Sanitary Problems and Trace Metals Bioaccumulation during Drip Irrigation with Treated Wastewater in Okra

Abstract

Water scarcity, mainly in arid and semi-arid zones, has encouraged efforts to adopt non-conventional waters for food production and agricultural development. Treated Wastewater (TWW) is one of the most continuously produced, accessible, and inexpensive water resources, with great potential for use in irrigation. The aim of this study was to investigate the combined effect of drip irrigation methods (surface vs. subsurface at 15 cm depth) and water quality (borehole water vs. treated wastewater) on soil water content, morphological and physiological traits, and nutrient content in the plant and fruit of okra grown in the Nabeul region of north-west Tunisia, a semi-arid zone. The results indicated that Okra yield was significantly affected by water quality rather than irrigation technique. Irrigation with TWW significantly increased the Okra plant height; leaf number; total fruit/m²; final yield and leaf area compared with borehole water. Nutrient levels (Fe, Cu, Zn, and Mn) in Okra plant parts (root, stem, leaf, and fruit) were also significantly increased with TWW in subsurface drip irrigation. Apart from these increased parameters were related to better soil moisture and increased available nutrients in the root zone. In terms of bioaccumulation, apart from Ni, the elements analyzed (Zn, Mn, Cu, Pb, Co, Cd) in plant and fruits showed higher values in treated wastewater than in borehole water with fruit values exceeding the toxicity threshold for Cd and Pb. Furthermore, the increase in the content of trace metal elements analyzed in the fruit following irrigation with TWW did not affect the human Health Risk Index (HRI), which remained below 1 for all treatments. Furthermore, with regard to bacterial and fungal contamination of fruit, we note that although these parameters are significantly higher in Irrigation with TWW, they remain below the toxicity thresholds. Thus, the long-term effect and continuous monitoring of the water and fruit quality in wastewater-irrigated areas to take remedial actions for sustainable agriculture development and protect ecosystems are recommended.