The potential of fluorescent dyes-comparative study of Nile red and three derivatives for the detection of microplastics.

During the last years, microplastics in the environment came to the fore in environmental science research. For an appropriate risk assessment, it is essential to know the levels of microplastic contamination in the environment. In the field of microplastic detection, extensive research has been carried out in recent years. While common methods such as Raman spectroscopy and pyrolysis GC-MS are time-consuming and require trained staff and expensive equipment, there is the need for a cheap and easily applicable method. Staining microplastics with the fluorescent dye Nile red (NR) has a high potential to fulfill these criteria. In our work, we tested Nile red and newly developed derivatives, with the aim of achieving greater selectivity for plastic particles and more intense fluorescence. In addition, the influence of using different solvents and water at different pH values in the dyeing process was investigated by analyzing solid sample fluorescence spectra of dyed microplastics and natural particles. Finally, the method developed from the acquired knowledge was tested for sea salt. Graphical abstract.

Method for rapid biofilm cultivation on microplastics and investigation of its effect on the agglomeration and removal of microplastics using organosilanes.

Since microplastics were recognized as a global environmental problem in the early 2000s, research began on possible solutions such as the removal of microplastics from waters. A novel and promising approach for this purpose is microplastics agglomeration-fixation using organosilanes. In this study, it is investigated how biofilm coverage of microplastics affects this process. The biofilm was grown on the microplastics by cultivating it for one week in a packed bed column operated with biologically treated municipal wastewater enriched with glucose. The biofilm was characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and Fourier-Transform infrared spectroscopy (FT-IR). The results show a partial coverage of the microplastics with attached bacteria and extracellular polymeric substances (EPS) after 7 days of incubation. Comparing five polymer types (polyethylene, polypropylene, polyamide, polyester, and polyvinyl chloride) and three organosilanes, the biofilm coverage caused a reduced removal efficiency for all combinations tested as it changes the surface chemistry of the microplastics and therefore the interaction with the organosilanes tested in this study. Treatment of biofilm covered microplastic with ultrasound partly recovers the removal. However, the results underline the importance of simulated environmental exposure when performing experiments for microplastic removal.

Extraction and derivatization for perfluorocarboxylic acids in liquid and solid matrices: A review.

Perfluorocarboxylic acids (PFCAs) are anthropogenic organic compounds with very unique and useful properties, for example, surfactant properties and immense stability. These substances are nowadays widely used in many industrial and consumer products. Their presence in human, biological, and environmental samples throughout the world has been described in numerous research articles. Unfortunately, PFCAs have also been found to be toxic, persistent, and bioaccumulative. Therefore, there is a great need for a constant and reliable detection of PFCAs in various matrices. Nowadays, the analysis based on liquid chromatography coupled to mass spectrometry (LC-MS and LC-MS/MS) is considered to be the method of choice. Determination of PFCAs by gas chromatography (GC) is not so well established as the LC methods. Nevertheless, GC can be considered as a complementary method, which can help to gain more reliable results and to crosscheck the LC analysis. The sample preparation is crucial, but also a time- and cost-consuming part of the PFCAs analysis. This article reviews the two most important sample preparation steps for the analysis of PFCAs: extraction and derivatization. It discusses the possible enrichment of PFCA using various extraction techniques used both for LC and GC. The derivatizing agents used prior to the GC analysis are described. The sample pretreatment as well as the most relevant problems and the sensitivity of the methods are presented. Moreover, advantages and disadvantages of LC and GC analysis are discussed.

Influence of various production methods on the microplastic contamination of sea salt produced in Java, Indonesia.

The extensive research on microplastics (MPs) in the last years has shown that it is not just an environmental problem anymore. As it can also be found in human food, it poses a potential risk for human health and food safety. Especially sea salt, which is produced by the evaporation of seawater, including its microplastic contamination, has been reported with different levels of MP contamination. Therefore, in this preliminary study, we investigated if different solar evaporation methods (traditional, geomembrane, and tunnel) influence the concentration of microplastic particles in sea salt production in Indonesia, one of the countries with the highest estimated level of plastic waste input into the ocean. The results show a significantly higher MP contamination in sea salt produced traditionally compared to the geomembrane and tunnel methods.

Structural investigation of perfluorocarboxylic acid derivatives formed in the reaction with N,N-dimethylformamide dialkylacetals.

A structural investigation of perfluorocarboxylic acid derivatives formed in the reaction with N,N-dimethylformamide dialkylacetals employing several techniques of mass spectrometry (MS) is described. Two derivatizing reagents, dimethylformamide dimethyl acetal (DMF-DMA) and dimethylformamide diethylacetal (DMF-DEA) were used. In contrast to carboxylic acids, perfluorocarboxylic acids are not able to form alkyl esters as the main product in this reaction. We found that perfluorooctanoic acid (PFOA) forms a salt with N,N-dimethylformamide dialkylacetals. This salt undergoes a further reaction inside the injection block of a gas chromatograph (GC) by loss of CO2 and then forms 1,1-perfluorooctane-(N,N,N,N-tetramethyl)-diamine. The GC-MS experiments using both electron ionization (EI) and positive-ion chemical ionization (PCI) revealed that the same reaction products are formed with either derivatizing reagent. Subjecting the perfluorocarboxylic acid derivative to electrospray ionization (ESI) and direct analysis in real time (DART), both positive- and negative-ion modes indicated that cluster ions are formed. In the positive-ion mode, this cluster ion consists of two iminium cations and one PFOA anion, while in the negative-ion mode, it comprises two PFOA anions and one cation. The salt structure was further confirmed by liquid injection field desorption/ionization (LIFDI) as well as infrared (IR) spectroscopy. We propose a simple mechanism of N,N,N',N'-tetramethylformamidinium cation formation. The structure elucidation is supported by specific fragment ions as obtained by GC-EI-MS and GC-PCI-MS analyses.

