PROLONGED WASTEWATER IRRIGATION AND HEAVY METAL ACCUMULATION IN SOILS, VEGETABLES AND FODDER CROPS

Worldwide wastewater loaded with toxic heavy metals, used as a reliable source for irrigating a variety of crops, have some risks and restrictions. The extent of wastewater heavy metal accumulation was investigated during 2009-10 in soils, vegetables and fodder crops grown in the periphery of District Dera Ismail Khan, Pakistan. The wastewater exhibited extreme basicity (pH 10.31) and the ratios of electrical conductivity, sodium adsorption, carbonates and bi-carbonates, and chloride concentration were beyond the prescribed standards suggesting that the use of wastewater could be a limiting factor. In addition, wastewater had abnormally higher levels of Fe, Cu, Zn, Ni, Mn, Pb, Cr, and Cd. Generally, in wastewater irrigated soil, the heavy metal concentration was higher than tube-well irrigated soil and was found beyond the permissible limits. Majority of the vegetables and fodder crops tested here accumulated excessive amounts of Cd, Cu, Pb and Zn, which were beyond the permissible limits. The concentrations of Cr, Ni, Mn and Fe on the contrary were below the permissible limits in vegetables and fodder crops. Utilization of wastewater for irrigating the food and feed crops might not be safe, which could possibly be due to high salinity and sodium adsorption ratio leading eventually to adverse impact on growth and yield of crops. Soils and crops irrigated with wastewater should closely be monitored for heavy metals deposition so that the human health problems could be avoided.