Influence of wastewater irrigation on soil chemical properties and buildup of heavy metals in soil

The contamination of soil and plants by heavy metals is one of the crucial issues to be faced in the world including Pakistan and requires attention because heavy metals above their normal ranges are highly threatened to both plants and animals. To monitor this situation, a survey study was conducted to diagnose the concentration of toxic metals and other chemical properties of wastewater irrigated soils. For this purpose, soil samples were collected from various districts of Punjab, Pakistan and analyzed for heavy metals (cadmium, lead, chromium, nickel) and chemical properties such as electric conductivity, pH, organic matter and macronutrients (Nitrogen, Phosphorus, Potassium and Sodium contents). Result showed that pH of wastewater irrigated surface soil was alkaline in nature. Results also revealed that use of wastewater irrigation improved the O.M content (upto 2%) in soils. Macronutrient dynamics also increased specially build up in total N up to 0.12%, Olsen P (45 mg kg(-1)), Extractable K and Na (608, 1525 mg kg(-1) respectively) was also observed in soils of wastewater irrigated areas. Furthermore, results also indicated that the concentration of heavy metal, cadmium was ranged from 0.004-3.44 mg kg(-1), lead 0.05-279.3 mg kg(-1), chromium 0.004-683 mg kg(-1) and nickel 0.01-221.7 mg kg(-1) in wastewater irrigated areas of Punjab. It was observed that, 28, 19, 15 and 5% samples were found above the permissible limits (35, 100, 0.8 and 85 mg kg(-1)) of Ni, Cr, Cd and Pb, respectively. Based on the results, the order of heavy metal contamination in the wastewater irrigated soil of Punjab occurred as Ni>Cr>Cd>Pb. This study concluded that untreated wastewater affect chemical properties of soil as well as degrades soil quality and at the same time it's continues use ultimately responsible for buildup of heavy metals in soils.