Evaluating the Social Value of a Marine Plastics Upcycling Project in Japan

Abstract

Marine plastic pollution poses severe ecological and economic threats, while people with disabilities (PwDs) often face limited meaningful employment opportunities. This study evaluated a unique social enterprise in Japan that addresses both challenges through upcycling marine plastic waste into accessories while providing employment for PwDs. Using the Social Return on Investment (SROI) methodology, we assessed the project’s social and environmental impacts over one year (2020). Data was collected through stakeholder surveys, interviews, and operational records. The analysis identified 15 outcomes across six stakeholder groups, including income generation, environmental awareness-raising, and sustained volunteer engagement. The project achieved an SROI ratio of 3.50, indicating that every JPY 1 invested generated JPY 3.50 in social value. Media exposure (30.5%), employment income (25.6%), and volunteer motivation (18.5%) comprised 74% of the total value. Despite processing only 50 kg of marine plastic annually, the project demonstrated significant symbolic impact through behavior change and public awareness. Key challenges include limited production capacity, wage constraints, and gender-biased consumer demographics. This case illustrates how small-scale, community-based upcycling initiatives can generate multidimensional social value by integrating environmental conservation with social inclusion objectives.

1. Introduction

Marine plastic pollution has become a global issue over the last decade. It is estimated that approximately 8 million t of plastic waste flow into the ocean annually [1]. More than 150 million t of plastic waste currently accumulate in the world’s oceans. At this trajectory, the total mass of ocean plastics will exceed that of all fish in the sea by 2050 [2]. The persistence of plastics—materials engineered for durability and resistance to degradation—has transformed them from convenient commodities into agents of ecological disruption. The consequences are far-reaching: marine ecosystems suffer as seabirds, sea turtles, and seals ingest plastic debris or become entangled in fishing nets and lines, resulting in significant mortality rates [3,4]. Beyond ecological impacts, marine plastic pollution imposes substantial economic burdens through degraded tourism from spoiled coastal scenery, contaminated fishery products, and escalating costs for waste collection and disposal [5]. In recent years, academic research on marine plastic and microplastic pollution has grown rapidly. Large-scale data syntheses and bibliometric analyses highlight increasing scholarly attention to the sources, impacts, and mitigation of plastic pollution, including its emerging links with climate change [6,7,8]. However, recent scenario-based assessments indicate that marine plastic pollution is likely to continue increasing without systemic interventions [9,10].

In Japan, the composition of marine plastic debris differs depending on the measurement perspective. National beach-litter monitoring by the Ministry of the Environment has found that fishing gear (e.g., nets, ropes, and floats) dominates by weight, whereas beverage bottles and containers constitute the majority by item count [11]. This suggests that lightweight plastic waste items such as bottles and containers are numerically the most common form of marine plastic debris reaching shorelines, supporting the relevance of targeting such items for upcycling initiatives. In this context, given the dual nature of plastics as both stable materials and environmental pollutants, upcycling strategies that transform marine plastic waste into value-added products represent a promising approach to mitigate this crisis while creating economic incentives for ocean cleanup efforts [12,13].

From a circular economy perspective, upcycling can be understood as a value-retention strategy that emphasizes quality, durability, and symbolic value rather than material throughput [14,15,16]. In recent years, numerous collaborative projects or products have been dedicated to the issue of marine plastic pollution [17,18]. The Swedish brand TRIWA has been selling the world’s first recycled watch, “TIME FOR OCEANS”, made from upcycled marine plastic waste since 2020 [19]. This product was developed in collaboration with the Swiss company #tide ocean material. A wide range of products has been launched, made from #tide ocean material to textiles (e.g., bags, belts, huts, caps), consumer products (e.g., mugs, clamps, sunglasses) [20]. ECOALF is a European sustainable fashion brand based in Spain that implements the “Upcycling the Oceans (UTO)” project [21]. The initiative collects marine debris, particularly PET bottles, retrieved by fishing activities in the Mediterranean Sea. The initiative expanded in Thailand and Japan. These plastics are sorted, recycled into fibers, and transformed into new apparel products (e.g., sneakers, bags, T-shirts) [22,23]. TerraCycle Japan procured marine plastic waste collected in Tsushima City, Nagasaki Prefecture. It collaborated with ITOCHU Corporation to manufacture shopping baskets that are now in use at the major convenience store chain FamilyMart [24]. In Japan, the Sea of Japan coast receives significant marine debris influxes driven by ocean currents and seasonal winds. While the collection and effective utilization of beach plastic waste is crucial not only for the landscape but also for preventing microplastic generation, most collected plastics are incinerated or landfilled. Against this backdrop, Kaeru Design (KD) in Kanazawa City has developed a unique model that addresses both environmental and social challenges simultaneously [25]. The project upcycles marine plastics into accessories, providing employment opportunities for people with disabilities (PwDs) while integrating social welfare objectives directly into its operational framework.

