44ª Reunião Anual Virtual da SBQ

Batch sorption experiments were conducted to evaluate the interaction of polyamide microplastics (~106 µm) with the atrazine herbicide and hormones (progesterone and testosterone). Two different approaches were used to assess sorption, one with contaminants in seawater (SW), collected from Guarujá beach, and the other in freshwater (FW), collected from Ribeirão das Pedras source. Kinetic experiments were conducted with the contaminant solutions in water (1 mg L-1) and 20 mg of microplastics. Sorption times of 0 h, 0.5 h, 1 h, 2 h, 3 h, 6 h, 12 h, 24 h, 48 h, 72 h, 96 h, and 108 h were evaluated. Contaminant solutions and microplastics were mixed into a glass tube and placed on an orbital shaker at 19 °C and 80 rpm. After the sorption times, 1 mL of the supernatant was filtered through a 0.22 µm syringe filter and analyzed by liquid chromatography coupled to a mass spectrometer in tandem (LC-MS/MS). Sorption isotherms (Langmuir and Freundlich) were performed with contaminant solutions set as 0.01, 0.05, 0.1, 0.2, 0.5, 1.0, and 2.0 mg L-1. All experiments were performed in triplicate. Pseudo first order and pseudo second order kinetic models were applied for the three contaminants. Experimental concentration sorbed on microplastics in SW at equilibrium (qe), in mg g-1, was 0.028, 0.054, and 0.087 for atrazine, testosterone, and progesterone, respectively. Similar qe were observed in FW, 0.021, 0.058, and 0.086 for these same three compounds, respectively. Theoretical qe and constants of kinetic models (k1 and k2) were obtained using these two approaches. The experimental data fitted better to the Langmuir model for both experiments (R2 > 0.93), indicating that the microplastic surface is homogeneous and the adsorption occurs on the microplastic outer surface. Sorption efficiency of about 20% was obtained for atrazine (Figure 1 – red data), which can be associated with a lower octanol-water coefficient when compared to other compounds. On the other hand, high sorption efficiencies were observed for testosterone, ranged from 40% to 70% (Figure 1 – green data), and progesterone, higher than 80% (Figure 1 – blue data). A slight increase in sorption efficiencies (about 6%) was observed in the SW experiment, for all contaminants in seven different concentrations. The SW salinity was more than 110 times higher than FW, thus salinity may change the aqueous solubility of compounds allowing their sorption in solid phases.