A novel approach to characterizing plastic waste releases from land-based sources using material flow analysis: The case of Thailand

The PW generation process

Before the application of any PW assessment method, it is critical to understand the PW generation process and potential PW leakage points (Figure 1). For any context, the PW generation process is complex and cumulative and involves several players (Bureecam et al., 2018; Lobelle et al., 2024; Schwarzböck et al., 2016). PW can be generated during polymer production stages, consumer product utilization stages and even PW recycling stages. The quality and volume of PW generated at these various stages determine the complexities associated with the collection, pre-processing, recycling and valorization of the PW arisings. PW generated during the production stage can be expected to be clean, homogeneous and easier to collect and reprocess than post-consumer PW arisings (Plastics Europe, 2021). Even when additives are already present in these wastes, their recycling and re-incorporation into the production process is easy since their factory-level composition is generally known (Pinter et al., 2021; Van Eygen et al., 2018; World Bank Group, 2021). The quality of source-separated PW generally depends on the polymer applications, and consumer behaviour during product use and storage of empty plastic containers. Industrial PW tends to be more homogeneous than post-consumer PW (Varvazovska and Prasilova, 2015). Post-consumer PW arisings are generally expected to be both more difficult and costly to recycle because their quality and volume cannot be easily predicted (OECD, 2022). Consumer behaviour, such as the use of single-use plastics, aggravates PW generation and potential leakage into the biosphere (Feil et al., 2017; Fogt Jacobsen et al., 2022). The terms mismanaged plastics and PW leakage can be understood differently depending on the context. In the current study, mismanaged PW includes the entire volume of waste that does not follow the formal management process and ends up being buried at the source, burned at the source, dumped in unprotected landfills or lost during the transfer processes. PW leakage entails the total volume of PW discarded in areas where it is directly in contact with the environment, gradually releasing contaminants, including toxic additives. What eventually leaks into the environment is therefore only a part of that which is mismanaged.

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Figure 1.

The PW generation process showing stages of potential leakage into the environment (adapted with modifications from BRS Secretariat (2021a)).

The methodology applied also quantified waste disposed of in controlled and uncontrolled landfills. Controlled landfills primarily referred to waste disposal areas with most of the requirements for a sanitary landfill in place whereas uncontrolled landfills referred to disposal sites which fall below the requirements of a sanitary landfill. For both controlled and uncontrolled landfills, an effort has been made by the responsible authorities to collect waste and send it to disposal sites. The nature of the disposal site determines whether the specific volume of waste in question is regarded as having been sent to a controlled or uncontrolled landfill site, which in turn determines how much PW leakage is to be expected. Landfill mining plays a vital role in recovering PW discarded and limiting leakages and groundwater contamination from both controlled and uncontrolled landfills (Yamahara et al., 2024). If this is coupled with appropriate measures to reduce PW throughput landfills, long-term environmental gains can be realized (Chen and Fei, 2023).

Data sources

The current study makes use of MFA as the principal tool for tracing PW flows by examining data obtained from field studies on PW generation and management. Unlike the traditional MFA approach, the methodology adopts a multi-thronged approach in estimating PW leakages from the waste management system (WMS) including site and activity-specific variables (such as the condition of waste transporting vehicles, the condition of waste receptacles and the specific characteristics of the waste disposal sites). In the absence of specific data for a study area, the tool uses proxy data drawn from similar contexts. These unique strengths underscore the primary reasons why the toolkit was adapted for the current study.

Thailand’s urban and rural areas differ significantly in waste management practices and infrastructure (ESCAP, 2020; Manomaivibool et al., 2018; Marks et al., 2023; Sandhya et al., 2019). Like many other developing countries, waste management services are less reliable in remote areas (Samitthiwetcharong et al., 2024). Advanced waste management approaches such as waste-to-energy (WtE) have only been implemented in larger cities such as Phuket and Hatyai (World Bank, 2022). To accommodate MSW and PW generation data variations across the Thai regions, the country data were divided into three archetypes with population size being the underlying factor. These were named Mega, Medium and Small archetypes in line with the BC methodology (Table 1). Archetypes share common traits, for example, level of economic affluence, population and MSW generation and management trends (BRS Secretariat, 2021a).

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Table 1.

