QUALITY OF SOIL AND GROUNDWATER IN AUTOMOBILE WORKSHOPS IN AKINYELE LOCAL GOVERNMENT AREA, OYO STATE, NIGERIA

Abstract

Heavy metal contamination from activities in automobile workshops is of public health concern. These heavy metals have capacity to remain in the environment over time. Several studies have been conducted on industrial water pollution but limited investigations have been carried out on water and soil quality around automobile workshops. This study therefore, was designed to assess the quality of soil and groundwater in automobile workshops in Akinyele Local Government Area (ALGA).

A Simple random sampling technique was employed to select three of six zones of automobile workshops in ALGA: Alphonso, Temidire and Ojoo with one residential area (Moniya - control site). Eight automobile workshops were selected from each zone based on: absence of other industries and presence of dug wells. Water samples were collected from dug well (0-50 m) around the workshops. Physico-chemical parameters (Total Dissolved Solids (TDS), Electrical conductivity, pH and Oil and grease) and heavy metals (Copper (Cu), Chromium (Cr) Cadmium (Cd) and Lead (Pb)) were determined using standard methods. Grab samples of top and sub soils were collected from the three locations and analysed. Values obtained were compared with WHO standards for potable water quality and United Kingdom Permissible Limits for soil quality. Data were analysed using descriptive statistics and ANOVA at p<0.05.

Mean results of water analysis revealed that TDS and Electrical conductivity for Alphonso, Temidire, Ojoo and Moniya were within WHO limits. The mean pH was 6.4±0.8, 6.8±0.7, 6.7±0.4 and 7.6±0.2 in Alphonso, Temidire, Ojoo and Moniya respectively. Median oil and grease content 1245 mg/l, 206 mg/l and 2650 mg/l in Alphonso, Temidire and Ojoo respectively, were above WHO limits. In the dug wells, mean concentrations of Cu (mg/l) was significantly higher in Alphonso (2.5±2.06) than other zones. Mean concentration of Cr (mg/l) was 0.34±0.28, 0.37±0.13 and 0.31±0.3 for Alphonso, Temidire and Ojoo respectively while it was not detected in Moniya. The median concentration for Cd (mg/l) in Alphonso, Temidire, Ojoo and Moniya were higher than the WHO limits. Lead was absent in all locations except Alphonso 8.50(0.0 -35.8) mg/l. Mean concentrations of all the metals were higher in all the zones than Moniya and WHO limits except for Cu in Temidire and Ojoo. In the soils, mean concentration of Cu (mg/kg) in Alphonso, Temidire, Ojoo and Moniya was 21.55±9.03, 50.41±2.65, 44.27±3.04 and 19.19±2.82 respectively. Mean concentrations of Cr (mg/kg) in Alphonso, Temidire, and Ojoo was 18.52±2.2, 22.52±3 and 15.4±1.73 respectively. Mean concentrations of Cd(mg/kg) in Alphonso, Temidire and Ojoo was 7.89±1.9, 5.3±3.14 and 6.07±5.6 respectively while mean concentrations of Pb (mg/kg) in Alphonso, Temidire and Ojoo was 80.19±7.43, 35.41±4 and 77.77±3.58 respectively. The mean concentrations of all the heavy metals (except Cd) were within the permissible limits for soil quality but higher than the control across the selected zones.

The concentration of heavy metals above regulatory limits in soils and dug wells indicates contamination. There is the need for strict enforcement of safe waste handling methods to reduce soil and water contamination around automobile workshops.