Development of an Ultrasound-Assisted Method for the Determination of Potentially Toxic Elements in Brazilian Water Hyacinth

Eichhornia crassipes (water hyacinth) is widely recognized for its ability to accumulate potentially toxic elements (PTEs), making it a species of interest for phytoremediation and environmental monitoring. This study aimed to develop, optimize, and validate an ultrasound-assisted acid decomposition method for the multielemental determination of Al, As, Cd, Cr, Cu, Ni, and Pb in water hyacinth by inductively coupled plasma optical emission spectrometry (ICP-OES). A factorial experimental design was employed to optimize the decomposition conditions with temperature identified as the only statistically significant factor. The optimized conditions consisted of 6 mL of HNO3, a decomposition time of 180 min, a temperature of 76.8 °C, and a sample mass of 250 mg. The method was validated using two certified reference materials and spike-recovery assays, yielding recoveries of 85–117% and 80–121%, respectively. Limits of detection and quantification ranged from 0.00002–0.00946 mg kg−1 and 0.00006–0.02838 mg kg−1, respectively. The applicability of the method was demonstrated using seasonal water hyacinth samples collected at two sites in the Salto Grande Reservoir, Brazil. Al, As, Cu, and Ni concentrations ranged from 0.483–7.84, 0.001–0.002, 0.011–0.036, and 0.003–0.022 mg kg−1, respectively, whereas Cd, Cr, and Pb were below their LODs Seasonal and spatial variations were observed, with higher concentrations of some elements occurring during autumn and winter. The proposed method provides a simple, low-cost, and lower-energy alternative to conventional decomposition procedures, with suitable analytical performance for multielemental determination of PTEs in water hyacinth.