme (SM&T) of the European Union) was applied to seven topsoil samples from refuse dump sites for the determination of Cu, Zn, Ni, Pb and Cd. The metals were partitioned into four operationally defined chemical fractions: acid extractable, reducible, oxidizable and residual, and analysed using flame atomic absorption spectrophotometry, FAAS.The results were compared with total metal concentrations obtained using HNO 3 , HClO 4 and HF digestion procedures. Results for total metal analysis ranged from -15.55 to 43.45 for Cu, 37.15 to 222.35 for Zn, 5.15 to 12.10 for Ni, 10.30 to 93.05 for Pb and 0.35 to 3.75 for Cd in µgg −1 dry weight. The results of the partitioning study showed that zinc prevailed in the more soluble fractions and was distributed between the acid-extractable (32.4%) and the reducible (40.3%) fractions, whereas Pb was distributed mainly in the reducible fraction. Copper and nickel were predominantly associated with the reducible and residual fractions -53.4, 33.3 and 51.1, 24.1% respectively. The ranking of the four fractions for the partitioning of cadmium was: reducible > residual > oxidizable > acid extractable. The percentage recovery for all metals when comparing total metal concentration with the fractional sum of the optimized BCR procedure, were of the order: Zn(93%) > Pb(83%) > Cu(78) > Cd > (68%) > Ni(63%).

The optimized BCR sequential extraction procedure was applied to nine roadside soil samples for the determination of Cd, Cr, Pb and Ni. The extractable metals were isolated into three operationally defined fractions viz: acid extractable, reducible and oxidizable. The residue was treated with aqua regia solution. Metal analysis was done using flame atomic absorption spectrophotometry with airacetylene flame. Results obtained showed the concentrations of the metals as relative abundance in the mobile phases of the samples (based on the sum of the first three fractions) are in the following order: Cd(91.9) [ Pb(82.8) [ Ni(49.5) [ Cr(39.0). The most non-mobilizable metals were Cr and Ni which are generally lithogenic, associated with the silicate matrix, and the order is as follows: Cr(61.0) [ Ni(50.5) [ Pb(17.2) [ Cd(8.1). The recovery of all the metals expressed as the ratio of total metal concentration to fractional sum of the optimized BCR sequential extraction procedure was of the order: Cr(95.6) [ Pb(95.0) [ Ni(94.8) [ Cd(92.4).

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.

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