Synthesizing Laboratory and Field Experiments to Quantify Dominant Transformation Mechanisms of 2,4-Dichlorophenoxyacetic Acid (2,4-D) in Aquatic Environments

Synergistic degradation of 2,4-dichlorophenoxyacetic acid in water by interfacial pre-reduction enhanced peroxymonosulfate activation derived from novel zero-valent iron/biochar

Iron-based biochar exhibits great potential in degrading emerging pollutants and remediation of water environments. In this study, a highly efficient catalytic Fe0/biochar (MZB-800) was synthesized by the co-pyrolysis of poplar sawdust and K2FeO4 at 800 °C. A novel water purification technology of pre-reduction followed by PMS activation for MZB-800 was proposed to degrade the refractory 2,4-dichlorophenoxyacetic acid (2,4-D) pesticide. The corrosive effect of the strong oxidizing potassium salt endowed the MZB-800 surface with more Fe0 and porous structure, achieving greater 2,4-D adsorption binding energy. The removal efficiency of MZB-800 on 2,4-D was greater than that of biochar (BC) and conventional Fe0/biochar (Fe-BC) prepared by FeCl3·6 H2O as the precursor. The proposed novel water purification technology showed the synergistic effect between the interfacial pre-reduction and the PMS activation derived by MZB-800. Regarding 2,4-D degradation and dechlorination performance, the synergistic coefficient between pre-reduction and subsequent PMS activation for MZB-800 were 2 and 1.4 respectively. Based on the normalized kinetic analysis and the Langmuir-Hinshelwood model, we proposed the underlying mechanism of MZB-800 interfacial pre-reduction and subsequent PMS activation for synergistic removal of 2,4-D. The large amount of Fe2+ and hydroxyl density accumulated by the Fe0 and hydroquinone structures on the MZB-800 surface during the pre-reduction stage provided abundant active sites for the subsequent activation of PMS. The improved activation reaction rate generated more reactive oxygen species, further strengthening the removal efficiency of 2,4-D. This work manifested that the novel water purification technology of pre-reduction/PMS activation of iron-based biochar is feasible for removing emerging pollutants in the water environment. ENVIRONMENTAL IMPLICATION: Extensive abuse of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide with high solubility and refractory degradation has caused environmental pollution and ecological deterioration. This manuscript described a novel water purification technology, centered on high-efficiency Fe0/biochar and utilizing pre-reduction and PMS reactivation strategies to synergistically degrade 2,4-D, which had strong environmental relevance. By elucidating the synergistic removal mechanism, the research provided valuable insights into removing emerging pollutants, thus promoting environmental sustainability and safeguarding ecosystem health. Overall, it is of high importance to provide a feasible and efficient method for removing hazardous 2,4-D from water environments, which contributes to addressing pressing environmental problems.

The effects of commercial 2,4-D herbicide on game fish species: Natural lake water vs. laboratory system water

Aquatic herbicides with active ingredient 2,4-dichlorophenoxyacteic acid (2,4-D) are commonly used to control and combat aquatic non-native species that cause detrimental impacts including habitat destruction, strained resources among biota, and biodiversity loss. While many (eco)toxicology studies are performed in the laboratory under highly controlled circumstances, these studies may disregard the nuances and disorder that come with the complexity of natural aquatic ecosystems. Therefore, we conducted a series of laboratory experiments using laboratory system water, different lake waters, and different water parameters to determine the effects of ecologically relevant concentrations of 2,4-D (0.00-4.00 ppm a.e.) on the development and survival of two freshwater game species (Sander vitreus and Esox lucius). For 2,4-D exposures using different water sources, there were significant main effects of 2,4-D concentration and water source on walleye embryo and larval survival, however, there was no significant interaction between 2,4-D exposure and water source. For 2,4-D exposures and pH (5-9 pH), there were significant main effects of 2,4-D concentration and pH on walleye and northern pike embryo survival and a significant interaction between 2,4-D exposure and pH. Our results indicate that 2,4-D exposures in controlled laboratory system water can predict similar outcomes as 2,4-D exposures in natural lake water. Moreover, individual water parameters, such as pH, play a significant role in the toxicity of 2,4-D. Taken together, these results suggest that highly controlled laboratory studies are a useful tool for predicting impacts on survival of non-target fish in natural waters, but it is crucial for management agencies to consider individual water sources and specific lake water parameters in herbicide risk assessments to minimize the impacts to non-target organism.

