Geographical and temporal assessment of the photochemical decontamination potential of river waters from agrochemicals: A first application to the Piedmont region (NW Italy)

Photodegradation potential of selected non-steroidal anti-inflammatory drugs in a middle-order Alpine river downstream of a wastewater treatment plant, during a year of enduring water scarcity

The year 2022 was characterised by significant water shortages and droughts in Italy, with the most pronounced impact observed in the North-Western regions, including Piemonte. In conditions of water scarcity, treated wastewater undergoes little dilution by natural flows and this can deeply affect the chemistry of water-poor rivers and streams. However, increased pollution by wastewater would be partially offset by fast photodegradation of pollutants in shallow water and by the longer time allowed to photochemical reactions if water flows more slowly. We assessed the latter phenomena in the Stura di Lanzo, a middle-order Alpine river tributary of the largest Italian river, the Po, and affected by a wastewater treatment plant (WWTP). In 2022, the concentration values of the photochemically significant parameters nitrate, nitrite, and DOC were usually higher downstream of the WWTP outlet, which could slightly favour indirect photodegradation reactions. Direct and indirect photodegradation was assessed for the non-steroidal anti-inflammatory drugs paracetamol, diclofenac, and naproxen, all undergoing rather fast photoreactions. Photochemistry model results show that the three compounds would undergo 10-40 % photodegradation in spring and summer along the stretch separating the wastewater outlet from the confluence of Stura into the Po. Photodegradation would continue in the latter, but other WWTPs might contribute additional pollution in the meanwhile. Albeit significant, photodegradation could only partially promote the elimination of the contaminants.

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

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 (t1/2) of the pollutants ranged from a few hours to one week.

New insights into the occurrence and removal of 36 pesticides in pesticide wastewater treatment plants in Korea

This study investigates the occurrence of 36 pesticides-including 33 that were monitored from 2007 to 2019 in Korean rivers-in wastewaters from pesticide manufacturing facilities (PMFs) and in 13 pesticide wastewater treatment plants (PWWTPs). Furthermore, an approach for the effective removal of these pesticides from pesticide wastewater (PW) is proposed. Among the 36 pesticides investigated, 32 were found to be present in the PMF wastewater and PWWTP influents (at concentrations ≤466.8 mg/L). In addition, 24 of the 36 pesticides were detected in PWWTP effluents, indicating that effluents are discharged without the complete removal of many pesticides. Moreover, the PWWTP effluent influences the presence of pesticides in river (confidence interval: ≥ 95%; p < 0.05). Although the chemical oxidation-activated sludge process is frequently recommended for the treatment of PWs, the findings from the current study indicate that an activated sludge-activated carbon adsorption process is more suitable for PW treatment due to its superior removal efficiency, treatment stability, and economic feasibility. Consequently, its application for the treatment of PWs can markedly decrease the levels of pesticides discharged into rivers.

Direct photolysis of contaminants in surface freshwaters, within the equivalent monochromatic wavelength (EMW) approximation

Abiotic photochemical reactions are usually very important degradation pathways for biorecalcitrant pollutants in surface freshwaters. Therefore, the assessment of photolytic lifetimes of contaminants helps estimate their impact on aquatic systems. This is commonly carried out by combining irradiation experiments and modelling, where the latter considers mathematical functions with polychromatic parameters, such as sunlight spectra, photolysis quantum yields (when Kasha's rule does not hold), and absorption coefficients. With the polychromatic approach, the photolytic lifetime is calculated by solving several integrals, which requires quite demanding modelling resources. In this work, we applied a recently developed approach, which is based on the equivalent monochromatic wavelength (EMW) approximation, to compute the direct-photolysis lifetimes of a range of >40 pollutants in inland waters. The EMW approximation allowed for easier modelling procedure, at the same time providing very good agreement with the polychromatic system. To further show EMW potentialities, lifetimes of three contaminants were mapped over the Piedmont region (NW Italy), as an example of how easy it becomes to geographically EMW-assess the potential of watercourses, to get photochemically decontaminated from pollutants.

Environmental photochemical fate of pesticides ametryn and imidacloprid in surface water (Paranapanema River, São Paulo, Brazil)

In addition to direct photolysis studies, in this work the second-order reaction rate constants of pesticides imidacloprid (IMD) and ametryn (AMT) with hydroxyl radicals (HO^●), singlet oxygen (¹O₂), and triplet excited states of chromophoric dissolved organic matter (³CDOM^*) were determined by kinetic competition under sunlight. IMD and AMT exhibited low photolysis quantum yields: (1.23 ± 0.07) × 10^-2 and (7.99 ± 1.61) × 10^-3 mol Einstein^-1, respectively. In contrast, reactions with HO^● radicals and ³CDOM* dominate their degradation, with ¹O₂ exhibiting rates three to five orders of magnitude lower. The values of k_IMD,HO● and k_AMT,HO● were (3.51 ± 0.06) × 10⁹ and (4.97 ± 0.37) × 10⁹ L mol^-1 s^-1, respectively, while different rate constants were obtained using anthraquinone-2-sulfonate (AQ2S) or 4-carboxybenzophenone (CBBP) as CDOM proxies. For IMD this difference was significant, with k_IMD,3AQ2S* = (1.02 ± 0.08) × 10⁹ L mol^-1 s^-1 and k_IMD,3CBBP* = (3.17 ± 0.14) × 10⁸ L mol^-1 s^-1; on the contrary, the values found for AMT are close, k_AMT,3AQ2S* = (8.13 ± 0.35) × 10⁸ L mol^-1 s^-1 and k_AMT,3CBBP* = (7.75 ± 0.80) × 10⁸ L mol^-1 s^-1. Based on these results, mathematical simulations performed with the APEX model for typical levels of water constituents (NO₃^-, NO₂^-, CO₃^2-, TOC, pH) indicate that the half-lives of these pesticides should vary between 24.1 and 18.8 days in the waters of the Paranapanema River (São Paulo, Brazil), which can therefore be impacted by intensive agricultural activity in the region.

Fluorophores in surface freshwaters: importance, likely structures, and possible impacts of climate change

Fluorescence spectroscopy is one of the most useful techniques currently available for the characterisation of organic matter in natural water samples, because it combines easy availability of instrumentation, high sensitivity and limited requirements for sample treatment. The main fluorophores that can be found in natural waters are usually proteins (and/or free amino acids) and humic substances (humic and fulvic acids). The identification of these fluorescent compounds in water samples helps to obtain information about, among others, biological activity in the water body, possible transport of organic matter from soil, and the phenomenon of photobleaching that decreases both the absorbance and (usually) the fluorescence of natural organic matter. Interestingly, all these phenomena can be affected by climate change, which could alter to different extents the ratio between aquagenic and pedogenic fluorophores. Several events induced by warming in natural waters (and especially lake water) could enhance algal growth, thereby also enhancing the production of aquagenic organic matter. Intense precipitation events could increase the export of pedogenic material to surface waters, while photobleaching would be enhanced in the epilimnion of lakes when summer stratification becomes longer and more stable because of higher temperatures. Interestingly, photobleaching affects humic substances to a higher extent compared to protein-like material, thus protein fluorescence signals could be more preserved in stratified waters.