Indirect transmission through aquatic environments is critical to interspecies transmission of influenza, but knowledge of sunlight inactivation of the virus, or any enveloped virus, in water is lacking. This study characterizes the photoinactivation of two enveloped viruses (Phi6 and influenza A virus, IAV), and a nonenveloped virus (MS2) in clear and colored surface waters using simulated sunlight. We measured light-screening corrected decay rate constants ( k ) using infectivity assays. k values were greater, especially for IAV, in colored surface water versus clear water. k values were generally greatest for IAV, followed by Phi6, then MS2, suggesting greater susceptibility of enveloped viruses to sunlight. Most k values for IAV and Phi6 did not differ with UV irradiance variations in colored surface water, indicating dominance of indirect, photochemically produced reactive intermediate-mediated inactivation pathways. Additional experiments with Phi6 as a representative enveloped virus suggest the importance of hydroxyl radicals, indicate adsorption of NOM promotes photoinactivation, and sublethal damage of the virus may occur. For IAV, modeled time for 99% inactivation in a well-mixed 1 m deep wetland water column is 1.2 h, compared to 1.8 h in clear water. These findings, particularly those for IAV, can inform human and animal health protection strategies.

Advancing a common understanding about the chemical composition, size, and three-dimensional (3D) structure of dissolved organic matter (DOM) is paramount to deciphering its impact on and involvement in environmental processes, such as the fate and transport of contaminants and carbon cycling. Traditionally, DOM has been described as a collection of solvent-separated molecules or macromolecules. More recently, DOM has been depicted as a "supramolecular assembly", a collection of individual molecules and associations of molecules held together by non-covalent interactions. The supramolecular assembly model has been broadly invoked to rationalize certain behaviors and properties of DOM, yet the complexity of DOM has made it difficult to fully unravel the nature and contributions of its intermolecular interactions. Discussed in this perspective is evidence regarding thermodynamic drivers of intermolecular associations, DOM molecular size, sorption of organic contaminants to DOM, and optical properties of DOM. While single observations may be rationalized by former structural models, such as the supramolecular assembly model, combined evidence shows that the 3D structure of DOM is best described by a mixed dynamic assembly model (MDAM). The MDAM depicts DOM as a collection of solvent-separated molecules and small, tightly knit assemblies held together by strong hydrogen bonds, which may form large assemblies through weak intermolecular interactions only at specific pH values, high ionic strength, or high DOM concentration.

Polyethylene glycols (PEGs), a major class of water-soluble polymers (WSPs), are widely used in diverse applications which may lead to their release into the environment. This work investigates the reaction of PEGs with photochemically produced hydroxyl radicals (•OH), an important environmental oxidant, and assesses the effect of reaction-induced molecular weight (MW) decreases on PEG biodegradation dynamics in soil and sediment. Probabilistic kinetic modelling revealed a significant reduction in PEG MW after only a few •OH-induced chain scissions on initial PEG molecules. The simulation results were experimentally validated by reacting 13C-labeled PEGs (average MW = 6200 Da) with photochemically produced •OH, resulting in pronounced shifts in the size distribution of PEGs towards lower MWs with increasing reaction extents. Incubations of the initial non-reacted and three incrementally •OH-reacted PEG mixtures over a 150-day period in sediment and soil demonstrated increasing rates and extents of PEG biodegradation to 13CO2 with increasing •OH-reaction extent and thus decreasing PEG average MW. This study underscores the importance of considering the MW distributions of WSPs and their dynamic changes through biotic or abiotic chain scission reactions — showcased herein by reacting PEGs with photochemically produced •OH — in mechanistically understanding WSP biodegradability in natural and engineered receiving environments.

