Microplastics in the environmental compartments: occurrence and characterization

Microplastic (MP) contamination has emerged as a global environmental problem due to the spread of plastic debris in various environmental compartments, including oceans, freshwater systems, soil, and air. Microplastics are small plastic particles, less than 5 mm in size, that can be generated from both primary sources, such as microbeads in personal care products, and secondary sources, such as the breakdown of larger plastic debris. Microplastics can have harmful effects on aquatic and terrestrial organisms and can also have implications for human health [1]. They can act as vectors for toxic chemicals and pathogens, and can also accumulate in the food chain, potentially leading to the ingestion of microplastics by humans. Research efforts are in particular devoted to understand the extent and impacts of microplastic contamination in the environmental compartments, as well as to develop strategies for mitigating its effects; these efforts include the development of new methodologies for detecting and quantifying microplastics. In this regard, within this work, we comprehensively investigated the MP contamination in several natural compartments, i.e. natural waters, marine sediments, soils, as well as in selcted biota, i.e. oysters. For each of the above mentioned matrices, specific anlytical protocols were optimized, all of them based on a similar combined approach. Firstly, an oxidation of the interfering organic matter was performed testing several solutions such as KOH, NaClO, H₂O₂, avoiding the degradation of MPs, followed by a density separation, to isolate MPs from residual species. For each matrix, five types of micropolymers were investigated, namely PE-HD and PE-LD, PET, PA, PS (both as particles and fibers). All the protocols were fully validated in terms of extraction yields from fortified samples, obtaining recoveries no lower than 80% for all the MPs in all the matrices. In addition, the optimized methods were shown not to alter the polymer lattice of plastics, making them recognizable at identification through FT-IR. The developed methods were successfully applied for the analysis of MP contamination in selected water basins and in agricultural and urban soils belonging from the Piedmont Region (Italy), as well as in ocean sediments and oysters from the Atlantic Ocean (Portugal). Contaminations from 30 to 90 MPs/L were detected in the water basins, with a prevalence of PP and PE partcles, rather than fibers. From 1800 to 3500 MPs/kg were detected in soils, with higher concentrations (in particular of LDPE fibers) detected in acrigultural soils, in agreement with the intensive use of mulching. From 10 to 700 MPs/g of MPs were detected in the ocean sediments, the majority of which were fibers, as expected from the thorough use of fishing nets, recognized as possble input sources of PA microplastics. Finally, from 10 to 50 MPs/g were detected in oysters. The above mentioned detected concentrations were similar to those already reported in previous literature studies (when available).