Data archetypes.

Archetype	Description	City/town (examples)	Total population
Mega	All metropolitan assemblies and cities which comprise urban centres with populations over 250,000.	Bangkok Metropolitan area, City of Phatthaya, and non-municipal area around Phatthaya	6,099,641
Medium	All municipal assemblies comprising single-town councils with populations of 95,000 or more.	Udoni Thani, Nonthaburi City, Hat Yai, Chiang Mai, Surat Thani, etc.	11,278,171
Small	All district assemblies comprising smaller towns and rural areas with low population density and minimal access to waste collection and management services.	Town municipalities of Yala, Ratchaburi, Phuket, Nakhon Sawan, Rayong, etc.	48,712,663

Primary data were obtained from multiple sources including site visits and key informant interviews, whereas secondary data were sourced from peer-reviewed literature and published institutional reports. The PW imports data (Code HS-3915) used for the current study was based on the 2020 estimates obtained from the Thailand Customs Department (Thai Customs Department, 2023).

The secondary data used were cross-checked by considering the sources and comparing data from several researchers and authors. To generate an understanding of the reliability of the assessment, the data were subjected to a data reliability test along three dimensions: reliable, somewhat reliable and less reliable (Supplemental Appendix Figure A1). The data were therefore classified accordingly with a different score for each classification. Some data gaps exist within the MSW data for Thailand (e.g. the proportion of PW in mixed waste received at landfills across the three archetypes) and to close them, authors resorted to less reliable estimates.

Plastic waste leakage estimation

Eight experts drawn from various stages along the PW value chain including municipal waste collection crews, transfer station operators and landfill site managers were requested to provide additional information used in determining PW leakage estimates. To ensure consistency in key informant interviews, the participating experts were requested to fill in pre-designed data collection templates. Estimates of the PW leakage potential for their specific archetype were made by considering several leakage influencers for every stage of the waste management process. Leakage influencers (Supplemental Appendix Table A1) include the type and nature of MSW collection containers, the method of waste loading and primary transportation, waste handling, storage, sorting and extraction of recyclables as well as subsequent waste transfer to aggregation or sale points. Experts indicated their perceived degree of PW leakage at each stage of the PW value chain by assigning a score against each of the leakage influencers. The dataset developed as part of this study has been included in the Supplemental Material. The input from the elicitation process before data normalization is shown in the tabs named ‘Leakage estimation’, which are included across the three Archetypes.

The scores differed in scale (e.g. one leakage influencer could have a scale ranging from 0.1 to 5, whereas another had a 0 to 100) but generally depicted the perceived degree along a harmonized scale from low to very high. During data analysis, the scales were normalized to allow for comparisons by converting them over a percentile scale, with 0 representing the lowest degree of leakage and 100 representing the highest degree of leakage. Normalization was performed to allow for comparisons and results visualization in radar charts.

Unlike the traditional MFA, the methodology adopted in this article allows for an analysis of PW leakages from different parts of the WMS to be made, which makes it easier for targeted interventions to be implemented. For instance, when excessive leakages occur during waste collection and transportation, the need to improve waste storage systems, waste handling and methods of transporting the waste from one point to another becomes imperative. A detailed overview of the data input process and leakage estimation is provided in Supplemental Material.

Data validation in STAN 2.7

Validation in the context of this study sought to check if the material flows obtained from using the BC toolkit are consistent with the mass-balance principles of MFA. This should therefore not be regarded as a confirmation of real measurements in the environment. The output data from the toolkit used was validated by tracing the PW flows for the case being investigated in STAN 2.7 (Brunner and Rechberger, 2016; Cencic, 2022). This was performed in two ways: firstly, a successful calculation in STAN 2.7 was needed to confirm that the output from the toolkit is consistent with MFA, and secondly, the output values in STAN 2.7 must not differ from the output values from the toolkit by a wide margin. We assumed that a margin within 10% could be reasonably low enough to validate the results. In principle, for STAN 2.7 to accept the data and successfully perform calculations shows that the assessments made using the tool kit are valid material flows since the toolkit itself follows the MFA principles. Furthermore, if the toolkit results were manipulated in any way, the estimates obtained in STAN 2.7 would differ from the outputs made using the toolkit by a very wide margin. The toolkit used the same mass balance principle employed by MFA software such as STAN 2.7. However, apart from using data about PW generated, collected, recycled and disposed of, the toolkit also incorporates input from the consulted experts.

