Photochemical Pathways of Rotenone and Deguelin Degradation: Implications for Rotenoid Attenuation and Persistence in High-Latitude Lakes

Simple on-site extraction and GC-MS analysis of rotenone and degradation products for monitoring invasive fish eradication treatments in fresh and brackish waters

The introduction of invasive fish species to aquatic ecosystems has been demonstrated to cause disastrous ecological effects. Current conservation strategies regard rotenone-containing piscicide formulations, such as commercial product CFT Legumine, as a potentially viable alternative to the cumbersome traditional approaches to fish eradication. This consideration relies on the fast degradation of rotenone and its relatively rapid dissipation from the environment. Piscicide treatments in fragile aquatic ecosystems should thus monitor not only rotenone concentrations following application, but also other byproducts and degradation products. We present a methodology for the analysis of rotenoids in fresh and brackish waters that addresses two main challenges: the accurate determination of applied concentrations in different salinity concentrations by performing a simplified on-site solid-phase extraction, overcoming the fast degradation of rotenone in sample storage conditions, and the selective analysis of rotenoid byproducts and degradation products by gas chromatography coupled to mass spectrometry. Limits of quantification were below the ecological no-effect concentration of rotenone (2 µg/L) and average recoveries exceeded 80%. Accuracy (compared to expected values) and precision (deviation of replicates) ranged from 78 to 103% and 3 to 14%, respectively, across various rotenoid concentrations. These metrics are more than satisfactory for the intended application of this simplified procedure. The method was applied to piscicide-treated samples, revealing significant and fast degradation of parent rotenoids in storage conditions, as well as a non-negligible accumulation of rotenone in the particulate fraction of water that could impact the effectivity of eradication efforts.

Non-target analysis of crude oil photooxidation products at high latitudes and their biological effects

With new oil and gas lease sales in high-latitude regions, there exists a need to better understand the chemical fate of spilled oil and its effects on biological life. To address this need, laboratory simulations of crude oil spills under sub-Arctic conditions were conducted using artificial seawater and exposure to solar irradiation to create Hydrocarbon Oxidation Products (HOPs). HOPs characterization and their biological effects were assessed using ultra high-performance liquid chromatography (UHPLC) with high resolution mass Orbitrap spectrometry and the aryl hydrocarbon receptor (AhR) chemically activated luciferase gene expression (CALUX) assay. Non-target UHPLC-Orbitrap mass spectrometry analysis identified 251 HOPs that were in greater abundance in light-exposed samples than dark controls. Oxidized polycyclic aromatic hydrocarbons were also detected, including phenanthrene quinone, anthraquinone, hydroxyanthraquinone, and 9-fluoreneone. The composition of HOPs were consistent with photo-products of alkylated two to four ring PAHs, primarily compounds between 1 and 3 aromatic rings and 1-3 oxygens. The HOP mixture formed during photochemical weathering of Cook Inlet crude oil induced greater AhR activity than parent petroleum products solubilized in dark controls, indicating that HOPs, as a complex mixture, may contribute to petroleum toxicity more than the parent petroleum compounds. These non-targeted approaches provide the most comprehensive analysis of hydrocarbon oxidation products to date, highlighting the diversity of the complex mixture resulting from the photooxidation of crude oil and the limitations of targeted analyses for adequately monitoring HOPs in the environment. Taken together, these data identify a critical "blind spot" in environmental monitoring and spill clean-up strategies as there is a diverse pool of HOPs that may negatively impact human and ecosystem health.

