<p>During an expedition in January 2020, nanoplastics were sampled at a depth of -5170m over Cape Basin in the South Atlantic Ocean. Using photo-induced force microscopy, it was identified that these were polyethylene terephthalate (PET) particles with an approximate diameter of 50 nm at different stages of degradation. Using a state-of-the-art Lagrangian 3D simulation that includes an idealized fragmentation scheme, we backtracked virtual particles from the sampling location to establish the possible origins of the PET nanoplastics. We performed several simulations with different fragmenting timescales, for 13 years from the date of sampling, using the GLO12V3R1 hydrodynamic data from Copernicus Marine Environment Monitoring Service. We found that the nanoparticles (smaller than 1μm) could not have fragmented into nanoplastics at the surface and reached the sampling location within 13 years. The most likely scenario is that these particles started to sink from the surface as microplastics (larger than 1μm) and then fragmented in the water column far from the surface. This suggests that the fragmentation happened through processes like slow thermal oxidative degradation or hydrolysis and not photodegradation. We also found that less than 0.2% of the virtual particles came from the coast and that the fragmentation timescale prescribed to the modelled particles, affects how they drift in the ocean by controlling the time they drift at different depths. This study contributes to understanding the fate and sources of nanoplastics suspended deep in the ocean.</p>

No abstract

No abstract

Most marine plastic pollution originates on land. However, once plastic is at sea, it is difficult to determine its origin. Here we present a Bayesian inference framework to compute the probability that a piece of plastic found at sea came from a particular source. This framework combines information about plastic emitted by rivers with a Lagrangian simulation, and yields maps indicating the probability that a particle sampled somewhere in the ocean originates from a particular river source. We showcase the framework for floating river-sourced plastic released into the South Atlantic Ocean. We computed the probability as a function of the particle age at three locations, showing how probabilities vary according to the location and age. We computed the source probability of beached particles, showing that plastic found at a given latitude is most likely to come from the closest river source. This framework lays the basis for source attribution of marine plastic.