Blastofiltration of Copper by Sunflower (Helianthus annuus) Seedlings: Rapid Removal, Hormetic Growth, and a Dose-Dependent Desorption Limit

Copper water contamination is a persistent environmental and public health problem, and conventional treatment methods are often expensive and generate secondary waste. Blastofiltration represents the use of germinating seedlings to filter contaminants from the water and offers an environmentally friendly and low-cost alternative. The present study evaluated Helianthus annuus (sunflower) seedlings for the removal of copper from synthetic aqueous solutions, on a wide gradient of concentrations. The seedlings were exposed for 48 h to six nominal concentrations of Cu2+ (0.5; 1; 2; 4; 6 and 8 mg/L), together with two distilled-water control samples (growth) and abiotic controls, without plants. Copper was photometrically determined at nine time intervals, and biomass and morphometric parameters were recorded at 48 h. The plant-free controls, one for each tested concentration, remained essentially constant near their initial values, suggesting that copper removal was plant-mediated, not due to abiotic processes. All planted variants showed rapid aqueous removal, reaching a minimum of around 6–12 h, with maximum removal efficiencies of 88–99%; lower concentrations (0.5–2 mg/L) fell below the limit of quantification in 6–8 h. After reaching the minimum, copper partially returned to solution in a clearly dose-dependent desorption phase, most pronounced at 8 mg/L (residue increasing from 0.9 mg/L at 12 h to 2.8 mg/L at 48 h). The total dry biomass followed a hormesis pattern, increasing compared to the control at ≤4 mg/L, but decreasing by 28–32% to 6–8 mg/L. These results indicate that sunflower seedlings represent a potential efficient blastofiltration agent for low to moderate copper contamination, while showing a toxicity-induced desorption limit, which restricts performance and contact time to higher concentrations.