HEAVY METAL CONTAMINATION OF VEGETABLES IRRIGATED WITH WASTE WATER IN GUJRANWALA DISTRICT, PUNJAB, PAKISTAN

Abstract

Heavy metals are the foremost contaminants of food crops especially vegetables, hence considered a peril to environment. Wastewater irrigation as a substitute to freshwater has further aggravated the situation by increasing metal load in agricultural soils and food commodities especially vegetables. Intake of heavy metals via consumption of contaminated vegetables is notorious for a wide variety of deleterious health impacts in human population. In Gujranwala, along with other sources such as tube well and canal water irrigation, wastewater irrigation in urban and peri-urban areas for the cultivation of vegetables is a common practice which could be a potential source of metal contamination. The study area hosts several commercial and industrial centers as well as support a good amount of agriculture. The current study was therefore carried out is to evaluate concentration of toxic metals viz Lead, Cadmium, Chromium, Nickle, Mercury and Arsenic in vegetables (chilli, tomato, onion, spinach, okra, coriander, watermelon, cauliflower, capsicum and bitter gourd) irrigated with waste water, tubwell water and canal water in Gujranwala and estimate associated health risk in the inhabitants due to dietary exposure via consumption of afore mentioned vegetables. The concentration levels of Pb, Cr, Cd, As and Hg assessed with the aid of atomic absorption spectrophotometer in vegetables were in range 0.09 - 6.46, 0.00 - 7.69, 0.01 - 4.32, 0.00 - 2.31 and 0.00 - 0.78 mg/kg respectively. Overall trend generated on the basis mean concentration in vegetables is Pb> Cr > Cd > As > Hg. Hazard Index (HI) values for cauliflower (2.95), spinach (1.68), onion (1.42), chilli (1.24), watermelon (1.05) and coriander (1.03) were exceeding 1 for adults, whereas for children HI values for cauliflower (4.42), spinach (2.59), onion (2.21), chilli (1.78), tomato (1.63), coriander (1.62), watermelon (1.60) and okra (1.34) were higher the standard indicating potential non-carcinogenic risk associated with their consumption on a longer run. Results revealed that children are at higher risk than adults. Cancer risks associated with Pb, Cr, Cd and As ranged 1.74E-06 - 1.05E-05, 1.13E-04 - 6.40E-04, 1.27E-05 - 2.67E-04 and 0.00E+00 - 9.74E-04 respectively forv adult consumers. In children risk of cancer was higher for Pb, Cr, Cd and As, ranging from 3.74E-06 - 2.24E-05, 1.62E-04 - 9.22E-04, 1.83E-05 - 3.85E-04 and 0.00E+00 - 1.40E-03 respectively. It can be concluded that consumers are at low cancer risk due to consumption of vegetables understudy. However, heavy metals even at low concentration are not desirable and continuous monitoring on regular basis is a dire need for safe and health consumption of vegetables as well as to avoid ecological hazards.