The evaluation of corporate social activities has gained momentum, particularly accelerated since the adoption of the United Nations Sustainable Development Goals (SDGs) in 2015. Several frameworks have emerged to quantify social impacts beyond traditional financial metrics [26,27]. There are several corporate case studies that focus on environmental effects and visualize the value generated. For instance, AMITA Corporation’s “MEGURU STATION” project, which operates resource circulation hubs across Japan, has employed social impact assessment methodologies to measure benefits including CO₂ emission reductions, community engagement, and educational outcomes [28]. Similarly, Mercari, Japan’s leading online marketplace platform, has quantified the environmental and social value generated through product reuse, estimating annual CO₂ reductions and economic benefits to users [29]. Recent research on upcycling agricultural waste into value-added biopolymers has further demonstrated that low-volume, low-tech upcycling of waste materials can generate environmental and social value beyond conventional recycling pathways [30]. However, despite growing interest in upcycling as a waste management strategy that creates products of higher quality or value than the original materials, social impact evaluations of upcycling initiatives remain scarce in academic literature. A recent systematic review of circular economy practices further indicates that social value generated through day-to-day business operations is substantially under-researched [31]. Prior studies on social enterprises further emphasize that small-scale, community-based initiatives may generate disproportionate social value relative to their economic scale, particularly in terms of social inclusion, well-being, and community engagement [32,33]. In particular, some small-scale, community-based projects that integrate social welfare objectives may generate disproportionate social returns, yet they often lack the resources or frameworks to systematically document their impacts. For example, Sridan et al. [34] conducted a Social Return on Investment (SROI) analysis of a community-based waste bank initiative in Thailand that captured economic, environmental, and social benefits under a circular economy framework and reported a positive return (SROI = 2.65).

This study aims to evaluate the social value and impact of the KD project through SROI analysis. The first objective is to quantify the multidimensional benefits generated by KD’s upcycling activities, including environmental conservation, employment creation for PwDs, and community engagement. The second objective is to assess the project’s viability and scalability as a sustainable business model. This paper is structured as follows: Section 2 describes the KD project background, project overview, and SROI analytical procedures; Section 3 presents the results of impact measurement and SROI calculations; Section 4 discusses the significance of findings, limitations, and policy implications; Section 5 concludes with recommendations for future research and practice. This study contributes to the literature by (1) applying SROI to marine plastic upcycling initiatives, (2) explicitly integrating social inclusion outcomes, and (3) testing the robustness of media-related impact valuation through sensitivity analysis.

2. Materials

2.1. Study Site and Project Background

The project was launched in fall 2019 through a partnership between Kaeru Design, a creative team of three professionals, and Rehas, a Type-A continuous employment support facility operated by Creators Co., Ltd. in Kanazawa City, Ishikawa Prefecture, Japan. Type-A facilities provide formal employment contracts for PwDs within Japan’s welfare employment system, where participants are regarded as workers and paid at least the minimum wage. The facilities offer adapted work environments for individuals who have difficulty accessing regular employment, with the aim of eventually supporting their transition to jobs in the open labor market. Despite these objectives, many such facilities, including Rehas, face challenges with low-wage simple tasks (such as light assembly work), making it difficult for users to earn sufficient income for independent living. Rehas operates both a design division and a cleaning division. Within the design division, it undertakes the production and sale of its own products, as well as the design of leaflets, flyers, and similar materials. Rehas had been producing local souvenirs using Noto cypress wood (e.g., postcards and bookmarks) and leather goods, but struggled with unstable revenues.

To address this issue, Rehas hired a creative director from Kaeru Design in June 2019 to develop new business ventures. Drawing on his long-standing interest in environmental issues, he focused on the marine plastic pollution problem. In summer 2019, he organized a beach cleanup at Senkouji Beach in Kanazawa with Rehas users, where they collected large amounts of diverse plastic waste. Accessories were chosen as the product category for several reasons: the team included an accessory designer, they required minimal capital investment, and, as wearable items, they could spark conversations about environmental issues in daily life. Prototype accessories received positive feedback, leading to the official project launch in October 2019 and sales beginning in December. In May 2021, they established a limited liability company. Beyond marine plastic accessories, KD has expanded to other upcycled products, including accessories made from discarded flowers and dishcloths made from coffee bean sacks.

2.2. Project Overview

2.2.1. Acquisition of Marine Plastic

The project initially began with Rehas staff and users collecting marine plastic waste from local beaches as raw materials. As the production and sales activities gained visibility through Instagram and Facebook posts, people from across Japan who had collected plastic waste during their own beach cleanup activities began sending their collected plastic waste to the project, asking for their plastic waste to be upcycled into accessories.

