Anthropogenic Impact and Geo-accumulation of Heavy Metal Levels of Soils in Owerri, Nigeria

Abstract

Industrialization has been the major source of waste generation leading to heavy metal accumulation in soils. It has become major environmental challenge especially as it affects soil quality, biota, ecosystem processes and ground water pollution. This study was targeted at determining the contributions of human activities on heavy metal levels of soils in Owerri, eastern Nigeria, by applying Index of geo-accumulation (I-geo) and Contaminant factor (Cf) models on heavy metal levels at major locations. Soil samples were collected during the rainy season with the aid of a hand-dug soil auger (2.50 cm diameter) from three different composite sites: refuse dumps, auto-mechanic villages and a control sample from a virgin land at depths of 0-15 cm, 15-30 cm and 30-45 cm respectively. These were subjected to standard chemical analyses. There were significant variations (P<0.05) in heavy metals concentrations at different depths. There were no significant variations (P>0.05) in pH.  pH (5.9-5.2) was acidic at different soil depths, which might favor ionization of metals; electrical conductivity at the contaminated sites was higher (300.4-248.4 µs/cm) than at the control site (195.8-150.6 µS/cm) which might imply high concentration of ionized dissolved chemicals from waste dumpsites. Copper (Cu) from contaminated areas ranged from 19.1-16.4 mg/kg against control value that was insignificant (P>0.05); Lead (Pb) ranged from 58.2-28.2 mg/kg against 0.4-0.2 mg/kg; Iron (Fe) ranged from 5.6-2.6 mg/kg against 5.6-2.6 mg/kg; Zinc (Zn) ranged from 140.3-119.4 mg/kg against 3.3-2.5 mg/kg of control. I-geo for all metals fell in the categories of 4-5 and >5. All categories with values within 4-5 were soils that were highly polluted to very highly polluted, while those with values greater than 5 were soils that were very highly polluted. The Cf values of metals were quite >1.5 which implied that the activities at the mechanic villages and waste dumpsites contributed significantly to the heavy metal burden of the soils. Anthropogenic impacts on heavy metal levels on the samples were between 97.6 and 99.9%. Anthropogenic activities should be controlled to prevent heavy metal pollution of soils and sustain quality soil health.