Tyre Wear Particles and Small Microplastics (SMPs <100 Μm) From Highway Stormwater Runoff: Sampling, Pre-Treatment Procedures and First Results

Highway stormwater runoff is a direct pathway for conveying microplastics (MPs) and other environmental pollutants from land-based sources to the aquatic and terrestrial environment. However, the concerns on stormwater for microplastic pollution and the other components of microlitter (additives and plasticizers) have grown exponentially and the knowledge on their pathways and impacts are now very limited. Important sources of microplastic in stormwater runoff are related to traffic vehicles, polymer-modified bitumen, road paint, atmospheric deposition and the wear of tyres. Hence, due to their small size, smaller MPs (SMPs, &lt; 100 μm), additives and tyre wear particles (TWPs) can pose a risk for the environments as they can be ingested by different kinds of biota and can cause potential health problems for human beings. Only very limited studies have been paid attention to microplastics, especially SMPs, and TWPs from highway stormwater runoff with a consequent lack of knowledge regarding the amounts, size, and composition of these pollutants emitted in the different environmental pathways. There are currently no standardized methods and harmonized techniques for the collection, pretreatments, contamination procedures, and analysis of SMPs and TWPs from stormwater runoff, making significant differences in the data of these pollutants studies difficult to compare. In this study, stormwater runoff samples were collected during different rainfall events from a trafficked highway near Venice, Italy. A pre-treatment procedure (e.g., oleo-extraction, purification, and filtration) was developed and optimized in a Clean Room (ISO 7) at Ca’ Foscari University of Venice to prevent any possible plastic contamination. Quantification and simultaneous chemical identification were performed via MicroFTIR for SMPs, TWPs, additives, and plasticizers in stormwater runoff samples. Further, pyrolysis gas chromatography-mass spectrometry (Pyr-GC/MS) was developed to confirm the presence of specific SMPs and TWPs in the same samples analyzed. The cross-validation among MicroFTIR and Pyr-GC/MS techniques allows the standardization of pretreatment and analytical methods. Regarding TWPs, different tests were carried out and the first results of quantification and chemical identification of specific markers were obtained.