Photolysis of dinotefuran in aqueous solution: Kinetics, influencing factors and photodegradation mechanism

Photodegradation of Diquat in water under UV irradiation: Identification of transformation products and elucidation of photodegradation pathway

In aquatic settings, photodegradation is a significant non-biodegradation method of pesticide degradation. In this investigation, the photodegradation of the herbicide Diquat in aqueous solution was examined under distinct conditions and concentrations. The initial concentration of Diquat and the pH value of the water environment significantly affected the half-life of photodegradation of Diquat, and the opposite was true for different types of water. The photodegradation transformation products (PTPs) formed by the photodegradation of Diquat in an aqueous solution under UV-Vis irradiation were separated and identified using ultra-high-performance liquid chromatography coupled with time-of-fight mass spectrometry (UPLC-QTOF-MS). Based on mass spectral information, four main transition products were identified. Calculations of constituent composition, a comparison of structural analogs, and extant literature all contributed to the structure's determination. The main pathways of photodegradation were found to be oxidation, pyridine ring-opening, cleavage of [C-C] on the piperazine ring, Demethylation reaction and Hydroxylation. These results serve as a foundation for further environmental risk assessment and help explain how Diquat behaves in aquatic environments.

Photodegradation of typical psychotropic drugs in the aquatic environment: a critical review

Continuous consumption combined with incomplete removal during wastewater treatment means residues of psychotropic drugs (PDs), including antidepressants, antipsychotics, antiepileptics and illicit drugs, are continuously entering the aquatic environment, where they have the potential to affect non-target organisms. Photochemical transformation is an important aspect to consider when evaluating the environmental persistence of PDs, particularly for those present in sunlit surface waters. This review summarizes the latest research on the photodegradation of typical PDs under environmentally relevant conditions. According to the analysis results, four classes of PDs discussed in this paper are influenced by direct and indirect photolysis. Indirect photodegradation has been more extensively studied for antidepressants and antiepileptics compared to antipsychotics and illicit drugs. Particularly, the photosensitization process of dissolved organic materials (DOM) in natural waters has received significant research attention due to its ubiquity and specificity. The direct photolysis pathway plays a less significant role, but it is still relevant for most PDs discussed in this paper. The photodegradation rates and pathways of PDs are influenced by various water constituents and parameters such as DOM, nitrate and pH value. The contradictory results reported in some studies can be attributed to differences in experimental conditions. Based on this analysis of the existing literature, the review also identifies several key aspects that warrant further research on PD photodegradation. These results and recommendations contribute to a better understanding of the environmental role of water matrixes and provide important new insights into the photochemical fate of PDs in aquatic environments.

Photodegradation process and mechanism of 2,3,6-trichloronaphthalene on kaolinite surfaces under ultraviolet-A irradiation: Role of fulvic acid and density functional theory calculations

Polychlorinated naphthalenes (PCNs), a class of persistent organic pollutants (POPs), pose significant environmental and health risks, with trichloronaphthalene being a predominant congener in atmospheric particulate matter. This study investigates the photodegradation of 2,3,6-trichloronaphthalene (CN-26) on kaolinite surfaces under ultraviolet-A (UV-A) irradiation, focusing on the impact of fulvic acid (FA), temperature, humidity, and pH. The photodegradation mechanism of CN-26 was inferred via radical quenching experiments and density functional theory (DFT) calculations. The optimized degradation rate of CN-26 was 75.57 % at 25 °C, 70 % humidity, and pH 7 when FA was added at a concentration of 30 mg kg-1. Based on the radical quenching experiments, •OH are the primary active species involved in the degradation of CN-26, followed by electrons. In the absence of FA, •OH contributed 82.21 %, while electronic was 17.79 %. Conversely, in the presence of FA, the contribution rates of •OH, and electronic are 68.32 % and 21.21 % respectively. DFT calculations indicated that the 6 C site of CN-26 exhibited the highest susceptibility to radical attack, with the highest FED2HOMO+FED2LUMO value (0.25273), corroborated by averaged local ionization energy (ALIE) analysis. In the analysis of the reaction of •OH with CN-26, the lowest transition state ΔrG value of 1.09 kcal mol-1 was observed for compound 6 C, indicating that this site is the most susceptible to •OH attack. The degradation products of CN-26 were detected using gas chromatography-mass spectrometry (GC-MS), and the possible photodegradation pathways were proposed, which included dechlorination, hydroxylation, and aromatic ring opening. This study would provide insights into the photochemical behaviors of PCNs.

The association between estrogenic activity evolution and the formation of different products during the photochemical transformation of parabens in water

