ABSTRACT

ABSTRACT.

         

An assessment is presented of the distribution characteristics of heavy metals in the urban top-soil from the city of Benin, Edo state, Nigeria. Soil and street dusts samples (twenty in total) were collected from an aggregate of five samples per grid for the twenty samples. The samples were taken from Industrial areas, heavy and light traffic points, waste-dump/metal dump sites and less developed areas of Benin City, the capital of Edo state. The concentrations of Nickel, Copper, Zinc, Lead, Strontium, Barium, Chromium, Cobalt, Vanadium, Arsenic, Cadmium, Gold, etc, were determined using Inductively Coupled Plasma Atomic Emission Spectrometry. An evaluation of background values for topsoil was carried out by means of lognormal distribution plots.

The highest level of metal concentrations were found in the soil samples and in dusts of heavy traffic roads and heavy metal dumpsites (around new Benin market) and Industrial discharge (around the Guinness and Bendel breweries), except for metals like Arsenic, Cadmium, Antimony, Gold and Silver whose values are below the detection limit invariably implying that no contamination threat is expected from these metals. The mean metal concentration values in the soil samples are in the order Zn (638.11ppm) > Mn (376.55ppm) > Cu(153.35ppm) > Pb (121.8ppm) > Ba (87.75ppm) > V(47.4ppm) > Cr(41.25ppm) >Sr (40.9ppm) > Ni (13.4ppm) > Co (11.15ppm) > La (10.2ppm) > Th (6.06ppm), Table 4.1.

Statistical analyses were performed with SPSS, data were log-transformed prior to principal component analysis to reduce the effects of high data. Principal components analysis was carried out to ascertain the contribution of various factors on the concentrations of metals in the samples and thereby infer the sources of metal pollution. The factor loadings obtained by principal component analysis with varimax for various metals are given in tables 4.5-4.6.

The study area has anomalous elevated concentrations of Pb, Cu, Zn and Co and moderate contamination with metals like Sr, Ba, Ni, V and Mn. These metals could contaminate the groundwater resource of the study area. The predominance of the sand and ‘likely’ absence of clay minerals explains for the lesser concentrations of radioactive metals like Thorium and Uranium.