Effects of freshwater and seawater dissolved organic matter on the photodegradation of three antiviral drugs (2023)

Dissolved organic matter (DOM) is an essential component of environmental systems. It usually originates from two terminal members, including both allochthonous and indigenous sources. Previously, links were established between the origins/sources of DOM and their biogeochemical reactivities. However, the influence of end-limb mixing-induced changes on DOM characteristics on DOM biogeochemical reactivities has not been clarified. In this study, we investigated variations in DOM reactivity that respond to the dynamics of DOM characteristics induced by different mixing ratios of two DOM end-members derived from humic acid (HA) and algae, respectively. Four biogeochemical reactivities of DOM were evaluated, including biodegradation, ·OH production, photodegradation and redox capacity. The results showed that variations in DOM characteristics due to the mixing of the two end members have a significant impact on their biogeochemical reactivities. However, not all spectral parameters and reactivities followed the conservative mixing behavior. In contrast to the ·OH production and redox capacity reactivities, the mixed samples showed apparent deviations from conservative linear relationships in biodegradation and photodegradation due to the interaction between the two end members. Regarding the role of DOM properties influencing reactivity changes, the A and M peaks were recognized as the most stable parameters. However, peak C and SUVA₂₅₄were identified as the most important contributors to explaining variations in DOM reactivity. These findings suggest that no general model can be proposed to describe the dynamic relationship between source DOM and reactivity. Therefore, the dynamics of DOM reactivity in various ecosystems cannot be estimated simply by the "more or less" reactivity of an individual end member. The effect of end member mixing should be evaluated on a given reactivity rather than a generalization. This study provides important information for a greater understanding of the dynamics of the environmental role of DOM in different ecosystems influenced by variations in input sources. Going forward, more field investigations are needed to further verify our findings in this study, especially in the end-member mixing scenario.

Triplet excited states of dissolved organic matter (³DOM*) are one of the most important photochemically produced reactive intermediates, leading to the transformation of organic pollutants. However, the relationships of photodegradation kinetics of different dissociation states of organic phenolic contaminants with chemical components or properties of³DOM* are largely unknown. In this study, the roles of³DOM* was investigated in the photodegradation of polyhydroxyphenolic (Gs) genistein at pH 5, 8 and 12 taking five types of DOM from different sources as an example. Relationships were constructed between photodegradation kinetic constants and DOM properties. The results showed that the contributions of³DOM*-induced reactions for total indirect photobleaching of Gs and second-order reaction rate constants (k_DOM,Gs) of G com³DOM* increased with increasing pH. This was mainly attributed to the decrease in the vertical ionization energy of Gs at higher pH, endowing Gs with greater electron donating capacity.k_DOM,Gswas found to be positively correlated with the specific ultraviolet absorption at 254 nm, reflecting the aromaticity of DOM, and negatively correlated with the absorption ratio at 254 and 365 nm and the content of dissociated acid functional groups of DOM, representing the molecular weights of DOM , antioxidants and the repulsive forces between³SUN* and Gs. This study provided a new perspective on the relationship between MOD properties and indirect photodegradation kinetics of phenolic pollutants in aquatic environments.

Dissolved organic matter derived from microplastics (MP-DOM) is ubiquitous in the aquatic environment and exhibits photosensitivity. However, little is known about the effects of MP-DOM on the photodegradation of organic micropollutants in natural waters. In this study, we investigated the effect of MP-DOM derived from two typical plastics, namely polystyrene (PS) and polyethylene (PE), on the photodegradation of a typical organic micropollutant sulfamethoxazole (SMX) in a simulated natural water system. MP-DOM exerted significant inhibition on SMX photobleaching, mainly attributed to direct inhibition of SMX photolysis caused by inner filter effect and complexation effect. Despite improved generation of reactive oxygen species (ROS) with increasing its steady-state concentration by 41.1-160.7%, PS-DOM exhibited a high resistance to oxidation, which caused inhibition of SMX photobleaching probably via electron transfer to SMX intermediates. This study helps to deepen the understanding of the photochemical behavior of microplastics in natural water.

The photochemical behavior of a model PAH, naphthalene, was investigated under simulated solar irradiation with different dissolved organic matter (MOD) in seawater. The results revealed that naphthalene was prone to direct photolysis (Fi_d=1,34×10^-3) and can be degraded by³DOM*/¹O₂reactions induced with fulvic acid (FA) and humic acid (HA) at low concentrations. However, the DOM at high level drastically decreased thek_observationdue to higher light attenuation and radical competition effect. The presence of AF resulted in lower³DOM*/¹O₂generation and quantum yield compared to HA, but achieved higher degradation kinetics due to higher reactivity between³FA* and naphthalene and their lower binding effect. Naphthalene degradation in natural waters with different depths and MOD was modeled based on experimental results, which revealed the important role of indirect photolysis initiated by inorganic constituents. Furthermore, several degradation intermediates were identified by GC-MS and three possible pathways were proposed. Quantitative evaluation of structure-activity relationships (QSAR) revealed that some intermediates are more toxic than the original naphthalene. This study offers more information about the photochemical behavior of PAHs, which will facilitate our understanding of the persistence and ecological risks of organic contaminants in natural waters.

