Fluorinated Pharmaceutical and Pesticide Photolysis: Investigating Reactivity and Identifying Fluorinated Products by Combining Computational Chemistry,19F NMR, and Mass Spectrometry.

Fluorinated breakdown products from photolysis of pharmaceuticals and pesticides are of environmental concern due to their potential persistence and toxicity. While mass spectrometry workflows have been shown to be useful in identifying products, they fall short for fluorinated products and may miss up to 90% of products. Studies have shown that 19F NMR measurements assist in identifying and quantifying reaction products, but this protocol can be further developed by incorporating computations. Density functional theory was used to compute 19F NMR shifts for parent and product structures in photolysis reactions. Computations predicted NMR spectra of compounds with an R2 of 0.98. Computed shifts for several isolated product structures from LC-HRMS matched the experimental shifts with <0.7 ppm error. Multiple products including products that share the same shift that were not previously reported were identified and quantified using computational shifts, including aliphatic products in the range of -80 to -88 ppm. Thus, photolysis of fluorinated pharmaceuticals and pesticides can result in compounds that are polyfluorinated alkyl substances (PFAS), including aliphatic-CF3 or vinyl-CF2 products derived from heteroaromatic-CF3 groups. C-F bond-breaking enthalpies and electron densities around the fluorine motifs agreed well with the experimentally observed defluorination of CF3 groups. Combining experimental-computational 19F NMR allows quantification of products identified via LC-HRMS without the need for authentic standards. These results have applications for studies of environmental fate and analysis of fluorinated pharmaceuticals and pesticides in development.

Animal Feedlots and Domestic Wastewater Discharges are Likely Sources of N-Nitrosodimethylamine (NDMA) Precursors in Midwestern Watersheds.

N-nitrosodimethylamine (NDMA) precursor concentrations along four major rivers in Minnesota, USA were quantified and correlated with watershed land cover types, anthropogenic activity, and organic matter characteristics. River water samples (36 in total) were chloraminated under uniform formation conditions (UFC) before and after lime-softening treatment, and the resulting NDMA concentrations were quantified (NDMAUFC). Regarding land cover, NDMAUFC in raw river water exhibited weak positive correlations with urban land (ρ = 0.33, p = 0.05) and cropland coverage (ρ = 0.35, p = 0.04). For anthropogenic activity, NDMAUFC in raw river water positively correlated with the number of feedlots (ρ = 0.57), total weight of animals (ρ = 0.68), and total number of domestic wastewater treatment plants (WWTPs; ρ = 0.63) with p < 0.01. NDMAUFC positively correlated with region IV fluorescence intensity from fluorescence excitation-emission spectra (ρ = 0.70, p < 0.01). Lime softening of river water typically increased NDMAUFC and preferentially removed organic matter that fluoresces in region V, suggesting that the organic matter in this region decreases NDMAUFC by competing for available chloramines. Overall, animal feedlots, along with domestic WWTPs, are predominant sources of NDMA precursors in the studied watersheds, while croplands and urban runoff are of lesser importance.

Quaternary Ammonium Compounds (QACs) in Wastewater Influent and Effluent Throughout the COVID-19 Pandemic.

Quaternary ammonium compounds (QACs) are used in consumer and industrial products, including disinfectants. Due to the COVID-19 pandemic, disinfectant use has increased, purportedly increasing loads to wastewater treatment plants and the environment. To understand how the increased usage has affected QAC loadings to treatment plants and to determine how effectively plants remove QACs from liquid effluent that is discharged to surface and groundwaters, influent and effluent wastewater samples were collected from four treatment plants (treatment capacities < 5 MGD to > 100 MGD) for 21 months beginning in May 2020. Influent QAC concentrations were hundreds of µg/L and effluent QAC concentrations were < 1 µg/L, corresponding to an average removal of 98% from all four plants. The most prevalent QACs in influent were those used most commonly in disinfectants, specifically benzylalkyldimethylammonium compounds (BACs) and short-chain dialkyldimethylammonium compounds (DADMACs), and influent levels of these compounds were correlated with QAC sales. Prior to this study, ethylbenzylalkyldimethylammonium compounds (EtBACs) had not been studied, and they comprised 13 ± 6% of QACs in influent. While removal was high at all plants, low µg/L concentrations were still continuously discharged into the environment. For QACs with equivalent alkyl chain lengths, those with aromatic substituents (BACs and EtBACs) appear to be removed more effectively than those with only alkyl chains (DADMACs).

