Nutrients, Metals, and Carbon in Soils Irrigated With Treated Versus Untreated Wastewater

Background Reuse of wastewater for irrigation can mitigate pressure on water resources and support closing nutrient cycles in an agriculture–sanitary economy but is associated with health and environmental risks, which can be mitigated by wastewater treatment. Aim This study investigates the effects of water treatment on soluble metals, nutrients, and organic carbon (C org ) in an incubation experiment with soils, long‐term irrigated with untreated wastewater. Methods Leptosol, Phaeozem, and Vertisol topsoils were mixed with either wastewater treatment plant (WWTP) influent (unspiked or spiked with antibiotics and disinfectants) or WWTP effluent (unspiked or spiked). Results WWTP effluent contained less total C org , N, and P than influent. Soil type significantly influenced almost all analyzed parameters, including soil pH and contents of water‐extractable C org , nutrients (N, P, and S), and metals, except for Na. Irrigation with WWTP effluent instead of influent reduced the availability of N and ortho ‐P in soils but increased soluble concentrations of Cr, Fe, Mn, Na, and Ni. Conclusion This indicates that treatment of wastewater used for irrigation bears the risks of decreasing nutrient availability in soils and mobilization of metals, including previously accumulated trace metals. Further, considering soil properties is essential for assessing the effects of water treatment on soil nutrients, carbon, and metals.