Recycling Ocean Plastic in Data: Degradation, Chlorine and Cost

The difficulty of recycling ocean plastic, in data

This page sets out, from research and public sources, the challenges of recycling plastic washed up on beaches as material. It is organised in three parts, degradation, salt and chlorine, and sorting and cost, and lists the figures and statements found in the sources. In Tsushima City's FY2025 survey, recyclable categories made up 22.54% of collected stranded litter by weight.

This page was compiled by Karatsu Farm & Food as part of the Karatsu Data Bank. It lists only the figures and statements in the sources, without conclusions or evaluations. It covers recycling ocean plastic into material and products, and its treatment. Using marine litter for art or as environmental education material is not covered. Quotations from Japanese sources are our translations; the originals prevail. Figures on the amount of ocean plastic and leakage in Japan are in Plastics in Numbers.

1. Degradation

Plastic that has been in the sea or on beaches changes with UV light and seawater. A University of Wollongong study (Environmental Pollution 334 (2023)) exposed PET, PP, PC and PLA to UVA in water simulating land, ocean and river conditions. It found that PET and PP changed colour, "making them unsuitable for upcycling purposes", and that "PET and PP could still be recycled into lower value products (i.e., construction materials)". PC showed little change. These are results under simulated laboratory conditions, not of actual stranded plastic.

A review of mechanical recycling of marine plastics (Frontiers in Marine Science (2025)) states that degradation "can significantly deteriorate the mechanical performance of recycled marine plastics" and lists the "difficulty in eliminating pollutants in marine plastics, such as salt, sand, shell, algae and marine plants". A review of technologies against marine litter in developing countries (Sustainability 13(9) (2021)) states that it is "commonly accepted that the quality of plastics for recycling is lower when recovered from oceans".

In Japan, a document from the National Institute for Land and Infrastructure Management (NILIM, Japan, year not stated) says that stranded plastic "cannot be collected once it degrades and fragments under UV light", and that "even if collected, salt and attached matter make it difficult to recycle, and it cannot be incinerated" (our translation).

2. A record of recycling degraded plastic (Maldives)

The Precious Plastic community, which recycles plastic in small workspaces, has a record from a workspace in the Maldives that tried ocean plastic (Precious Plastic Community). The aim was to see how "the extended exposure to saltwater/UV/contamination affects its recyclability". Rope came clean of most sand and other contaminants when soaked in water, but shredded rope was hard to feed into the machine, so the hopper was redesigned. The degraded bottle was considerably weaker before recycling, but beams made from it showed no substantial difference in bending and compression tests, and the record says more testing is needed. Foams, foils and thermosets such as rubber were not covered. It is a record of a small number of workspace trials.

Type	Chlorine content (representative value)
PET bottles	0.03%
Other plastics	0.07%
Expanded polystyrene	0.27%
Wood	2.60%
Fishing buoys	10.05%

RPF grade	Total chlorine (mass fraction)
RPF-coke	0.6% or less
RPF A	0.3% or less
RPF B	over 0.3% to 0.6%
RPF C	over 0.6% to 2.0%

3. Salt and chlorine

Okinawa Prefecture measured chlorine content by type while studying the use of coastal litter as RPF solid fuel (Okinawa Prefecture FY2014 report, Ch. 5). Fishing buoys contained 10.05% chlorine; the RPF standard for grade A is 0.3% or less. The FY2014 report records, as a finding of the FY2013 study, that "from the viewpoint of chlorine content, fishing buoys should not be made into fuel", and lists as a task "finding a simple way to separate PVC buoys and considering making fuel from the others" (our translation). Problems raised in the FY2012 study were "insufficient calorific value, uneven quality, unstable supply, lack of a collection system, cost, and chlorine content".

A Ministry of the Environment FY2021 report (Ministry of the Environment FY2021 report, Ch. IV) reviewed literature and cases on treating marine litter and states that "disposal fees for waste plastics charged by waste contractors appear to be set high because of salt attached to the plastics (several cases, such as JPY 50,000 per tonne and JPY 100 per kg)". It also cites a city that does not accept litter because of its salt content, concern about rising salt in incinerator cooling water, and a report that "fishing buoys are unsuitable as raw material because they contain salts, and separating materials and removing attached matter is difficult" (our translations). For plastic recovered from the sea, the review cited above (Sustainability 13(9) (2021)) notes contaminants such as salt, sludge and lead, requiring sorting, cutting, lead separation, crushing and desalting.

These statements in Japanese public sources concern fuel use and incineration. We have not been able to confirm, in Japanese public sources, the effects of PVC mixed into material recycling by melting and moulding.

Item	Value
Total project cost	JPY 5,057,671 thousand
National share	JPY 3,311,092 thousand
Prefectural share	JPY 1,219,279 thousand
Municipal share	JPY 571,058 thousand
Amount collected	35,570.7 tonnes

Fiscal year	Initial budget	Supplementary	Total
FY2020	3,695	3,525	7,220
FY2021	170	7,889	8,059
FY2022	170	3,525	3,695
FY2023	170	none	170

4. Sorting and cost

In the Ministry of the Environment survey (Ministry of the Environment survey (FY2024 results)), coastal litter project costs in FY2024 totalled JPY 5,057,671 thousand nationwide, with 35,570.7 tonnes collected. The Ministry of Finance budget execution survey (Ministry of Finance budget execution survey) found gaps between the highest and lowest prefectures of "about 14 times in collection unit costs and about 10 times in treatment unit costs" (our translation). Comparing island-only projects by prefecture, collection unit costs ranged from JPY 1.528 million to JPY 7,000 per tonne (projects in FY2020-2021).

