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.