Mia Hughes, Ian Kane, Michael Andrew Clare

Microplastics pervade the sea surface, the water column, and the deep seafloor. They are vectors for other pollutants, such as heavy metals and persistent organic pollutants. A question remains as to how microplastics reach the seabed, over what time scales, and where they will end up. Many plastics initially float due to their low density, or to being incorporated into items with air cavities, but this buoyancy can reverse over time due to the growth of biofilms, or mineralisation of surfaces, and the breakdown of larger plastic objects. Understanding the spatial and temporal scales of ocean pollution is challenging, e.g., how can we understand the behaviour of a single microplastic bead in an ocean the size of the Pacific? Traditionally, particle settling is expressed using simple equations to express settling velocity in 1D. Here we provide two interactive online models for students to investigate the fate of microplastics floating in 1D, replicating a laboratory, and 2D replicating an ocean. Microplastic densities, sizes, biofilm growth, water salinity can be varied. In the 2D case an ocean surface current shows the distance which microplastics may float before sinking due to biofouling. Simple exercises can be developed for classroom teaching allowing students to test these parameters in a fun applet-based platform. Depending on the pedagogical objectives, students can use a range of provided parameters, or perform research to find their own. A series of exercises are provided, and an analysis of their use in the classroom is presented. This active learning model has clear pedagogical benefits over simple passive learning approaches, communicating environmental pollution and the scales of earth systems, for students from high school to university levels and in classroom, hybrid or remote teaching scenarios.