Distribution of heavy metals in soils of Port Harcourt and its environs, Niger Delta, Nigeria

Abstract

Geochemical evaluation of the distribution of heavy metals in soils of Port Harcourt and its environs in the Niger Delta region is presented in respect of anthropogenic factor and index of geoaccumulation. Sixteen (16) soil samples were collected from two horizons (0–10 cm and 100 cm) from the various grids and analyzed. The geochemical analyses showed the vertical and horizontal distributions of heavy metals. The results showed the ranges of the metals determined as follows: Pb (6.86–2.49)×10⁻⁶, with an average of 4.63×10⁻⁶; Cd (0.05–0.00)×10⁻⁶, with an average of 0.02×10⁻⁶, As (0.01–0.00)×10⁻⁶, with an average of 0.00×10⁻⁶. Cu (15.36–10.80) ×10⁻⁶, with an average of 13.36×10⁻⁶, and V (1.36–0.20)×10⁻⁶, with an average of 0.94×10⁻⁶. Quantification of the degree of pollution was carried out using anthropogenic factor (AF) and index of geoaccumulation (I _geo). The Igeo values of 0.06, 0.02 and 0.00 for Pb, Cd and As, respectively indicate low-level contamination while Zn (1.14) and V (1.40) show medium-level contamination. The sources of contamination are attributed to urbanized anthropogenic activities. The majority of the samples analyzed show that the AF values are less than 1 with the exception of vanadium (V) whose AF values range from 2.73 to 13.60×10⁻⁶. Vanadium is more enriched than As, Cd, Pb, and Cu. The order of degrees of anthropogenic contamination and index of geoaccumulation in the soil is V >Zn >Pb >Cu >Cd >AS. Metals were retained near the top soil and their concentrations in the deepest horizons were lower and normal for uncontaminated soils. Metal concentrations in the top soil horizons were significantly related to distance from the industrial and human activities.