Supplemental Tables S1–S3 show the input data for the Small, Medium and Mega archetypes, respectively, used in building PW flows in STAN 2.7 during the validation process. This data are drawn directly from the output of the toolkit calculations (i.e. the toolkit section named, ‘Calculation of flows’).

Our study introduced two new flows not originally included in the BC toolkit namely energy and off-gases from incineration and recyclates and new goods produced from recycling. The original toolkit presents recycling and incineration as end processes, essentially making them stock processes with an accumulation of materials in them (Supplemental Figure S2). However, incineration and recycling lead to mass transfer from the system and are better shown as ‘exports’ from the system. When waste is incinerated, there is evident mass reduction (Joshi et al., 2021; Jung and Ro, 2023). Since, in reality, that mass is not lost, we considered the mass reduction to represent mass exported from the system. The same applies to plastic recyclates and new goods produced from recyclates. The new goods cannot be considered as waste anymore, but they represent a mass transfer from the system. These realities informed the need to create these two new flows, which appear in all the mass tables (Figure 3 and Supplemental Figures S3–S5).

Although STAN 2.7 is an excellent tool for either performing MFA calculations or for validating estimates made using other tools, it has its limitations. The software is data-intensive. If excessive data gaps exist, the software cannot be used. Furthermore, using the software requires a good level of expertise, without which the assessment can be extremely difficult. Having a large dataset for the current study helped us to overcome these challenges. Furthermore, our previous experience with the older versions of STAN (2.5 and 2.6) made it fairly easy to use STAN 2.7 in the current assessment.

The Supplemental Material provides additional details on this data and how it relates to the data validation process. The complete dataset used in PW leakage evaluation for the current study is available as a data repository at https://data.mendeley.com/datasets/xnshrwww43/1.

Overview of PW leakages from Thailand’s WMS

With an MSW generation rate of 1.19 kg (capita × day)⁻¹ (national average) and a PW content of 16.9%, Thailand generates 11,956 MT of PW daily from 77 provinces (Supplemental Appendix Table A1). This translates to an estimated 4.4 million MT of PW each year. By comparison, the United States, China, India, Brazil and Japan generated 42 MT, 21.6 MT, 26.3 MT, 10.7 MT and 4.9 MT of PW, respectively, in 2016 (Park, 2018; Statista, 2016; Tun et al., 2023; World Bank, 2018). Metropolises like Bangkok face particularly unique challenges owing to the large volumes of waste they manage when compared to smaller, less-crowded towns and remote areas (Adelina and Archer, 2024; Areeprasert et al., 2017). Even though policy enforcement is stricter in large cities, land for establishing new landfills and large waste treatment facilities is scarce and expensive (Boontaveeyuwat, 2024).

The current assessment revealed that 80% of Thailand’s PW is still mismanaged, with 1,177,643 MT leaking through various pathways and 2,304,300 MT remaining uncollected in the environment (Figure 2). As would be expected, much of this mismanaged PW is found in undesignated waste heaps and sub-standard disposal sites (termed uncontrolled landfills in this study) being waste discarded by members of the public and waste formally collected by responsible authorities but sent to sub-standard waste disposal sites (Figure 3 and Supplemental Figures S3–S5). Given the Thai population, this reality entails PW leakages amounting to 0.53 kg (capita × day)⁻¹. Our study confirms earlier assessments by IUCN-EA Quantis (2020). By comparison, PW leakages for Vietnam and the Philippines were less than a quarter of this, at 13 and 4.18 kg of PW (capita × day)⁻¹, respectively, in 2023 (Tosi Robinson et al., 2024). China has higher leakage rates though, and still landfills more than 900 million tonnes of PW annually (Han et al., 2024).

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Figure 2.

PW leakage at various points along the value chain and the resulting share of PW by management pathway.

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Figure 3.

Thailand’s PW flows for the most remote areas, represented by the SMALL Archetype.

