Attenuation photochemical potential of Pontal of Paranapanema river waters (Brazil) from agrochemicals: geographical and temporal assessment

Abstract

Knowledge of the environmental photochemical fate of pesticides is essential to assess their potential impacts. However, there are few studies in the literature focused on the photochemical attenuation of micropollutants in Brazilian rivers. In this context, this study characterized the surface waters of the Pontal of Paranapanema region (region which concentrates more than 80% of Brazilian sugarcane cultivations), in order to determine its photochemical attenuation potential against micropollutants in different seasons. Thus, the steady-state concentrations of the photochemically produced reactive intermediates (PPRIs) (hydroxyl radical, HO^•; singlet oxygen, ¹O₂, and triplet-excited state chromophoric dissolved organic matter, ³CDOM^*), formed in the rivers, were simulated by using the APEX model (Aquatic Photochemistry of Environmentally-occurring Xenobiotics), considering the sunlight irradiance, water chemistry, and depth. Based on our simulations, these concentrations vary between 0.35 × 10⁻¹⁵ and 4.52 × 10⁻¹⁴ mol L⁻¹ for HO^•, 1.3 × 10⁻¹⁵ and 1.2 × 10⁻⁻¹⁴ mol L⁻¹ for ³CDOM^*, and 2.5 × 10⁻¹⁵ and 2.5 × 10⁻¹⁴ mol L⁻¹ for ¹O₂. Finally, mathematical simulations were used for predicting persistence of pesticides atrazine (ATZ) and diuron (DIR) in Pontal of Paranapanema surface waters and the half-life times (t_1/2) of the pollutants ranged from a few hours to one week.