Monitoring of pellets and mesoplastic fragments on Dutch beaches in 2022 : Summary Report

There has emerged a need in the past years for the monitoring of pellets on beaches (see 1.2).
The Netherlands has cooperated in the development of an EU monitoring method for pellets and mesoplastic fragments on beaches (Galgani et al., 2023) and started Dutch monitoring in 2021 (Wenneker et al., 2022). We first established that there are strong relationships between the number and weight of both pellets and mesoplastic fragments (Van Loon et al., 2023). Therefore, it was chosen to only present number data, in order to present uniform and clearer results. The average weight per pellet is 26.9 mg, and per mesoplastic fragment is 39.6 mg. In addition, we established that there is a strong relation between the median and mean number results per survey, and that the median value is on average 0.57 of the mean value (Van Loon et al., 2023). This shows that the data are not normally distributed; and that the median is correct to report. This is consistent with the use of the median for beach litter results.

The main results for the Dutch coastline for 2022, based on four locations, are: pellets: 615 per 100 m beach length and mesoplastic fragments: 235 per 100 m beach length. These results were monitoring using the EU guidelines with a larger sampling area from July 2022 onwards, and therefore probably still slightly underestimate the concentrations. We expect that this monitoring programme will have sufficient power and precision to reveal possible trends (due to reduction measures) after a period of six years. The monitoring of five morphology classes of mesoplastic fragments provides additional information and shows a dominance of mesoplastic fragments.