The Okinawa report (Okinawa Prefecture FY2014 report, Ch. 5) puts the sales price of RPF at JPY 2,000 to 10,000 per tonne (interviews with the RPF industry association and others) and notes that its estimates show "collection and transport costs are the bottleneck" (our translation). The review cited above (Sustainability 13(9) (2021)) puts the average cost of collecting litter in rivers at about USD 600 per tonne, not including downstream processing.

Item	Volume (L)	Share of volume	Weight (kg)	Share of weight
PET bottle caps	58	0.08%	6	0.11%
PET bottles (under 1 L)	4,293	5.93%	205	3.49%
PET bottles (1 L or more)	2,555	3.53%	78	1.33%
Plastic buoys (20 cm or more)	9,361	12.93%	468	7.98%
Conger eel traps	635	0.88%	26	0.44%
Plastic tanks	1,735	2.40%	108	1.84%
Plastic baskets	6,000	8.29%	209	3.57%
Foam buoys	9,513	13.14%	178	3.04%
Glass drink bottles	115	0.16%	39	0.66%
Aluminium cans	70	0.10%	4	0.07%
Steel cans	7	0.01%	1	0.01%
Total	34,341	47.43%	1,322	22.54%

5. Recyclable categories in the Tsushima City survey

Tsushima City, Nagasaki, monitors stranded litter on its beaches every year. In the FY2025 report (Tsushima City FY2025 report, Part 2), recyclable categories (plastic buoys, plastic tanks, plastic baskets, foam buoys, drink bottles and cans, etc.) totalled 34,341 L (47.43%) by volume and 1,322 kg (22.54%) by weight of the litter collected in the survey plots.

The report (Tsushima City FY2025 report, Part 4) notes that the "recycling rate" is "not based on the amount actually recycled, but shows the share of target items in the total", that not all of the listed items are necessarily recycled, and that "items with many attachments or contaminants, small items and others that do not meet the recycling criteria are excluded" (our translation). The figures cover the survey plots only and exclude the city's collection programme and volunteer clean-ups.

6. A report by a European environmental organisation

In a 2022 briefing (Surfrider Foundation Europe (2022)), Surfrider Foundation Europe reviewed corporate claims about plastics and the ocean. It states that "exposure to the marine and/or coastal environment degrades plastic", so that the material that can be recovered is very limited and products cannot be made from it alone. It adds that "'marine plastic' may also be highly contaminated" and that collecting plastics in the marine environment is "extremely difficult and costly". On labels claiming "ocean plastic", it says they give the impression that buying a product cleans up plastic pollution. Data on claims and labels are in Greenwashing in Data.

FAQ

Q1. Can plastic washed up on beaches be recycled?

Some categories have recycling routes. In Tsushima City's FY2025 survey, recyclable categories such as buoys, plastic tanks and PET bottles made up 22.54% of collected stranded litter by weight and 47.43% by volume. The report notes that this is not the amount actually recycled, and that items with many attachments or contaminants, or that are too small, do not meet the criteria.

Q2. Does weathering at sea affect the quality of recycled plastic?

Studies show effects. A simulation by the University of Wollongong (Environmental Pollution 334, 2023) found that PET and PP exposed to UV in seawater-like water changed colour, making them unsuitable for upcycling, though they could still be recycled into lower-value products such as construction materials. A Precious Plastic workspace in the Maldives, on the other hand, reported no substantial difference in bending and compression tests of beams made from degraded bottles.

Q3. Why are salt and chlorine in stranded plastic a problem?

Japanese public sources raise them in the context of fuel use and incineration. Okinawa Prefecture's FY2014 report gives 10.05% chlorine for stranded fishing buoys (FY2013 measurements) and records, against the RPF solid fuel standard (0.3% or less for grade A), the finding that fishing buoys should not be turned into fuel. A Ministry of the Environment FY2021 report cites disposal fees for waste plastics set higher because of attached salt (e.g. JPY 50,000 per tonne).

Q4. How much does collecting and treating coastal litter cost?

The Ministry of the Environment's survey (FY2024 results) shows total coastal litter project costs of JPY 5,057,671 thousand nationwide and 35,570.7 tonnes collected. The Ministry of Finance budget execution survey (FY2023) reports gaps of about 14 times in collection unit costs and about 10 times in treatment unit costs between the highest and lowest prefectures.

Q5. Is this page against using ocean plastic?

This page sets out figures and statements from research and public sources on the challenges of recycling ocean plastic into material and products, without conclusions or evaluations. Using marine litter for art or environmental education is not covered.

Sources

What this page does not cover

Using marine litter for art or as environmental education material is not covered. Comparisons or evaluations of recycling methods and products of specific companies or organisations are not covered. Beach clean-up unit costs outside Japan and the effects of PVC in material recycling by melting are not included because they could not be confirmed in primary sources. Values that could not be confirmed in a primary source are not included.

About this page

Compiled by Hiroaki Kojima (Vice Director, Karatsu Farm & Food) / Contact: info@karatsu-f-f.com (contact form) / Published: October 19, 2026 / Markdown: en/ocean-plastic-recycling-data.md

This page is made together with AI. See this data bank and AI for how.

Related links

▶ Karatsu Data Bank
▶ Plastics in Numbers
▶ Greenwashing in Data
▶ Precious Plastic in Numbers
▶ 海洋プラスチックのリサイクルの難しさ（日本語）