Heavy metals contamination in vegetables irrigated with wastewater: a case study of underdeveloping regions of Pakistan.

Abstract

Irrigation of food crops with untreated wastewater leads to the accumulation of heavy metals in their edible parts. Exposure to toxic elements through consumption of contaminated vegetables even at very low concentration is becoming a serious problem for human health in many countries. This issue of heavy metals contamination needs great attention especially in Pakistan where irrigation by wastewater has become a common practice in urban and periurban areas. The present study was conducted to assess the contamination of different heavy metals including nickel (Ni), cadmium (Cd), lead (Pb) and chromium (Cr) in vegetables irrigated with wastewater in different districts of Punjab (Pakistan) like, Faisalabad, Lahore, Gujranwala, Sargodha, Sahiwal, Multan, Rawalpindi and Bahawalpur during years 2016-2019. The maximum contamination factor (Ni, 1.39; Cd, 5.86; Pb, 3.99; Cr, 2.24), pollution load index (2.92) and degree of contamination (13.48) were observed in wastewater irrigated agricultural soils of district Gujranwala as compared to other districts. Mean metal concentration in vegetables grown with untreated wastewater and transfer factor varied with plant type, frequency of irrigation and soils types/series of different districts of Punjab. The highest metal contamination was observed in Gujranwala where 44% vegetable samples were contaminated with Ni, 87% with Cd, 97% with Pb and 88% with Cr. Radar analysis and hierarchical cluster analysis showed that mustard leaves, spinach and lettuce were more contaminated vegetables compared to other vegetables. This study contributes to the evidence-based conclusion that cultivation of vegetable with untreated wastewater should be prohibited and required treatment of wastewater is needed.