Effect of Water Stress and Urban Wastewater on the Heavy Metals Concentration, Yield and Quality of Basil

Confronting the crisis of water scarcity and the looming challenge of dwindling water resources is undeniably a grave concern. Consequently, the focus of agricultural science researchers has shifted towards the utilization of wastewater. One of the notable advantages of incorporating wastewater in agriculture is the potential to curtail the expenses associated with procuring irrigation water and employing chemical fertilizers.
 
Sari has a longitude and latitude of 53°01′ E and 36°33′ N, respectively, and its weather conditions are humid according to De-marten's climate classification. Its elevation is 21 above sea level and average annual temperature and precipitation, are17.9 ºC and 650 mm, respectively). In order to evaluate the effect of water stress and urban wastewater on the concentration of heavy metals, yield and some characteristics of basil, an experiment in a factorial format based on a completely randomized design with experimental treatments including; The first factor is the source of irrigation (I): [treated wastewater (TWW) and well water (WW)], and the second factor is water stress (S): [the lowest stress (S1, S2), medium stress (S3, S4) and severe stress (S5, S6)] were performed in three replications at the research farm of Sari University of Agricultural Sciences and Natural Resources (SANRU), Iran. Finally, the obtained data were analyzed using ANOVA of SAS9.2, and the SNK post hoc test was employed to compare treatment means.
 
Based on the findings, Irrigation with wastewater increased plant height, stem diameter, fresh and dry weight compared to irrigation with well water. So that the highest plant height, stem diameter, wet and dry weight were related to irrigation with wastewater with 44.3 cm, 3.1 mm, 8.5 and 3.3 g, respectively. Also, the effect of using treated wastewater on chlorophyll a, chlorophyll b, total chlorophyll and carotenoids was significant (P ≤ 0.01). while it did not have significant effect on flavonoid, phenol and antioxidant activity. In the lowest stress, especially the S1 level, the amount of chlorophyll a, chlorophyll b, total chlorophyll, carotenoid, flavonoid, phenol and antioxidant activity compared to the S6 level decreased by 63.3, 32.8, 40.7, 45.8, 46.3, 55.5, and 9.8%, respectively. while the highest amount of plant height, fresh weight, dry weight and stem diameter at the S1 level was observed with 48.6 cm, 11.5 g, 3.51 g and 3.4 mm, respectively. The result shown that the Pb and Cd concentration in basil under irrigation with wastewater was 3.4 and 2.5 mg.kg-1, respectively, which increased by 13 and 9% compared to well water. Water stress affected the Pb and Cd concentration, but the Cr and Ni concentration did not change significantly. The highest Pb and Cd concentration was related to high stress level S5 and medium stress level S4 and the lowest level was observed in the lowest stress levels (S1 and S2). Also, the results showed that the Pb and Cd concentration was affected by the interaction effect of irrigation source and water stress. Thus, the highest Pb concentration was observed in irrigation with wastewater and water stress levels S4 and S5 with 3.41 and 3.40 mg.kg-1, respectively, and the lowest was related to irrigation with well water and water stress level S1 with 2.2 mg.kg-1. The highest Cd concentration was related to irrigation with wastewater and stress levels S4 and S5 with 2.6 and 2.5 mg/kg, respectively, and the lowest amount were observed in well water irrigation and stress levels S1 and S2, with 1.51 and 1.50 mg.kg-1, respectively. while the Cr and Ni concentrations did not significant.
 
Based on the findings of this research, irrigation with treated wastewater and application of water stress had significant effect on the morphological and phytochemical characteristics of basil. while the use of treated wastewater was ineffective on the biochemical characteristics of basil and only water stress conditions affected their levels. The Pb and Cd concentration in basil increased under the influence of irrigation with wastewater and water stress levels. But this increase was lower than the standards authorized reported by the researchers and did not cause much concern. the results shown that the water stress levels S4 and S5 can be considered appropriate in water efficiency and recommend the use of treated wastewater in basil irrigation considering the authorized standards.