Research, Know and Learn調べる・知る・学ぶ

[Question] Do you eat plastics every day, without fail?

Right answer is… 「YES !」

What? You may feel that way. Have you heard of micro-plastics?

 ☑ What is micro-plsastic?

 ☑ 「Micro-plastic」 VS. 「NPO Arakawa River Clean-aid Forum」

Q: “What is「micro-plastics」 (referred to as “MPs” hereafter)?”
A:“It is a collective term for plastics 「with 5 millimeter or less in diameter size

Plastics exist abundantly around us.

Plastic as material has useful features such as lightness, durability and easiness to craft, beyond some other materials such as paper, wood or metal. It can be said that it is a material which is indispensable for our life. However, while it is a good material, plastic inevitably deteriorates as time passes. Further, it becomes fragmented in smaller pieces. Regardless of the original size of any plastic products, eventually they become small MPs (unless they are incinerated). For instance, plastic-made clothespins become fragile over time and crack producing small fractions and/or powdery substance. They are MPs.

Besides, plastic fractions lager than 5 millimeter in diameter are called “macro-plastics”.

POINT:Plastics become MPs by deterioration.

Q:“Where are MPs located?”
A: “Wherever, all over the world – in soil, in the atmosphere, in deep sea, and even within human bodies…”

Plastic is a 「sturdy」material.

While pieces of plastics would become smaller over time, plastic does not stop being plastic however small it becomes. Larger plastics (macro-plastics) just turn into smaller plastics (MPs). For plastics to be truly decomposed by microorganism, like paper or wood, it takes an enormous amount of time. Eventually, they become so small that cannot be seen with human eyes.

MPs are small and light would move to anywhere on the earth by winds and water. Now, they exist from the top of the Mt. Everest to depth of the Mariana Trench and also within the bodies of creatures (including those of humans). Since amount of plastic products production continues to increase (see the diagram below), impact of MPs on natural environment ever increases.

POINT:Plastics stay to be plastics however small they become.

Q:How does MP affect creatures and humans?
A:Plastic, which is a “foreign substance” to the natural world, can break the balance of the natural world.

Until humans created plastic, there was (almost) no plastic in nature. (*)

Therefore, we do not have a mechanism for returning human-made plastics to nature again, and decomposing it requires a very long time(called “hard decomposition”). At least, it will not returned nature in the “100 years” that is said to be the average life expectancy of the Japanese in the future (Nakajima, 2019).

The natural world is made up of food chains, but its balance is very delicate and fragile. Plastics, which continue to exist in large quantities in nature, are “foreign substances” and continue to accumulate. Nowadays, the “foreign substance” called plastic is trying to break the balance in nature.

(*) There are substances that can be called plastics in the natural world, such as amber and beeswax made by bees.

① Impact to Creature

Various creatures of all sizes accidentally ingest plastic.

Seabirds tangled with fishing lines and sea turtles and whales that mistakenly eat plastic for food are talked about in the news, but it is said that 90% of seabirds, and more than 200 species of marine life mistakenly eat plastic trash (Takada et al., 2019).

We humans do not often mistake plastic for food. Even small pieces of plastic are rejected due to sense of discomfort if they get in your mouth. But several of the creatures cannot do make this distinction.

POINT:Many creatures mistakenly eat plastic for food.

(Reference) 『For hungry sea turtles, undersea plastic bags smell like food』(CNN,2020/03/11)

② Impact to Humans

MPs have also been detected in many foods and drinks that we eat.

Humans also eat plastics from seafood. We cannot notice a small MP that you can’t see.

It is said that, even if MP is ingested, it will not be absorbed by the human body but it will be excreted, so currently, it is said that there is no major health impact. However, due to the nature of plastics to adsorb chemical pollutants in water, humans may have ingested pollutants including MP. There are still many unclear points about the health effects of ingesting MP, and research is ongoing (Gendatsu, 2020).

You wouldn’t want to eat food with plastic in it, even if you are told, “There is no health risk (for now).”

POINT:Humans also eat MP (impact on health is unclear)

(Reference) 『Ingestion of plastic into the body, research results for one credit card per week』(AFPBB News,2019/06/12)

So far, we have been introducing “MP”…

How is「 “Arakawa River Clean-aid Forum” 」「“ACF”」)
facing the MP problem?

Q:What is 「Arakawa River Clean-aid」?
A:It is an activity to collect Arakawa River’s trash before it flows into the sea!

As the name implies, the main activity of ACF is “Arakawa River Clean-aid”.
Roughly speaking, it is “cleaning the riverbank”.

