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Iodinated disinfection by-products (I-DBPs) are of growing concern due to their elevated toxicity compared to their chlorinated counterparts, with links to adverse health effects such as bladder cancer and miscarriages. Medical imaging agents like iohexol, commonly used in healthcare facilities, introduce iodine into wastewater systems. This study investigates the photodegradation of iohexol and the subsequent formation of products, including I-DBPs, during simulated final wastewater treatment under chlorination and sunlight exposure. Experiments were conducted with solutions containing 30 μM iohexol, 3 mg L−1 humic acids, and 5.5 mg L−1 hypochlorite. Samples were irradiated at λ ≥ 295 nm and subject to ion chromatography monitoring of I−, IO3−, Cl−, and ClO3−, providing mechanistic insight into the fate of iodide released from iohexol. UV-visible spectroscopy was employed to monitor the degradation profile of iohexol and the concurrent release of iodide. Electrospray ionization mass spectrometry (ESI-MS) identified a range of anionic products based on their mass-to-charge ratios (m/z), including low molecular weight carboxylic acids, their carcinogenic haloacetic derivatives (chloroacetic acid (m/z 93), iodoacetic acid (IAA, m/z 185), and hydroxyiodoacetic acid (m/z 201)) as well as phenolic halides. Notably, IAA was present at a concentration of 0.16 μM at the conclusion of the reaction. These findings elucidate photodeiodination-coupled radical attack, photooxidative cleavage, and halogenation transformation pathways of iodinated compounds during disinfection and underscore the potential risks associated with their presence in wastewater. The results provide valuable insights for medical facilities and wastewater treatment plants aiming to mitigate the formation of hazardous I-DBPs. 

Phenolic aldehydes are widespread pollutants in water and soil, originating from lignin-based agro-industries. With increasing wastewater pollution, improved treatment systems are necessary to degrade phenolic aldehydes into less hazardous compounds. Over the past two decades, ozonolysis wastewater treatment has been implemented in the United States, Japan, and South Korea. However, the mechanistic understanding of phenolic aldehyde ozonolysis in water remains incomplete. This study investigates the ozonolysis of three model phenolic aldehydes (syringaldehyde, vanillin, 4-hydroxybenzaldehyde) in representative concentrations for wastewater of 0.5–1.5 mM and pH 4–8. Each compound solution was sparged for 30 min at a fixed O3(g) flow (0.20 to 1.00 L min−1), providing steady-state dissolved concentrations of 5.4 to 16.2 μM. Reactant loss and product generation were monitored using UV–visible (UV–vis) spectroscopy, ultra-high pressure liquid chromatography (UHPLC) with UV–vis and mass spectrometry (MS) detection, and ion chromatography with conductivity and MS detection of anions. Identified products based on their mass-to-charge ratio (m/z−) included oxalic acid (89), glycolic acid (75), formic acid (45), and maleic acid (115). Additional intermediate products were identified under various reaction conditions, revealing competing mechanisms in the degradative oxidation of aqueous phenolic aldehydes exposed to O3(g). A unifying mechanism is proposed to explain the production of smaller, less toxic molecules during phenolic aldehyde ozonolysis, enhancing water quality. This mechanism serves as a basis for evaluating the implementation of ozonolysis in scaled-up water treatment processes. 

As the Special Issues “Feature Papers in Photochemistry” and “Feature Papers in Photochemistry II” conclude, it is crucial to acknowledge the remarkable progress and persistent gaps that continue to shape the journey of photochemistry research [...] 

Landfills for disposing of solid waste are designed, located, managed, and monitored facilities expected to comply with government regulations to prevent contamination of the surrounding environment. After the average life expectancy of a typical landfill (30 to 50 years), a large investment in the construction, operation, final closure, and 30-year monitoring of a new site is needed. In this case study, we provide a holistic explanation of the unexpected development of elevated temperature landfills (ETLFs), such as that in the city of Bristol (United States) on the border of the states of Virginia and Tennessee, including the initial role played by coal ash. Despite the increasing frequency of ETLF occurrence, there is limited knowledge available about their associated environmental problems. The study uses mixed (qualitative, quantitative, and mapping) methods to analyze (1) the levels of odoriferous reduced sulfur compounds, ammonia, and volatile organic compounds (VOCs) emitted, (2) the ratio of methane to carbon dioxide concentrations in five locations, which dropped from unity (normal landfill) to 0.565, (3) the location of gas well heads with gradients of elevated temperatures, and (4) the correlation of the filling rate (upward of ~12 m y−1) with depth for registered events depositing coal ash waste. The work identifies spatial patterns that support the conclusion that coal ash served as the initiator for an ETLF creation. The case of the city of Bristol constitutes an example of ETLFs with elevated temperatures above the regulatory United States Environmental Protection Agency (EPA) upper threshold (65 °C), having alongside low methane emissions, large production of leachate, land subsidence, and a large production of organic compounds. Such landfills suffer abnormal chemical reactions within the waste mass that reduce the life expectancy of the site. Residents in such communities suffer intolerable odors from fugitive emissions and poor air quality becomes prominent, affecting the well-being and economy of surrounding populations. Conclusive information available indicates that the Bristol landfill has been producing large amounts of leachate and hazardous gases under the high pressures and temperatures developed within the landfill. A lesson learned, which should be used to prevent this problem in the future, is that the early addition of coal ash into the landfill would have catalyzed the process of ETLF creation. The work considers the public health risks and socioeconomic problems of residents exposed to emissions from an ETLF and discusses the efforts needed to prevent further incidents in other locations.