Elevated Temperatures Decrease the Photodegradation Rate of Pyrethroid Insecticides on Spinach Leaves: Implications for the Effect of Climate Warming

The Chemical Landscape of Leaf Surfaces and Its Interaction with the Atmosphere

Atmospheric chemists have historically treated leaves as inert surfaces that merely emit volatile hydrocarbons. However, a growing body of evidence suggests that leaves are ubiquitous substrates for multiphase reactions-implying the presence of chemicals on their surfaces. This Review provides an overview of the chemistry and reactivity of the leaf surface's "chemical landscape", the dynamic ensemble of compounds covering plant leaves. We classified chemicals as endogenous (originating from the plant and its biome) or exogenous (delivered from the environment), highlighting the biological, geographical, and meteorological factors driving their contributions. Based on available data, we predicted ≫2 μg cm-2 of organics on a typical leaf, leading to a global estimate of ≫3 Tg for multiphase reactions. Our work also highlighted three major knowledge gaps: (i) the overlooked role of ambient water in enabling the leaching of endogenous substances and mediating aqueous chemistry; (ii) the importance of phyllosphere biofilms in shaping leaf surface chemistry and reactivity; (iii) the paucity of studies on the multiphase reactivity of atmospheric oxidants with leaf-adsorbed chemicals. Although biased toward available data, we hope this Review will spark a renewed interest in the leaf surface's chemical landscape and encourage multidisciplinary collaborations to move the field forward.

Mechanistic insight into the impact of interaction between goethite and humic acid on the photooxidation and photoreduction of bifenthrin

Numerous application of pyrethroid insecticides has led to their accumulation in the environment, threatening ecological environment and human health. Its fate in the presence of iron-bearing minerals and natural organic matter under light irradiation is still unknown. We found that goethite (Gt) and humic acid (HA) could improve the photodegradation of bifenthrin (BF) in proper concentration under light irradiation. The interaction between Gt and HA may further enhance BF degradation. On one hand, the adsorption of HA on Gt may decrease the photocatalytic activity of HA through decreasing HA content in solution and sequestering the functional groups related with the production of reactive species. On the other hand, HA could improve the photocatalytic activity of Gt through extending light absorption, lowing of bandgap energy, hindering the recombination of photo-generated charges, and promoting the oxidation and reduction reaction on Gt surface. The increased oxygen vacancies on Gt surface along with the reduction of trivalent iron and the nucleophilic attack of hole to surface hydroxyl group contributed to the increasing photocatalytic activity of Gt. Electron paramagnetic resonance and quenching studies demonstrated that both oxidation species, such as hydroxyl radical (•OH) and singlet oxygen (1O2), and reducing species, such as hydrogen atoms (H•) and superoxide anion radical (O2•-), contributed to BF degradation in UV-Gt-HA system. Mass spectrometry, ion chromatography, and toxicity assessment indicated that less toxic C23H22ClF3O3 (OH-BF), C9H10ClF3O (TFP), C14H14O2 (OH-MBP), C14H12O2 (MBP acid), C14H12O3 (OH-MBP acid), and chloride ions were the main degradation products. The production of OH-BF, MPB, and TFP acid through oxidation and the production of MPB and TFP via reduction were the two primary pathways of BF degradation.

Fate characteristics and risk identification of thifluzamide in buckwheat across China: Analytical method development, occurrence, and health assessment

Elaborating on the fate tendency of thifluzamide (thiazole-amide fungicide) in buckwheat based on nationwide application is vital for grain security and human health based on nationwide application. A rapid and sensitive analytical method was developed to trace thifluzamide in buckwheat matrices using an ultrahigh-performance liquid chromatography-tandem triple quadrupole mass spectrometer (UHPLC-MS/MS), with a retention time of 2.90 min and limit of quantitation (LOQ) of 0.001 mg/kg. Thifluzamide could be stably stored for 84 d in buckwheat matrices under -20 °C under dark condition. The occurrence, dissipation and terminal magnitudes of thifluzamide were reflected by the primary deposition of 0.02-0.55 mg/kg, half-lives of 12-14 d, and highest residues of 0.41 mg/kg. The long-term risks (ADI%) of thifluzamide were 37.268 %-131.658 % in registered crops, and the risks for the rural population were significantly higher than those of the urban population. The unacceptable dietary risks of thifluzamide should be continuously emphasized for children aged 2-7 with an ADI% values of 100.750 %-131.658 %. A probabilistic model was further introduced to evaluate the risk discrepancy of thifluzamide in buckwheat, showing the risks in Tartary buckwheat (Fagopyrum tararicum Gaerth) were 1.5-75.4 times than that in sweet buckwheat (Fagopyrum esculentum Moench). Despite the low risks for dietary buckwheat, the high-potential health hazards of thifluzamide should be pay more attention given the increasing applications and cumulative effects.