Biodegradable aliphatic-aromatic copolyesters are commercially important and used in diverse applications, including soil-biodegradable mulch films. This work investigates the effects of copolyester chemical structure on soil biodegradability using 13C-labeled variants of polybutylene adipate-co-terephthalate (PBAT) and polybutylene sebacate-co-terephthalate (PBSeT), as well as 13C-labeled cellulose as a positive biodegradation control. Biodegradation in soil was assessed by monitoring polyester and cellulose mineralization to 13CO2 throughout multimonth incubations and quantifying the nonmineralized polyester in the soil after incubations. Mass balances on polyester- and cellulose-added 13C over the incubations were closed. The soil biodegradability of PBSeT was higher than that of PBAT for variants with a molar ratio of terephthalate (T) to total diacid of 50%. PBAT biodegradability substantially increased as its T content decreased from 50% to 47, 30, 20, and 0%. Increasing biodegradability with decreasing T content also resulted in preferential biodegradation of aliphatic-rich domains in the initial phase of the incubations. Polyesters undergoing extensive mineralization also showed substantial incorporation of polyester carbon into the soil microbial biomass. Differences in polyester soil biodegradability were rationalized based on differences in their enzymatic hydrolyzability. Qualitative chemical structure-biodegradability relationships can lead to tailoring polyester biodegradability to specific applications and the biodegradation potentials of receiving environments.

The Editors-in-Chief of the Environmental Science journals introduce the Best Papers of 2022.

The Editors-in-Chief of the Environmental Science journals introduce the Best Papers of 2021.

The Editors-in-Chief of the Environmental Science journals introduce the Best Papers of 2020.

We report a dual probe system based on 4'-substituted biphenyl-2-carboxylic acids (BPAs) for analysis of photooxidants generated by dissolved organic matter. The BPA probes are converted to the corresponding benzocoumarins (BZCs) at different rates depending on the mechanism of oxidation; thus, two probes used simultaneously can differentiate strong triplet excited state sensitizers from hydroxylating species such as hydroxyl radical (•OH) present in dissolved organic matter (DOM). Comparison of the ratios of BZC-CH3 and BZC-CF3 product formation using model photooxidants such as NaNO2, a •OH precursor, and model triplet sensitizer lumichrome gave a range of 2 to 250. Application of these probes to DOM isolates and whole natural waters afforded intermediate ratios. Although the oxidation potential of BPAs (>ca. 1.80 V SHE) is significantly higher than the estimated average reduction potential of typical 3CDOM* samples, these results have demonstrated the presence of a small pool of oxidants in the selected DOM isolates and whole water samples that is capable of oxidizing aromatic carboxylates. As an analytical tool, this probe pair can be used between pH 4-6 without affecting the product formation ratio and may find applications in various systems involving complex mixtures of photochemically produced oxidants of differing natures.

Bacitracin is a mixture of nonribosomal peptides (NRPs) that is extensively used as an antibiotic in both human and veterinary medicine. Despite its widespread use over the past six decades, very few studies have addressed the environmental fate of bacitracin and zinc-bacitracin complexes. In this study, the photochemical transformation of bacitracin components (i.e., cyclic dodecapeptides) in the aquatic environment was investigated. A high resolution mass spectrometry (HRMS)-based approach enabled monitoring of the photochemical degradation kinetics of individual bacitracin components, investigation of the relative contribution of reactive oxygen species (e.g., singlet oxygen, (1)O2) in dissolved organic matter-sensitized photoreactions, and identification of oxidative modifications in bacitracin photoproducts. The results of this study support the hypothesis that indirect photochemical oxidation of the histidine (His) residue by (1)O2 is a major degradation pathway for bacitracin A, the most potent congener of the mixture. Furthermore, the photooxidation rate of bacitracin A with (1)O2 decreased upon bacitracin A coordination with Zn(2+), demonstrating that the photochemistry of metal-bound His is different from that of metal-free His. Overall, these results provide insight into the fate of bacitracin components in the aquatic environment and highlight the potential of utilizing this HRMS-based methodology to study transformations of other environmentally relevant NRPs.

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The existence of an allowed transition from the ground state of Mg-23 to the 0.44-Mev excited state of Na-23 is reported. (C.J.G.)