Phytoremediation potential of <i>Calendula officinalis</i> L. and <i>Verbena hybrida</i> for chromium detoxification in tannery wastewater

A b s t r a c t. Chromium (Cr) contamination from tannery wastewater (TWW) poses significant environmental and health risks particularly in regions where untreated wastewater is commonly used for irrigation.This study explores the potential of ornamental plants, Calendula officinalis L. and Verbena hybrida, as promising species for Cr remediation.A completely randomized pot experiment with different TWW concentrations (0, 25, 50, 75, 100%) with and without 5 mM citric acid (CA) was conducted.Seedlings were treated twice weekly with TWW for one month.Increasing the TWW concentration reduced growth parameters, such as shoot and root length, leaf number, and biomass, with the greatest decline at 100% TWW.Photosynthetic pigments decreased, while malondialdehyde, hydrogen peroxide, and proline levels increased.Antioxidant enzyme activities peaked at 50% TWW with CA.The highest Cr accumulation occurred at 100% TWW with CA, with C. officinalis L. accumulating 3633 mg kg -1 in roots and 2780 mg kg -1 in shoots, and V. hybrida accumulating 2965 mg kg -1 in roots and 3673 mg kg -1 in shoots.C. officinalis L. was identified as Cr-tolerant (translocation factor < 1), whereas V. hybrida served as a Cr-phytoextractor (bioconcentration and translocation factors > 1).These findings underscore the potential of these plants for sustainable Cr remediation in contaminated environments.K e y w o r d s: wastewater, chromium, citric acid, phytoextraction, phytostabilization Ta b l e 1. Physicochemical parameters of wastewater utilized for irrigation Parameter Value pH 3.27 EC 4 000 S cm -1 COD 2 799 mg L -1 BOD 885 mg L -1 TDS 3 200 ppm