Untreated cattle manure contains high concentrations of dissolved organic matter (MOD), which can enter the environment through leaching and eluviation, having a significant impact on the environment. In this investigation, fresh chicken manure from a large-scale poultry farm was collected as a source of MOD. The infrared spectrum of the original DOM was characterized. TOC analysis, UV spectrum and 3D fluorescence spectrum were used to measure DOM properties before and after photobleaching. Infrared spectroscopy results show that chicken manure DOM may contain aliphatic and aromatic compounds, alcohols, phenols, polysaccharides and some protein substances; In three systems, the order of DOM TOC removal rates was water + UV system (85%) >> water system + simulated sunlight (7.2%) > ice system + simulated sunlight (4.5% ) ); Changes in UV spectra, fluorescence spectra, molecular weight distribution and pH value show that, in three systems, as the lighting time increased, photodegradation decreased the pH value of the systems, the aromaticity and the content of humus from the DOM, while increasing the proportion of medium and/or small molecular weight components from the DOM. The amounts of all these changes were proportional to the rates of DOM photobleaching in the system. The binding capacity of DOM with Cu²⁺and zinc²⁺in aqueous solution significantly decreased after photobleaching.

The presence of pharmaceuticals and personal care products in coastal waters has caused concern in the last decade. Sulfadiazine (SD) is a very common antibiotic widely used as a human and fisheries medicine, and dissolved organic matter (MOD) plays an important role in indirect photodegradation of DS; however, the influence of DOM compositions on indirect photobleaching of SD is poorly understood. In this study, the roles of reactive intermediates (RI) in the indirect photolysis of SD were evaluated. The reactive DOM triplet states (³DOM∗) played an important role, while HO y¹O₂played insignificant roles. DOM was divided into four components using excitation emission matrix spectroscopy combined with parallel factor analysis. The components included three allochthonous humic-like components and one indigenous humic-like component. Allochthonous humic-type components contributed more to the generation of IR and indirect photolysis of DS than the autochthonous humic-type component. A significant relationship was found between indirect SD photobleaching and the decay of fluorescent DOM components (correlation coefficient, 0.99), and the different indirect SD photobleaching in various DOM solutions can be attributed to the different DOM components. SD indirect photolysis rate first increased and then decreased with increasing pH. SD photolysis improved with low salinity but remained stable with high salinity. Increasing carbonate concentration inhibited SD photolysis, while nitrate had almost no effect in this study.

Total Environmental Science, Volume 709, 2020, Article 136243

Journal of Hazardous Materials, vol. 30-3

The effect of dissolved organic matter (MOD) fractions on the photodegradation of phenanthrene (PHE) in ice was investigated. DOM in surface water and wastewater samples was fractionated using XAD-8/XAD-4 resins into five fractions: hydrophobic acid (HPO-A), neutral hydrophobic (HPO-N), transphilic acid (TPI-A), transphilic neutral (TPI -N) and hydrophilic fraction (HPI). The photodegradation rate of PHE in ice was approximately 40% higher than in water. The detection effect and the extinction effect contributed 3-12% and 88-97% to the inhibition of MOD fractions in the photodegradation of PHE on ice, respectively. The singlet oxygen contribution ratios (¹O₂) and hydroxyl radical (OH) produced from DOM fractions at PHE photobleaching rates on ice were 9-31% and 2-13%, respectively. Among the five DOM fractions, HPO-A was the most efficient in advancing the photodegradation of PHE on ice through¹O₂mechanism. By excluding the photosensitizing effect of¹O₂yOH produced from DOM fractions, the quenching effect of DOM fractions on the photodegradation of PHE in ice was closely related to its binding capacity to PHE.

Water Research, Volume 179, 2020, Artigo 115885

DNA free bases are widely present in environments and can be used by bacteria for the synthesis of their nucleic acids or as sources of nutrition. In sunlit natural waters, these free bases would likely undergo photodegradation, which would alter the content of bioavailable bases. Although DNA photobleaching has been investigated, the photobleaching behaviors of free bases can be quite different from those of DNA-bound bases, given their different chemical environments. Here, the photodegradation of four free bases (guanine, adenine, thymine and cytosine) was investigated. The results show that the direct photodegradation of free bases in the phosphate buffer caused by UV rays was slow. However, the photodegradation of these free bases was greatly increased in the dissolved organic matter (MOD) solution. In the presence of 10-50 mg/L DOM, free base photobleaching rates increased 1.85-14.6-fold compared to controls without DOM. DOM can result in indirect photodegradation by the production of hydroxyl radicals (•OH) and singlet oxygen (¹O₂) under irradiation, and this indirect photobleaching enhanced and dominated the freebase photobleaching. •OH was involved in the photodegradation of the four bases, while the¹O₂participated only in the photodegradation of guanine. In the phosphate buffer, the bases that photodegraded most rapidly were pyrimidines, however, guanine became the most rapidly photodegradable base in the DOM solution due to the selective oxidation of guanine by¹O₂. In summary, DOM can be a determining factor for the photodegradation of free bases in natural waters and thus profoundly influence the fate of free bases in aquatic environments.