Comparative study of the influence of linear and branched alkyltrichlorosilanes on the removal efficiency of polyethylene and polypropylene-based microplastic particles from water.

Microplastics are a global environmental pollution. Due to this fact, new solutions are needed to reduce the amount in various aquatic environments. A new concept introduced by Herbort and Schuhen from the year 2016 describes the agglomeration of microplastics in water using silicon-based precursors. In the study presented here, alkyltrichlorosilanes with different linear and branched alkyl groups and a chain length between 1 and 18 carbon (C-) atoms are investigated for their suitability to fix microplastics (mixtures of polyethylene (PE) and polypropylene (PP)) and to form larger agglomerates. As the alkyl group has a major influence on the reaction rate and agglomeration behavior, we present here the extensive data collection of the evaluation of the best case. The removal efficiency is determined gravimetrically. The reaction behavior and the fixation process are characterized by hydrolysis kinetics. 29Si-MAS-NMR spectroscopy, IR spectroscopy, and thermogravimetry (TGA) are used to characterize the chemical composition of the agglomerates. Finally, the use of optical coherence tomography (OCT) allows the visualization of the formed agglomerates. The results show that the different alkyl groups have a strong impact on the suitability of the alkyltrichlorosilanes for the agglomeration, as they influence the hydrolysis and condensation kinetics in water and the affinity to the microplastics. Best suited for microplastic removal were intermediate chain length between 3 and 5 C-atoms.

Dispersive solid-phase extraction followed by triethylsilyl derivatization and gas chromatography mass spectrometry for perfluorocarboxylic acids determination in water samples.

A new, simple derivatization method for the determination of perfluorocarboxylic acids (PFCAs, C3-C12) in water is presented. The method is based on an acid-catalyzed esterification of perfluorinated carboxylic acids with triethylsilanol. During the reaction, a triethylsilyl ester is formed which can be easily analyzed by gas chromatography-mass spectrometry (GC-MS). The classic ion exchange solid phase extraction used for PFCAs (DIN 38407-42) has been significantly modified and adopted for the newly developed derivatization method. The new method offers a linear range from 8 to 10,000 ng l-1 for PFOA, with a limit of quantification ranging from 4 to 48 ng l-1 depending on the actual PFCA. Due to sample preparation simplicity, the presented method can be applied to form PFCAs esters prior to GC-MS analysis of water samples. The method was successfully applied in the analysis of effluents from two water treatment plants in Baden-Württemberg, Germany. Additionally, to confirm the laboratory evaluation, the standard solutions and samples were also measured by an external laboratory using LC-MS2.

A new approach for the agglomeration and subsequent removal of polyethylene, polypropylene, and mixtures of both from freshwater systems - a case study.

Based on a new concept for the sustainable removal of microplastics from freshwater systems, a case study for a pH-induced agglomeration and subsequent removal of polyethylene and polypropylene particles from water is presented. The two-step-based process includes firstly a localization and secondly an aggregation of microplastic particles (250-350 µM) in a physicochemical process. The research describes a strong increase in the particle size independent of pH of the aquatic milieu induced by the addition of trichlorosilane-substituted Si derivatives. The resulting Si-based microplastic aggregates (particle size after aggregation is 2-3 cm) could be easily removed by use of, e.g., sand traps. Due to the effect that microplastic particles form agglomeration products under every kind of process conditions (e.g., various pH, various polymer concentrations), the study shows a high potential for the sustainable removal of particles from wastewater.

A concept for the removal of microplastics from the marine environment with innovative host-guest relationships.

Environmental pollution caused by inert anthropogenic stressors such as microplastics in aquatic media is constantly increasing. Through the proliferating use of plastic products in daily life, more and more plastic particles enter waters as primary microplastics. Even though large scale plastic items such as plastic bottles and bags represent the highest percentage of plastic waste, their degeneration also generates microparticles and nanoparticles (secondary microplastics). Modern sewage treatment plants require innovative ideas in order to deal with this man-made problem. State-of-the-art technology offers approaches to minimise the amount of microplastics in aquatic systems. These technologies, however, are either insufficient or very costly, as well as time-consuming in both cases. The conceptual idea presented here is to apply innovative inorganic-organic hybrid silica gels which provide a cost-effective and straightforward approach. Currently, the synthesis of preorganised bioinspired compounds is advancing in order to produce functionalised hybrid silica gels in a further step. These gels have the ability to remove stressors such as microplastics from waste water. By means of the sol-gel process, bioinspired silane compounds are currently being permuted to macromolecules and examined with respect to their properties as fixation and filter material in order to remove the hydrophobic anthropogenic stressors sustainably. Here, the reproduction of biological systems plays a significant role. In particular in material sciences, this approach is becoming increasingly important. Among other concepts, new biomimetic molecules form the basis for the investigation of innovative host-guest relationships for anthropogenic stressors in the environment and their implementation in technical processes.