About 10 million people live in the basin of Arakawa River, which flows through Saitama Prefecture and Tokyo.

It is said that most of the trash that flows into the sea comes from the activities of people on land. Only a small percent of the 10 million people may inadvertently or deliberately throw away the trash that pass through waterways in each region and Arakawa river and finally flowing into Tokyo Bay (Pacific Ocean).
*Of course there are some source of trash.

The ocean is tremendously large and wide.
Once a small piece of trash has flowed into the ocean, it is almost impossible to collect it.
ACF uses a river clean aid method to collect trash before it enters the sea.

POINT:“Arakawa River Clean-aid” collects trash before it flows into the ocean.

Q:What effect does River Clean-aid have on MP problems?
A:① You can collect plastic trash before it becomes MPs
  ② The changes in the participants will turn into great power

① Collect plastic trash before it becomes MP

As Clean-aid participants pick up trash such as plastic bottles and notice the presence of colorful MPs mixed with sand and pebbles. And realize the difficulty of collecting MPs.

The MP is very small, and there are many that crumble due to deterioration.

If you leave the plastic trash as is, it will definitely be MP.
And, it will eventually be reduced to a level that is invisible to humans.
Once this happens, you can no longer retrieve them. The only option is to collect them at the stage where people can pick it up.

No matter how many times a large-scale Clean-aids are carried out through dozens if not hundreds of people, before we know it, a large amount of trash will accumulate on the banks of the Arakawa River. But, if we can collect the trash there, we can reduce the amount of MP following into the ocean from the rivers. However, the trash washed up on the riverbank is only the tip of the iceberg. Much more is flowing into the Pacific than is recovered by ACF cleanup activities. Unfortunately, clean-aid alone cannot solve the MP problem…

POINT:It is a battle to collect plastic trash before it becomes MP

② The changes within participants into great power

It is estimated that in 2010, about 4.8 to 12.7 million tons of plastic trash was released to the ocean (Jambeck et al., 2015). If plastic production and ocean spills continue at this pace, it is reported that by 2050, the weight of plastics in the ocean will exceed the total weight of fish (Ellen MacArthur Foundation, 2016).

Seeing is believing

Clean-aid participants are stunned by the large amount of debris in front of them. While also having feelings of fun, participants have intense feelings while collecting trash. Through grappling with MP that cannot be picked up because it quickly deteriorates, participants experience the seriousness of ocean pollution caused by plastic.

It is true that MP problems cannot be solved by the Arakawa River Clean-aid alone.
However, if the awareness of everyone involved in Clean-aid to the MP problem changes, it will spread to their daily life and work. This change is the greatest effect to the Clean-aid MP problem.

POINT: Changing the hearts and minds of the participants is the best power we have against MP.

QWhat is the target of ACF?
A:① To let as many people as possible know about the micro-plastic problem through Clean-aid
 ② To expand Arakawa’s activity model all over Japan and all over the world.

As mentioned above, in order to solve the micro-plastic problem, let as many people as possible know the current state and seriousness of the problem, and as many as one of them take action in their daily lives and workplaces. Will be a great power.

The method of Clean-aid, which allows you to see and understand the seriousness of micro-plastic problems, has the impact of making participants feel that micro-plastic problems are their own problems.)We would like more people to participate in Clean-aid mainly on Arakawa River, and we would like to increase the number of friends aiming to solve micro-plastic problems. (Annual; about 190 location, about 11,700 people in total)

☆Message of the ACF staff

Arakawa River Clean-aid cannot solve the micro-plastic problem.

The sea is connected to the world. In order for river clean-aid to be effective in solving micro-plastic problems on a global scale, clean-aid must be carried out in rivers around the world.

ACF aims to expand this model all over Japan and all over the world, using activities on Arakawa River as a model. And we will collaborate with colleagues around the world who aim to solve micro-plastic problems.

ACF is not needed if there is no trash from the river after thorough reduction of plastic trash (prevention) and cleaning of the river (treatment). The final goal is “dissolution of organization.”

