Wastewater driven trace element transfer up the food chain in peri-urban agricultural lands of Lahore, Pakistan

Abstract

In peri-urban agricultural lands of Lahore city, untreated wastewater from trans-boundary Hudiara drain is widely used for agriculture. The irrigated water may pose a hazard of trace element (TE) contamination in agricultural produce and consequently threat to human health. This study was designed to investigate the quality and transferability of TE contamination in water, soil, fodder and buffalo milk. Samples from the 4 assets and products were collected at upstream, midstream and downstream sites along Hudiara drain. Potentially toxic elements (Cd, Cu, Ni and Zn) were analyzed using standard methods. Physicochemical analysis of water, bioaccumulation factor (BAF) from soil to fodder and Pearson correlation of metal contamination in water, soil, fodder and milk were determined. TE contamination increased from upstream to downstream site. Highest Cd concentration in water, soil, fodder and milk was 0.29 mg/L (downstream), 1.10 mg/kg (midstream), 2.12 mg/kg (downstream) and 0.29 mg/L (downstream), respectively, which surpassed permissible limits for all the 4 mediums. Similar results were found with Cu, Ni and Zn which increased downstream and the concentrations higher than permissible limits in all mediums except soil. Significantly high Hazard Index (HI) values were recorded for irrigation wastewater (23.25–31.75), fodder (7.41–11.13), and milk (11.12–17.85), which were increasing down the stream of drain. All 4 metals have shown strong positive correlation among water, soil, fodder and milk, showing transferability risk up to food chain. Transfer of TE from soil to fodder was highest for Ni (BAF 8.44) and lowest for Zn (BAF 0.41) with the following ascending trend: Zn < Cd < Cu < Ni. The physicochemical parameters of drain water also did not meet the permissible limits for wastewater irrigation. Use of untreated water of Hudiara drain for agriculture in peri-urban areas of Lahore needs to be stopped until appropriate treatment and reuse.