Photolysis Products of Fluorinated Pharmaceuticals: A Combined Fluorine Nuclear Magnetic Resonance Spectroscopy and Mass Spectrometry Approach.

The aqueous photolysis of four pharmaceuticals with varying fluorinated functional groups was assessed under neutral, alkaline, advanced oxidation, and advanced reduction conditions with varying light sources. Solar simulator quantum yields were 2.21 × 10-1 mol Ei-1 for enrofloxacin, 9.36 × 10-3 mol Ei-1 for voriconazole, and 1.49 × 10-2 mol Ei-1 for flecainide. Florfenicol direct photolysis was slow, taking 150 h for three degradation half-lives. Bimolecular rate constants between pharmaceuticals and hydroxyl radicals were 109 to 1010 M-1 s-1 . Using a combined quantitative fluorine nuclear magnetic resonance spectroscopy (19 F-NMR) and mass spectrometry approach, fluorine mass balances and photolysis product structures were elucidated. Enrofloxacin formed a variety of short-lived fluorinated intermediates that retained the aryl F motif. Extended photolysis time led to complete aryl F mineralization to fluoride. The aliphatic F moiety on florfenicol was also mineralized to fluoride, but the resulting product was a known antibiotic (thiamphenicol). For voriconazole, the two aryl Fs contributed more to fluoride production compared with the heteroaromatic F, indicating higher stability of the heteroaromatic F motif. The two aliphatic CF3 moieties in the flecainide structure remained intact under all conditions, further supporting the stability of these moieties found in per- and polyfluoroalkyl substances under a variety of conditions. The advanced treatment conditions generating hydroxyl radicals or hydrated electrons accelerated the degradation, but not the defluorination, of flecainide. The combination of 19 F-NMR and mass spectrometry proved powerful in allowing identification of fluorinated products and verifying the functional groups present in the intermediates and products. The results found in the present study will aid in the understanding of which fluorinated functional groups should be incorporated into pharmaceuticals to ensure organofluorine byproducts are not formed in the environment and help determine the water-treatment processes that effectively remove specific pharmaceuticals and more generally fluorinated motifs. Environ Toxicol Chem 2023;00:1-12. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Spatiotemporal Variability in N-Nitrosodimethylamine Precursor Levels in a Watershed Impacted by Agricultural Activities and Municipal Wastewater Discharges and Effects of Lime Softening.

The Crow River, a tributary of the Mississippi River in Minnesota, U.S.A., that is impacted by agricultural activities and municipal wastewater discharges, was sampled approximately monthly at 12 locations over 18 months to investigate temporal and spatial variations in N-nitrosodimethylamine (NDMA) precursor levels. NDMA precursors were quantified primarily by measuring NDMA formed under the low chloramine dose uniform formation conditions protocol (NDMAUFC) and occasionally using the high dose formation potential protocol (NDMAFP). Raw water NDMAUFC concentrations (2.2 to 128 ng/L) exhibited substantial temporal variation but relatively little spatial variation. An increase in NDMAUFC was observed for 126 of 169 water samples after lime-softening treatment. A kinetic model indicates that under chloramine-limited UFC test conditions, the increase in NDMAUFC can be attributed to a decrease in competition between precursors and natural organic matter (NOM) for chloramines and reduced interactions of precursors with NOM. NDMAUFC concentrations correlated positively with dissolved nitrogen concentration (ρ = 0.44, p < 0.01) when excluding the spring snowmelt period and negatively correlated with dissolved organic carbon concentration (ρ = -0.47, p < 0.01). Overall, NDMA precursor levels were highly dynamic and strongly affected by lime-softening treatment.

Biodegradation, photolysis, and sorption of antibiotics in aquatic environments: A scoping review.

