Facile nanoplastics formation from macro and microplastics in aqueous media.

The immense production of plastic polymers combined with their discordancy with nature has led to vast plastic waste contamination across the geosphere, from the oceans to freshwater reservoirs, wetlands, remote snowpacks, sediments, air and multiple other environments. These environmental pollutants include microplastics (MP), typically defined as small and fragmented plastics less than 5 mm in size, and nanoplastics (NP), particles smaller than a micrometer. The formation of micro and nanoplastics in aqueous media to date has been largely attributed to fragmentation of plastics by natural (i.e., abrasion, photolysis, biotic) or industrial processes. We present a novel method to create small microplastics (≲ 5 µm) and nanoplastics in water from a wide variety of plastic materials using a small volume of a solubilizer liquid, such as n-dodecane, in combination with vigorous mixing. When the suspensions or solutions are subjected to ultrasonic mixing, the particle sizes decrease. Small micro- and nanoparticles were made from commercial, real world and waste (aged) polyethylene, polystyrene, polycarbonate and polyethylene terephthalate, in addition to other plastic materials and were analyzed using dark field microscopy, Raman spectroscopy and particle size measurements. The presented method provides a new and simple way to create specific size distributions of micro- and nanoparticles, which will enable expanded research on these plastic particles in water, especially those made from real world and aged plastics. The ease of NP and small MP formation upon initial mixing simulates real world environments, thereby providing further insight into the behavior of plastics in natural settings.

Tracking the distribution of microfiber pollution in a southern Lake Michigan watershed through the analysis of water, sediment and air.

Microplastic waste is a worldwide problem, heavily afflicting marine and freshwater environments; the loading of this pollution in water, sediment and living organisms continues to escalate. Synthetic microfibers, resulting from the release of microscopic fibers from synthetic textiles, constitute the most prevalent type of microplastics pollution in aquatic environments. This study investigated the origin and distribution of synthetic microfibers in a representative Lake Michigan watershed in Indiana (USA) by analyzing water, sediment and air samples above and below wastewater treatment plant discharges, downstream in the watershed and water from the Lake Michigan shoreline. Synthetic microfibers were also quantified in wastewater from a local wastewater treatment plant (WWTP) and in laundry effluent. Laboratory testing of numerous fabrics suggests that Fenton oxidation, used to break down natural fibers, effectively eliminates non-polluting, natural fibers from the samples. However, the hydroxyl radical-mediated oxidation bleaches the dye from certain synthetic microfibers, which likely leads to under-reported values for these microplastics in natural samples. The data collected from the watershed samples indicate that approximately 4 billion synthetic microfibers are transported daily through the Lake Michigan tributary. Wastewater effluent is not the only source of synthetic microfibers, since surface water samples above the WWTP contained a similar load to downstream samples. Repeated sampling exhibited variability in the number of microfibers detected, substantiating the heterogeneous distribution of these pollutants and the requirement for multiple samples for a given site. The average load of synthetic microfibers from water sampled at the Lake Michigan shoreline was higher than the tributary water, suggesting the shoreline functions as a repository for the microfibers. Given the extent and potential consequences of this pollution, quantification of the ubiquitous plastic fibers can be instituted as part of the traditional total suspended solids (TSS) water quality monitoring parameter.

31P NMR study of the activated radioprotection mechanism of octylphenyl-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) and analogues.

We report a 31P NMR investigation into the activated radioprotection mechanism of octylphenyl-N,N-diisobutyl-carbamoylmethyl phosphine oxide (CMPO) and analogues in the presence of a gamma radiation field. CMPO exhibits significantly enhanced radiation resistance in the presence of high nitric acid concentrations, compared to other ligands proposed for recovery of the trivalent actinides from spent nuclear fuel. The fundamental mechanism behind this activated radioprotection has been investigated using 31P NMR and other supporting analytical techniques (GCMS and LCMS) in conjunction with systematic gamma irradiation studies, covering solvent system formulation and structural effects through the use of the CMPO analogues, dioctylphenylphospine oxide (DOPPO) and trioctylphosphine oxide (TOPO). These experiments have demonstrated that the acid-dependent, radioprotection mechanism requires a protonated phenyl-phosphine oxide motif to activate. Further, contacting these three ligand loaded organic phases with a range of mineral acids (nitric, sulfuric, hydrochloric, and perchloric acids) shows specificity for nitric acid (HNO3), and the formation of a distinct [ligand·HNO3] complex for CMPO and DOPPO, as identified by 31P NMR, and predicted by DFT calculations. We propose that this complex is capable of sequential n-dodecane excited state quenching through the conjugated aromatic functionalities on the constituent CMPO and DOPPO molecules.

