Transport and Accumulation of Plastic Pellets along the Scheldt Estuary between Vlissingen (Netherlands) and Melle (Belgium)

The world’s future is threatened by a triple planetary crisis of climate change, biodiversity loss and pollution. Plastic pollution is linked to various consequences for biota and is a major concern for policy makers. Since the 1970s the widespread presence of industrial plastic pellets, with dimensions between 25 and 50 mm, have been observed in surface waters and beaches all over the world, raising concerns about the potential environmental impacts of plastic pellets .

We present a case study along the Scheldt estuary, encompassing the port of Antwerp, a large polymer hub for production, handling and distribution of plastic pellets. Beginning decades ago, pellets are being unintentionally released into the environment and find their way to the Scheldt river, where plastic transportation and accumulation on the riverbanks are determined by the physicochemical properties of the pellets (polymer type, density, size, shape, …) as well as hydrological processes and other factors, e.g. surface morphology, vegetation,… . Efforts have been made to quantify plastic pollution in the Scheldt estuary. However there is a paucity of data to evaluate plastic pellet pollution in particular and  there is no harmonized sampling methodology that is suitable for measuring pellet concentrations on the estuary’s riverbanks, with its great spatial and temporal diversity in occurrence and heterogeneity in landscape.

To elucidate transport and accumulation patterns of the released plastic pellets, we set up an extensive monitoring campaign. Pellets were manually sampled on 28 locations along the Scheldt riverbank between Vlissingen and Melle, using a 50 by 50 cm quadrat. To capture the spatial heterogeneity of the pellet concentration, at each location 9 replicates were taken in a standardized manner. The surface materials within the quadrats were collected and air dried before pellets were separated manually and counted.

The spatial distribution of the number of pellets on the riverbanks revealed that most pellets were found in the Antwerp port area (3,352 pellets per m²). Upstream from the port (314 pellets per m²) more pellets were found compared to the locations downstream from the port (110 pellets per m²). Significantly more pellets were found on locations close to a physical barrier (e.g. a bridge, a quay, an unnatural bulge, …), located in the outer bend or on a straight part of the river, oriented in Southern, Western or Southwestern wind direction, with a surface other than flat sandy and on locations with high or very high vegetation.

Fourier-transform infrared spectroscopy was used to determine the polymer type of the pellets, revealing that most pellets consisted of polyethylene and polypropylene. The images obtained by stereomicroscopy, confocal microscopy and scanning electron microscopy revealed changes in colour and breakdown of the surface of pellets.

Insights into the magnitude and spatial distribution of plastic pellet pollution on the Scheldt riverbanks provide an estimate of the transportation patterns of the port of Antwerp’s plastic pellets. The easy sampling methodology provides opportunities to scale up or standardize monitoring campaigns, also in a non-marine environment, which could improve the knowledge about plastic pellet occurrence and its potential ecological risk worldwide.