Chemosphere, Volume 242, 2020, Article 125200

Cyclic methylsiloxanes (CMS) have been listed as candidate substances of very high concern in 2018 by REACH. These compounds can enter ambient waters and potentially cause harmful effects to aquatic organisms and humans. So far, the reaction mechanisms of these pollutants with hydroxyl radicals (HO) in aqueous phase were unknown. In this study, the reaction mechanisms of three typical CMS (D4∼D6) with HOin aqueous phase were investigated using UV/H₂O₂experiments and functional theoretical calculations of density. Bimolecular reaction rate constants (k_A·) of D4∼D6 as HOwere determined ask_{HO (D4)}=8k_H·O·(D5)=12k_(D6)=6,6×10⁸Lmol⁻¹s⁻¹. HO half-livesD4∼D6 oxidation ranged from 12 to 140 days in [HO]=10⁻¹⁵dock⁻¹in sunlit surface waters, and were comparable to (D4, D5) or much shorter (D6) than hydrolytic half-lives. HO reactivitydecreased with increasing size of the siloxane ring in the aqueous phase, in a completely opposite order to that of the gas phase. The calculation results indicated that HOthe oxidation of the three CMS occurred spontaneously through an exothermic process of H abstraction in the first step. Water molecules participated in the extraction of H from CMS and caused a higher energy barrier of D5 than D4. Therefore, H bonds formed by water molecules were responsible for the inverse reactivity of CMS in the aqueous phase. This work provided basic evidence suggesting a completely different environmental persistence of CMS in the aqueous phase than in the gas phase.

Chemosphere, Volume 280, 2021, Article 130633

Dissolved organic matter (DOM) is ubiquitous in aquatic environments, whose behavior and fate are highly related to chemical compositions and size distribution. In this study, the UV-induced photobleaching properties of DOM with different origins (ie, derived from macrophytes and algae) were investigated using absorption and fluorescence spectroscopy, as well as flux field flux fractionation (FlFFF). The results showed that, regardless of the origin of the DOM, the chromophore components can be photodegraded more efficiently than the non-chromophores. Although the two DOMs were characterized with similar fluorophores, the photobleaching properties showed obvious heterogeneities in the origins and molecular weights (MW) of the DOMs. Compared to macrophyte-derived DOM (MDOM), algal-derived DOM (ADOM) exhibited a higher rate of degradation and efficiency due to the abundance of labile components such as newborn protein-like substances. The FlFFF results revealed a high photopreference of protein-like MDOM of 100 kDa-0.45 μm and the same photosensitivity of humic-like portions fractionated by size, demonstrating the reduction of molecular sizes during photodegradation. However, the increase in the relative percentage of 100 kDa protein-like components in 0.45 µm and 5 to 15 kDa humic-like residues implied a possible increase in ADOM molecular sizes during the initial period (i.e., the first hour) of photobleaching. This study provides new insights into origin-related heterogeneities in compositions and size distributions for DOM transformation.

Water Research, Volumen 112, 2017, págs. 120-128

In the present study, the formation of the triple states of organic matter (³ABOUT^∗) of effluent organic matter (EfOM) under simulated solar irradiation. EfOM was separated into hydrophobic (HPO), transphilic (TPI) and hydrophilic (HPI) components. The quantum efficiency coefficients (ƒ_TMP) of³ABOUT^∗were measured for each component and compared with those of the reference natural organic matter (MNO). NaBH₄reduction was performed on EfOM, and the effect of aromatic ketone residues on triplet formation was also determined. Furthermore, the apparent quantum yield of¹O₂(FI_1O2) EU₂^•−(FI_O2•−) has been scaled. Our results suggested that the HPI fraction acted as a sink for³ABOUT^∗. A linear correlation was observed between ƒ_TMPe F_1O2for NOM/EfOM, except for NaBH₄-Reduction of effluents and HPI components. Both ƒ_TMPe F_1O2were positively correlated with NaBH listing rates₄-reducible residues (aromatic ketones) to³ABOUT^∗. Aromatic ketones were primarily responsible for the production of³ABOUT^∗of EfOM, while quinone residues played a key role in the production of³ABOUT^∗in solutions enriched with NOM. Understanding the role of chemical components in EfOM/NOM photoactivity is essential to provide useful information about their photochemical effects in aquatic systems.