Time-resolved and steady-state irradiation of hydrophilic sulfonated bis-triazinyl-(bi)pyridines - modelling radiolytic degradation.

Efficient separation of the actinides from the lanthanides is a critical challenge in the development of a more sophisticated spent nuclear fuel recycling process. Based upon the slight differences in f-orbital distribution, a new class of soft nitrogen-donor ligands, the sulfonated bis-triazinyl-(bi)pyridines, has been identified and shown to be successful for this separation under anticipated, large-scale treatment conditions. The radiation robustness of these ligands is key to their implementation; however, current stability studies have yielded conflicting results. Here we report on the radiolytic degradation of the sulfonated 2,6-bis(1,2,4-triazin-3-yl)pyridine (BTP(S)) and 6,6'-bis(1,2,4-triazin-3-yl)-2,2'-bipyridine (BTBP(S)) in aerated, aqueous solutions using a combination of time-resolved pulsed electron techniques to ascertain their reaction kinetics with key aqueous radiolysis products (eaq-, H˙, ˙OH, and ˙NO3), and steady state gamma radiolysis in conjunction with liquid chromatography for identification and quantification of both ligands as a function of absorbed dose. These data were used to construct a predictive deterministic model to provide critical insight into the fundamental radiolysis mechanisms responsible for the ligands' radiolytic stability. The first-order decays of BTP(S) and BTBP(S) are predominantly driven by oxidative processes (˙OH and, to a lesser extent, H2O2), for which calculations demonstrate that the rate of degradation is inhibited by the formation of ligand degradation products that undergo secondary reactions with the primary products of water radiolysis. Overall, BTP(S) is ∼20% more radiolytically stable than BTBP(S), but over 90% of either ligand is consumed within 1 kGy.

Oxidative remediation of 4-methylcyclohexanemethanol (MCHM) and propylene glycol phenyl ether (PPh). Evidence of contaminant repair reaction pathways.

A large spill of 4-methylcyclohexanemethanol (MCHM) and propylene glycol phenyl ether (PPh) into the Elk River near Charleston, West Virginia on January 9, 2014 led to serious water contamination and public concerns about appropriate remediation. To assess the feasibility of advanced oxidation processes (AOPs) for remediation of waters contaminated with these compounds, we induced hydroxyl radical (HO˙) reactions using time-resolved and steady-state radiolysis methods. Detailed product analyses showed initial HO˙ attack was at the benzene ring of PPh, and occurred through H-atom abstraction reactions for MCHM. Pulse radiolysis and steady state radiolysis experiments conducted using pure compound solutions, mixtures of the compounds and real water solvents allowed us to obtain mechanistic insights of hydroxyl radical attack and establish the fate of the compounds using AOP remediation technologies. These results demonstrate that hydroxyl radical induced oxidization of PPh can lead to "repair-type" reactions, which regenerates this contaminant. The study further highlights the importance of such counterproductive reactions for the quantitative estimate of the required amount of oxidant in any large-scale treatment approaches.

Virulence and biodegradation potential of dynamic microbial communities associated with decaying Cladophora in Great Lakes.

Cladophora mats that accumulate and decompose along shorelines of the Great Lakes create potential threats to the health of humans and wildlife. The decaying algae create a low oxygen and redox potential environment favoring growth and persistence of anaerobic microbial populations, including Clostridium botulinum, the causal agent of botulism in humans, birds, and other wildlife. In addition to the diverse population of microbes, a dynamic chemical environment is generated, which involves production of numerous organic and inorganic substances, many of which are believed to be toxic to the sand and aquatic biotic communities. In this study, we used 16S-rDNA-based-amplicon sequencing and microfluidic-based quantitative PCR approaches to characterize the bacterial community structure and the abundances of human pathogens associated with Cladophora at different stages (up to 90days) of algal decay in laboratory microcosms. Oxygen levels were largely depleted after a few hours of incubation. As Cladophora decayed, the algal microbial biodiversity decreased within 24h, and the mat transitioned from an aerobic to anaerobic environment. There were increasing abundances of enteric and pathogenic bacteria during decomposition of Cladophora, including Acinetobacter, Enterobacter, Kluyvera, Cedecea, and others. In contrast, there were no or very few sequences (<0.07%) assigned to such groups in fresh Cladophora samples. Principal coordinate analysis indicated that the bacterial community structure was dynamic and changed significantly with decay time. Knowledge of microbial communities and chemical composition of decaying algal mats is critical to our further understanding of the role that Cladophora plays in a beach ecosystem's structure and function, including the algal role in trophic interactions. Based on these findings, public and environmental health concerns should be considered when decaying Cladophora mats accumulate Great Lakes shorelines.