Photodegradation of the pure and formulated scoparone in liquid solutions: kinetics and mechanism

Scoparone (hereafter SPR) is a prominent candidate of plant-derived acaricide. The photodegradation of the pure SPR was first investigated under different light sources, initial concentrations, pH values, temperatures, organic solvents, aqueous media, and the photolytic characteristics of its formulation in pure water were also studied. The photodegradation rates of pure SPR under different light sources showed the following sequence: 28 W ultraviolet lamp (0.3045 h-1) > 500 W xenon lamp (0.1094 h-1) > 300 W xenon lamp (0.0312 h-1). Under the irradiation of 500 W xenon lamp, the lower initial SPR concentrations, higher pH value, and higher temperatures increased the photodegradation rates of SPR, especially, when the temperature increased higher than 35℃, the degradation rate of SPR increased slowly and maintained at a stable level, the pH and temperatures had small effects on the photodegradation of SPR. The photodegradation rates of pure SPR in organic decreased comparing to in aqueous media. The removal efficiency of 98% SPR technical material (TC) was higher than 5% SPR emulsifiable concentrate (EC) in pure water, indicating that the components present in formulated SPR greatly affected the photodegradation kinetics. Detecting the photoproducts by HPLC/ESI-MS indicated that three main types of reaction including photorearrangement, photohydrolysis, and photooxidation occurred in the photodegradation of SPR at aqueous solution. These results will be helpful for the rational use of SPR and provide a scientific reference for environmental risk evaluation of SPR.

Nitrous Oxide (N2O) Emissions Decrease Significantly under Stronger Light Irradiance in Riverine Water Columns with Suspended Particles

Nitrous oxide (N2O) emissions from riverine water columns with suspended particles are important for the global N2O budget. Although sunlight is known to influence the activity of nitrogen-cycling microorganisms, its specific influence on N2O emissions in river systems remains unknown. This study analyzed the influences of light irradiance on N2O emissions in simulated oxic water columns with 15N-labeling and biological molecular techniques. Our results showed that N2O emissions were inhibited by light in the ammonium system (only 15NH4+ was added) and significantly decreased with increasing light irradiance in the nitrate system (only 15NO3- was added), despite contrasting variations in N2 emissions between these two systems. Lower N2O emission rates in the nitrate system under higher light conditions resulted from higher promotion levels of N2O reduction than N2O production. Increased N2O reduction was correlated to higher organic carbon bioavailability caused by photodegradation and greater potential for complete denitrification. Lower N2O production and higher N2O reduction were responsible for the lower N2O emissions observed in the ammonium system under light conditions. Our findings highlight the importance of sunlight in regulating N2O dynamics in riverine water columns, which should be considered in developing large-scale models for N2O processing and emissions in rivers.

Measuring the photostability of agrochemicals on leaves: understanding the balance between loss processes and foliar uptake

BACKGROUND

Photostability is an important property in agrochemicals, impacting their biological efficacy, environmental fate and registrability. As such, it is a property that is routinely measured during the development of new active ingredients and their formulations. To make these measurements, compounds are typically exposed to simulated sunlight after application to a glass substrate. While useful, these measurements neglect key factors that influence photostability under true field conditions. Most importantly, they neglect the fact that compounds are applied to living plant tissue, and that uptake and movement within this tissue provides a mechanism to protect compounds from photodegradation.

