In fiscal 2023, Pirika, Inc. (“Pirika”) carried out a survey of river litter in Aichi Prefecture. Much marine plastic litter comes from land. So the survey looked at areas around rivers (banks and riverbeds), which are the routes litter takes from land to the sea. Its aim was to understand how litter is distributed and what it is made of, and to propose effective ways to reduce it. Besides survey methods based on guidelines from the Ministry of the Environment and the Ministry of Land, Infrastructure, Transport and Tourism, we also used Pirika’s own technology and services.

1. Choosing survey sites with documents and data from Takanome (car version)

We gathered documents on the population, area, length and surrounding land use of several rivers in Aichi Prefecture. We also turned data from the car version of Takanome, a land litter survey service, into numbers. With these, we chose the waters and sites that let us understand river litter effectively and efficiently.

For Takanome, a smartphone is mounted in a vehicle, and AI detects litter on the road from video taken while driving. It shows the litter situation as numbers, so we can compare how much litter there is between areas, days and months. Several companies help with filming. In this survey too, we analyzed data filmed by partner companies in Aichi Prefecture.

The litter density data for Aichi Prefecture showed high density near main stations and bridges in the crowded areas of the Owari region, including Nagoya City, and at river junctions. Density was low in the Nishi-Mikawa and Higashi-Mikawa regions.

2. Ranking the amount of litter on riverbanks and riverbeds

After choosing the sites, we did a general survey to understand the amount of scattered litter and bulky waste. Following the Ministry of the Environment’s “Guidelines for Surveying Scattered Litter” and the Ministry of Land, Infrastructure, Transport and Tourism’s “River Litter Survey Manual”, we walked the banks and riverbeds at each site and picked a spot with an average amount of litter. At that spot, we marked off a 10 m strip along the river and recorded the amount of litter in it, measured in 20 L garbage-bag equivalents. If bulky waste had been dumped, we also recorded its number, amount, type and location.

We ranked the results by amount of litter and showed them on a map. We also made graphs by water area and by river to find trends for the whole prefecture. As expected, areas with many people had more litter, and areas with few people had less. But we also found that population affects bulky waste somewhat less, and that some places have little litter even in populous areas, such as near well-kept parks.

3. Collecting litter and measuring number, volume and weight by category

From the general survey sites, we chose 8 sites for a detailed survey that measures the number, volume and weight of litter by category. The categories follow the Ministry of the Environment’s “Guidelines for Surveying the Composition of Litter Washed Ashore, for Local Governments”. The main (top-level) categories are plastic, polystyrene foam, rubber, glass and ceramics, metal, paper and cardboard, natural fiber and leather, wood, electrical and electronic equipment, natural items, and others. This survey looked at the make-up of all litter except natural items.

At every site, plastic had the largest share by number, volume and weight. Among plastic items, the most common by number were plastic bags, cigarette butts (filters) and PET bottles under 1 L, in that order. By volume they were tape (such as packing bands), PET bottles under 1 L and plastic bags. By weight they were plastic bags, “other” and PET bottles under 1 L. This shows that plastics common in everyday life are leaking into the environment. When we compared this with a survey of litter washed ashore on Aichi’s coast, plastic made up an even larger share there. This suggests that light, easily moved plastic litter easily becomes marine litter. (For details, see here (Japanese).)

4. Toward effective ways to reduce litter

The area that affects a river is wide, so effective litter measures are said to be difficult. Still, this survey gave us many hints for planning measures that fit local conditions, such as population density, land use, and infrastructure like bridges and parks. In particular, Takanome data showed “hotspots” with a lot of street litter. This information can help estimate where river litter comes from, and to guide cleanups to places with a lot of litter, which may make reduction measures more effective.

Takanome’s litter distribution data is added to every day by partner companies, so we can follow changes day by day. At one survey site with a high litter rank, we saw areas of high litter density move from upstream to downstream as days passed. More detailed information is needed from many angles to understand this movement. But Takanome may be a way to check how litter on land flows into rivers.

Pirika can also propose using the Pirika App (a litter-picking app) to call for and manage cleanups, and using its illegal dumping report function to report litter that individuals cannot handle to the local government. This leads to concrete actions that help solve environmental problems, such as planning a cleanup event at a litter-heavy spot near a river.

Closing

The results of the Aichi Prefecture river litter survey led to one effective way to reduce litter. Near rivers, which are routes to the sea, a technology that shows how much litter there is, like Takanome, can guide cleanups to “hotspots” with especially a lot of litter.

Pirika has developed many services for collecting and surveying litter, aiming to solve the problem of litter leaking into nature. We will keep developing new methods and proposing highly effective measures.

Summary of the fiscal 2023 Aichi Prefecture river litter survey results: here (Japanese)

Ministry of the Environment, Guidelines for Surveying Scattered Litter: here (Japanese)

Ministry of the Environment, Guidelines for Surveying the Composition of Litter Washed Ashore, for Local Governments: here (Japanese)

Ministry of Land, Infrastructure, Transport and Tourism, River Litter Survey Manual: here (Japanese)