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1. Quaternary Ammonium Compounds: A Chemical Class of Emerging Concern

   Arnold, W.A.; Blum, A.; Branyan, J.; Bruton, T.A.; Carignan, C.C.; Cortopassi, G.; Datta, S.; DeWitt, J.; Doherty, A.-C.; Halden, R.U.; et al (May 2023, Environmental science and technology)

   Quaternary ammonium compounds (QACs), a large class of chemicals that includes high production volume substances, have been used for decades as antimicrobials, preservatives, and antistatic agents, and for other functions in cleaning, disinfecting, personal care products, and durable consumer goods. QAC use has accelerated in response to the COVID-19 pandemic and the banning of 19 antimicrobials from several personal care products by the US Food and Drug Administration in 2016. Studies conducted before and after the onset of the pandemic indicate increased human exposure to QACs. Environmental releases of these chemicals have also increased. Emerging information on adverse environmental and human health impacts of QACs is motivating a reconsideration of the risks and benefits across the life cycle of their production, use, and disposal. This paper presents a critical review of the literature and scientific perspective developed by a multidisciplinary, multi-institutional team of authors from academia, governmental, and nonprofit organizations. The review evaluates currently available information on the ecological and human health profile of QACs and identifies multiple areas of potential concern. Adverse ecological effects include acute and chronic toxicity to susceptible aquatic organisms, with concentrations of some QACs approaching levels of concern. Suspected or known adverse health outcomes include dermal and respiratory effects, developmental and reproductive toxicity, disruption of metabolic function such as lipid homeostasis, and impairment of mitochondrial function. QACs’ role in antimicrobial resistance has also been demonstrated. In the US regulatory system, how a QAC is managed depends on how it is used, for example, in pesticides or personal care products. This can result in the same QACs receiving different degrees of scrutiny depending on the use and the agency regulating it. Further, the EPA’s current method of grouping QACs based on structure, first proposed in 1988, is insufficient to address the wide range of QAC chemistries, potential toxicities, and exposure scenarios. Consequently, exposures to common mixtures of QACs and from multiple sources remain largely unassessed. Some restrictions on the use of QACs have been implemented in the US and elsewhere, primarily focused on personal care products. Assessing the risks posed by QACs is hampered by their vast structural diversity and a lack of quantitative data on exposure and toxicity for the majority of these compounds. This review identifies important data gaps and provides research and policy recommendations for preserving the utility of QAC chemistries while also seeking to limit adverse environmental and human health effects. 

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2. Metallocene QACs: The Incorporation of Ferrocene Moieties into monoQAC and bisQAC Structures

   https://doi.org/10.1002/cmdc.202000605  

   Sommers, Kyle_J; Bentley, Brian_S; Carden, Robert_G; Post, Savannah_J; Allen, Ryan_A; Kontos, Renee_C; Black, Jacob_W; Wuest, William_M; Minbiole, Kevin_P_C (November 2020, ChemMedChem)

   Abstract Inspired by the incorporation of metallocene functionalities into a variety of bioactive structures, particularly antimicrobial peptides, we endeavored to broaden the structural variety of quaternary ammonium compounds (QACs) by the incorporation of the ferrocene moiety. Accordingly, 23 ferrocene‐containing mono‐ and bisQACs were prepared in high yields and tested for activity against a variety of bacteria, including Gram‐negative strains and a panel of clinically isolated MRSA strains. Ferrocene QACs were shown to be effective antiseptics with some displaying single‐digit micromolar activity against all bacteria tested, demonstrating yet another step in the expansion of structural variety of antiseptic QACs. 

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3. Quaternary ammonia compounds in disinfectant products: evaluating the potential for promoting antibiotic resistance and disrupting wastewater treatment plant performance

   https://doi.org/10.1039/D3VA00063J  

   Lu, Zihao; Mahony, Anna K.; Arnold, William A.; Marshall, Christopher W.; McNamara, Patrick J. (February 2024, Environmental Science: Advances)

   Quaternary ammonium compounds (QACs) are a class of compounds that were widely used as disinfectants during the COVID-19 pandemic and continue to be used as disinfecting agents. 

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4. Boronium Salt as an Antiviral Agent against Enveloped Viruses Influenza A and SARS-CoV-2

   https://doi.org/10.3390/applbiosci1030018  

   Ravine, Terrence J; Rayner, Jonathan O; Roberts, Rosemary W; Davis, James H; Soltani, Mohammad (December 2022, Applied Biosciences)

   Quaternary ammonium compounds (QACs) are routinely used as disinfectants in a variety of settings. They are generally effective against a wide range of microbes but often exhibit undesirable toxicity. Consequently, companies are constantly seeking alternatives to QACs that are just as effective but with reduced health and environmental hazards. Two boronium salt derivatives were tested against influenza A and SARS-CoV-2 viruses. One salt possessed a terminal benzyl group, while the other lacked the same terminal benzyl group. Both salts demonstrated virus inactivation similar to a commercial QAC disinfectant. The non-benzylated form exhibited the same cell toxicity profile as the QAC. However, the benzylated form displayed less cell toxicity than both the non-benzylated form and QAC. These results suggest that the boronium salts may be suitable for use as a disinfecting agent against enveloped viruses in lieu of using a QAC. Continued evaluation of the boronium salts is warranted to determine the lowest effective concentration capable of effectively controlling influenza A and SARS-CoV-2 viruses that also demonstrates low cytotoxicity. 

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5. Diatom volatile organic compound production is driven by diel metabolism and the cell cycle

   https://doi.org/10.3389/fmicb.2025.1620542  

   Padaki, Vaishnavi G; Palmer, Emily; Jiang, Yuan; Buchholz, Holger H; Kimbrel, Jeffrey A; Halsey, Kimberly H (October 2025, Frontiers in Microbiology)

   IntroductionVolatile organic compounds (VOCs) are small, low-vapor-pressure molecules emitted from the surface ocean into the atmosphere. In the atmosphere, VOCs can change OH reactivity and condense onto particles to become cloud condensation nuclei. VOCs are produced by phytoplankton, but the conditions leading to VOC accumulation in the surface ocean are poorly understood. MethodsIn this study, VOC accumulation was measured in real time over a 12 h day−12 h night cycle in the model diatomPhaeodactylum tricornutumduring exponential growth. ResultsSixty-threem/zsignals were produced in higher concentrations than in cell-free controls. All VOCs, except methanol, were continuously produced over 24 h. All VOCs accumulated to higher concentrations during the day compared to the night, and 11 VOCs exhibited distinct accumulation patterns during the morning hours. Twenty-seven VOCs were associated with known metabolic pathways inP. tricornutum, with most VOCs involved in amino acid and fatty acid metabolism. DiscussionPatterns of VOC production were strongly associated with diel shifts in cell physiology and the cell cycle. Diel VOC production patterns give a fundamental understanding of the first steps in VOC accumulation in the surface ocean. 

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