RESULTS

In this work, we introduce a new photostability assay incorporating leaf tissue as a substrate, designed to run at medium throughput under standardized laboratory conditions. Using three test cases, we demonstrate that our leaf-disc-based assays provides quantitatively different photochemical loss profiles to an assay employing a glass substrate. And we also demonstrate that these different loss profiles are intimately linked to the physical properties of the compounds, the effect that those properties have on foliar uptake and, thereby, the availability of the active ingredient on the leaf surface.

CONCLUSIONS

The method presented provides a quick and simple measure of the interplay between abiotic loss processes and foliar uptake, supplying additional information to facilitate the interpretation of biological efficacy data. The comparison of loss between glass slides and leaves also provides a better understanding of when intrinsic photodegradation is likely to be a good model for a compound's behaviour under field conditions. © 2023 Society of Chemical Industry.

Synergistic Effects of Organic Ligands and Visible Light on the Reductive Dissolution of CeO2 Nanoparticles: Mechanisms and Implications for the Transformation in Plant Surroundings

Cerium oxide (CeO2) nanoparticles are one of the most important engineered nanomaterials with demonstrated applications in industry. Although numerous studies have reported the plant uptake of CeO2, its fate and transformation pathways and mechanisms in plant-related conditions are still not well understood. This study investigated the stability of CeO2 in the presence of organic ligands (maleic and citric acid) and light irradiation. For the first time, we found that organic ligands and visible light had a synergistic effect on the reductive dissolution of CeO2 with up to 30% Ce releases after 3 days, which is the highest release reported so far under environmental conditions. Moreover, the photoinduced dissolution of CeO2 in the presence of citrate was much higher than that in maleate, which are adsorbed on the surface of CeO2 through inner-sphere and outer-sphere complexation, respectively. A novel ligand-dependent photodissolution mechanism was proposed and highlighted: upon electron-hole separation under light irradiation, the inner-sphere complexed citrate is more capable of consuming the hole, prolonging the life of electrons for the reduction of Ce(IV) to Ce(III). Finally, reoxidation of Ce(III) by oxygen was observed and discussed. This comprehensive work advances our knowledge of the fate and transformation of CeO2 in plant surroundings.

Climate warming inhibits neonicotinoid photodegradation on vegetable leaves: Important role of the olefin group in leaf wax

Neonicotinoid photodegradation is seldom considered in different vegetable leaves after spraying under climate warming. This study investigated the effect of elevated cultivated temperature from 15/10 °C to 21/16 °C on the photodegradation of dinotefuran, thiamethoxam, acetamiprid, and thiacloprid on four vegetable leaves under simulated sunlight irradiation. The photodegradation rates of neonicotinoids on spinach leaves were 1.1-1.6, 1.1-2.0, and 1.4-2.4 times higher than those on pak choi, Chinese cabbage, and radish leaves, respectively. The higher production concentrations of hydroxyl radicals (•OH) and superoxide radicals in spinach leaf wax may contribute to the fastest photodegradation among four vegetables. When the cultivated temperature increased from 15/10 °C to 21/16 °C, neonicotinoid photodegradation rates decreased by 1.4-2.8 times on the four vegetables. Elevated cultivated temperature decreased the polarity of wax, which reduced the contact probability of neonicotinoids with reactive species on vegetable leaves and photodegradation rates. A positive linear correlation was found between the content of CHCH groups in wax determining •OH generation and the neonicotinoid photodegradation rates on four vegetable leaves cultivated at three temperatures (R² = 0.67-0.94). Insights into neonicotinoid photodegradation on edible vegetables under climate warming are of great significance for better evaluating human exposure to neonicotinoids through the dietary pathway.

Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system

Terrestrial organisms and ecosystems are being exposed to new and rapidly changing combinations of solar UV radiation and other environmental factors because of ongoing changes in stratospheric ozone and climate. In this Quadrennial Assessment, we examine the interactive effects of changes in stratospheric ozone, UV radiation and climate on terrestrial ecosystems and biogeochemical cycles in the context of the Montreal Protocol. We specifically assess effects on terrestrial organisms, agriculture and food supply, biodiversity, ecosystem services and feedbacks to the climate system. Emphasis is placed on the role of extreme climate events in altering the exposure to UV radiation of organisms and ecosystems and the potential effects on biodiversity. We also address the responses of plants to increased temporal variability in solar UV radiation, the interactive effects of UV radiation and other climate change factors (e.g. drought, temperature) on crops, and the role of UV radiation in driving the breakdown of organic matter from dead plant material (i.e. litter) and biocides (pesticides and herbicides). Our assessment indicates that UV radiation and climate interact in various ways to affect the structure and function of terrestrial ecosystems, and that by protecting the ozone layer, the Montreal Protocol continues to play a vital role in maintaining healthy, diverse ecosystems on land that sustain life on Earth. Furthermore, the Montreal Protocol and its Kigali Amendment are mitigating some of the negative environmental consequences of climate change by limiting the emissions of greenhouse gases and protecting the carbon sequestration potential of vegetation and the terrestrial carbon pool.

Mechanism and Kinetics of Prothioconazole Photodegradation in Aqueous Solution

This study investigated the effects of light source, pH value, and NO₃^- concentration on the photodegradation of prothioconazole in aqueous solution. The half-life (t_1/2) of prothioconazole was 173.29, 21.66, and 11.18 min under xenon, ultraviolet, and high-pressure mercury lamps, respectively. At pH values of 4.0, 7.0, and 9.0 under a xenon lamp light source, the t_1/2 values were 693.15, 231.05, and 99.02 min, respectively. Inorganic substance NO₃^- clearly promoted the photodegradation of prothioconazole, with t_1/2 values of 115.53, 77.02, and 69.32 min at NO₃^- concentrations of 1.0, 2.0, and 5.0 mg L^-1, respectively. The photodegradation products were identified as C₁₄H₁₅Cl₂N₃O, C₁₄H₁₆ClN₃OS, C₁₄H₁₅Cl₂N₃O₂S, and C₁₄H₁₃Cl₂N₃ based on calculations and the Waters compound library. Furthermore, density functional theory (DFT) calculations showed that the C-S, C-Cl, C-N, and C-O bonds of prothioconazole were the reaction sites with high absolute charge values and greater bond lengths. Finally, the photodegradation pathway of prothioconazole was concluded, and the variation in energy of the photodegradation process was attributed to the decrease in activation energy caused by light excitation. This work provides new insight into the structural modification and photochemical stability improvement of prothioconazole, which plays an important role in decreasing safety risk during application that will reduce the exposure risk in field environment.

Opposite impact of DOM on ROS generation and photoaging of aromatic and aliphatic nano- and micro-plastic particles

Dissolved organic matter (DOM) plays a significant role in the photochemical behavior of nano- and micro-plastic particles (NPs/MPs). We investigated the influence of DOM on the mechanism on the photoaging of NPs/MPs with different molecular structures under UV₃₆₅ irradiation in water. DOM components used in this study are mainly humic acid and fulvic acid. The results showed that DOM promoted the weathering of aliphatic NPs/MPs (polypropylene (PP)), but inhibited or had only a minor effect on the photoaging of aromatic NPs/MPs (polystyrene (PS) NPs/MPs, carboxyl-modified PS NPs, amino-modified PS NPs, and polycarbonate MPs). NPs with a large surface area may adsorb sufficient DOM on the particle surfaces through π-π interactions, which competes with NPs for photon absorption sites, thus, can delay the photoaging of PS NPs. Aromatic MPs may release phenolic compounds that quench •OH, thereby weakening the photoaging process. For aliphatic MPs, the detection of peracid, aldehyde, and ketone groups on the polymer surface indicated that DOM promoted weathering of PP MPs, which was primarily because the generation of •OH due to DOM photolysis may attack the polymer by C-C bond cleavage and hydrogen extraction reactions. This study provides insight into the UV irradiation weathering process of NPs/MPs of various compositions and structures, which are globally distributed in water.

