Fractionation of heavy metals and their uptake by vegetables growing in soils irrigated with sewage effluent

Authors: FARZANA BASHIR, MUHAMMAD TARIQ, MUHAMMAD HAMMAD KHAN, RAUF AHMAD KHAN, SADIA ASLAM

Abstract: Fractionation of heavy metals helps to determine their binding form, toxicity, and availability in terrestrial environments. Wastewater irrigation may lead to the accumulation of these metals in soil and plants. Wastewater irrigated soils and vegetables were collected from 6 sites in the vicinity of Lahore and analyzed for cadmium, nickel, chromium, zinc, manganese, cobalt, and copper. The quality of wastewater used for growing crops was also determined. In soil, sequential extraction was adopted to demarcate 5 metal fractions: exchangeable, acid-soluble, reducible, oxidizable, and residual, which were quantified by inductively coupled plasma optical emission spectrometry. The accumulations of these metals in vegetables (spinach and bitter gourd) were also assessed and it was found that concentrations of all studied toxic metals in edible parts of the vegetables were above the critical level. The total metal contents in soil were in the order of Mn > Co > Zn > Cr > Ni > Cu > Cd. Correlation analysis between metal concentrations in different fractions of soil and vegetables was performed at 95% and 99% confidence levels. Positive and negative correlations were observed; positive values indicated the bioavailability of these metal fractions to vegetables, while negative values showed that metal concentrations in particular fractions were not bioavailable to plants.

Keywords: Heavy metals, vegetables, sewage, plant uptake, bioavailable

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