Effect of counterions on Cr(III) removal: A novel approach in phytoremediation to enhance removal efficiency

Background Chromium (Cr) is a significant environmental pollutant, particularly in wastewater containing Cr(III) ions and various anions. Objective This study investigates the effects of different anions and their concentrations on Cr(III) removal using three macrophytes: Eichhornia crassipes , Pistia stratiotes , and Salvinia molesta . Methodology Young plantlets were exposed to Cr(III) salt solutions, and Cr(III) removal was measured after 1, 2, 5, and 10 days. The concentrations of Cr(III) and counter-ions were quantified using Atomic Absorption Spectrophotometry and Suppressed Ion Chromatography. Results Results showed that Cr(III) removal was highest with acetate, with values of 3.15, 3.08, and 0.73 mg g⁻¹ for the three species, respectively. The lowest removal occurred with fluorides (0.33, 0.45, and 0.42 mg g⁻¹). Cr(III) removal varied by species, and counter-ion combinations were less effective than single-ion solutions. Conclusion and novelty P. stratiotes was the most efficient at removing Cr(III). This study is the first to evaluate the impact of counter-ions on metal removal by macrophytes. Importantly, this study is the first to demonstrate that the type of counter-ion plays a critical role in Cr(III) uptake by macrophytes , highlighting acetate as the most favorable anion for enhanced metal removal. These findings provide new insights into optimizing phytoremediation strategies for Cr-contaminated wastewater.