Reports on the occurrence of particulate plastics (nano- and microplastic particles and fibers) in the environment emerge on a weekly basis, but quantitative data are still limited due to analytical difficulties and inconsistencies of the methods applied to detect these diverse materials in complex environmental matrices. Investigation of transport processes is key to understanding environmental fate scenarios and material flows from e.g. urban areas into the environment. While progress is still ongoing to develop analytical methods to measure particulate plastic in field studies, researchers who study the fate, transport and biological interactions and effects of nano- and microplastics in bench top or pilot scale studies can take advantage of an entirely different approach. In our research, we have synthesized a variety of particulate plastics (nanoplastic particles, fibers) with an embedded inorganic fingerprint which can be used to detect plastic by common analytical techniques for metals analysis, such as ICP-MS. This allows us to more quickly and quantitatively assess plastic in complex matrices than is currently possible with other analytical techniques. To highlight the utility of this approach, we used these materials to conduct a detailed investigation of the fate and transport of particulate plastic in a pilot-scale WWTP representing the activated sludge process. With a recovery rate of spiked particulate plastics of over 90%, our findings show that over 98% of plastics (both nanoplastic particles and microplastic fibers) were associated with the sludge and were therefore removed from the wastewater stream. While surveys of municipal treatment plants have shown similar trends in the magnitude of microplastics removed, we have now validated the retention of nanoplastics and microplastic fibers with a more complete mass balance study. With a better understanding of emissions from WWTP, one can suggest estimated annual loads of particulate plastics to surface waters or applied to fields with sewage sludge, which could, by extension, be used as a starting point for fate modelling. Beyond the case study specifically highlighted here, these metal laden particulate plastics are suitable to study the mobility and eco-toxicity at trace concentrations. A brief overview of these other applications will also be presented, including nanoplastic transport in porous media and interactions with biota.

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Bio

Dr. Denise M. Mitrano is a Group Leader and Swiss National Science Foundation Ambizione Fellow at Eawag (Swiss Federal Institute of Aquatic Science and Technology) in the Process Engineering Department. She obtained her Ph D in Geochemistry from Colorado School of Mines (USA) in 2012 while developing methods to measure trace levels of inorganic nanomaterials in complex matrices, including environmental and biological samples. Through her postdoctoral work at Empa (Swiss Federal Laboratories for Materials Science in Technology) between 2013 and 2016, she further investigated inorganic nanomaterial release from products and subsequent transformations through their entire life cycle (production, manufacturing, use, disposal, environmental fate) both in the laboratory and using materials flow modeling. In 2017, she began leading her own research team on the fate, transport and biological interactions with particulate plastic (nanoplastics, fibers, microplastic fragments). Underpinning the research was the development of plastics with a metallic fingerprint that could be used as a proxy for plastic measurement, which allowed for more fast, easy, and quantitative measurements using standard analytical methods for metals. These developments enabled her research team to approach particulate plastic analysis in a unique way and conduct process studies on both the lab and pilot scales to systematically understand particulate plastic environmental fate and transport and biological interactions. Furthermore, her interest in tacking a “safer-by-design” approach for both nanomaterials and plastic continues by working on the boundary of materials science, environmental science and policy.