Accepted materials are limited to plastics thin enough to be cut with scissors and small enough to fit in one cardboard box. At the time of our interview (July 2020), plastics had been sent from around 30 locations, including Chigasaki (Kanagawa), Shonan (Kanagawa), Suma (Kobe), Kikaijima (Kagoshima), and Obama (Fukui), with the network expanding to regions such as Kyoto and Okinawa. The collection period and methods vary by organization. For this project, approximately 50 kg of marine plastic waste was collected from Kanazawa and other regions across Japan and used as raw material for upcycling activities.

In Chigasaki, the organizer hosts a regular collection week event, and some environmentally conscious shops in the coastal area have permanent collection boxes in their stores. This permanent collection box fosters communication between those who bring marine plastics and shopkeepers, which may also lead to economic benefits. In Shonan, since August 2020, the organizer has held monthly beach cleanup events and sends suitable accessories to KD once a sufficient quantity has accumulated. The organizer in Obama has long been tackling marine litter, providing the collected plastic to KD and other upcycling organizations.

2.2.2. Accessory Production

Collected or shipped marine plastics are first cleaned with baking soda and water to remove dust, such as stones, and then sorted by color after drying. The sorted materials are blended, heat-pressed with an iron into flat sheets, cut into accessory shapes, and coated with resin before being assembled into finished accessories. Initially, the product line consisted only of earrings and necklaces, but has since expanded to include hair clips, tie pins, and pin badges. No specialized equipment is required, and all work is conducted within the Rehas facility.

Production occurs daily for approximately four hours. Consistently, 2–5 users are engaged in marine plastic accessory production, and about half of the users participated when including tasks such as cleaning, processing, and packaging. The work has had significant positive psychological impacts on users, providing a sense of purpose and fulfillment through the creative process and social significance. The number of PwDs at Rehas fluctuates monthly, but there are approximately 24 to 27 users. Approximately half have mental health conditions (such as schizophrenia, bipolar disorder, or depression), 20% have physical disabilities, another 20% have developmental disabilities, and the remaining 10% have intellectual disabilities.

2.2.3. Sales of Accessories

Sales are primarily conducted through the KD’s online shop. Since each piece of jewelry is unique, they cannot be sold in batches; each item must be individually photographed, listed on the website, and packaged upon sale. Each accessory includes information about its origin (e.g., “Made from plastics from XX location”) printed on the backing card (Figure 1), serving as a conversation starter about ocean conservation even for those not initially interested in marine issues.

Figure 1. Marine plastic accessory: (a) hairpin and (b) front and backside of backing card. Note: scale bar = 5 cm.

Products are also sold through consignment at 17 fair trade and ethical shops within and outside the prefecture. Some stores carry products year-round, while others feature them during special events. Additionally, the project participates in irregular pop-up shops at major department stores and returns accessories to donor organizations for sale at their locations. Retail displays feature product information alongside samples of collected marine plastic waste.

Most items are priced at JPY 3000–4000. During the evaluation period, 518 units were sold via the online shop, and 694 units were sold via consignment sales. A portion of sales proceeds is donated to the Japan Environmental Action Network (JEAN), an organization conducting marine litter surveys and cleanup activities supporting ocean conservation efforts.

2.3. SROI Procedure

This study follows the Social Return on Investment (SROI) methodology as outlined in established guidelines [35], which has also been widely discussed and critically examined in the academic literature as a tool for capturing social value beyond conventional financial metrics [36].

We followed the methodology outlined in the SROI Guide [35] and employed a six-step process:

• Defining the scope and identifying key stakeholders;
• Mapping outcomes (creating an impact map);
• Evidencing outcomes and assigning values;
• Verifying the impact of activities;
• Calculating the SROI ratio;
• Reporting findings and drawing conclusions.

Step 1 involved conducting online interviews with KD and Rehas representatives in July and October 2020 via Zoom (Zoom Video Communications, San Jose, CA, USA). This session helped define the scope of their activities and identify key stakeholders.

Step 2 focused on developing an impact map by identifying the inputs (time, funding, and materials) contributed by each stakeholder, outlining project activities (outputs), and defining the resulting changes (outcomes) experienced by stakeholders.

Step 3 involved evaluating and assigning monetary values to these outcomes. We conducted additional data collection through questionnaires and qualitative interviews. The timing and measurement content of each survey are detailed in Appendix A. The sample size for each stakeholder group was limited because the analysis comprised a single case study of one Type-A facility and its immediate partner organizations. For KD users and staff, the survey targeted all eligible participants within the facility, and the response numbers therefore reflect the actual size of the organization rather than a subsample drawn from a larger population. For partner organizations and volunteers, the number of respondents corresponds to the full set of individuals directly involved in KD’s marine plastic activities during the evaluation year, rather than a randomly selected sample. No formal statistical tests were applied to pre- and post-survey responses due to the small sample size and the exploratory nature of the study; instead, changes are interpreted descriptively and in combination with qualitative evidence.

