ИСТИНА

Freshwater reservoirs (rivers, lakes, bogs) located near large industrial cities are exposed to microplastics resulting from the discharge of industrial and domestic wastewater into natural reservoirs. The main source of microplastic formation in water bodies is household laundry, due to that municipal wastewater treatment plants are not designed to completely remove microplastics. To obtain reliable data on the content of microplastics in natural waters, careful validation of the methodology used to determine it is required. In addition, it is important to evaluate not only the amount of microplastics in natural waters, but also the amount of solid particles of other origin in order to avoid false positive results. Fluorescence microscopy is widely used as a tool for visualization and quantitative analysis of microplastics, but its metrological characteristics depend on many parameters, such as sample preparation, choice of fluorescent dye, visualization conditions, and image processing algorithms. Additionally, thermogravimetry can be used to estimate the total mass content of solid particles of both natural and synthetic origin. Thus, the aim of this study was to develop an approach for determining microplastics by combining fluorescence microscopy with thermogravimetric analysis to estimate the mass and quantity of microplastics among solid particles recovered from natural waters with high precision and accuracy. In this work, several methods of sample preparation of natural water samples, obtained from river and bogs from Moscow region have been tested. As a result, an approach providing the highest degree of microplastics recovery has been chosen. The microplastic content in the recovered solid particles was assessed using thermogravimetric analysis For selective visualization microplastics isolated from natural water samples were stained with a commercially available fluorescent dye, giving the opportunity to distinguish polymer particles from mineral ones and organic matter residues. The shooting conditions, providing high-quality microscopic photographs, were selected using both model objects and real samples of natural waters. The correctness of the measurements obtained using the proposed approach was assessed by spiked recovery tests. The results showed that the proposed method provides conditions for quantitative determination of microplastics in natural waters.