Effect of Irrigation with Secondary Treated Effluent on Essential Oil, Antioxidant Activity, and Phenolic Compounds in Oregano and Rosemary

Shortage of water throughout the world dictates utilization of marginal water for irrigation. Treated urban wastewater is a common alternative water source for irrigation in arid and semiarid regions. In this study we aimed to evaluate the effect of irrigation with secondary-treated effluent on plant development, essential oil yield, antioxidant activity and selected antioxidant phenolic compounds in two commercial cultivars of the aromatic species, oregano (Origanum vulgare L.) and rosemary (Rosmarinus officinalis L.). The applied treated effluent contained higher levels of Na, Cl, HCO3-1, P, K, NH4+1, NO3-1, Ca+Mg, B, Mn, and Fe than the local potable water used as control, and were characterized by higher values of electrical conductivity (EC), pH, and sodium absorption ratio (SAR). Since effluent effects on plants can become apparent only following several years of exposure, the plants were exposed to the water treatments for 3 yr. Despite the differences in water quality, the effluent did not affect yield quantity and quality in either crop. Plant morphological development, biomass production, percent dry leaves of the total biomass, quantity and composition of the essential oil produced, antioxidant activity, and contents of selected antioxidant-phenolic compounds were not affected by irrigation with treated effluent compared with potable water. Our results demonstrate that both oregano and rosemary are suitable as industrial crops for essential oil and antioxidant production under irrigation with secondary-treated municipal effluent because their yield quantity and quality were not affected.