In Step 4, impacts are verified by determining the extent to which observed changes can be attributed to the project. This verification applies three adjustment factors—deadweight, attribution, and displacement—to ensure that only outcomes genuinely caused by the project are included in the impact calculation. In Step 5, the SROI ratio was calculated using Equation (1):

$$SROI={\displaystyle \frac{Total Outcome}{Total Input}}$$

(1)

For example, an SROI ratio of 3 indicates that every JPY 1 invested in the project generated JPY 3 in social and environmental value.

Step 6 involved reporting the SROI calculation results to KD in April 2021 and exchanging ideas and possible recommendations to improve and expand the project.

3. Results

3.1. Identifying Stakeholders

This study focused specifically on KD’s marine plastic accessories project over a one-year period from December 2019.

Based on our initial analysis, six key stakeholder groups were identified: PwD employees (users of Rehas), KD staff, retailers, support persons/organizations, government, and consumers.

3.2. Mapping Outcomes

An impact map (logic model) was developed to visualize the relationship between inputs, activities, outputs, and expected outcomes for each stakeholder (Figure 2). The project provided stable employment for PwDs, enabling them to gain income (Outcome 1) and increase motivation to work (Outcome 2). Participants expressed pride in their work, leading to a decline in absenteeism rates. Some users shared their experiences with family and friends or purchased accessories for themselves, thereby fostering a sense of social participation and belonging (Outcome 3). In our interview, several participants reported behavioral changes, such as carrying reusable bottles instead of buying bottled drinks, indicating greater environmental awareness (Outcome 4). At the intermediate outcome level, these changes contributed to enhanced work engagement and stable income, which are stepping-stones toward economic independence. For the project operator, stable sales improved financial sustainability (Outcome 5) and the quality of welfare services.

Figure 2. Logic model of the marine plastic accessory project.

The project also had clear environmental impacts. By transforming collected marine plastic waste into accessories, it contributed to raising public awareness of marine plastic issues and encouraging waste reduction behaviors (Outcome 15). Partner organizations that collaborated in beach cleanings or consignment sales reported higher motivation to continue environmental activities (Outcome 10) and were able to secure operational funding through sales commissions (Outcome 11). These intermediate outcomes—such as strengthened community engagement and pro-environmental behaviors—contributed to broader outcomes like reduced waste treatment costs (Outcome 14) and improvement in the coastal ecosystem through reduced marine litter (Outcome 13). The ultimate long-term outcome is the mitigation of marine plastic pollution.

3.3. Evidencing Outcomes

Each outcome was quantified and monetized following the SROI framework. Table 1 summarizes the 15 outcomes and their estimated annual social value.

Table 1. Financial proxies for outcome evaluation.

Stakeholder	No.	Outcome	Indicator	No. of People Affected	Monetary Value (JPY 1000/Year)	Basis for Calculation
Users	1	Gaining income	Amount of wage payment	6	4798	Based on interviews: number of people × hourly wage (JPY 833) × 4 h/day × 240 working days/year.
Users	2	Increased motivation to work	Attendance rate	26	1455	Improvement in attendance (from 87.5% in 2019 to 94.5% in 2020 = 7%) × average daily wage (JPY 833 × 4 h) × 240 days × number of people.
Users	3	More social interaction	Frequency of social activities	26	156	Based on survey: 50% increase in social interaction × 2 café visits/month × JPY 500 [37] each.
Users	4	Increased environmental awareness	Reduced single-use plastic amount	26	0.4	Reduction rate of single-use plastic (from user survey) × CO2 emission factor (5.0 kg-CO2/kg) [38] × J-Credit average price (JPY 1473/t-CO2) [39].
Project operator	5	Improved financial stability	Sales revenue	-	3444	Based on sales of 518 items (online) + 694 (consignment), average price JPY 3316, profit rate 75%.
Project operator	6	Environmental contribution through donation to JEAN	Pollution avoided	-	2.0	Actual donation JPY 36,185 × 37% used for activities × marine waste collected (0.001 kg/JPY) × avoided disposal cost (JPY 150/kg) [40].
Project operator	7	Raised awareness of marine plastic issues	Number of media coverages	-	11,440	11 local newspapers × JPY 600,000 + 2 national papers × JPY 1647,000 + 2 TV reports × JPY 320,000 + 3 web articles (10,000 page views × JPY 30) [41,42,43].
Project operator	8	Increased environmental awareness	Reduced single-use plastic amount	10	0.5	Reduction rate (from staff survey) × CO2 emission factor × J-Credit price (same as above).
Retailers	9	Increased environmental awareness	Reduced single-use plastic amount	10	0.5	Reduction rate (from retailer survey) × CO2 emission factor × J-Credit price (same as above).
Partner Orgs, etc.	10	Sustained motivation for activities	Annual activity hours	200	4330	Voluntary work hours: 200 people × 24 h/year × JPY 902/h (national weighted average minimum wage, FY2020) [44].
Partner Orgs, etc.	11	Secured funding for activities	Sales commission income	-	166	200 items sold × Sales commission rate 25%× average price JPY 3316.
Partner Orgs, etc.	12	Increased environmental awareness	Reduced single-use plastic amount	200	0.6	Voluntary work hours: 200 people × 24 h/year × JPY 902/h (national weighted average minimum wage, FY2020).
Government	13	Avoided damage from marine plastic	Amount of collected marine plastic	-	8.5	Based on global marine plastic outflow (8 million t) and economic loss (USD 13 billion), converted to damage per 50 kg of marine plastic [45].
Government	14	Reduced waste treatment cost	Amount of collected marine plastic	-	7.5	50 kg of plastic × avoided administrative disposal cost (JPY 150/kg).
Consumers	15	Increased environmental awareness	Reduced single-use plastic amount	-	15	Reduction rate (from buyer survey) × CO2 emission factor × J-Credit price (same as above).
		Total			25,824

