Scaling of dimensions and concentrations of plastics in two Dutch rivers

Plastic pollution raised great environmental concerns due to its persistence and widespread presence. To model ecological impacts, such as ingestion by wildlife, information on the abundance and dimensions of plastic particles is fundamental. Our study examined the relationships between size dimensions (length, area, circumference) of individual particles and the length of particles, their concentration, and cumulative surface area. Plastic particles were collected with trawl nets from upstream and downstream sites in two Dutch rivers in 2023 and 2024. Particle dimensions, including length (defined as the longest axis), surface area, circumference, and the number of particles, were measured. Geometric means of particle concentrations and cumulative surface area concentrations were calculated for equal-sized bins based on length and plotted against particle length on a log-log scale. Reduced major axis and ordinary linear least squares regressions determined the power relationships between size dimensions of individual particles. For length-based bins, we evaluated how concentrations and total surface area co-varied with length classes. Size dimensions were strongly and positively related, indicating differences in shape across size classes. Contrary to previous research, the length of plastic particles was not strongly correlated to their concentration in the Meuse River and varied between sampling locations. The cumulative surface area concentration increased significantly with length. The findings of the study should be viewed with caution, as they were based on two Dutch rivers. Even greater caution is warranted for the relationships between particle length and concentration, and between particle length and cumulative surface area, as they were based solely on measurements in the Meuse.