Effects of sewage water irrigation on heavy metals accumulation in vegetables in peri-urban areas of Faisalabad, Pakistan

Abstract

Untreated sewage effluents are frequently used for irrigation, posing a risk of heavy metal accumulation in edible crops. The present study aimed to assess the concentrations of heavy metals in water, soil, and two commonly consumed vegetables, Spinach (Spinacia oleracea L.) and Cauliflower (Brassica oleracea var. botrytis), collected from Ghulam Muhammad Abad (Site-I) and Chokera (Site-II) in Faisalabad, Pakistan. Water and soil samples were analyzed for pH, electrical conductivity (EC), and heavy metals, while plant samples were evaluated for biomass, photosynthetic pigments, antioxidant enzyme activities, and metal accumulation. Heavy metals, including Cd, Co, Cr, Pb, Cu, Ni, and Hg, were quantified using inductively coupled plasma optical emission spectrometry (ICP-OES). Results showed that water EC exceeded safe limits (Site-II: 29.86 NTU), while soil EC remained below 1 dS m⁻¹, indicating no salinity issues. Heavy metal concentrations in water exceeded WHO permissible limits, particularly Cd (0.50 mg L⁻¹ at Site-II) and Hg (1.92 mg L⁻¹ at Site-II). Soil samples had elevated Co and Pb levels, with Site-II showing 6.09 mg kg⁻¹ Co and 5.39 mg kg⁻¹ Pb. In vegetables, Cd, Co, Ni, and Pb exceeded safe limits, with spinach showing Cd (3.58 mg kg⁻¹) and Co (4.71 mg kg⁻¹), and cauliflower showing Cd (3.92 mg kg⁻¹) and Co (5.55 mg kg⁻¹). Heavy metal exposure significantly reduced root and shoot lengths (up to 74% decrease in fresh biomass and 59% in dry biomass) and photosynthetic pigments, while antioxidant enzyme activities (CAT: 142 Unit g⁻¹ F. wt, POD: 125 Unit g⁻¹ F. wt) were elevated, indicating oxidative stress. These findings demonstrate that the continued use of untreated sewage water for irrigation poses substantial health risks through heavy metal accumulation in food crops. The study highlights the urgent need for monitoring and remediation strategies to ensure food safety.