Note: USD values were converted to JPY using an exchange rate of USD 1 = JPY 105 (as of 25 September 2020).

Gaining income: As mentioned earlier, 2 to 5 users are primarily involved in accessory production, though when including tasks such as packaging, around half of the workforce may be engaged. We assumed that this outcome reflects the financial benefit for six users who gained income through project employment. The amount was calculated using the number of users, the minimum wage in Kanazawa at that time (JPY 833), multiplied by four working hours per day and 240 working days per year. The total monetary value was estimated at JPY 4,798,000.

Increased motivation to work: This was evidenced by a significant 7% increase in the attendance rate, rising from 87.5% (Nov. 2019–Mar. 2020) to 94.5% (Nov. 2020–Mar. 2021) among 24–27 participants. The corresponding benefit was calculated by multiplying the minimum wage (JPY 833 × 4 h) by the number of working days, resulting in a total value of JPY 1,455,000.

More Social Interaction: According to survey results, users’ frequency of social interactions increased by approximately 50%, equivalent to two café visits per month (JPY 500 each) [37]. This improvement in social connection was monetized by equating the emotional benefit to the cost of such activities, yielding a total value of JPY 156,000.

Increased environmental awareness (Users): Using estimated data on the annual consumption and reduction rates of single-use plastic (see Appendix B for detailed calculation), CO₂ emission factor (5.09 kg CO₂/kg) [38], and J-Credit carbon price (1473 JPY/t-CO₂, Jan. 2020) [39], we estimated that the total monetary value was JPY 360.

Improved Financial Stability (Project Operator): The project operator’s sales revenue increased through online sales (518 items) and with a profit rate of 75% for consignment sales (694 items) at an average price of JPY 3316. The annual financial benefit is JPY 3,444,000.

Environmental Contribution through Donation: The project donated JPY 36,185 to a marine conservation NGO (JEAN). Based on the proportion used for beach cleaning activities and the avoided disposal cost (150 JPY/kg) [40], we estimate the environmental contribution value is approximately JPY 2000.

Raised Awareness of Marine Plastic Issues: Media exposure—comprising 11 local newspaper articles, two national newspaper articles, two television reports, and three web articles—was used as a proxy for public awareness. Using advertising equivalency rates (JPY 30 per 10,000 page views and JPY 320,000–1,647,000 for mass media) [41,42,43], we estimate the total media value is JPY 11,440,000.

Increased Environmental Awareness (Project Operator): From staff survey data, the project’s efforts led to measurable reductions in single-use plastic. Based on annual consumption, CO₂ emission reductions, and J-Credit prices, we estimated that the total monetary value was JPY 477.

Increased Environmental Awareness (Retailers): Retailers participating in the project reduced their use of single-use plastics through improved awareness and practice. Based on annual consumption, CO₂ emission reductions, and J-Credit prices, we estimated that the total monetary value was JPY 463.

Sustained Motivation for Activities (Partner Organizations): This outcome represents the unpaid time spent by approximately 200 volunteers engaged in beach-cleaning-related activities. Using the national weighted average minimum wage (JPY 902/h) [44] for 24 h per year, the total value was estimated at JPY 4,330,000.

Secured Funding for Activities: Partner organizations benefited from commission income on 200 items sold through the project’s sales platform. Applying a 25% commission rate to the average sales price (JPY 3316), the total annual benefit amounted to JPY 166,000.

Increased Environmental Awareness (Partner Organizations): For volunteers and partner organizations, plastic-use reduction was also monetized based on CO₂ reductions and J-Credit prices, yielding a small benefit of JPY 596.

Avoided Damage from Marine Plastic (Government): The project’s collection of marine plastic contributed to avoided economic losses, based on global estimates of 13 billion USD in annual damages from marine debris [45]. Scaled to the project’s contribution of 50 kg, the benefit was valued at JPY 6825.

Reduced Waste Treatment Cost (Government): By collecting 50 kg of marine plastic, the project reduced administrative disposal costs, estimated at 150 JPY/kg, leading to savings of 600 JPY.