Leakages from uncontrolled landfill sites (836,861 MT) and controlled landfill sites (163,861 MT) constitute the biggest share (85%) of the PW losses from the waste collected formally for disposal. Waste collection activities also contribute to significant (11%) PW leakages, whereas activities linked to waste transportation, sorting and recycling present the least (4%) of Thailand’s PW leakages. Using a slightly different scope for what PW leakage entails, ESCAP (2020) reported that 47% of plastic pollution in Thailand emanates from PW leakage during waste collection activities. The current study includes waste disposed of in uncontrolled landfills as part of PW leakage, making the contribution from collection activities lower than what was reported by ESCAP (2020). A previous study singled out improper waste disposal as a significant source of microplastics and a carrier of plastic additives (Yamahara et al., 2024).

The most remote districts (represented by the ‘Small’ data archetypes) contribute the largest share (85%) of PW leakages (Figure 3). This is mostly because waste management infrastructure in these areas is less developed, and waste collections are irregular, creating a huge incentive for open dumping. Here, the volume of uncollected PW is very high, making up 66% of Thailand’s mismanaged PW. About 68% of this is produced in municipal and non-municipal areas (e.g. Bang Kruai, Bang Muang, Bang Yai, Rong Kwang and Santi Suk), suggesting a need to increase formal waste collection by responsible LAOs.

Effect of the leakage influencers on PW releases from land-based sources

Figure 4 illustrates the impact of each leakage influencer on the PW management system using normalized expert ratings and visualizing the results in radar charts. Details about the normalization process are provided in the Supplemental Appendices.

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Figure 4.

The effect of each leakage influencer in the three archetypes.

The leakage influencers impacted the small archetype more than the other two. This could be attributed to peculiar challenges in the remote areas including limited access to formal waste collections, and limited technical and financial capacity for the LAOs to deal with basic service delivery demands (Popattanachai, 2021; Sukholthaman et al., 2017). Limited budget allocations for waste management can lead to inadequate investment in transportation infrastructure, and landfill maintenance can potentially exacerbate leakages (Marks et al., 2023). The method of waste handling, loading and primary transportation had a near-uniform impact on the mega and medium archetypes and a greater effect on the smaller archetype. Waste handling during disposal, waste covering and the condition of fencing around final disposal sites posed a greater impact on the mega and medium archetypes than the smaller archetype. To improve the PW management system, the findings suggest the need to improve the type of waste collection containers and the methods of waste handling in the smaller Thai districts and peripheral areas with limited waste management services. In the urban areas, policy interventions must focus more on improving the infrastructure for waste loading, transportation and disposal.

Plastic waste recycling

PW recycling plays a pivotal role in reducing leakages into the ecosphere (Fogt Jacobsen et al., 2022; Hahladakis and Iacovidou, 2019; Soni and Das, 2022). The study shows that only 377, 156 MT of PW is effectively recycled (representing 8.6% of the total generated; Figure 2). This is not comparable to the 1.2 million MT of PW that leaks into the environment and the 2.3 million MT of PW that remains uncollected. By comparison, the United States, Canada, China and India recycle 4%, 6%, 9% and 13% of their PW arisings, respectively (OECD, 2023). For recycling to be sustainable, the highest quality of plastics for recycling comes from municipally collected and potentially source-separated wastes (Feil et al., 2017; Winterstetter et al., 2021). Thailand’s efforts to achieve 100% PW recycling by 2027 are currently impeded by numerous obstacles, among them the limited source-separation of PW and the continuous production of plastics at unsustainably high rates (Marks et al., 2023). Limited public participation in recycling programmes also makes it difficult to produce enough high-quality recyclables for the local market (Pongpunpurt et al., 2024; Poyai et al., 2024). In contrast, in countries like Sweden, Japan and the Netherlands, high public participation and a heightened sense of ownership of the problem among citizens have helped to reduce plastic pollution drastically (Yamamoto and Eva, 2022). In Swedish society for example, close collaboration between waste management companies and citizens was catalytic to increased repair of products, reuse and reduced waste throughput to other management options (Moalem and Schmidt, 2023). These interventions are transferrable lessons that can be applied to the Thai context.

