1. Key points

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As the problem of plastic waste in the ocean garners increased attention, the use of biodegradable plastics, which may be degraded by microbes, is emerging as an effective countermeasure to plastic pollution. However, the degradation behavior of such plastics on the deep seafloor is still unknown.

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Biodegradable plastics will be loaded onto an Edokko-1 Type 365 device, which is designed to observe the deep seafloor environment, and a year-long biodegradability test at a depth of over 5,000 m will begin for the first time worldwide.

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The results of this study will be useful for the application and popularization of biodegradable plastics, and are expected to contribute to the establishment of further tests and analytical methods on the deep seafloor.

2．Overview

The Japan Agency for Marine–Earth Science and Technology (JAMSTEC) will begin a long-term biodegradability test in March of 2020. Testing will be conducted as part of a project accepted via public offering for use in the deep sea environment, the “Development of Innovative Technologies for Exploration of Seep Sea Resources” project (*1) in the Cross-ministerial Strategic Innovation Program (*2) and in collaboration with the Japan BioPlastics Association (JBPA, *3). The test will consist of exposing biodegradable plastic samples on the deep seafloor (depth: >5,000 m below sea level) for approximately one year to the waters surrounding Minami-Tori-shima (a.k.a., Marcus Island) using an Edokko-1 Type 365 (*4) untethered benthic lander. This study will be conducted based on an industry–academia–government collaboration, joined by JAMSTEC, JBPA, Dr. Atsuyoshi Nakayama of the National Institute of Advanced Industrial Science and Technology (AIST), and Prof. Tadahisa Iwata of the University of Tokyo. After retrieval of the Edokko-1 Type 365, samples will be analyzed and the degradation behavior of biodegradable plastics on the deep seafloor will be revealed. The free-fall Edokko-1 Type 365 will be set for navigation, beginning on March 7th.

3. Background

In the “Development of Innovative Technologies for Exploration of Seep Sea Resources” project, observation devices, such as the Edokko-1 Type 365, are deployed and collected in the ocean surrounding Minami-Tori-shima on a yearly basis as part of an effort to assess the environmental impacts of the deep-sea resource development, and perform long-term observations of the deep seafloor environment. From July to September of 2019, the division overseeing this project sought public proposals, from a wide-range of sectors, including private firms, on tests and research themes based on innovative ideas, with the goal of expanding the use of the deep-sea environment by research institutions other than those in the maritime sectors. In the end, the test proposal outlined here was adopted.

Ocean pollution from plastic waste has become a global issue. It has been estimated that more than 8 million tons of plastic waste ultimately enter the oceans every year through various channels. One important means of preventing further increases in ocean plastic waste is to promote the development and popularization of plastics that fulfill the function of a product and are degradable in the ocean or on the seabed. Biodegradable plastics are ultimately degraded into water and carbon dioxide through the action of microbes. On the deep seafloor, the mechanisms of microbial activity are assumed to differ from those on land due to the absence of sunlight, and the existence of high pressures and low temperatures. It is therefore essential to observe degradation behaviors on the deep seafloor in order to determine the utility of biodegradable plastics.

4. Test details

Samples of biodegradable plastics will be attached to the Edokko-1 Type 365 that will be deployed offshore of Minami-Tori-shima from the deep sea research vessel KAIREI, and will be set on the deep seafloor for approximately one year. Using the time-lapse imaging function of the Edokko-1 Type 365, the degradation process of such samples will be captured on video. Samples in this test will include biodegradable plastics that have already been commercialized, as well as those currently under research and development. Biodegradability tests of biodegradable plastics have previously been conducted in the shallow waters of coastal regions. However, this will be the first biodegradability test attempted on the deep seafloor at a depth of >5,000 m worldwide.

5. Future prospects

By confirming the degradability of biodegradable plastics on the deep seafloor, the development of materials that can degrade stably in a wide range of maritime environments, from the surface layer to the deep seafloor, is expected to accelerate. Additionally, comparisons of the degradation behaviors between samples will lead to improved product development that can achieve a balance between biodegradability and durability. Furthermore, JBPA has been commissioned by the Japan Plastics Industry Federation to organize discussions and determine new standards in compliance with international standards concerning plastic biodegradation. Therefore, the findings of this test should lead to the establishment of improved analytical methods for biodegradability tests in deep-sea environments and contribute to the international standardization of plastic biodegradation.