Guidelines for Harmonizing Ocean Surface Microplastic Monitoring Methods. Version 1.1.

Marine litter, including microplastics, is a current global challenge. Determining the existing distributions and quantities of microplastics in the ocean is an urgent task. A comparison of reported microplastic abundances, however, is difficult due to diverse monitoring methods. Hence, harmonization of monitoring methods for marine litter, including microplastics, is recognized as an important task/activity. To remedy the situation, the Ministry of the Environment, Japan (below, MOEJ) has been promoting efforts to ascertain the actual state of marine pollution by encouraging horizontal distribution mapping of microplastic densities at the ocean surface worldwide. The MOEJ has developed Guidelines(Version 1.0) to harmonize ocean surface layer microplastic sampling and analytical methods in 2019, based on the results of two projects implemented by scientists. These Guidelines were prepared to enable anyone implementing ocean surface-layer microplastics-monitoring to design their monitoring protocols, compare their results with other monitoring results and interpret them based on such comparisons. After that, the MOEJ implemented a new project to extend the scope of the guidelines. Additional notes based on the results of the project to the Guideline(Version 1.1) include that precautions should be taken to enable monitoring even with small research vessels and fishing boats, and measures such as shortening the towing time with repeated sampling should be taken when clogging of the net is inevitable.