Sinking characteristics of microplastics in the marine environment

Abstract

Plastic pollution is presently one of the most widespread and minimally understood problems. Vast quantities of plastics that have entered the marine environment should be detected floating on the sea surface are seemingly missing from the global budget. A vertical transfer process should be able to explain the imbalance in mass, as well as the findings of buoyant plastics at the bottom of the sea. These processes are of paramount importance to modelling efforts on the fate of plastics and microplastics in the marine environment. In order to fill this gap and develop correlations that could be used in modelling activities, we have designed and performed a 300-day long field experiment to monitor the interactions between microplastics (pellets and films) and the marine environment for five types of plastic polymers. Fouling, changes in diameter, gravimetric weight and sinking velocity were monitored and the correlations between them were studied using principal component analysis (PCA). Density, fouling and sample form (strip or pellet) were found to greatly affect the sinking characteristics of the polymers, leading to an increase or decrease in the sinking velocity. Finally, mathematical expressions for the estimation of fouling attachment and the sinking velocity with respect to time for each type of plastic were determined from the experimental data.

Keywords: Buoyancy; Fouling; Marine environment; Microplastics; Modelling; Sinking velocity.