Application of pollution risk evaluation models in groundwater systems in the vicinity of automobile scrap markets in Owerri municipal and environs, southeastern Nigeria

Abstract

This study is aimed at the application of risk and pollution models in evaluating the quality of groundwater samples in the vicinity of automobile scrap markets in Owerri municipal and its environs. Soil samples from the study area were analyzed using energy dispersive x-ray fluorescence spectrometer (EDXRF) which revealed the identities and percentages of metallic contaminants in the soil. Identified metallic pollutants were subsequently determined in the groundwater samples with an atomic absorption spectrophotometer (AAS). Physicochemical parameters of the water samples were ascertained using standard procedures. The EDXRF results revealed the presence of fourteen metallic pollutants in varying percentage concentrations with aluminum and iron showing the highest concentrations. Low pH values (3.98 – 4.34) were recorded in all the groundwater samples below acceptable limits, while elevated nitrate levels were observed but are however within recommended limits. High concentrations of nickel (0.18±0.03 mg/L) and lead (0.04±0.02 mg/L) above threshold values for safe drinking water were observed in the groundwater samples within the study area. Strong positive correlations were recorded for the metallic contaminants in both soil and groundwater samples. This was also confirmed by principal component analysis (PCA) which grouped the metals into three and two groups for soil and water samples respectively. However, Hierarchical cluster analysis (HCA) revealed that the soil and water samples were polluted mainly by two distinct sources. Single-factor pollution index (SFPI) revealed values > 0.1, as the metal index (MI) suggests serious water pollution. Both the degree of contamination (DC) and heavy metal evaluation index (HMEI) revealed medium contamination and moderate-to-heavy metal index respectively. The heavy metal pollution index (HMPI) value > 100 was recorded in the samples suggesting the unsuitability of the groundwater for drinking. Hazard quotient (HQ) values of all the metallic pollutants studied except Cd in sample B were lower than one (<1), and the hazard index (HI) value of sample B revealed that there could be adverse health effects due to Cd contamination. Carcinogenic risk (CR) analysis for Cd, Cr, and Pb showed values above 10−6 (> 10−6), which implies the tendency of carcinogenic risk after prolonged intake of water samples from the area. Hence, it is recommended that appropriate government agencies should as a matter of urgency provide treated pipe borne water to the area to avert possible health challenges due to the consumption of water from groundwater sources in the study area.