It seems that it will still take some time to dissolve if you see a large amount of trash that is increasing…

Responsibility: TERAMACHI (ACF Division)

[Reference/Citation source]
『脱プラスチックへの挑戦 持続可能な地球と世界ビジネスの潮流』山と渓谷社,堅達京子ら,2020
Jambeckら,「plastic trash inputs from land into the ocean」science (2015)
Ellen MacArthur Foundation「The New Plastics Economy: Rethinking the future of plastics」(2016)

The Mitsui & Co. Environment Fund(1st: Oct. 2016 ~Sep.2019 )(2nd : April 2020 ~Mar. 2022)

ストップ!プラごみ 海へ出る前に(三井物産環境基金のサイトへ)

The Project for Studying Marine Litter Reduction Measures in Urban River Arakawa

[Background and Issue Summary]

There are concerns that artificial litter (mainly plastics) could cause multifaceted problems in ecosystems, food issues, water, and sustainable consumption and production. It is said that 90% of marine litter is discharged from 10 rivers in developing countries, mainly in Asia, and we need to solve this problem as soon as possible before it causes more serious damage. On the other hand, the amount of river litter per unit population is based on data from Europe and the United States, and domestic data is considered to be necessary. This project will examine the amount of river litter and its control, targeting the Arakawa River, which has one of the largest populations in Japan.
*Some of the activities in this project are not open to the public.

[Purpose of this project]

According to Jambeck et al’s article(2015), the amount of marine litter generated in Japan is estimated at 20,000-60,000 tons and is becoming more prevalent.
Japan’s annual plastic production is 9 million tonnes, of which 2-7% is a figure that many in Japan question the estimation method.
It is necessary to determine and verify the amount of litter per unit population in the Arakawa River, which has one of the largest populations of rivers in Japan.


Now on going…

ストップ!プラごみ 海へ出る前に


生態系に入り込んだマイクロプラの影響に関する研究事例は少なく、非常にゆっくりと影響が生じた場合、結果として分からないままとなるだろう。 これらの課題は近年徐々に明らかになってきたが、市民活動レベルでの課題解決手法に至っては未だ具体策は得られていない。



モニタリングによってプラスチックごみの滞留状況と潮汐(潮位)の関係について調べ、回収後にどの程度で再滞留するのか等のメカニズムを分析し、効率的な回収手法、タイミングの確立を目的とする。 小流域あたりの人工系ごみの流出量を調べる 業界団体である日本プラスチック工業連盟等と協調し、市民ととともにプラスチックごみの課題について共有する。


  • ・プラスチックごみの効率的な回収手法の確立。
  • ・荒川から海洋へと流出するプラスチックごみを削減・抑制する。


  • 当該活動による調査・分析結果を発信し、各河川が抱えるプラごみ問題の解決の糸口として活用してもらう。
  • 河川管理上の基礎データとして、行政機関等と共有する。





  • 当該エリアに流入する河川ごみの量は流出量より1桁~2桁大きい。
  • 潮が満潮から干潮に変わる際に上流端開口部から多くの河川ごみが流入する。
  • 詳細は片岡ら(2017)の論文参照。



  • 流速の遅い陸側に河川ごみが滞留⇒橋脚付近の流れ場で陸側に寄せられる。
  • 足場の鋼管に支えられたヨシ群落が導入路をつくり、北風に寄せられる。


流域人口が分かっている支川にて、本川とつなぐがる排水ポンプ場を対象に、トラップされる河川ごみの量を調べる。 単位人口当たりが排出する河川ごみの量を推定するのに用いる。 行政と連携して実施している。

・当該都市の人口密度 9,376人/km2
・流域面積 18.5km2
・排水ポンプ稼働状況 1t/sec 2台が常時運転

  • 河川ごみの構成比は・・・(時期調査にて)
  • 流域人口あたりの河川ごみの量は・・・(時期調査にて)
本事業は三井物産環境基金の支援(2016-2019)を受けて実施しました。 案件担当者:今村かずゆき

■発生源対策に関する考え方 限界効用逓減の法則*に照らし合わせると、河川/海洋に流出するごみを完全に0にするのは難しい。厳正な管理をしても自然界に出てしまうごみは確率論的に必ず一定量存在する(人口比率)。当該事業は自然界に出てしまったごみを如何に効率的に回収するかに焦点をあてたものである。もちろん、発生源対策において、過剰包装など本当に必要のない使い捨てプラの利用削減の方が優先度が高い。




iOS application SOIL / by Dr. KAKO Satoshi
~the Earth~

“Soil” is a remake application of the scene (terrain) in KAKO Satoshi’s masterpiece “Chikyuu sono naka wo sagurou” (The Earth, Let’s explore it), published in 1975, drawn by KAKINUMA Tsutomu with the theme of “soil”.

In addition to this work, we created “Arakawa River Estuary 1 (Micro) and Arakawa River Estuary 2 (Macro)” as EXTRA STAGE to think about “river litter problem”.