The presence of antibiotics in surface waters is a potential driver of antibiotic resistance and thus of concern to human and environmental health. Key factors driving the potential impact of antibiotics are their persistence and transport in rivers and lakes. The goal of this study was to describe the peer-reviewed published literature on the photolysis (direct and indirect), sorption, and biodegradation of a selected group of antibiotic compounds following a scoping review methodology. Primary research from 2000 to 2021 was surveyed to compile information on these processes for 25 antibiotics from 6 classes. After compilation and assessment of the available parameters, the results indicate that information is present to predict the rates of direct photolysis and reaction with hydroxyl radical (an indirect photolysis process) for most of the selected antibiotics. There is insufficient or inconsistent information for including other indirect photolysis processes, biodegradation, or removal via sorption to settling particles for most of the targeted antibiotic compounds. Future research should focus on collecting fundamental parameters such as quantum yields, second-order rate constants, normalized biodegradation rates, and organic carbon or surface area normalized sorption coefficients rather than pseudo-first order rate constants or sorption equilibrium constants that apply only to specific conditions/sites.

Quaternary Ammonium Compounds: A Chemical Class of Emerging Concern.

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 work 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 US Environmental Protection Agency'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.

Wavelength-Dependent UV-LED Photolysis of Fluorinated Pesticides and Pharmaceuticals.

The wavelength dependence of photoproduct formation and quantum yields was evaluated for fluorinated pesticides and pharmaceuticals using UV-light emitting diodes (LEDs) with 255, 275, 308, 365, and 405 nm peak wavelengths. The fluorinated compounds chosen were saflufenacil, penoxsulam, sulfoxaflor, fluoxetine, 4-nitro-3-trifluoromethylphenol (TFM), florasulam, voriconazole, and favipiravir, covering key fluorine motifs (benzylic-CF3, heteroaromatic-CF3, aryl-F, and heteroaromatic-F). Quantum yields for the compounds were consistently higher for UV-C as compared to UV-A wavelengths and did not show the same trend as molar absorptivity. For all compounds except favipiravir and TFM, the fastest degradation was observed using 255 or 275 nm light, despite the low power of the LEDs. Using quantitative 19F NMR, fluoride, trifluoroacetate, and additional fluorinated byproducts were tracked and quantified. Trifluoroacetate was observed for both Ar-CF3 and Het-CF3 motifs and increased at longer wavelengths for Het-CF3. Fluoride formation from Het-CF3 was significantly lower as compared to other motifs. Ar-F and Het-F motifs readily formed fluoride at all wavelengths. For Het-CF3 and some Ar-CF3 motifs, 365 nm light produced either a greater number of or different major products. Aliphatic-CF2/CF3 products were stable under all wavelengths. These results assist in selecting the most efficient wavelengths for UV-LED degradation and informing future design of fluorinated compounds.

Fluorous Liquids for Magnetic Resonance-Based Thermometry with Enhanced Responsiveness and Environmental Degradation.

Accurate temperature measurement via magnetic resonance is valuable for both in vitro and in vivo analysis of local tissue for evaluating disease pathology and medical interventions. 1H MRI-based thermometry is used clinically but is susceptible to error from magnetic field drift and low sensitivity in fatty tissue and requires a reference for absolute temperature determination. As an alternative, perfluorotributylamine (PFTBA), a perfluorocarbon liquid for 19F MRI thermometry, is based on chemical shift responsiveness and approaches the sensitivity of 1H MRI thermometry agents; however, environmental persistence, greenhouse gas concerns, and multiple resonances which can lead to MRI artifacts indicate a need for alternative sensors. Using a 19F NMR-based structure-property study of synthetic organofluorine molecules, this research develops new organofluorine liquids with improved temperature responsiveness, high signal, and reduced nonmagnetically equivalent fluorine resonances. Environmental degradation analysis using reverse-phase HPLC and quantitative 19F NMR demonstrates a rapid degradation profile mediated via the aryl fluorine core of temperature sensors. Our findings show that our lead liquid temperature sensor, DD-1, can be made in high yield in a single step and possesses an improved responsiveness over our prior work and an 83% increase in aqueous thermal responsiveness over PFTBA. Degradation studies indicate robust degradation with half-lives of less than two hours under photolysis conditions for the parent compound and formation of other fluorinated products. The improved performance of DD-1 and its susceptibility to environmental degradation highlight a new lead fluorous liquid for thermometry applications.