N-nitrosodimethylamine (NDMA) formation from the ozonation of model compounds.

Nitrosamines are a class of toxic disinfection byproducts commonly associated with chloramination, of which several were included on the most recent U.S. EPA Contaminant Candidate List. Nitrosamine formation may be a significant barrier to ozonation in water reuse applications, particularly for direct or indirect potable reuse, since recent studies show direct formation during ozonation of natural water and treated wastewaters. Only a few studies have identified precursors which react with ozone to form N-nitrosodimethylamine (NDMA). In this study, several precursor compound solutions, prepared in ultrapure water and treated wastewater, were subjected to a 10 M excess of ozone. In parallel experiments, the precursor solutions in ultrapure water were exposed to gamma radiation to determine NDMA formation as a byproduct of reactions of precursor compounds with hydroxyl radicals. The results show six new NDMA precursor compounds that have not been previously reported in the literature, including compounds with hydrazone and carbamate moieties. Molar yields in deionized water were 61-78% for 3 precursors, 12-23% for 5 precursors and <4% for 2 precursors. Bromide concentration was important for three compounds (1,1-dimethylhydrazine, acetone dimethylhydrazone and dimethylsulfamide), but did not enhance NDMA formation for the other precursors. NDMA formation due to chloramination was minimal compared to formation due to ozonation, suggesting distinct groups of precursor compounds for these two oxidants. Hydroxyl radical reactions with the precursors will produce NDMA, but formation is much greater in the presence of molecular ozone. Also, hydroxyl radical scavenging during ozonation leads to increased NDMA formation. Molar conversion yields were higher for several precursors in wastewater as compared to deionized water, which could be due to catalyzed reactions with constituents found in wastewater or hydroxyl radical scavenging.

Free-radical-induced oxidative and reductive degradation of sulfa drugs in water: absolute kinetics and efficiencies of hydroxyl radical and hydrated electron reactions.

Absolute rate constants and degradation efficiencies for hydroxyl radical and hydrated electron reactions with four different sulfa drugs in water have been evaluated using a combination of electron pulse radiolysis/absorption spectroscopy and steady-state radiolysis/high-performance liquid chromatography measurements. For sulfamethazine, sulfamethizole, sulfamethoxazole, and sulfamerazine, absolute rate constants for hydroxyl radical oxidation were determined as (8.3 +/- 0.8) x 10(9), (7.9 +/- 0.4) x 10(9), (8.5 +/- 0.3) x 10(9), and (7.8 +/- 0.3) x 10(9) M(-1) s(-1), respectively, with corresponding degradation efficiencies of 36% +/- 6%, 46% +/- 8%, 53% +/- 8%, and 35% +/- 5%. The reduction of these four compounds by their reaction with the hydrated electron occurred with rate constants of (2.4 +/- 0.1) x 10(10), (2.0 +/- 0.1) x 10(10), (1.0 +/- 0.03) x 10(10), and (2.0 +/- 0.1) x 10(10) M(-1) s(-1), respectively, with efficiencies of 0.5% +/- 4%, 61% +/- 9%, 71% +/- 10%, and 19% +/- 5%. We propose that hydroxyl radical adds predominantly to the sulfanilic acid ring of the different sulfa drugs based on similar hydroxyl radical rate constants and transient absorption spectra. In contrast, the variation in the rate constants for hydrated electrons with the sulfa drugs suggests the reaction occurs at different reaction sites, likely the different heterocyclic rings. The results of this study provide fundamental mechanistic parameters, hydroxyl radical and hydrated electron rate constants, and degradation efficiencies that are critical for the evaluation and implementation of advanced oxidation processes (AOPs).