Scaling up resource recovery of plastics in the emergent circular economy to prevent plastic pollution: Assessment of risks to health and safety in the Global South

Over the coming decades, a large additional mass of plastic waste will become available for recycling, as efforts increase to reduce plastic pollution and facilitate a circular economy. New infrastructure will need to be developed, yet the processes and systems chosen should not result in adverse effects on human health and the environment. Here, we present a rapid review and critical semi-quantitative assessment of the potential risks posed by eight approaches to recovering value during the resource recovery phase from post-consumer plastic packaging waste collected and separated with the purported intention of recycling. The focus is on the Global South, where there are more chances that high risk processes could be run below standards of safe operation. Results indicate that under non-idealised operational conditions, mechanical reprocessing is the least impactful on the environment and therefore most appropriate for implementation in developing countries. Processes known as ‘chemical recycling’ are hard to assess due to lack of real-world process data. Given their lack of maturity and potential for risk to human health and the environment (handling of potentially hazardous substances under pressure and heat), it is unlikely they will make a useful addition to the circular economy in the Global South in the near future. Inevitably, increasing circular economy activity will require expansion towards targeting flexible, multi-material and multilayer products, for which mechanical recycling has well-established limitations. Our comparative risk overview indicates major barriers to changing resource recovery mode from the already dominant mechanical recycling mode towards other nascent or energetic recovery approaches.

Here we present information on: i) Criteria for assessing commercial and technological maturity (Table S1); (ii) Water consumption and wastewater used in mechanical reprocessing (Table S2); iii) Multimedia evidence review for brick and tile production in the Global South; iv) Contaminants found in syngas (Table S4); v) Comparison of emission thresholds for incineration (Table S5); vi) Summary of environmental and health risks for each of the eight approaches (Table S6); vii) Scoring of technological and commercial maturity (Table S7); and viii) International definitions of recycling (Table S8). Table S1: Criteria for assessing commercial and technological maturity.

Rank Description
Low maturity Technology is still on the technological readiness level (TRL) scale as described by the U.S. Department of Energy (2011). It may be at TRL 9, having proved it can operate under the full range of expected conditions, but there is limited evidence of commercially sustainable implementation.

Medium-low maturity
Evidence of commercially sustainable implementation but either at small scale or there are doubts about commercial viabilityapproach may be subsisting on innovation funding.