Photochemical transformation is a critical factor influencing the environmental fate of pharmaceutical and personal care products in aquatic ecosystems. However, the relationship between toxicity evolution and the formation of various transformation products has been seldom explored. This study investigates the behavior and changes in estrogenic activity during the photochemical transformation of a series of typical endocrine-disrupting parabens (PBs), focusing on the effects of increasing alkyl-chain length (MPB, EPB, PPB and BPB). Based on MS/MS analysis, four types of transformation products were identified: (1) p-hydroxybenzoic acid (HB), which exhibits no estrogenic activity; (2) hydroxylated products (OH-PBs); (3) dimer products formed between HB and PBs (HB-PBs); and (4) dimer products formed from identical PBs (PBs-PBs), comprising three distinct isomers. In the absence of standard sample, OH-PBs were synthesized and their estrogenic activity was evaluated using a yeast two-hybrid reporter assay. The EC50 values were determined to be <1 × 10-3 M for OH-MPB, 2.05 × 10-4 M for OH-EPB, 5.05 × 10-5 M for OH-PPB, and 1.89 × 10-5 M for OH-BPB. These indicate that the estrogenic activity of OH-PBs is one order of magnitude lower than that of the corresponding PBs. Both HB-PBs and the three isomers of PBs-PBs exhibited significantly higher estrogenic activities than their corresponding parent compounds, increasing 9 - 14 and 32 - 184 times, respectively, based on theoretical calculations. Among the three PBs-PBs isomers, the highest estrogenic activity was observed in the ether dimer, followed by the biphenyl dimers. Consistent with the parent compounds, the estrogenic activities of OH-PBs, HB-PBs, and PBs-PBs increased with the length of the alkyl-chain. The estrogenic activity of MPB and EPB followed an overall downward trend during the photochemical transformation, whereas PPB and BPB remained stable initially before declining rapidly. This behavior was associated with the contributions of toxic transformation products. These findings elucidate the relationship between molecular structure, transformation products, and estrogenic activity, highlighting the importance of understanding estrogenic activity evolution during the photochemical transformation of PBs.

Photodegradation of the novel herbicide pyraclonil in aqueous solution: Kinetics, identification of photoproducts, mechanism, and toxicity assessment

Pyraclonil is a new type of pyrazole herbicide, whose photochemical fate in aqueous solution has not been reported yet. In this study, effects on the photolysis rate such as light source, pH, NO3-, Fe3+, fulvic acid (FA) and riboflavin (RF) were investigated. Pyraclonil photodegraded in pure water under both UV and simulated sunlight with half-lives of 32.29 min and 42.52 h, respectively. Under UV, the degradation rate of pyraclonil in pH 4 solution (0.0299 ± 0.0033 min-1) was about twice higher than that in pH 9 (0.0160 ± 0.0063 min-1). Under simulated sunlight, low concentration (0.1-1 mg/L) of FA, NO3-, Fe3+ and RF noticeably promoted the photodegradation of pyraclonil. Then, with the combination of experimental UPLC-Q-TOF/MS and computational calculation of density functional theory (DFT), fourteen transformation products (TPs) of pyraclonil were identified with possible mechanism of C-N bond cleavage, photorearrangement, demethylation, hydroxylation and oxidation. Additionally, acute toxicity assessment was conducted through ECOSAR prediction and laboratory bioassays. The prediction results indicated that toxicity of TP157 to daphnid and green algae was 1.3 and 1.4 times higher than that of the parent, respectively. The bioassay results indicated that toxicities of TP157 and TP263 to C. vulgaris were about 1.6 and 5.9 times higher than that of the parent, respectively. The results provided a reference for elucidating the potential hazards of pyraclonil to non-target organisms and promoting its rational use.

Fabrication of zein-coated brush-like silica nanocarriers for high foliage deposition and responsive release of pesticide

Responsive release systems have received extensive attention to enhance pesticide utilization efficiency and reduce environmental pollution. In this study, pH/GSH dual responsive release system based on brush-like silica (bSiO2) carriers was constructed to enhance the utilization of pesticides. The bSiO2 carriers present core-shell structure, length of 550 nm, diameter of 350 nm and shell thickness of 100 nm. The carrier had a high pesticide loading (20.0 %, w/w) for dinotefuran (Din). After loading Din, zein was covalently linked with cysteine-bridge to seal the loaded pesticides (namely Din@bSiO2@Zein). The Din@bSiO2@Zein exhibited superior foliar affinity, retention and photostability, and retention rate still remain above 95 % with 220 min UV irradiation. Din@bSiO2@Zein displayed pH/GSH responsive release and the cumulative release within 92 h was up to 81 % under pH=9/CGSH=6 mM, mimicking the microenvironment of lepidopteran. The Din@bSiO2@Zein possessed good control efficacy against Plutella xylostella. Appreciably, Din@bSiO2@Zein could be transported bi-directionally to various regions of tobacco plants within 24 h, which had potential to promote pesticide efficacy. This work offers a strategy to minimize the pesticide dosage and encourage sustainable agricultural development.

Exploring the neurotoxicity of chiral dinotefuran towards nicotinic acetylcholine receptors: Enantioselective insights into species selectivity

Dinotefuran is a chiral neonicotinoid that is widely distributed in environmental matrices, but its health risks to different organisms are poorly understood. This study investigated the neurotoxic responses of honeybee/cotton aphid nicotinic acetylcholine receptors (nAChRs) to chiral dinotefuran at the enantiomeric scale and demonstrated the microscopic mechanism of species selectivity in nAChR-mediated enantioselective neurotoxicity. The findings indicated that (S)-dinotefuran had a higher affinity for honeybee nAChR than (R)-dinotefuran whereas both enantiomers exhibited similar bioactivity toward cotton aphid nAChR. The results of dynamic neurotoxic processes indicated the association of conformational changes induced by chiral dinotefuran with its macroscopic neurotoxicity, and (R)-dinotefuran, which exhibit low toxicity to honeybee, was found to induce significant conformational changes in the enantioselective neurotoxic reaction, as supported by the average root-mean-square fluctuation (0.35 nm). Energy decomposition results indicated that electrostatic contribution (ΔGele) is the critical energy term that leads to substantial enantioselectivity, and both Trp-51 (－2.57 kcal mol-1) and Arg-75 (－4.86 kcal mol-1), which form a hydrogen-bond network, are crucial residues in mediating the species selectivity for enantioselective neurotoxic responses. Clearly, this study provides experimental evidence for a comprehensive assessment of the health hazards of chiral dinotefuran.