The Impact of Microplastics and Emerging Micropollutants in Highway Runoff: The Italian Job

Roads and highways runoff is a major pollutant sources for receiving water bodies because of stormwater carrying a large variety of pollutants. The stormwater runoff has two different kinds of impact: chronic and acute. Chronic impacts are caused by the complex matrix of contaminants carried characterized by high toxicity and persistence in the environment. Gas pollutants like endothermic motors exhausts are dissolved in rainwater and can then infiltrate natural water reservoirs contaminating the environment with heavy metals such as copper, zinc, and iron, or with complex chemicals like PFAS (known for its high toxicity and carcinogenic properties). For these contaminants' treatment solutions, usually physical ones, can be applied because the pollutant composition is known. Acute impacts, instead, derive from accidental or voluntary spills and car accidents. They can occur during dry or wet weather and the nature and occurrence of the unwanted spill is unknown and cannot be predicted. Whenever such a spill occurs it is of the utmost importance to have contingency plans and infrastructure to prevent big environmental damage with incredible high costs, social and economical of clean-up. SWI Group has a decennial experience in designing, construction, and maintenance of stormwater treatment plant in Italian highways and big infrastructure. Both impacts are managed by SWI Group in Italy and Europe with integrated filtering treatment plants and systems able to detect and prevent the dispersion of polluted spills in water bodies. This is possible thanks to the patented technologies able to prevent any dispersion in the environment. In Veneto Region SWI Group have done, and now is doing maintenance, of 150 km of highways infrastructure with almost 250 treatment plants, anyone with monitoring sensor 24h/365. This is a huge and unique laboratory for data collection and a big data background has been constructed. Plants, equipped with water quality parameter sensor and level and rain sensor, permit to have basic information on water quality and the amount of water discharged in the environment. Since 2019 SWI Group financed three University research project with three full-time researchers regarding the evaluation of the presence and impact of emerging pollutants and microplastics in highway stormwater runoff. Stormwater has been sampled using different sampling techniques and new ones has been tested. For the research projects sampling techniques ensuring average concentrations instead of instantaneous one have been preferred. The growth, both in volumes and in variety, of emerging micropollutants, such as small microplastics, unknown in quantity and impact drive the scientific community to increase the understanding of their fate, loading, and movement by sampling and monitoring treatment facilities. SWI Group strongly believe that sharing data and practices is the only way to approach this challenge, thus creating lasting and efficient solutions. Thus, the purpose of this abstract is to contribute to that goal, by presenting the complex array of studies we are performing in stormwater treatment plants along the highways regarding real-time monitoring and new sampling techniques. Online multi-parameter sensors (measuring pH, turbidity, conductivity, and temperature), weather stations, passive chemical samplers, and innovative laboratory analysis techniques have been combined in an innovative set of projects aimed both at data sampling and developing solutions in real-time. The stormwater treatment plants have been monitored and sampling campaigns have been performed focusing on heavy metals and emerging contaminants such as small microplastics and pesticides. Data were collected with different sensors and probes, both active (manual sampling of inlet and outlet water and small local shrimps) and passive (multi-parameter sensor, passive sampler, water-level sensors, rain sensors, weather stations, flux meters). The in-situ sampling campaigns and data analysis were conducted in collaboration with Cà Foscari University of Venice, Technical University of Denmark (DTU) in Copenhagen, Danish Technological Institute, Consiglio Nazionale delle Ricerche (CNR) and Concessioni Autostradali Venete (CAV), the owner of the plants along the highway. Different matrices have been sampled: water (first and second flush), sediments, road dust, rainwater, air, and biota. With this study, a mass balance of different contaminants and a precise characterization of pollutant loads can be evaluated considering the high inherent variability of stormwater pollutant release and transport processes. Microplastics have been sampled in the inlet and in the outlet of a treatment plant to have the possibility to compare the results and evaluate the efficiency of the treatment, as well as evaluating the amount of microplastics in stormwater runoff and in the water discharged in the receiving water bodies from the plant after treatment. Microplastics are one of the current emerging environmental threats. More than 8 million tonnes of plastic are dumped into the environment every year and around 97% of the plastic in the oceans is made up of microplastics. All the different matrix mentioned before having been sampled to search for small microplastics (5-100 µm). Each sample underwent a specific extraction and purification procedure (fundamental in the analysis of microplastics) inside a Clean Room (Ca' Foscari University of Venice) to avoid any type of plastic contamination. The aim of the project was to evaluate the occurrence and abundance of small microplastics in this matrix related to stormwater. A matrix specific sampling and analytical method have been developed, in particular oleo extraction for stormwater and Micro-FTIR and PyrGCMS for tire wear particles which is presented in Rosso et al. (Journal of Environmental Management, 2021). One of the main sources of small microplastics in stormwater runoff is car tires and with the acquired data a comparison can be done between water sample taken during summer and winter tires usage due to use of different additives in the manufacturing of tyres. From the preliminary results, in one liter of highway stormwater runoff it's estimated the presence of 16.000 particles of small microplastics. Future development will be the assessment of SMP flux removal potential of existing highway stormwater treatment technologies. The same sampling approach have been used to investigate the abundance of micropollutants. An initial study focused on glyphosate has been published in Water Air Soil Pollution (Feltracco et al. 2022) regarding the occurrence of glyphosate and its degradation products in the urban stormwater. Glyphosate is one of the most widely used herbicides in the world. Different aspect has been taken into account: the evaluation of unexpected degradation products formed during transportation, the assessments of variables influencing highly polar pesticides in highway runoff to enhance ecosystem protection and water reuse, an analysis of the mitigation strategies adopted at international level in relation to the legislation on the use of pesticides. This paper review highlights the need to study the aerosol as a polluting source and the importance of considering the dry weather between one meteorological event and another. The information provided by the study can be used for water quality modelling, to improve the efficiency of existing stormwater treatment solutions and thereby evaluate the potential for reuse of highway runoff and to find a relation with the length of dry period before the rain. Now we are driven to work to understand how we can reduce the impact of these pollutants on the environment.