The use of fluorescence methods for identification of microplastics: the case of the Metaponto beach (Basilicata, Italy)

Microplastic (MP) pollution in the natural environment is currently the subject of growing interest both for the scientific community and for the World Health Organization. This interest is confirmed by hundreds of scientific articles published every year. The growing attention to this type of contamination in the various environmental matrices and, consequently, of living organisms, is caused by the following factors: increase of production and consumption of plastic, relatively small recycling rate of synthetic polymers at the end of life (only between about 9 and 15% is recycled from about 400 million tons of plastic produced annually worldwide), and the inability of current treatment plants to treat this type of waste, especially as regards textile fibers that are difficult to estimate. The purpose of this thesis is to evaluate the efficiency of expeditious optical microscopy techniques and the related sample preparation techniques for the recognition of MPs in marine sediments. The analyzed samples were taken with appropriate sampling from the coast of Metaponto, a city located in Basilicata (Ionian coast, southern Italy), to detect the presence of this type of pollutant. The experimental research was carried out using electrostatic and densimetric separation methods, using for the last one a NaCl solution. The identification and counting of MPs have been made by optical microscope with UV flashlight both in the absence and in the presence of Nile Red dye, which currently appears to be one of the least studied identification techniques, and which was mainly used in the field of biology and medicine until 2010, but not in the field of ecology. It was possible to check the efficiency of the electrostatic separator in order to reduce the sample volume and increase the concentration of MPs contained in it. In general, among the analyzed MPs, the most common size range was found to be those <0.5 mm. Meanwhile, synthetic fibers, transparent under LED, and fluorescent under UV light, were found to be the predominant ones. From identification under the microscope, they appear to be on average 1.41 MPs/g. This result is comparable to the one obtained after staining with Nile Red, which is equal to 1.56 MPs/g. From further analysis of the examined sample, however, despite the similar numbers, in half of the cases, the Nile Red colored other objects and not those that were identified through the microscope as MPs. Therefore, a further study of the combination of these technologies is necessary with the aid of spectroscopic techniques (FT-IR, Raman), which are capable to provide the chemical composition of the material under examination. The analysis of numerous scientific articles on the subject of MPs, carried out during the experimental research, also with the aim of refining and improving the methods of followed investigation, led to finding of some contradictions in the results of the studies published so far. This fact leads to further confusion in a research field, which is already quite complex and multifaceted, and which currently does not have standard protocols. One of the major causes of errors and uncertainties in MPs recognition and counting is visual identification using the UV light microscope, which can lead to both overestimating and underestimating the amount of MPs, if a researcher relies on this method alone and did not combine it with other more reliable ones, especially when the threshold of <0.5 mm is exceeded, which is precisely the most frequently detected dimensi