Comparative Analysis of Trace Elements Found in Commonly Used Vegetables Irrigated By Fresh And Waste Water in Karachi, Pakistan

Abstract

Use of municipal waste water (both treated and untreated) has now become a common practice in urban and peri-urban areas. Mostly vegetables in urban cities like Karachi are being irrigated by sewerage water. In this study a comparison of sewage and fresh water-irrigated vegetables has been made with respect to trace metals. Among commonly used vegetables, green onion, cabbage, pumpkin, eggplant, bird’s eye chili and okra were selected. Two sets of these vegetables were collected, one from local farm where irrigation was done with well water and other set of samples was collected from Malir, Karachi where irrigation was done with waste water. Samples were analyzed for heavy metals i.e. K, Na, Pb, Zn, Cu, Cd, Fe, and As by Atomic Absorption Spectroscopy. It showed that both sets of samples were found to contain metal concentrations beyond the limits set by WHO/EU. Apart from tomato, the concentration of only Cd was near the standard value for both sets. Similar results were obtained for K except for pumpkin in which the concentration for waste water irrigated samples was fairly high. Amount of Cu and Fe were moderately higher than the standard in both samples. Arsenic in all the samples was considerably high while maximum concentration was obtained for Pd against the limits. These findings suggest waste water irrigated vegetables pose high risk to  human health. The concentrations of As and Pb were high in fresh water samples possibly, the well water may contain metals, therefore it is important to know the source.

Keywords: Trace metals, fresh water, wastewater, world health organization (WHO).