Finding Fluorine: Photoproduct Formation during the Photolysis of Fluorinated Pesticides.

The photolysis of pesticides with different fluorine motifs was evaluated to quantify the formation of fluorinated products in buffered aqueous systems, advanced oxidation (AOP) and reduction processes (ARP), and river water. Simulated sunlight quantum yields at pH 7 were 0.0033, 0.0025, 0.0015, and 0.00012 for penoxsulam, florasulam, sulfoxaflor, and fluroxypyr, respectively. The bimolecular rate constants with hydroxyl radicals were 2 to 5.7 × 1010 M-1 s-1 and, with sulfate radicals, 1.6 to 2.6 × 108 M-1 s-1 for penoxsulam, florasulam, and fluroxypyr, respectively. The rate constants of sulfoxaflor were 100-fold lower. Using quantitative 19F-NMR, complete fluorine mass balances were obtained. The maximum fluoride formation was 53.4 and 87.4% for penoxsulam and florasulam under ARP conditions, and 6.1 and 100% for sulfoxaflor and fluroxypyr under AOP conditions. Heteroaromatic CF3 and aliphatic CF2 groups were retained in multiple fluorinated photoproducts. Aryl F and heteroaromatic F groups were readily defluorinated to fluoride. CF3 and CF2 groups formed trifluoroacetate and difluoroacetate, and yields increased under oxidizing conditions. 19F-NMR chemical shifts and coupling analysis provided information on hydrogen loss on adjacent bonds or changes in chirality. Mass spectrometry results were consistent with the observed 19F-NMR products. These results will assist in selecting treatment processes for specific fluorine motifs and in the design of agrochemicals to reduce byproduct formation.

Identifying the spatiotemporal vulnerability of soils to antimicrobial contamination through land application of animal manure in Minnesota, United States.

Antimicrobials may reach the soil environment from a variety of sources and pathways, including land application of human biosolids and animal manure. Once in soil, antimicrobials can affect the abundance and activity of soil microorganisms and exert selection pressures that enhance the emergence and spread of antimicrobial resistance (AMR). To mitigate the spread of AMR it is important to understand the spatial and temporal interactions between antimicrobials and soil. The goal of this study was to assess the vulnerability of Minnesota (U.S.) soil to contamination with specific antimicrobial compounds at temperatures experienced throughout the year. Soil contamination potential was estimated based upon specific antimicrobial drug binding and permanence, and average monthly temperature. Minnesota soil vulnerability was estimated by incorporating spatially explicit soil contamination potential, land cover type, and livestock density. Assessment of antimicrobials used in livestock production showed that soils are most vulnerable to antimicrobial contamination in southwestern Minnesota, to enrofloxacin, chlortetracycline, and oxytetracycline, and in the months of April and October. While the assessment herein was not based on actual on-farm antimicrobial use data and subsequent excretion of antimicrobial metabolites into the environment, this study provides an overview of the spatial and temporal potential for Minnesota soil to be contaminated by several antimicrobial drugs and demonstrates how specific vulnerability assessments might be conducted for geographic areas with known exposure (e.g., cropland fertilized with livestock manure and/or human biosolids). Such assessments might be used to identify best practices for mitigating antimicrobial exposure to soils and guide additional research to understand the role of environmental antimicrobial contamination in the problem of AMR.

Tracking Fluorine during Aqueous Photolysis and Advanced UV Treatment of Fluorinated Phenols and Pharmaceuticals Using a Combined 19F-NMR, Chromatography, and Mass Spectrometry Approach.