Like many other countries, poorly functioning markets for recycled plastics, insufficient local capacity and low profitability of PW recycling operations keep PW recycling low and dominated by the informal sector (Johnson and Trang, 2019; OECD, 2022). There are also concerns over hazardous or problematic additives in recycled plastics (Atthirawong and Luangpaiboon, 2022).To address these challenges, the Thai government needs to invest in enhancing and creating a separate demand for recycled plastics, improving mechanisms for at-source separation and curbing the consumption of virgin plastics.

Alongside larger companies such as Wongpanit, Thailand’s informal recycling sector plays a pivotal role (PCD, 2024). Our study shows that informal mixed waste collection and informal recycling operations collectively manage an estimated 1.6 million tonnes of PW annually. This represents 37% of the PW generated nationwide making the informal sector an important player in the PW value chain. In Bangkok’s Sai Mai district for example, informal workers collect an estimated 14,454 tonnes of various recyclable wastes each year, helping Thailand to avoid 21,681 tonnes of CO₂ equivalent emissions from the waste sector (Johnson and Trang, 2019). Informal PW recyclers also recover composite wastes such as plastic-coated electric cables (Arain et al., 2022). Despite their contributions, players within Thailand’s PW informal recycling sector (including Itinerant waste pickers or Salengs) are socially marginalized and not recognized and have meagre earnings (in most cases, below the Thai minimum wage; Adelina and Archer, 2024). Correcting this may require recognizing and formalizing the informal sector, improving informal waste pickers’ working conditions and raising public awareness and possibly, acceptance of their role (Pottinger-Glass et al., 2024). This can potentially enhance PW recovery and recycling, an outcome reported following similar interventions in China (Linzner and Salhofer, 2014). A study by Hung (2024) also recommended the need for Thai policymakers to expedite the formalization of the informal sector.

PW recycling objectives must go beyond the need to reduce throughput to landfills but must support the transition to a circular economy. According to the Thai PCD, this transition is impended by numerous obstacles including the absence of regulations, low public participation, limited source segregation of plastics, inefficient waste collection systems and poorly functioning plastics drop-off stations (Pongpunpurt et al., 2024). One successful initiative implemented in Thailand’s urban areas is the ‘Send Plastic Home’ project which promoted the re-integration of PW into production processes to advance the circular economy (Poyai et al., 2024). Product redesign, reuse and material recovery represent additional actionable interventions.

Plastic waste conversion to energy

The study indicates that only a small proportion (about 213,456 MT per annum, representing 4.89% of the total generated) of PW is diverted for thermal treatment with energy recovery. Plastics are extremely important for WtE power plants and are often used to maintain good combustion on incineration grates (Lombardi et al., 2015; Schwarzböck et al., 2016). Within the circular economy framework, WtE can be instrumental in dealing with non-recyclable plastics and minimizing their throughput to landfills (BRS Secretariat, 2021b). If implemented properly, WtE plants can complement waste management strategies without frustrating recycling efforts (Winterstetter et al., 2021). Developed countries like Sweden and Denmark have scored successes in this regard. For example, Sweden treats more than 45% of mixed MSW with energy recovery and can still recycle up to 53% of plastic packaging waste leaving a very small portion of residual waste (Esguerra et al., 2024). The energy recovered from WtE can augment conventional supplies and reduce dependence on fossil fuel-based fuel sources (Istrate et al., 2019). Unlike recycling, WtE can tolerate end-of-pipe collected PW better provided that robust flue gas treatment mechanisms are in place (Malinauskaite et al., 2017).

Since 1999, Thailand has implemented WtE projects as part of both the MSW management system and also in pursuit of its alternative energy goals (Menikpura et al., 2016). Phuket Incineration Plant set up in 1999 receives 300 MT of mixed MSW daily for treatment with energy recovery (MONRE, 2021). For PW ESM, only plastics that cannot be recycled must be incinerated (GRID-Arendal and Basel Convention Secretariat, 2021). However, with rapidly rising volumes of PW generated worldwide, WtE may continue to be a relevant (and in some cases, unavoidable) alternative to landfilling (Brunner and Rechberger, 2015; Pinter et al., 2021; Van Eygen et al., 2018). The Thai government needs to increase investments in new WtE plants to complement existing waste management strategies.

