The crucial role of circular waste management systems in cutting waste leakage into aquatic environments

Global municipal solid waste (MSW) generation is rising rapidly, creating a critical waste crisis that threatens the environment, climate, and human health. Depending on socioeconomic pathways, waste generation could increase 20% to 68% by 2050. Presently, 64% of global MSW is mismanaged: 29% open-burned, 18% dumped, and 17% scattered. Scattered waste is mobilized by physical, climatic, and geographic factors and is the dominant source of marine litter, of which about 80% is plastics. Although many policies target plastics, leakage fundamentally reflects shortcomings in MSW systems. Existing global and regional studies often emphasize plastic leakage, providing estimates of plastic entering oceans from coastal populations and rivers, and highlighting heterogeneous, subnational hotspots. However, comprehensive global assessments that integrate scenario narratives (SSPs), MSW generation and management storylines, and spatial differentiation of urban versus rural areas to project MSW leakage and test mitigation potential are lacking. This study addresses that gap by combining a global MSW systems model with spatial analysis to identify leakage hotspots and evaluate how circular waste management systems can cut leakage to rivers, lakes, and coastal areas up to 2040.

Policy responses have expanded, including 2019 Basel Convention amendments on plastic waste and the 2022 UNEA resolution to end plastic pollution; by 2018, 127 countries regulated plastic bags and single-use plastics. Global estimates suggest that in 2010, 275 Mt of plastic waste was generated across 192 coastal countries, with 1.75%–4.61% entering the ocean; more recent work attributes 80% of riverine plastic emissions to roughly 1000 rivers. Studies also reveal strong spatial heterogeneity and the need for subnational interventions, with hotspots in cities exhibiting high infrastructure but lower wealth. Regional analyses include rural plastic emissions to Izvoru Muntelui Lake in the Eastern Carpathians (majority from rural municipalities), Carpathian watercourses below 750 m being highly affected by mismanaged plastics, and Indonesian cities where about a quarter of waste enters waterways with high accumulation in major rivers. In the United States, substantial amounts of generated plastic were illegally dumped or exported and inappropriately managed abroad. Economic impact assessments of plastic pollution by IUCN for island states and regions underscore diverse methodologies and scopes: some track macroplastics along life cycles or use spatial, population-based models; others quantify micro- and macro-plastic leakage via corporate footprinting. While these studies focus largely on plastics, few comprehensively connect MSW systems evolution under SSPs with spatial leakage modeling for all MSW streams.

The assessment uses the IIASA GAINS model MSW module with global coverage of 180 countries/regions in 5-year steps, differentiating urban and rural areas and eight MSW streams (food, plastic, paper, glass, metal, textile, wood, other). MSW generation per capita is linked to income per capita; population, GDP, and urbanization projections are taken from the SSP Public Database v2.0. Waste composition and management are applied via a technology matrix (e.g., open burning, unmanaged disposal, landfills with/without gas recovery, incineration with energy recovery, anaerobic digestion, composting, recycling), constrained to sum to 100% by fraction. Spatial analysis combines HydroRivers, HydroLakes, and FAO coastlines to construct buffer zones around rivers, lakes, and coastlines in four concentric 250 m bands up to 1 km. Population counts for 2020 are taken from the JRC GHSL grid and classified urban/rural via Degree of Urbanization; each cell is assigned to the nearest relevant waterbody type, avoiding overlap. Estimates for future years up to 2040 apply SSP growth to urban/rural shares, assuming density increases but not area expansion. Potential leakage is estimated by downscaling scattered MSW (uncollected minus openly burned) within 1 km of waterbodies, partitioned by distance band and applying fate factors that represent likelihood of leakage by proximity: 0–249 m: 0.85; 250–499 m: 0.75; 500–749 m: 0.55; 750–1000 m: 0.25. The approach is stream-agnostic regarding fate factors, acknowledging different behavior by material characteristics. Baseline (current legislation to 2018) scenarios are developed for each SSP; mitigation scenarios (MFR) represent circular MSW systems aligned with the EU waste hierarchy: reducing food and plastic generation, maximizing technically feasible recycling by stream, anaerobic digestion of food and garden waste with biogas recovery, high diversion from landfills and dumpsite upgrades, and incineration with energy recovery for residues. The analysis reports MSW generation, scattered waste, potential leakage to rivers, lakes, and coastal areas by stream and geography. Uncertainty in MSW generation was explored via Monte Carlo (1000 runs) and sensitivity analysis (100 samples), identifying uncollected waste shares as the most influential parameter.