Fluorine incorporation into organic molecules has increased due to desirable changes in the molecular physiochemical properties. Common fluorine motifs include: aliphatic fluorines and -CF3, or -F containing groups bonded directly onto an aromatic (Ar-CF3 and Ar-F) or heteroaromatic ring. Photolysis of these compounds, either in natural or engineered systems, is a potential source of new fluorinated byproducts. Given the potential persistence and toxicity of fluorinated byproducts, monitoring of product formation during photolysis of various fluorinated motifs is needed. 19F-NMR is a means to detect and quantify these species. Ar-CF3 and Ar-F model compounds (2-, 3-, and 4-(trifluoromethyl)phenol, 2-, 3-, 4-fluorophenol, and 2,6-, 3,5-difluorophenol) were photolyzed under a variety of aqueous conditions: pH 5, pH 7, pH 10, 1 mM H2O2 at pH 7 to form •OH, and 0.5 mM SO3 2- at pH 10 to form eaq -. Pharmaceuticals with the Ar-CF3 (fluoxetine) and Ar-F plus pyrazole-CF3 (sitagliptin) motifs were treated similarly. Parent molecule concentrations were monitored with high pressure liquid chromatography with a UV detector. Fluorine in the parent and product molecules was quantified with 19F-NMR and complete fluorine mass balances were obtained. High resolution mass spectrometry was used to further explore product identities. The major product for Ar-F compounds was fluoride. The Ar-CF3 model compounds led to fluoride and organofluorine products dependent on motif placement and reaction conditions. Trifluoroacetic acid was a product of 4-(trifluoromethyl)phenol and fluoxetine. Additional detected fluoxetine products identified using mass spectrometry resulted from addition of -OH to the aromatic ring, but a dealkylation product could not be distinguished from fluoxetine by 19F-NMR. Sitagliptin formed multiple products that all retained the pyrazole-CF3 motif while the Ar-F motif produced fluoride. 19F-NMR, mass spectrometry, and chromatography methods provide complementary information on the formation of fluorinated molecules by modification or fragmentation of the parent structure during photolysis, allowing screening for fluorinated photoproducts and development of fluorine mass balances.

Quantifying and predicting antimicrobials and antimicrobial resistance genes in waterbodies through a holistic approach: a study in Minnesota, United States.

The environment plays a key role in the spread and persistence of antimicrobial resistance (AMR). Antimicrobials and antimicrobial resistance genes (ARG) are released into the environment from sources such as wastewater treatment plants, and animal farms. This study describes an approach guided by spatial mapping to quantify and predict antimicrobials and ARG in Minnesota's waterbodies in water and sediment at two spatial scales: macro, throughout the state, and micro, in specific waterbodies. At the macroscale, the highest concentrations across all antimicrobial classes were found near populated areas. Kernel interpolation provided an approximation of antimicrobial concentrations and ARG abundance at unsampled locations. However, there was high uncertainty in these predictions, due in part to low study power and large distances between sites. At the microscale, wastewater treatment plants had an effect on ARG abundance (sul1 and sul2 in water; blaSHV, intl1, mexB, and sul2 in sediment), but not on antimicrobial concentrations. Results from sediment reflected a long-term history, while water reflected a more transient record of antimicrobials and ARG. This study highlights the value of using spatial analyses, different spatial scales, and sampling matrices, to design an environmental monitoring approach to advance our understanding of AMR persistence and dissemination.

Exploring the Utility of Compound-Specific Isotope Analysis for Assessing Ferrous Iron-Mediated Reduction of RDX in the Subsurface.

Subsurface contamination with the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) at ordnance production and testing sites is a problem because of the persistence, mobility, and toxicity of RDX and the formation of toxic products under anoxic conditions. While the utility of compound-specific isotope analysis for inferring natural attenuation pathways from stable isotope ratios has been demonstrated, the stable isotope fractionation for RDX reduction by iron-bearing minerals remains unknown. Here, we evaluated N and C isotope fractionation of RDX during reduction by Fe(II) associated with Fe minerals and natural sediments and applied N isotope ratios to the assessment of mineral-catalyzed RDX reduction in a contaminant plume and in sediment columns treated by in situ chemical reduction. Laboratory studies revealed that RDX was reduced to nitroso compounds without denitration and the concomitant ring cleavage. Fe(II)/iron oxide mineral-catalyzed reactions exhibited N isotope enrichment factors, εN, between -6.3±0.3‰ and -8.2±0.2‰, corresponding to an apparent 15N kinetic isotope effect of 1.04-1.05. The observed variations of the δ15N of ∼15‰ in RDX from groundwater samples suggested an extent of reductive transformation of 85% at an ammunition plant. Conversely, we observed masking of N isotope fractionation after RDX reduction in laboratory flow-through systems, which was presumably due to limited accessibility to reactive Fe(II).

