IRRIGATION OF CROPS WITH RAW SEWAGE: HAZARD ASSESSMENT OF EFFLUENT, SOIL AND VEGETABLES

,Untreated sewage effluent containing heavy metals are applied to raise crops, mostly vegetables. Thus these metals enter human food chain and could cause health hazards. Therefore, a study was conducted to evaluate metals contamination in effluents, soils and plants being irrigated with such effluents. For this purpose, a field survey was conducted and a number of farmers' fields were selected near Kernailwala, Judgewala, Marzipura and Uchkera villages in the suburbs of Faisalabad city. Effluent samples were collected fortnightly during summer and winter to evaluate irrigation quality and metal contamination. Composite soil samples were drawn from all the sites at 0-15, 15-30, 30-60, 60-90 and 90-120 cm soil depths. Similarly, vegetables viz. spinach, eggplant, pumpkin okra and bitter gourd were sampled from each field to evaluate metal concentration in roots, shoots and fruits. Effluent samples collected from drains were found unfit for irrigation with respect to EC, SAR and RSC. The Fe concentrations were maximum while that of Cd minimum. The concentration of Cr, Mn and Ni in all effluent samples while Cd at Kernailwala and Judgewala effluent samples was higher than the permissible limits. The EC and SAR of few soil samples were above the critical limits in 0-15 cm depth. The Fe contents were the highest and Cd the lowest in AB-DTPA extractable (plant-available) forms. The AB-DTPA extractable metals decreased with increasing soil depth. Almost all the metal ions were found above the safe limits in edible parts of above mentioned vegetables. Hence, untreated effluent irrigation will not only make the soil unproductive but also have adverse effects on human health through introducing toxic metals into the food chain.