A review of pesticide phototransformation on the leaf surface: Models, mechanism, and influencing factors

Phototransformation is an important environmental fate of pesticides on plant leaves. This review found that the photodegradation rates of pesticides on leaves might be faster or slower than those in organic solvents or on glass because of the different spectral patterns and light fluxes on the model surface. Wax was found to play an important role in pesticide phototransformation because it has photosensitizing properties, which might be stimulated under light irradiation to produce reactive species, such as hydroxyl radicals, singlet oxygen, methyl radicals, alkyl radicals, and superoxide radicals. These reactive species could accelerate pesticide photodegradation by several times. Wax can also decrease the photodegradation rate of pesticides by quenching reactive species or light-shielding effects. The environmental conditions and phytochemical properties of leaves play important roles in pesticide phototransformation primarily because the composition of wax varies with plant species and environmental factors. The phototransformation of pesticides on leaves was promoted by a low dosage of adjuvant because they act as photosensitizers and improve the dispersity of pesticides, while it was inhibited at a high concentration of adjuvant because of their light shielding effect. Finally, recommendations for future research were discussed, including (1) distinguishing the direct and indirect photodegradation of pesticides; (2) developing model, molecular level visualization and analysis techniques; (3) conducting more field research; and (4) considering the effect of climate change, especially the interaction of climatic factors. This review gives a comprehensive overview of the current knowledge of pesticide phototransformation on leaves and provides suggestions for future studies.

Environmental photochemistry on plants: recent advances and new opportunities for interdisciplinary research

Plants play a central role in the photochemistry of chemicals in the environment. They represent a major atmospheric source of volatile organic compounds (VOCs) but also an important environmental surface for the deposition and photochemical reactions of pesticides, gaseous and particulate pollutants. In this review, we point out the role of plant leaves in these processes, as a support affecting the reactions physically and chemically and as a partner through the release of natural constituents (water, secondary metabolites). We discuss the influence of the chosen support (leaves, needle surfaces or fruit cuticles, extracted cuticular waxes and model surfaces) and other factors (additives, pesticides mixture, and secondary metabolites) on the photochemical degradation kinetics and mechanisms. We also show how plants can be a source of photochemically reactive species which can act as photosensitizers promoting the photodegradation of pesticides or the formation and aging of secondary organic aerosols (SOA) and secondary organic materials (SOM). Understanding the fate of chemicals on plants is a research area located at the interface between photochemistry, analytical chemistry, atmospheric chemistry, microbiology and vegetal physiology. Pluridisciplinary approaches are needed to deeply understand these complex phenomena in a comprehensive way. To overcome this challenge, we summarize future research directions which have been clearly overlooked until now.

The inhibitory effects of sunlight on nitrogen removal in riverine overlying water with suspended particles

Overlying water with suspended particles is a hot spot for nitrogen removal in river systems. Although light exposure affects nitrogen transformations and nitrogen removal in some environments, such effects have rarely been explored and quantified in riverine overlying water. Herein, we examined the difference between dark and light conditions in the community composition and abundance of nitrogen transformation microbes in simulated overlying water by high-throughput sequencing and qPCR. Moreover, ¹⁵N-labeling techniques were used to investigate variation in nitrogen removal rates (N₂ and N₂O) as well as nitrification rates between dark and light conditions. We found apparent differences in the bacterial community between light and dark microcosms. The abundance of Cyanobacteria was greatly elevated in light microcosms, with the diazotroph nifH gene abundance being 7.4-fold higher in the light microcosm (P < 0.01). However, due to the vulnerability of some specifies to UV damage, the diazotroph species richness was reduced. The abundances of ammonia-oxidizing archaeal amoA, ammonia-oxidizing bacterial amoA, and denitrifying nirS genes were 80.1%, 46.3%, and 50.7% lower in the light microcosm, respectively, owing to the differential inhibition of sunlight exposure on these microbes. Both ¹⁵N-N₂ and ¹⁵N-N₂O were significantly produced regardless of conditions with or without light. Due to the combined effects of reduced nitrification and denitrification, as well as potentially enhanced nitrogen fixation, the accumulated amounts of ¹⁵N-N₂ and ¹⁵N-N₂O were 6.2% and 44.8% lower, respectively, in the light microcosm. This study quantifies the inhibitory effect of sunlight exposure on nitrogen removal in riverine overlying water and reveals the underlying mechanisms, providing insights into our understanding of nitrogen transformations in river systems.