Reactive Oxygen Species and Chromophoric Dissolved Organic Matter Drive the Aquatic Photochemical Pathways and Photoproducts of 6PPD-quinone under Simulated High-Latitude Conditions

The photochemical degradation pathways of 6PPD-quinone (6PPDQ, 6PPD-Q), a toxic transformation product of the tire antiozonant 6PPD, were determined under simulated sunlight conditions typical of high-latitude surface waters. Direct photochemical degradation resulted in 6PPDQ half-lives ranging from 17.5 h at 20 °C to no observable degradation over 48 h at 4 °C. Sensitization of excited triplet-state pathways using Cs+ and Ar purging demonstrated that 6PPDQ does not decompose significantly from a triplet state relative to a singlet state. However, assessment of processes involving reactive oxygen species (ROS) quenchers and sensitizers indicated that singlet oxygen and hydroxyl radical do significantly contribute to the degradation of 6PPDQ. Investigation of these processes in natural lake waters indicated no difference in attenuation rates for direct photochemical processes at 20 °C. This suggests that direct photochemical degradation will dominate in warm waters, while indirect photochemical pathways will dominate in cold waters, involving ROS mediated by chromophoric dissolved organic matter (CDOM). Overall, the aquatic photodegradation rate of 6PPDQ will be strongly influenced by the compounding effects of environmental factors such as light screening and temperature on both direct and indirect photochemical processes. Transformation products were identified via UHPLC-Orbitrap mass spectrometry, revealing four major processes: (1) oxidation and cleavage of the quinone ring in the presence of ROS, (2) dealkylation, (3) rearrangement, and (4) deamination. These data indicate that 6PPDQ can photodegrade in cool, sunlit waters under the appropriate conditions: t1/2 = 17.4 h tono observable decrease (direct); t1/2 = 5.2-11.2 h (indirect, CDOM).

Mechanistic investigation of direct photodegradation of chloroquine phosphate under simulated sunlight

Chloroquine phosphate (CQ) is an antiviral drug for Coronavirus Disease 2019 and an old drug for treatment of malaria, which has been detected in natural waters. Despite its prevalence, the environmental fate of CQ remains unclear. In this study, the direct photodegradation of CQ under simulated sunlight was investigated. The effect of various parameters such as pH, initial concentration and environmental matrix were examined. The photodegradation quantum yield of CQ (4.5 × 10^-5-0.025) increased with the increasing pH value in the range of 6.0-10.0. The electron spin resonance (ESR) spectrometry and quenching experiments verified that the direct photodegradation of CQ was primarily associated with excited triplet states of CQ (³CQ*). The common ions had negligible effect and humic substances exhibited a negative effect on CQ photodegradation. The photoproducts were identified using high-resolution mass spectrometry and the photodegradation pathway of CQ was proposed. The direct photodegradation of CQ involved the cleavage of the C-Cl bond and substitution of the hydroxyl group, followed by further oxidation to yield carboxylic products. The photodegradation processes were further confirmed by the density functional theory (DFT) computation for the energy barrier of CQ dichlorination. The findings contribute to the assessment of the ecological risk associated with the overuse of Coronavirus drugs during global public health emergencies.

Field and laboratory characterization of rotenone attenuation in eight lakes of the Kenai Peninsula, Alaska

Rotenone is a pesticide commonly used to eradicate Northern Pike (Esox lucius), an invasive species, in Southcentral Alaska. The present work incorporates a field investigation of rotenone attenuation in eight lakes of the Kenai Peninsula, following a CFT Legumine® treatment in October 2018 and a laboratory simulation to determine persistence under light/dark and sterile/nonsterile conditions representative of Southcentral Alaskan winters. In the field, rotenone degraded within <60 days of application in all lakes, while rotenolone, the primary product of rotenone degradation, persisted for up to <280 days post-treatment at two locations. Prolonged rotenolone attenuation was most likely caused by short days and ice cover between October and April. This hypothesis was supported by a laboratory simulation which revealed photolysis as the dominant process driving the overall degradation of rotenone and that microbial degradation will significantly contribute in the absence of sunlight under simulated "winter" conditions of 4 °C. Degradation model fit comparisons (pseudo-first order, multi-parameter linear, and gamma) indicate the most accurate prediction occurred when modeling all eight lakes grouped together in a single dataset, combined and treated with pseudo-first order model kinetics, based on Akaike information criteria (AIC) scores.