Nano-Selenium-Mediated Alleviation of Chromium Toxicity and Selenium Biofortification of Ipomoea aquatica Forssk. in Cyclic Hydroponic System

Chromium (Cr) contamination poses a serious threat to agricultural productivity and food safety, yet effective strategies for mitigating Cr toxicity under practical cultivation conditions remain limited. In this study, green-synthesized selenium nanoparticles (SeNPs), prepared from banana peel extract (average particle size: 112.9 nm), were evaluated against conventional sodium selenite (Na2SeO3) for alleviating Cr(VI) toxicity in Ipomoea aquatica Forssk. grown in a dynamic cyclic hydroponic system. Plants were exposed to 20 mg L−1 Cr(VI) and treated with SeNPs or Na2SeO3 at 1 and 10 mg L−1, respectively, for a duration of one week. Green-synthesized SeNPs exhibited excellent colloidal stability (zeta potential: −35.5 mV) and an amorphous spherical morphology. Relative to the Cr-only treatment, 10 mg L−1 SeNPs almost completely restored plant biomass and root growth, decreased shoot Cr accumulation by 62.2%, and recovered total chlorophyll content to 94.8% of the control level. By comparison, 10 mg L−1 Na2SeO3 restored total chlorophyll to 74.2% of the control and reduced shoot Cr accumulation by 50.6%. SeNPs also elicited a stronger antioxidant response, markedly increasing SOD, POD, and CAT activities while significantly lowering H2O2, MDA, and proline levels, demonstrating a greater capacity than selenite to alleviate Cr-induced oxidative damage. SeNPs also restored the uptake of essential mineral nutrients (N, P, K, Ca, and Mg), improved soluble sugar and protein contents, and promoted selenium biofortification in edible shoots. Although both selenium forms alleviated Cr-induced growth inhibition and oxidative damage, SeNPs consistently outperformed Na2SeO3 owing to their higher bioavailability and sustained physiological activity. Overall, this study demonstrates that green-synthesized SeNPs provide an efficient and sustainable strategy for reducing Cr accumulation while simultaneously improving crop growth, antioxidant capacity, and nutritional quality under agriculturally relevant hydroponic conditions, highlighting their potential for safer food production and agricultural waste valorization.