The effect of irrigation with treated and untreated wastewater on the yield and chemical composition of essential oil of Mentha spicata L. and Rosmarinus officinalis L.

Abstract

Today, the lack of quality water supply has led to the tendency to use unconventional water to irrigate agricultural products. Considering the importance and application of essential oils of mint plants in various pharmaceutical, food, and health industries and also considering the approach of using unconventional waters in the cultivation of medicinal plants, the present study aimed to investigate and compare the chemical composition of essential oils of two species of Mentha spicata L. and Rosmarinus officinalis L. which was designed and implemented for the first time under the influence of different treatments of municipal and industrial wastewater. For this purpose, first R. officinalis cuttings and roots of M. spicata were prepared and after preparing and leveling the ground, in the spring of 2020, it was transferred to the planting site and planted in the form of creek and ridges. The treatments studied in this study included well water (WW), treated municipal wastewater (TMW), untreated municipal wastewater (UMW), treated industrial wastewater (TIW), and untreated industrial wastewater (UIW) in a randomized complete block design with four repeat runs. After watering the plants continuously for 3 months, the plant branches were collected and transferred to the laboratory for drying. After extracting the essential oil by water distillation (Clevenger) method, the analysis and identification of the compounds were performed by a chromatograph coupled with a mass spectrometer (GC/MS). The results showed that the highest and lowest yields of M. spicata belonged to the samples treated with UMW and WW, respectively. Also, R. officinalis essential oil irrigated with UMW and UIW had the highest and lowest yields, respectively. The number of essential oil compounds in of M. spicata was between 5 and 19 and in R. officinalis between 14 and 23 under different treatments. The results of the analysis of essential oil compounds showed that d-carvone (57.77–57.44%) and d-limonene (8.70–26.65%) for M. spicata and α-pinene (26.12–34.85%), 1,8-cineole (18.95–23.70%), and camphene (9.93–12.80%) for R. officinalis were predominant compounds in all studied treatments. The results show that UMW is a suitable and efficient treatment to have the best quantity of M. spicata essential oil and the best quality and quantity of R. officinalis essential oil.