Increased Environmental Awareness (Consumers): Consumer surveys indicated reductions in single-use plastic use, valued using CO₂ emission factors and J-Credit prices, with a total benefit of 15,096 JPY.

While other positive effects, such as enhancing the corporate image of retailers, revitalizing local communities through the collection of marine plastics, were observed, they were excluded from the calculation due to a lack of benchmark data.

3.4. Verification of the Impact of Activities

To ensure the reliability of the valuation, three key adjustment factors were applied in accordance with SROI principles:

• Attribution: The project’s outcomes—particularly employment creation for PwDs and marine plastic upcycling—were unique to this initiative. Therefore, attribution was set at 100%, assuming these impacts would not have occurred otherwise.
• Deadweight: For environmental awareness outcomes, national-level policy effects (such as the 2020 plastic bag charge) were considered as deadweight. The proportion attributable to such policies was deducted from total impact values (ranging from 8% to 32%, depending on stakeholder group).
• Displacement: Since the project does not replace existing economic activities but creates new value in both welfare and environmental domains, displacement was assumed to be 0%.

Attribution was also set at 100% for awareness- and participation-related outcomes because the analysis focuses on changes observed among individuals directly engaged in the KD activities. These changes are considered to be primarily triggered by project participation rather than by broader societal trends. The influence of external factors, such as existing environmental awareness, social norms, and policy contexts, was addressed through the deadweight assumption for each outcome, which was also used as an additional safeguard against potential overlap and double-counting across outcomes. In particular, for media-related awareness (Outcome 7), a conservative deadweight of 50% was applied to account for broader societal attention to plastic pollution and the influence of external campaigns beyond the project itself [46,47]. After adjusting for these factors, the total present value of benefits amounted to JPY 18,768,000 (Table 2).

Table 2. Adjusted monetary valuation of project outcomes.

No.	Outcome	Monetary Value (JPY 1000)	Deadweight (%)	Adjusted Value (JPY 1000)	Basis for Calculation
1	Gaining income	4798	0%	4798
2	Increased motivation to work	1455	30%	1019	Based on comparison with similar welfare-type workplaces (Type A). Deadweight was assumed to be 30%.
3	More social interaction	156	20%	125	Assumed that 20% of the participants would have similar opportunities for interaction through other products or activities.
4	Increased environmental awareness	0.4	22%	0.3	Deadweight was estimated based on the proportion of users’ plastic bag reduction behavior attributable to national plastic bag charging policy (32% × 70%).
5	Improved financial stability	3444	0%	3444
6	Environmental contribution through donation to JEAN	2.0	0%	2.0
7	Raised awareness of marine plastic issues	11,440	50%	5720	Deadweight (50%) applied to account for broader societal influences.
8	Increased environmental awareness	0.5	17%	0.4	Deadweight estimated from staff’s share in overall plastic reduction (24%) × proportion attributable to national policy (70%).
9	Increased environmental awareness	0.5	8%	0.4	Deadweight estimated from retailers’ share in overall plastic reduction (11%) × proportion attributable to national policy (70%).
10	Sustained motivation for activities	4330	20%	3464	Assumed that 20% of volunteers would continue activities even without the marine-plastic jewelry project
11	Secured funding for activities	166	0%	166
12	Increased environmental awareness	0.6	0%	0.6	Deadweight was set at 0% since the volunteers’ share in total reduction effect was negligible (0%).
13	Avoided damage from marine plastic	8.5	0%	8.5
14	Reduced waste treatment cost	7.5	0%	7.5
15	Increased environmental awareness	15	11%	13	Deadweight estimated from consumers’ share in total plastic reduction (16%) × proportion attributable to national policy (70%).
6, 11, 13, 14	Outcomes for the Marine Environment			3648
1, 2, 3, 5	Outcomes for Persons with Disabilities and Facilities			9385
4, 7, 8, 9, 12, 15	Outcomes for Civil Society			5734
	Total	25,824		18,768

3.5. Inputs

Financial and in-kind inputs required to implement the project, including personnel costs, operational expenses, and supporting resources, constitute the investment component used as the denominator in the SROI calculation. The project’s total input was valued at 5.4 million JPY (Table 3). Inputs included instructors’ salaries (JPY 1,680,000), minor material purchases (JPY 387,000), the shipping cost of marine plastics (JPY 14,000), personnel and venue costs at department stores (JPY 1,608,000), and the implicit value of volunteer labor (JPY 1,666,000). Cleaning activities using minimal cleaning agents were conducted as part of routine work by users; therefore, no additional costs were separately allocated. Transportation costs were included for plastics shipped from outside the Kanazawa area, but locally collected materials did not incur additional shipping expenses. National subsidies for welfare-type businesses (Type A) were not counted as inputs since they are part of the base operation and are not specific to this project.

Table 3. Inputs of KD project.

