Method and challenges of tracing soil-surface transport of microplastic particles with an advanced-imaging sCMOS camera

Although the impact of microplastic particles (MPs) in different ecosystems has recently become subject of numerous studies, the knowledge of spatial distribution and transport of MP in terrestrial environments is still limited. While first studies in this field have focused on the abundance of MPs in soils and its vertical distribution, only little is known about the mechanisms of MP transport on the surfaces of sediments and soils. To analyse the interaction between soil surface roughness, inclination and irrigation rate, we investigate MP surface transport mechanisms and patterns by using images of an advanced scientific complementary metal–oxide–semiconductor (sCMOS) high-resolution camera. For this study an experimental set-up including a flume box with several surfaces and an artificial irrigation system was used. In this setup we traced pathways of fluorescent amorphously shaped polystyrene (PS) and Polymethyl methacrylate (PMMA) particles on surfaces of different roughnesses and inclination. Subsequently, time series of the images were analyzed by combining R and Python packages was. This included the calculation of MP particle size, estimation of pathways and path lengths.  Our first results suggest a large influence of the water film thickness and the microrelief of the studied surfaces leading to the creation of preferential pathways for the MP particles.