A novel Zn2+-coordination fluorescence probe for sensing HPPD inhibitors and its application in environmental media and biological imaging

Mesotrione, topramezone, tembotrione, and sulcotrione are four types of 4-hydroxyphenylpyruvate dioxidase (HPPD) inhibitor herbicides that are extensively employed in agricultural practices, but their usage also leads to environmental pollution and poses risks to human health. A probe (E)-1-((2-(pyridin-2-yl) hydrazineylidene) methyl) naphthalen-2-ol (CHMN) based on chelation enhancement (CHEF) effect synthesized. CHMN was first chelated with Zn2+ to form a probe system with green, which can be further used to detect mesotrione, topramezone, tembotrione and sulcotrione in complicated environment. CHMN-Zn2+ detection of four pesticides was accurate, with an excellent linear relationship between 0 and 100 μM. The detection limits were LODmesotrione = 7.79 μM, LODtopramezone = 1.91 μM, LODtembotrione = 1.38 μM and LODsulcotrione = 2.43 μM. The detection time is 1 min, and it is successfully applied in real water sample and bioimaging. This work can provide a novel method for studying the migration and behavior of environmental pollutants.

Laboratory measurements underestimate persistence of the aquatic herbicide fluridone in lakes

Fluridone is an aquatic herbicide commonly used to treat invasive freshwater plant species such as Eurasian watermilfoil, hydrilla, and curly-leaf pondweed. However, required exposures times are very long and often exceed 100 days. Thus, understanding the mechanisms that determine the fate of fluridone in lakes is critical for supporting effective herbicide treatments and minimizing impacts to non-target species. We use a combination of laboratory and field studies to quantify fluridone photodegradation, as well as sorption and microbial degradation in water and sediment microcosms. Laboratory irradiation studies demonstrate that fluridone is susceptible to direct photodegradation with negligible indirect photodegradation, with predicted half-lives in sunlight ranging from 2.3 days (1 cm path length) to 118 days (integrated over 1 meter). Biodegradation is attributable to microbes in sediment with an observed half-life of 57 days. Lastly, fluridone sorbs to sediments (Koc = 340 ± 28 L kg-1); sorption accounts for 16% of fluridone loss in the microcosm experiments. While the laboratory results indicate that all three loss pathways can influence fluridone fate, these controlled studies oversimplify herbicide behavior due to their inability to replicate field conditions. Fluridone concentration measurements in a lake following commercial application demonstrate a half-life of >150 days, indicating that the herbicide is very persistent in water. This study illustrates why caution should be used when relying on laboratory studies to predict the fate of pesticides and other polar organic compounds in the environment.

Insights on biotic and abiotic 2,4-dichlorophenoxyacetic acid degradation by anaerobic iron-cycling bacteria

The use of the phenoxy herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has been steadily increasing in recent years due to its selectivity against broad-leafed weeds and use on genetically modified crops resistant to 2,4-D. This increases the likelihood of 2,4-D persisting in agriculturally impacted soils, sediments, and aquatic systems. Aerobic microorganisms are capable of degrading 2,4-D enzymatically. Anaerobic degradation also occurs, though the enzymatic pathway is unclear. Iron-reducing bacteria (FeRB) have been hypothesized to augment anaerobic degradation through the production of a chemically reactive Fe(II) adsorbed to Fe(III) oxyhydroxides. To test whether this iron species can catalyze abiotic degradation of 2,4-D, an enrichment culture (BLA1) containing a photosynthetic Fe(II)-oxidizing bacterium (FeOB) "Candidatus Chlorobium masyuteum" and the FeRB "Candidatus Pseudopelobacter ferreus", both of which lacked known 2,4-D degradation genes was investigated. BLA1 produces Fe(II)-adsorbed to Fe(III) oxyhydroxides during alternating photoautotrophic iron oxidation and dark iron reduction (amended with acetate) cycles. No 2,4-D degradation occurred during iron oxidation by FeOB Ca. C. masyuteum or during iron reduction by FeRB Ca. P. ferreus under any incubation conditions tested (i.e., +/-Fe(II), +/-cells, and +/-light), or due to the presence of Fe(II) adsorbed to Fe(III) oxyhydroxides. Our results cast doubt on the hypothesis that the mineral-bound Fe(II) species augments the anaerobic degradation of 2,4-D in anoxic soils and waters by iron-cycling bacteria, and further justify the need to identify the genetic underpinnings of anaerobic 2,4-D degradation.

