Balancing Nutrient Enrichment and Heavy Metal Stress: Impacts of Wastewater Irrigation on Aromatic Crops.

The increasing demand for irrigation water, together with declining freshwater availability, has intensified interest in wastewater reuse in agriculture. Although wastewater may enhance plant growth because of its nutrient and mineral content, it can also contain salts and heavy metals that may alter plant biochemical quality and raise safety concerns. This study evaluated the morphological, physiological, phytochemical, and antioxidant responses of three aromatic plants-Mentha arvensis, Coriandrum sativum, and Trigonella foenum-graecum-to two irrigation treatments under pot conditions: T0 (distilled water, control) and T1 (100% untreated wastewater). Plant height, selected morphological traits, chlorophyll content, qualitative phytochemical characteristics, antioxidant activity (DPPH assay), and wastewater chemical composition were assessed. Wastewater irrigation promoted vegetative growth in all three species. Plant height increased by 51% in C. sativum (43 to 65 cm), 32% in M. arvensis (68 to 90 cm), and 36% in T. foenum-graecum (33 to 45 cm) under T1 compared with T0. Total chlorophyll increased in C. sativum (96.0 to 111.7 mg/g) and M. arvensis (45.2 to 49.9 mg/g), while it remained nearly unchanged in T. foenum-graecum (110.2 to 109.9 mg/g). In contrast, antioxidant activity generally declined under wastewater irrigation, particularly in the leaves of C. sativum (1.30 to 0.76 mg/mL) and T. foenum-graecum (2.90 to 2.10 mg/mL), with a slight reduction in M. arvensis leaves (1.60 to 1.50 mg/mL). Qualitative phytochemical screening also indicated treatment-related changes in the distribution of secondary metabolites across plant organs. Wastewater analysis showed the presence of nutrient-related constituents alongside potentially toxic elements, including Pb, Ni, and Cd. Overall, untreated wastewater improved short-term growth performance, but it was also associated with altered biochemical responses that may affect crop quality. These findings suggest that wastewater reuse in aromatic crop production should be approached cautiously and supported by treatment, monitoring, and long-term assessment of soil and crop safety.