Medium-high maturity
Evidence of commercially sustainable implementation, but has yet to reach widespread prevalence as a preferred approach to treatment or may not be scalable.
High maturity Approach is prevalent, mature and has been implemented at scale for many years or decades. Table S2: Water consumption and waste-water discharge (L t -1 material processed) at plastics reprocessing facilities in China; after Chen et al. (2019).
3 Table S3: Summary of practices involving the production of mineral-polymer composite paving and tiles in the Global South observed on multimedia posts. Hazard codes as follows: 1) Unguarded fast or high torque machinery in close proximity to workers; 2) Worker interaction with machinery resulting in risk of being drawn in; 3) High temperature equipment in close proximity to workers risking burns; 4) Risk of interaction with unknown potentially hazardous materials or substances; 5) Risk of burns from caustic substance; 6) Particle loss to the environment likely; 7) Risk of aerosolised hazardous substance; 8) Risk of ballistic injury to hands, feet, body from interaction with sharp or heavy objects.  Notes: a all emission limits except opacity are measured at 11% oxygen, dry basis at standard conditions (State Environmental Protection Administration of China, 2001a); b all emission limits are measured at 10% oxygen, dry basis at standard conditions (European Union, 2000); c the daily average limit is 200 mg m -3 for new and existing plants with more than six tonnes per hour capacity, and 400 mg m -3 for existing plants with no more than six tonnes per hour capacity; d for unit with an individual municipal waste combustion capacity of 250 tonnes per day or less, all emission limits except opacity are measured at 7% oxygen, dry basis at standard conditions (U.S. Environmental Protection Agency, 2000); e the limit varies by combustor technology; f the limit is 150 ppm by volume for Class I units (located at municipal waste combustion plants with an aggregate plant combustion capacity more than 250 tonnes per day of MSW) or 500 ppm by volume for Class II units (located at municipal waste combustion plants with an aggregate plant combustion capacity no more than 250 tons per day of MSW); g dioxins/furans on total mass basis measured as tetra-through octachlorinated dibenzo-p-dioxins and dibenzofurans. Not toxic equivalent (TEQ) value; h for unit with an individual municipal waste combustion capacity of greater than 250 tonnes per day, all emission limits except opacity are measured at 7% oxygen, dry basis at standard conditions (U.S. Environmental Protection Agency, 2006c); i the limit varies by combustor technology; j the limit varies by combustor type for existing unit, while for new unit it is 180 ppm by volume in the first year of operation and 150 ppm by volume after first year of operation; k the limit is 30 ng/m3 for non-electrostatic precipitator (ESP) equipped unit or 35 ng m -3 for ESP-equipped unit.  Lower carbon emissions than most other processes, particularly waste to energy incineration and SRF cement kiln incineration (Lazarevic et al., 2010;Bernardo et al., 2016)  Hot-water washing has the potential to increase overall life-cycle emissions, though the evidence to support this assertion is limited (Krogh et al., 2001;Frees, 2002)  If waste-water discharge is controlled and managed, both debris and biochemical emissions are likely or have the potential to be minimal (Lassen et al., 2015;Cole and Sherrington, 2016;Boucher and Friot, 2017;Operation Clean Sweep, 2020)  Emissions from extrusion of packaging plastics are generally well regulated and controlled through a variety of mechanical processes alongside duty of care systems to establish material provenance (Unwin et al., 2013;Cook et al., 2020)  Workplace hazard management is broadly aligned with other sectors  In some cases, carbon emissions may be lower due to greater manual processing in comparison to the Global North  There is some evidence that coal combustion is used to generate heat (Aryan et al., 2019)potentially cancelling out any benefit  Water containing biological material washed from the surface of plastic has the potential to harm aquatic environments if not treated (Aryan et al., 2019)  Waste-water discharge may not always be controlled resulting in pellet an fragment loss to surface and foul-water drainage ( Table 4)  Evidence of lack of management for atmospheric emissions from extrusion and lack of respiratory protective equipment ( Table 4)  Evidence of workers being exposed to a variety of workplace hazards including risk of being drawn in to fast-moving or high-torque machinery, contact with hot machinery and lack of PPE (  Health implications are considered similar to mechanical recycling although the use of only one polymer (PET) that is mainly used in packaging may lower the risk of contamination from materials that have been used in other applications, for instance end of life vehicles or electrical equipment (see above)  As conventional mechanical reprocessing for extrusion (see above)  As conventional mechanical reprocessing for extrusion (see above) 3a Mineral-fibre composites: roads  Objective reasoning suggests that increased durability of polymer modified surfaces will reduce the need for replacement inferring a strong case for the use of plastics in these applications  Risk of plastic particle emissions to the environment exists though there is virtually no empirical data to help determine the magnitudeone study reports it as likely minimal and due mainly to studded tyres used in low temperature climates (Rødland, 2019;Vogelsang et al., 2020)  Very little evidence for health implications however objective reasoning suggests it is broadly similar to plastics extrusion albeit at lower temperatures (Tsai et al., 2009;Yamashita et al., 2009;He et al., 2015)  Although there is limited evidence to suggest it might happen, the potential for plastics being added to road surfaces as a method of disposal rather than to enhance durability should be considered. In such a scenario, the overall lifecycle case for this approach and result in increased particle emissions  Very little evidence for health implications however objective reasoning suggests it is broadly similar to plastics extrusion albeit at lower temperatures  Evidence of polymers combusting briefly in tile making (Kumi-Larbi Jnr, personal communication 10 December 2020) which may also occur in asphalt formulations, resulting in workers being exposed to hazardous substances 3b Mineral-fibre composites: bricks & tiles  n/a  n/a  Objective reasoning suggests a strong lifecycle benefit as a consequence of avoided concrete or ceramic production and use of otherwise wasted resources  No evidence for microplastic production exists and it is recommended that this is investigated  Black carbon emissions from open fire combustion may counteract any avoided burdens gained from off-setting concrete production  Evidence of polymers combusting briefly and resulting in workers being exposed to hazardous substances emitted into the atmosphere (Kumi-Larbi Jnr, personal communication 10 December 2020)  Melt formulation may also emit hazardous substances though there is limited information to evidence Pyrolysis & gasification  Though pyrolysis and gasification technologies are maturing, they are generally used for fuel production where the lifecycle emissions are greater than mechanical recycling but fewer than incineration with energy recovery (Khoo, 2019) (Schwarz et al., 2021)  The outputs from these processes are mostly hazardous to human health and potentially fatal with low exposure. They should be carefully controlled to ensure that workers and the public are protected from exposure (Williams and Williams, 1999;Block et al., 2019;Budsaereechai et al., 2019;Miandad et al., 2019)  The potential for fugitive emissions from both gasification and pyrolysis may negate any lifecycle emission savings as a result of these technologies  In addition to controlling emissions from the processing of feedstock, local emissions from heat generation by coal, oil and recirculated gasses may result in the production of substances that may be harmful to human health (Block et al., 2019)  The outputs of both of these processes require stringent control and regulatory oversight to ensure that they are handled safely. In particular the residues (char and tar) from these processes contain highly hazardous substances that would require a full duty of care system to ensure that they are treated or disposed of in a way that does not result in future harm to human health and the environment (Wolfesberger et al., 2009;Benedetti et al., 2017;Lopez et al., 2018;Zeng et al., 2020) 7 Co-processing in cement kilns  The evidence for lifecycle emission from co-firing plastic packaging in cement kilns is limited, though strongly driven by the avoided burdens and fugitive methane emissions during coal extraction (Spath et al., 1999)  However the limited data indicate it is not different to incineration with energy recovery and worse than conventional mechanical recycling (Jenseit et al., 2003;Shonfield, 2008;Schmidt et al., 2009;Lazarevic et al., 2010;Meys et al., 2020)  Emissions from cement kilns in the Global North are managed by managing the process parameters, the feedstock com position and using air pollution control technology  As Global North  No data was identified to evidence emissions from cement kiln co-firing with post-consumer plastic packaging waste in the Global South. However the risk of operating in jurisdictions where insufficiently resourced environmental regulation and enforcement should be considered

