Monitoring of pellets and mesoplastic fragments on Dutch beaches in 2021: a pilot study

In recent years, a clear information need has emerged within OSPAR (www.ospar.org) and the European Task Group for Marine Litter (TGML) for sufficiently reliable and comparable data on pellets on a European level. For example, OSPAR has defined a Regional Action Plan (RAP) measure to obtain zero pellet loss, the EU is working at regulation to combat pellets and the IMO has presented a draft proposal to classify plastic pellets as hazardous materials. In addition, it is acknowledged in TGML and OSPAR that the data on mesoplastic fragments collected by European countries are probably not comparable because they are difficult to monitor accurately visually and sometimes because of their high numbers. Mesoplastic fragments are ecologically relevant because they can be ingested easily. Therefore, there is an additional need to obtain sufficiently reliable and comparable data on mesoplastic fragments. These two information needs can well be combined into the aim for a dedicated European monitoring method for pellets and mesoplastic fragments on beaches. In this report, a first pilot monitoring method and first results for pellets and mesoplastic fragments on Dutch beaches are presented. These methods and results are intended as a stepping stone towards a harmonized European monitoring method, to be developed within the TGML.
This pilot monitoring project shows that pellets and mesoplastic fragments are present on Dutch beaches in significant amounts. An estimated median value of 215 pellets per 100 m was found in the top layer (1-2 cm) of the Dutch beach high springtide line. This estimated value is based on a measured median 10.8 pellets per 5 m beach length (aggregation of 5 sampling units of 1 m2, top layer 1-2 cm). The amount of pellets per 100 m beach is obviously larger if the full tidal zone of the beach would have been sampled. However, it is assumed that a substantial part of the pellets has accumulated and has been sampled in the high springtide zone. Pellets were found in significant amounts on all four beach locations. However, the number of pellets on the beaches of Monster (near river mouth) and Neeltje Jans (near estuarine mouth) are approx. two times higher than the more rural beaches of Bergen and Texel, respectively. A draft conversion factor of 22.2 mg per pellet was calculated from the results. These are the first quantitative monitoring results on the number of pellets on Dutch beaches.
An estimated median value of 285 mesoplastic fragments per 100 m beach was found in the top layer of the Dutch beach high springtide line. This estimated value is based on a measured median 14.3 pellets per 5 m beach length (aggregation of 5 sampling units of 1 m2). The amount of mesoplastic fragments per 100 m beach is obviously larger if the full tidal zone of the beach would have been sampled. However, it is assumed that a substantial part of the pellets has accumulated and has been sampled in the high springtide zone. In the Dutch beach macrolitter monitoring report 2021, it was reported that the median number of mesoplastic fragments visually found on top of the beach for the period 2015-2020 is 15 (Boonstra et al., 2021). This shows that when the presented monitoring method, being both more precise as well as sampling within the sand (top layer 1-2 cm), much more of these ecologically relevant mesoplastic fragments are found. A draft conversion factor of 34.4 mg per fragment was calculated.