Abstract

Freshwater scarcity under changing climatic conditions has increased the need to evaluate treated urban wastewater as an alternative irrigation resource in agricultural systems. This study investigated the interactive effects of irrigation water source and growing environment on plant growth, water use efficiency, photosynthetic pigments, biochemical traits, and heavy metal accumulation. A factorial experiment was conducted in a completely randomized design with five replications. The first factor consisted of two growing environments (greenhouse and open field), while the second included five irrigation water sources: well water as the control and 25%, 50%, 75%, and 100% urban wastewater. The interaction between growing environment and irrigation water source significantly affected water use efficiency, photosynthetic pigments, and all biochemical traits (P<0.01). The highest shoot dry weight (5.5 kg ha⁻¹) was obtained in the greenhouse, while the greatest vegetative biomass was recorded under 100% wastewater irrigation, which may be associated with the nutrient-supplying effect of wastewater. The highest total chlorophyll content (0.89 mg kg⁻¹) was observed under 100% wastewater in the greenhouse, whereas the highest essential oil content (498 mg kg-1) and flavonoid content were obtained with 75% wastewater in the open field; 100% wastewater reduced essential oil yield. Although lead and cadmium accumulation increased with increasing wastewater proportion, their concentrations under 100% wastewater remained below the WHO permissible limits (4.5 and 0.13 mg kg⁻¹, respectively). Overall, 75% urban wastewater irrigation under open-field conditions provided a more suitable balance between essential oil production and freshwater conservation, although continuous monitoring of heavy metal accumulation is necessary for long-term wastewater reuse.