Limitations of conventional approaches to identify photochemically produced reactive intermediates involved in contaminant indirect photodegradation

Dissolved organic matter (DOM) mediated indirect photodegradation can play an important role in the degradation of aquatic contaminants. Predicting the rate of this process requires knowledge of the photochemically produced reactive intermediates (PPRI) that react with the compound of interest, as well as the ability of individual DOM samples to produce PPRI. Key PPRI are typically identified using quencher studies, yet this approach often leads to results that are difficult to interpret. In this work, we analyze the indirect photodegradation of atorvastatin, carbamazepine, sulfadiazine, and benzotriazole using a diverse set of 48 waters from natural and engineered aquatic systems. We use this large data set to evaluate relationships between PPRI formation and indirect photodegradation rate constants, which are directly compared to results using standard quenching experiments. These data demonstrate that triplet state DOM (3DOM) and singlet oxygen (1O2) are critical PPRI for atorvastatin, carbamazepine, and sulfadiazine, while hydroxyl radical (˙OH) contributes to the indirect photodegradation of benzotriazole. We caution against relying on quenching studies because quenching of 3DOM limits the formation of 1O2 and all studied quenchers react with ˙OH. Furthermore, we show that DOM composition directly influences indirect photodegradation and that low molecular weight, microbial-like DOM is positively correlated with the indirect photodegradation rates of carbamazepine, sulfadiazine, and benzotriazole.

Quantifying the Role of Simultaneous Transformation Pathways in the Fate of the Novel Aquatic Herbicide Florpyrauxifen-Benzyl

Predicting the fate of organic compounds in the environment is challenging due to the inability of laboratory studies to replicate field conditions. We used the intentionally applied aquatic herbicide florpyrauxifen-benzyl (FPB) as a model compound to investigate the contribution of multiple transformation pathways to organic compound fate in lakes. FPB persisted in five Wisconsin lakes for 5-7 days with an in-lake half-life of <2 days. FPB formed four transformation products, with the bioactive product florpyrauxifen persisting up to 30 days post-treatment. Parallel laboratory experiments showed that FPB degrades to florpyrauxifen via base-promoted hydrolysis. Hydroxy-FPB and hydroxy-florpyrauxifen were identified as biodegradation products, while dechloro-FPB was identified as a photoproduct. Material balance calculations using both laboratory rates and field product concentrations demonstrated that hydrolysis (∼47% of loss), biodegradation (∼20%), sorption (∼13%), and photodegradation (∼4%) occurred on similar timescales. Furthermore, the combined results demonstrated that abiotic and plant-catalyzed hydrolysis of FPB to florpyrauxifen, followed by biodegradation of florpyrauxifen to hydroxy-florpyrauxifen, was the dominant transformation pathway in lakes. This study demonstrates how combined field and laboratory studies can be used to elucidate the role of simultaneous and interacting pathways in the fate of organic compounds in aquatic environments.

Elucidating the effects of acute and chronic exposure to 2,4-Dichlorophenoxyacetic acid on fathead minnow (Pimephales promelas) innate immunity

Aquatic herbicides, such as 2,4-dichlorophenoxyacetic acid (2,4-D) formulations, are commonly used for invasive species management throughout the United States. Ecologically relevant concentrations of 2,4-D can impair essential behaviors, reduce survival, and act as an endocrine disruptor; however, there is limited knowledge of its effects on the health of non-target organisms. Here, we investigate the acute and chronic exposure impacts of 2,4-D on adult male and female fathead minnow (Pimephales promelas) innate immune function. We exposed both adult male and female fathead minnows to three different ecologically relevant concentrations of 2,4-D (0.00, 0.40, and 4.00 mg/L) and took blood samples at three acute time points (6, 24, and 96 h) and one chronic time point (30 days). We found that male fatheads had higher total white blood cell concentrations when exposed to 2,4-D at the acute time points. For the females, only proportions of specific cell types were altered when exposed to 2,4-D at the acute time points. However, we did not observe any significant impacts of chronic exposure to 2,4-D on any innate immune responses for either males or females. Overall, this study is the first step in answering an important question for game fisheries and management agencies while providing insight to future studies that investigate the impacts of herbicide exposure to freshwater fish health and immunity.