Risk of Gastrointestinal Bleeding With Extended Use of Nonsteroidal Anti-Inflammatory Drug Analgesia After Joint Arthroplasty.

BACKGROUND: Chronic nonsteroidal anti-inflammatory drug (NSAID) use is associated with gastrointestinal bleeding via inhibition of endogenous mucosal protection and platelet aggregation. This study aimed to determine whether extended NSAIDs after joint arthroplasty is associated with increased risk of gastrointestinal bleeding. METHODS: This was a retrospective study examining 28,794 adults who underwent joint arthroplasty by one of 50 surgeons from 2016 to 2018. Episodes of gastrointestinal bleeding within 90 days postoperatively were identified prospectively. Postoperative medications were reported directly by patients with electronic questionnaires. The primary analysis was performed using binary logistic regression. RESULTS: A total of 74 (0.26%) episodes of gastrointestinal bleeding occurred within 90 days (median 8 days) postoperatively. Of 5086 patients with complete data included in the primary analysis, 59.6% had used NSAIDs with median duration of 2 weeks (interquartile range, 0-6 weeks). Patients with gastrointestinal bleeding were significantly older (71.3 vs 67.0 years), required longer hospitalizations (2.1 vs 1.5 days), and more commonly had a history of peptic ulcers (10.8% vs 0.9%). However, there was no positive association between NSAID use and gastrointestinal bleeding. In fact, the odds of gastrointestinal bleeding were lower in patients taking NSAIDs. Gastrointestinal bleeding was associated with anticoagulants, antiplatelet agents, and, to a lesser extent, aspirin. CONCLUSION: NSAIDs were not associated with gastrointestinal bleeding and may be prescribed safely for a majority of patients after joint arthroplasty. The greatest odds of gastrointestinal bleeding occurred in patients with peptic ulcer disease and those who received antiplatelet and anticoagulation agents. Increasing age and bilateral surgery were also associated with gastrointestinal bleeding. LEVEL OF EVIDENCE: Level III.

Neonicotinoid Insecticides in Surface Water, Groundwater, and Wastewater Across Land-Use Gradients and Potential Effects.

Neonicotinoid insecticides cause adverse effects on nontarget organisms, but more information about their occurrence in surface and groundwater is needed across a range of land uses. Sixty-five sites in Minnesota, USA, representing rivers, streams, lakes, groundwater, and treated wastewater, were monitored via collection of 157 water samples to determine variability in spatiotemporal neonicotinoid concentrations. The data were used to assess relations to land use, hydrogeologic condition, and potential effects on aquatic life. Total neonicotinoid concentrations were highest in agricultural watersheds (median = 12 ng/L), followed by urban (2.9 ng/L) and undeveloped watersheds (1.9 ng/L). Clothianidin was most frequently detected in agricultural areas (detection frequency = 100%) and imidacloprid most often in urban waters (detection frequency = 97%). The seasonal trend of neonicotinoid concentrations in rivers, streams, and lakes showed that their highest concentrations coincided with spring planting and elevated streamflow. Consistently low neonicotinoid concentrations were found in shallow groundwater in agricultural regions (<1.2-16 ng/L, median = 1.4 ng/L). Treated municipal wastewater had the highest concentrations across all hydrologic compartments (12-48 ng/L, median = 19 ng/L), but neonicotinoid loads from rivers and streams (median = 4100 mg/d) were greater than in treated wastewater (700 mg/d). No samples exceeded acute aquatic-life benchmarks for individual neonicotinoids, whereas 10% of samples exceeded a chronic benchmark for neonicotinoid mixtures. Although 62% of samples contained 2 or more neonicotinoids, the observed concentrations suggest there were low acute and potential chronic risks to aquatic life. This the first study of its size in Minnesota and is critical to better understanding the drivers of wide-scale environmental contamination by neonicotinoids where urban, agricultural, and undeveloped lands are present. Environ Toxicol Chem 2021;40:1017-1033. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Photolysis of atrazine: Role of triplet dissolved organic matter and limitations of sensitizers and quenchers.