Despite their advantages, WtE has significant environmental, social and economic implications. For example, implementing such a high-tech waste management solution without addressing primary problems, such as the absence of a functional WMS and reaching sufficiently high waste collection rates may create new problems (World Bank, 1999). Without high waste collection rates, WtE incinerators may lack feedstock, operate at below-installed capacities and eventually stall (Panepinto and Zanetti, 2018). Additionally, WtE plants are costly investments and require high-end expertise in implementation, operation and maintenance. From a technical perspective, WtE incineration plants cannot operate on revenues from energy sales alone. Up to 70% of the operating costs must be met from tipping fees (Aleluia and Ferrão, 2017; Makarichi et al., 2018). Furthermore, given significant public opposition to waste incineration plants in Thailand, earnest and transparent communication about the benefits and risks, involving communities in decision-making processes or demonstrating successful WtE projects in other regions are useful strategies to improve public trust and confidence and avert possible not-in-my-backyard sentiments.

Plastic waste transboundary movement

The study has shown that Thailand has significant PW imports amounting to at least 150,000 MT annually to supply its recycling industry with clean and easy-to-recycle waste (BAN, 2023). Most of the PW imports are from Japan, the United States, the EU and the United Kingdom (Thai Customs Department, 2023). Thailand’s PW imports soared in 2018 following China’s ban on PW imports (Dell, 2024; Liang et al., 2021). The country now aims to ban PW imports by 2025 (MonRE PCD, 2023). If successful, this can create a strong local demand for plastic recyclates and can aid improvements in the Thai plastic recycling sector. There is growing evidence that the general public is willing to respond positively to government efforts in dealing with plastic pollution (Jirapornvaree et al., 2023). Increasing the demand for source-separated clean plastics can potentially stimulate increased participation by citizens and disincentivize open dumping (Janmaimool et al., 2024). Increased investment in PW recycling infrastructure, intensifying public advocacy for PW at-source separation, providing incentives to both formal and informal players in the sector and expanding existing Extended Producer Responsibility (EPR) mechanisms represent logical and actionable policy interventions for the country (Poyai et al., 2024).

Addressing PW leakages associated with disposal sites

The study shows that an estimated 1,763,044 MT of plastics in mixed MSW is sent to disposal sites annually, representing 40% of the PW generation in Thailand (Figure 2). Consequently, an estimated 1,000,215 MT of PW leaks from Thailand’s controlled and uncontrolled disposal sites annually. Specific causes include the absence of secure perimeter fencing to keep disposed plastics within the site, the prevalence of waste-burning activities and generally poor waste-handling practices, especially in the smaller districts and remote areas (Figure 3). In larger cities, efforts to upgrade waste disposal sites, the formulation of guidelines for waste management by LAOs and publishing criteria and methods for waste characterization, separation and collection have been proposed (PCD, 2024). Recent studies show that these efforts are yet to generate significant positive outcomes (Pongpunpurt et al., 2024; Poyai et al., 2024). Impediments include the absence of a clear regulatory framework to support enforcement, limited public participation, limited source-separation of wastes, inefficient waste collection systems by LAOs and poorly functioning waste drop-off stations (Poyai et al., 2024). Unless there are mechanisms to completely seal off landfills and associated disposal sites, PW leakages from disposal sites are unavoidable (Fletcher et al., 2021; Sharma et al., 2021). Leachate collection and treatment mechanisms play a vital role in minimizing the contamination of groundwater sources with microplastics (Geyer et al., 2017). Although there are notable sanitary landfills in Thailand, there are numerous uncontrolled waste dumpsites, especially in the non-municipal areas, and these represent hotspots where PW leakages are very high making the need to transition from the use of uncontrolled waste disposal sites to modern, engineered sanitary landfills, both imperative and urgent. Innovative landfill management practices such as the use of bioreactor landfills, smart WMS, advanced leachate treatment and integrating the Internet of things with traditional practices can generate immense environmental and economic benefits (Goh et al., 2025; Igwegbe et al., 2024). Landfill mining can also play an instrumental role in recovering plastics and curbing further PW leakages from disposal sites (Han et al., 2024). It can also be a source of feedstock for WtE power plants (Muttaraid et al., 2023) even though this may come with additional problems such as low calorific value of recovered wastes, high concentration of metals and high ash content in the feedstock (Jain et al., 2023).