Effect of irrigation with wastewater on soil and plant pollution with some heavy metals according to international pollution standards

Abstract

To determine the effect of irrigation with wastewater on soil and plant contamination with some heavy metals, according to international pollution standards, a pot experiment was conducted in a field belonging to the Karbala Governorate sewage treatment plant using soil with a silty, mixed texture. A completely randomized design (CRD) was used with two types of irrigation water (sewage and tap water) and six replicates. Maize seeds of Sumer variety were planted at a rate of 5 seeds per pot, thinned to three seeds per pot after 15 days of planting. The experiment continued until appearance of male inflorescences. Soil and plant samples were taken after the end of experiment. The results showed the following: Total heavy metals concentration in soil increased compared to its counterpart in soil irrigated with tap water, reaching 3396.10, 16.13, 16.98, 0.68, 15.59, 20.33, 89.00, 13.15, and 98.23 mg kg^-1 for heavy metals Iron, Zinc, Copper, Vanadium, Cadmium, Lead, Nickel, Manganese, Cobalt, and Chromium, respectively. Concentration of heavy metals in tissues of Maize plants increased, reaching 20.30, 20.58, 5.00, 4.63, 2.16, 1.20, 6.55, 10.77, 4.91 and 10.73 mg kg^-1 dry matter for above heavy metals, respectively. High values ​​of pollution factor for heavy metals in soil reached 1.106, 1.015, 1.166, 1.110, 1.545, 1.111, 1.110, 5.350, 1.214, and 8.724 for heavy metals Zinc, Iron, Copper, Vanadium, Cadmium, Lead, Nickel, manganese, Ccobalt, and Chromium, respectively, which indicates the presence of medium pollution. As for Environmental Hazard Index (EHI) for heavy metals, values ​​decreased for all elements except Cadmium. Meanwhile, contamination degree (Cdeg) values ​​for soil irrigated with wastewater increased to 23.451, which falls within range of high contamination. Bioconcentration factor (BCF) values ​​for Zinc and Cadmium increased above one, it reached 1.275 and 3.176, respectively, indicating the movement and transfer of these two elements from soil to plant. The remaining elements had coefficient values ​​less than one, making them slow-moving and slow-transferring elements from soil to plant.