Atrazine, a widely used herbicide, is susceptible to photolysis. The role of triplet excited states of chromophoric dissolved organic matter (3CDOM*) in the photolysis of atrazine, however, is not well understood. The direct photolysis of atrazine under irradiation sources (natural sunlight/environmentally relevant simulated solar light) and its indirect photochemical reactivity with model triplet photosensitizers (benzophenone, 2-acetonaphthone, 3'-methoxy-acetophenone, 4-carboxybenzophenone, rose bengal, methylene blue, and anthraquinone-2-sulphonate) was investigated. The reactivity of the model sensitizers and DOM (Suwannee River natural organic matter, river/lake water, and wastewater effluent), were compared. The direct photolysis quantum yield was determined as 0.0196 mol Einstein-1 in a solar simulator and 0.00437 mol Einstein-1 under natural sunlight. Considerable photosensitization was induced by triplet state (n-π*) model sensitizers, while insignificant effects on atrazine loss were discerned in natural organic matter even when oxygen, a triplet quencher, was removed. The triplet sensitizers benzophenone and 2-acetylnaphthone reacted with L-histidine and 2-propanol that were intended to quench/ scavenge 1O2 and hydroxyl radical •OH, respectively, and benzophenone reacted with NaN3 as a 1O2 scavenger and furfuryl alcohol as a 1O2 trapping agent, indicating quenchers may have unanticipated effects when using model sensitizers. Atrazine loss via reaction with 3DOM* will be relevant only in selected conditions, and this work provides a more comprehensive view on the use of model photosensitizers to mimic triplet 3DOM*.

Prediction of Photochemically Produced Reactive Intermediates in Surface Waters via Satellite Remote Sensing.

Absorption of solar radiation by colored dissolved organic matter (CDOM) in surface waters results in the formation of photochemically produced reactive intermediates (PPRIs) that react with pollutants in water. Knowing the steady-state concentrations of PPRIs ([PPRI]ss) is critical to predicting the persistence of pollutants in sunlit surface waters. CDOM levels (a440) can be measured remotely for lakes over large areas using satellite imagery. Laboratory measurements of [PPRI]ss and apparent quantum yields (Φ) of three PPRIs (3DOM*, 1O2, and •OH) were made for 24 lake samples under simulated sunlight. The total rate of light absorption by the water samples (Ra), the rates of formation (Rf), and [PPRI]ss of 3DOM* and 1O2 linearly increased with increasing a440. The production rate of •OH was linearly correlated with a440, but the steady-state concentration was best fit by a logarithmic function. The relationship between measured a440 and Landsat 8 reflectance was used to map a440 for more than 10 000 lakes across Minnesota. Relationships of a440 with Rf, [PPRIs]ss, and Ra were coupled with satellite-based a440 assessments to map reactive species production rates and concentrations as well as contaminant transformation rates. This study demonstrates the potential for using satellite imagery for estimating contaminant loss via indirect photolysis in lakes.

Photochemical fate of quaternary ammonium compounds in river water.

Quaternary ammonium compounds (QACs) are not completely removed during wastewater treatment and are frequently detected in surface waters and sediments. The photochemical transformation of QACs has not been thoroughly investigated as a potential degradation pathway affecting their fate in the environment. Kinetic studies of common QACs with and without aromatic groups under simulated and natural sunlight conditions were performed with model sensitizers and dissolved organic matter to estimate photochemical half-lives in the aquatic environment. All QACs investigated react with hydroxyl radicals at diffusion-controlled rates (∼2.9 × 109 to 1.2 × 1010 M-1 s-1). Benzethonium reacted via direct photolysis (ΦBZT,outdoor = 1.7 × 10-2 (mol Ei-1)). Benzethonium also reacted with the triplet excited state model sensitizer 2-acetylnaphthalene, but evidence suggests this reaction pathway is unimportant in natural waters due to faster quenching of the triplet 2-acetylnapthalene by oxygen. Reactivity with singlet oxygen for the QACs was minimal. Overall, reactions with hydroxyl radicals will dominate over direct photolysis due to limited spectral overlap of sunlight emission and QAC absorbance. Photolysis half-lives are predicted to be 12 to 94 days, indicating slow abiotic degradation in surface water.