A new optical method for quantitative detection of microplastics in water based on real-time fluorescence analysis

Microplastics (MPs) have recently emerged as a new major and ubiquitous environmental pollutant with still undefined, yet potentially high risks for human health and ecosystems. This has prompted growing public concern along with an increasing number of scientific studies. In particular, recent research has highlighted the need for a standardized methodology to monitor microplastics in different media, particularly in water. This study reports on the use of a new particle counter for the quantitative detection of MPs in water samples based on real-time analysis of fluorescence emissions. The instrument was calibrated using two types of plastic particles, i.e., polyvinyl chloride and high-density polyethylene, selected as examples of high- and low-density plastics, respectively. Specific solvents were used to match the different plastic densities. Measurements were also carried out on particles obtained from wastewater samples collected at the inlet and outlet of specific units of a municipal wastewater treatment plant after sieving, filtering, digestion with hydrogen peroxide to remove degradable organic matter and resuspension in the solvents employed during the calibration step. A Fourier transform infrared spectroscopy analysis performed on the same wastewater samples confirmed the presence of MPs, and, in particular, of polyethylene, in some of the samples in which the highest concentrations were measured applying the proposed method. Therefore, the novel particle counter described in this paper could represent a promising method to quantitatively measure MP concentrations in water samples.