• Global MSW generation was about 2560 Mt in 2020, rising to 3320–3790 Mt by 2040 depending on SSP. Composition in 2020: food 1091 Mt (43%), plastic 260 Mt (10%), paper 366 Mt (14%), glass 113 Mt (4%), metal 73 Mt (3%), other 651 Mt (26). By 2040, food increases 26–40%, plastics 37–45%, paper 27–50% (pathway dependent). • Scattered MSW (uncollected minus openly burned) was ~350 Mt (14%) in 2020; 87% occurred in China (30%), South Asia (20%), Africa (20%), and India (17). About 70% of scattered MSW was urban. Under baseline management, scattered MSW grows to 427–475 Mt by 2040. • Rivers: In 2020, 74 Mt of MSW potentially reached rivers (21% of scattered; 3% of global MSW), with 70% from urban areas; food waste ~40 Mt and plastic ~7.4 Mt. By 2040, under baseline, river leakage rises to 90 Mt (SSP4) to 100 Mt (SSP5) per year. • Lakes: About 1.35 Mt of MSW potentially entered lakes in 2020 (58% urban; 42% rural), dominated by Africa and China (55% combined). Food ~0.73 Mt, plastic ~0.13 Mt, paper ~0.11 Mt. • Coastal areas: About 5.79 Mt of MSW potentially entered seas in 2020; food ~3.01 Mt, plastic ~0.57 Mt, paper ~0.52 Mt. Most coastal leakage originated from South Asia and Latin America & Caribbean. Differences from earlier plastic-only coastal estimates arise from distinct population buffers (1 km here vs 50 km in prior work) and methodology. • Total leakage to aquatic environments in 2020 was ~80.8 Mt, with rivers accounting for ~91%. Plastic leakage to aquatic environments was ~8.09 Mt, comparable to recent global assessments for 2019 and lower than some earlier estimates. • Mitigation (circular systems): In SSP1_MFR, scattered MSW declines by 50% by 2025, 73% by 2030, and ~99% by 2040 versus baselines. Recycling reaches ~35% in 2030 and ~45% in 2040; anaerobic digestion treats ~55% of food waste in 2030 and ~98% by 2040; ~98% of MSW is diverted from landfills by 2040. Leakage into aquatic environments falls 68–75% by 2030 and is virtually eliminated by 2040 relative to baselines, avoiding ~73 Mt (2030) and ~110 Mt (2040). • Regional mitigation impacts: China, South Asia, Africa, India, and LCAM account for ~88% of global scattered MSW reduction by 2030 in SSP1_MFR. Baseline leakage already declines in EU27+UK and Oceania OECD due to existing policies. • Alternative SSP mitigation outcomes: SSP5_MFR also virtually eliminates leakage by 2040 but with slower early reductions due to higher consumption and reliance on end-of-pipe solutions. SSP2_MFR leaves ~35 Mt at risk in 2040, ~95% in South Asia, China, Africa, LCAM, and India. SSP3_MFR leaves ~40 Mt at risk in 2040, with slow improvements and rural areas lagging; SSP4_MFR outcomes lie between SSP2_MFR and SSP3_MFR.

Findings show that MSW leakage to aquatic environments is primarily driven by collection deficits, urbanization patterns, and proximity of populations to waterbodies. Most leakage occurs in urban settings and into rivers, underscoring that passive, end-of-pipe approaches (e.g., interception at river mouths, ocean cleanups) cannot substitute for upstream systems change. Circular MSW management—combining waste prevention (notably food and plastics), separate collection, high recycling, anaerobic digestion, energy recovery for residuals, and landfill diversion—actively mitigates leakage across all material streams, not only plastics. Spatial heterogeneity implies that countries with high mismanaged MSW are not always those with highest leakage; the interplay of demographics near waterbodies and management quality creates distinct hotspots requiring tailored, often subnational interventions. Contrasting scenarios demonstrate that when institutional, financial, and social barriers are overcome (SSP1_MFR), leakage reductions are rapid and nearly total by 2040; in fragmented or unequal futures (SSP3_MFR, SSP4_MFR), MSW growth outpaces mitigation, particularly in rural areas of developing regions. The results reinforce the urgency of accelerating collection access, infrastructure deployment, and circular operations—especially in China, South Asia, Africa, India, and LCAM—to meet international goals, although even best-case pathways cannot fully eliminate leakage by 2030.

This study integrates global MSW systems modeling with spatial proximity analysis under SSP narratives to quantify potential leakage of all MSW streams into rivers, lakes, and coastal areas and to evaluate circular management strategies. Leakage totaled ~80.8 Mt in 2020 and could rise under baseline trajectories, with roughly 91% entering rivers and most originating from urban areas. Circular MSW systems can cut leakage 68–75% by 2030 and virtually eliminate it by 2040, but even a sustainability pathway will not fully meet the 2030 SDG waste-related targets. Achieving rapid reductions requires scaling separate collection, anaerobic digestion, and recycling; diverting from landfills; upgrading dumpsites; and integrating waste pickers, alongside behavioral waste prevention. Future work should further standardize MSW data, incorporate more environmental and geographic variables, develop Monitoring, Reporting, and Verification frameworks, and assess implementation costs and policy instruments to accelerate global adoption.

Uncertainties arise from limited and inconsistent reporting on MSW generation, composition, and management; scattered waste fractions require assumptions. Fate factors are assumed identical across streams, though materials behave differently by size, density, and degradability and are affected by climatic and geographic conditions. The model estimates leakage potential from uncollected waste and does not capture losses during collection, transport, or at disposal sites, nor transport within aquatic systems. Spatial population proximity is based on GHSL 2020 urban/rural distributions and applied across years and scenarios, potentially misrepresenting future settlement dynamics; lakes below 50 km² and small streams were excluded for processing efficiency. Spatial datasets (GHSL, HydroRivers, HydroLakes, FAO coastlines) have inherent uncertainties. Monte Carlo and sensitivity analyses indicate uncollected waste shares are the most influential parameter. Mitigation scenarios explore technical frontiers and do not include implementation costs or incentives, which may affect real-world feasibility.