Environment Health Environment (additional) Health (additional)
8 Incineration  Lifecycle carbon emissions are generally greater than for mechanical recycling (Shonfield, 2008;Laurent et al., 2014;Zheng and Suh, 2019;Bel Hadj Ali et al., 2020), though the impact of hot-water washing of biological surface contamination may tip the scales in favour of incineration in some circumstances Frees (2002)  LCAs are strongly dependent on the energy mix in the country where implemented, therefore as decarbonisation progresses, the case for incinerating plastics is likely to diminish  Hazardous emissions are generally minimal in well managed European incinerators (Douglas et al., 2017;Freni-Sterrantino et al., 2019;Ghosh et al., 2019), though there is some nonnegligible evidence of harm to human health in one or two studies (Ashworth et al., 2014;Tait et al., 2019)  The use of waste heat generated by incinerators in the Global South isn't well reported which may affect the life-cycle justification for their use  Emission control limit concentrations are becoming increasingly stringent in some countries (e.g. China) and comparable to European standards  There are serious concerns that emissions may not be managed, that regulation may not exists in some countries and that where it does exists it will not be enforced  'Recyclable' A characteristic of a product, packaging or associated component that can be diverted from the waste stream through available processes and programmes and can be collected, processed and returned to use in the form of raw materials or products.

International
Organization for Standardization (2013) ISO 18604:2013 Packaging and the environment -Material recycling 'Material recycling' reprocessing, by means of a manufacturing process, of a used packaging material into a product, a component incorporated into a product, or a secondary (recycled) raw material; excluding energy recovery and the use of the product as a fuel.
The Association of Plastics Recyclers (nd) n/a Recyclable per APR Definition 'Recyclable' These criteria must all be met for a package to be considered "Recyclable per APR Definition". At least 60% of consumers or communities have access to a collection system that accepts the item per the U.S. Federal Trade Commission "Green Guides". The item must have market value, or be supported by a legislatively mandated program. The item is most likely sorted correctly into a market-ready bale of a particular plastic meeting industry standard specifications, through commonly used material recovery systems, including single-stream and dual stream MRFs, PRF's, systems that handle deposit system containers, grocery store rigid plastic and film collection systems. The item can be further processed through a typical recycling process cost effectively into a postconsumer plastic feedstock suitable for use in identifiable new products. A product should not be labelled as 'recyclable' -even if it is technically capable of being recycled -if it is unlikely that the product will be recycled in its ordinary usage (e.g., a trash bag). If any component limits the ability to recycle of an attribute, such as shape or size, a recyclable claim would be deceptive. A product or package should not be marketed as recyclable unless it can be collected, separated, or otherwise recovered from the waste stream through an established recycling program for reuse or use in manufacturing or assembling another item. When recycling facilities are available to a substantial majority of consumers or communities where the item is sold, marketers can make unqualified recyclable claims. The term 'substantial majority' as used in this context means at least 60 percent. If recycling facilities are not available to a 'substantial majority' of consumers or communities can add qualifications clarifying facility availability. Marketers can make unqualified recyclable claims for a product or package if the entire product or package, excluding minor incidental components, is recyclable. ISO 18604: 2013 Characteristic of a product, packaging, or associated component that ca n be diverted.