Stakeholder	No.	Input	Measurement Indicator	Input Amount (JPY 1000/Year)
Users	1	Personnel costs	Instructor salaries (JPY 140,000/month × 12 months)	1680
Users	2	Other expenses	Material costs (hardware), equipment costs, packaging materials, online shop server operation fees, and credit card payment system	387
Users	3	Shipping costs	Actual shipping costs from regional organizations to Kanazawa (JPY 600 × 24 occasions)	14
Retailers	4	Personnel Costs	Sales staff wages (2 staff per day × 8 h × 7 days × Fukuoka Prefecture minimum wage JPY 842; 2 staff per day × 8 h × 7 days × Tokyo Metropolis minimum wage JPY 1013)	208
Retailers	5	Venue costs	Department store stall fee (JPY 100,000 × 7 days × 2 times)	1400
Partner Orgs, etc.	6	Personnel costs	Beach clean-up volunteer working hours (2000 h × Kanazawa City minimum wage JPY 833)	1666
		Total		5355

3.6. The SROI Calculation

The total monetized benefit was calculated as JPY 18,768,000. The total investment was JPY 5,306,623. The SROI ratio was calculated by dividing total benefit by total investment:

$$SROI={\displaystyle \frac{\mathrm{18,768,000}}{\mathrm{5,355,000}}}=3.50$$

Table 4 summarizes the total investment, total present value of benefits, and the resulting SROI ratio. This ratio indicates that every JPY 1 invested in the project generated approximately JPY 3.50 of social value in combined welfare and environmental outcomes. Although this SROI ratio is moderate compared to other reuse and recycling projects (2.65–11.77) [48,49,50,51], it clearly represents a positive and meaningful return, demonstrating that the project generated more value than the resources invested. Three outcomes dominated the total quantified value: media exposure (30.5%), employment income for PwDs (25.6%), and sustained volunteer motivation (18.5%), collectively representing approximately 74% of social value created.

Table 4. Summary of SROI results.

Item	Monetary Value	Unit
Total Present Value	18,768	JPY
Total Investment	5355	JPY
Social Return on Investment	3.50	Ratio

3.7. Sensitivity Analysis

To examine the robustness of the SROI results, we conducted sensitivity analyses focusing on media-related awareness outcomes, which account for a substantial share of the total social value. In addition to the base case, two conservative scenarios were tested: (1) an 80% reduction in the monetized value of media exposure, and (2) setting the deadweight to 100%, effectively excluding media exposure from the SROI calculation. The resulting SROI values were 2.86 and 2.44, respectively (see Appendix C for detailed calculation). In all scenarios, the resulting SROI ratios remained above 1, indicating that the overall conclusions are robust and not driven solely by media-related outcomes.

4. Discussion

The project began with simple beach cleanup activities, gradually evolving into a circular initiative that transforms collected marine plastic into accessories. Through this process, users (PwDs) experienced a strong sense of purpose and social contribution. Many users reported greater motivation to work, reflected in a notable decrease in absenteeism and increased continuity of employment. The activities also provided opportunities for outdoor engagement and communication with family and friends, contributing to improved well-being and social inclusion.

Although the actual amount of marine plastic incorporated into accessories is minimal (50 kg annually), its symbolic value is substantial. Wearing and sharing these accessories increases public awareness of marine litter issues and encourages broader behavioral change. The project’s extensive media exposure—including coverage in newspapers, television programs, and online media—generated the highest monetary value among all outcomes, underscoring the significance of awareness-raising as a social impact pathway. Furthermore, the project has created a motivational loop among partner organizations and volunteers. Through our observation and interview with the organization in Shonan, we found a stronger sense of fulfillment when their cleanup activities resulted in upcycled products and created employment for PwDs.

Despite these positive impacts, several managerial and structural challenges remain. First, both production capacity and sales capacity are limited. While more PwDs wish to work at KD, the Type-A facilities restrict the number of employees per facility, preventing expansion despite high demand. Second, although the product unit price has risen with improved craftsmanship and design, these gains have not yet translated into higher user wages. Although the welfare service system is the primary cause, balancing production volume, fair wages, and appropriate levels remains a key management issue.

With regard to Outcome 1 (wage improvement), higher earnings for PwDs could theoretically be achieved through increased product sales, higher unit prices supported by ethical premiums, or expanded market reach. In practice, however, Type-A welfare facilities face structural constraints, including limited capacity, fixed staffing arrangements, and regulatory frameworks, that make rapid wage increases or workforce expansion difficult. Accordingly, the primary contribution of the model lies in providing stable employment and promoting social inclusion rather than pursuing rapid wage growth or market sales expansion.

From a market perspective, the project’s main customers are women who may have already been environmentally conscious—a pattern consistent with prior research indicating that women tend to show stronger pro-environmental attitudes [52,53,54]. Since the current products are primarily accessories, the consumer base has a somewhat gender-biased composition. To achieve broader social impact and contribute more substantially to the mitigation of marine plastic pollution, it will be important to diversify upcycled products beyond accessories. Potential future product lines may include stationery, daily use items, or art objects that appeal to broader demographics, including men and younger audiences. Strategic communication targeting those who are less aware or less engaged in environmental issues will also be essential.

