Heavy metal concentration in wastewater from car washing bays used for agriculture in the tamale metropolis, Ghana

Car washing generates a lot of wastewater into our environment which flows into our water bodies or drains into soils. Water from these water bodies or drains is mostly used for vegetable crop irrigation purposes in urban areas. The study assessed heavy metal concentration in wastewater from car washing bays in the Tamale Metropolis of Ghana. Wastewater samples from three (3) different washing bays were analyzed for presence and concentration of Zinc (Zn), Copper (Cu), Cadmium (Cd), Chromium (Cr), Lead (Pb), Iron (Fe) and Manganese (Mn). Results indicate that concentration levels of Cr (0.42 mg/l), Fe (4.97 mg/l), Pb (0.28 mg/l) and Mn (2.36 mg/l) in the samples were in high levels. Zn (0.18 mg/l), Cd (< 0.002 mg/l) and Cu (0.06 mg/l) however recorded lower limits of concentration. ANOVA of the heavy metals indicates a significant difference with F-probability value of 0.027. It was also observed that the concentration and occurrence of Fe and Mn are inter- related whilst Mn was also inter-related with Zn, Cu, Cd, Cr and Pb. The bio-accumulation of these heavy metals in the soil and also downstream effect of them need to be checked. The use of wastewater from car washing bays for crop irrigation should therefore be with extreme caution as a result of contamination.