Press Release

November 07, 2023
  • Water & Soil

Revision of “Guidelines for Harmonizing Ocean Surface Microplastic Monitoring Methods”

1. The Ministry of the Environment (MOE), Japan, revised the Guidelines for Harmonizing Ocean Surface Microplastic Monitoring Methods to improve the comparability of ocean surface microplastic monitoring data.
2. MOE Japan will continue to lead the harmonization of global data, which is the basis for combating plastic pollution.


 Marine litter, including microplastics, is now a global challenge. In particular, pollution of the marine environment by microplastics has been recognized as a serious international issue. Determining the current status of distribution and quantity of microplastics in the ocean is an urgent task. It is important for policy making and implementation to be based on concrete scientific knowledge. 
 Microplastic monitoring is carried out by many institutions around the world using various methods. It is expected that monitoring will continue, but as different sampling and analytical methods are used - depending on the purpose of the surveys of each country and research institution - there is a fundamental lack of comparability among currently available data.
 At the G7 Elmau Summit in 2015, “supporting the initiation of a harmonized global marine litter monitoring effort and the standardization of methods, data and evaluation” was listed as one of the priority actions in the annex to the G7 2015 declarations. Subsequently, in November 2015, following the Elmau Summit, it was agreed that Japan would play a leading role in standardizing and harmonizing the monitoring methodologies for ocean microplastics. 
 Also, at the G20 Osaka Summit in 2019, marine plastic pollution was taken up as one of the priority issues, and the leaders endorsed the "G20 Implementation Framework for Actions on Marine Plastic Litter," which includes sharing scientific information and knowledge. In the first follow-up meeting and the G20 Workshop on Scientific Knowledge and Innovative Solutions for Marine Plastic Litter in 2019, it was identified that Japan (MOE Japan) voluntarily takes the lead in further elaborating key issues, such as harmonized monitoring and data compilation for the G20 Implementation Framework.
 To remedy the situation, MOE Japan published the first version of the "Guidelines for Harmonizing Ocean Surface Microplastic Monitoring Methods" in May 2019, based on a comparison studies of sampling and analysis methods through the demonstration projects and discussions at an international expert meeting consisting of domestic and international experts.

Summary of the revision

(1) Definition of maximum in “Feret diameter*”

 According to the definition in the Guidelines, the maximum Feret's diameter is the length in the direction perpendicular to the minimum Feret's diameter. However, that definition may not be the “maximum” in many cases. Also, the maximum diameter measured by image analysis software, such as “ImageJ,” shows the maximum Feret's diameter differently from how it is defined above.
 Therefore, the definition of “Feret's diameter” was revised, and the new definition is defined as the distance between the two parallel planes restricting the object perpendicular to that direction. The shortest Feret's diameter is called “minimum Feret’s diameter” and the longest is called “maximum Feret’s diameter.”
*a measure of an object‘s size along a specified direction

(2) Definition and categories of "Fundamental data items"

 The definition of “fundamental data items” was revised in order to facilitate further accumulation of the monitoring data.
 The new definition is that the fundamental data items are the minimum requirements to identify the abundance of microplastics, the sampling time and location, and microplastic density which can be displayed in any of the four units (number of particles/m3 or km2, weight/m3 or km2). Also, the category of “fundamental data items” was divided into two categories (FA and FB).

FA: All the “FA” are necessary for displaying the density.
FB: At least one (1) item in “FB” is necessary for displaying the density.