This study has several limitations. First, the evaluation period (2020) coincided with the COVID-19 pandemic, during which numerous unusual external factors may have influenced the results. Online sales of accessories may have been temporarily boosted due to increased e-commerce activity during periods of restricted mobility. Conversely, volunteer participation may have been constrained by public health measures, potentially leading to an underestimation of community engagement outcomes. At the same time, changes in consumption patterns during the pandemic—including increased reliance on single-use plastics—may have influenced public awareness and attitudes toward plastic waste. These contextual factors should be considered when interpreting the results. Second, the data collection period was limited to one year. It is difficult to project longer-term effects for more robust estimation of sustained outcomes. Third, some outcomes have been excluded or underestimated due to insufficient data. The monetization of media exposure using advertising equivalency rates, while standard practice, may overestimate the actual environmental awareness change impact. The sensitivity analysis addresses key uncertainties associated with media valuation and demonstrates that the overall findings remain robust under conservative assumptions. Beyond this, several positive outcomes—such as enhanced corporate image for retailers and strengthened community cohesion—were excluded due to a lack of reliable proxies, suggesting the total social value may be underestimated. Comparable data from other Type A welfare service providers were unavailable, making it difficult to estimate a precise deadweight rate. Consequently, the deadweight assumptions used in this study may lack accuracy, posing a limitation to the rigor of the impact estimation. Collection from partner organizations was limited to three groups (two in Kanagawa Prefecture and one in Obama City), and volunteer data were obtained from only eight participants in the Shonan area. Thus, the sample may not fully represent the diversity of collaborators/volunteers. Future research should address these limitations by collecting longitudinal data across multiple years and applying repeated SROI calculations, which will allow for more reliable estimation of counterfactual effects and enhance the precision of SROI calculations.

5. Conclusions

This study demonstrates that even small-scale marine plastic upcycling initiatives can generate substantial social value when evaluated through an SROI framework, particularly when environmental action is integrated with employment support for PwDs. The analysis identified 15 outcomes across 6 stakeholder groups, including income generation, environmental awareness-raising, and sustained volunteer engagement. Overall, the analysis indicated that the project generated an SROI of 3.50, demonstrating substantial social and environmental value relative to the initial investment. Media exposure (30.5%), employment income (25.6%), and volunteer motivation (18.5%) comprised 74% of the total value. Despite processing only 50 kg of marine plastic annually, the project demonstrated significant symbolic impact through behavior change and public awareness.

The project not only enhances public awareness of marine plastic pollution but also encourages concrete behavioral changes among citizens, such as reducing single-use plastics and participating in coastal cleanup activities. The products created from marine plastics serve as tangible reminders of the environmental issue, transforming discarded materials into items of value and spreading the concept of “upcycling” as an approach to sustainable resource use. From the perspective of social inclusion, the initiative provides participants with a sense of purpose and social connection by engaging them in work that is both meaningful and visible to the community. The improvement in attendance rates and job retention among employees with disabilities suggests that involvement in environmentally and socially beneficial activities can strengthen motivation and workplace stability.

If this model proves economically viable and scalable, it could serve as a valuable reference for other Type A continuous employment support facilities in Japan, many of which struggle with chronic deficits. However, the pursuit of “scaling up” the production and sales of marine plastic accessories raises a potential paradox; while growth may improve financial sustainability, excessive production could contradict the goal of sustainability itself. Future efforts should therefore focus on balancing social, environmental, and economic objectives—perhaps by expanding into other upcycled product categories (e.g., stationery, household items, or art objects) that can engage a broader demographic.

Like other single-case SROI studies, this analysis has methodological limitations. The one-year evaluation period and the small sample sizes limit the generalizability of the quantitative findings, meaning that the results should be interpreted as indicative rather than statistically representative. These constraints were mitigated through triangulation of survey responses, interview data, and operational records, as well as sensitivity analysis to test key outcome assumptions.

This case study illustrates how an inclusive, community-based upcycling initiative can ultimately generate multidimensional social value. To ensure its long-term sustainability, continued evaluation of both environmental and social outcomes, alongside adaptive management of production and outreach strategies, will be essential. Recent studies on social enterprises and work integration initiatives [55,56] similarly emphasize that the value of inclusive employment should be understood in multidimensional terms rather than solely through financial performance indicators. Prior research applying SROI and related impact measurement approaches has highlighted the importance of capturing well-being, social participation, and community-level effects, particularly under constrained economic or crisis conditions [55,56]. In this respect, this study contributes to the growing literature by demonstrating how an environmentally oriented upcycling initiative can also function as a platform for social inclusion and meaningful work.