Introduction

Plastic pollution represents one of the most significant environmental challenges of the modern era, with millions of tonnes of waste entering natural ecosystems annually. Microplastics, defined as plastic particles ranging from 1 μm to 5 mm in size, originate from primary sources like agriculture, textile fibres released during laundering, and tyre abrasion, or as secondary particles from the fragmentation of larger debris. Current Life Cycle Impact Assessment (LCIA) methods frequently fail to account for the effects of these microplastics, leading to an underestimation of their impact on ecosystem quality. This research, conducted as part of the MarILCA framework, bridges this gap by developing regionalised characterisation factors (CFs) for marine, freshwater, and terrestrial ecosystems while accounting for fate across environmental compartments including sediments.

Methods

The primary objective of this work was to calculate Characterisation Factors (CFs) through a multi-step process involving the development of a fate model based on SimpleBox4Plastic adapted to the USEtox methodology. The researchers implemented Exposure and Effect Factors (EEFs) sourced from literature for organisms in aquatic, sedimentary, and terrestrial environments. The CFs were scaled from the compartment to the ecosystem level using Species Distribution Factors (SDFs) following two distinct approaches. The surface approach indicates the proportion of species lost over an area, expressed in PDF⋅m2⋅yr/kg, while the species approach quantifies the proportion of species lost from main ecosystems, expressed in PDF⋅yr/kg or species⋅yr/kg.

The fate model characterises 14 different polymers, including expanded polystyrene (EPS), polypropylene (PP), polyethylene (PE) variants, and tyre and road wear particles (TRWP). These are evaluated across five size categories ranging from 1 μm to 5000 μm and nine environmental compartments. To align with USEtox, the model was regionalised across eight global regions: North America, Latin America, Europe, Africa and Middle East, Central Asia, Southeast Asia, Northern regions, and Oceania. Several mechanisms were adjusted, including the merging of air and cloud water compartments and the calculation of degradation rates using Specific Surface Degradation Rates (SSDR).

Results and discussion

The study found that endpoint CFs range from 1.87E-04 to 2.95E+04 PDF⋅m2⋅year/kgemitted for the surface approach and 1.57E-19 to 5.14E-08 PDF⋅year/kgemitted for the species approach. Fate Factors (FFs) in the study range from 0 to 1.86E+06 kgin compartment/(kgemitted/days), depending on the region and polymer properties. High-density microplastics tend to settle in sediments, where the concentration of species is greater, while low-density microplastics accumulate in the water column where exposure via feeding is higher. Larger microplastic emissions typically correspond to higher CFs due to longer degradation times, as degradation rates are size-dependent.

Regional variations in CFs are more pronounced in the species approach. In the surface approach, variations are lower because every ecosystem surface is given equal weight. However, some differences exist for low-density microplastics emitted in soil across regions, primarily driven by variations in precipitation and runoff fractions. Regions with low precipitation retain more microplastics in the soil, preventing them from entering freshwater and marine compartments where the exposure effect factor is significantly higher. The greatest variation across different sizes for a specific polymer was observed with polyhydroxyalkanoate (PHA), spanning up to 11 orders of magnitude in the species approach.

The developed CFs were tested in an illustrative case study comparing biodegradable and non-biodegradable agricultural mulch films used for lettuce production. Scenario 1, using non-biodegradable low-density polyethylene (LDPE), showed an impact of 15.55 PDF⋅m2⋅year. Scenarios 2 and 3, utilizing biodegradable mulch films made of polybutylene adipate terephthalate (PBAT) and starch, both exhibited a lower impact of 2.88 PDF⋅m2⋅year. The physical effects on biota accounted for between 0.34% and 2.40% of the overall impact on Ecosystem Quality (EQ) across the mulch film scenarios.

Conclusion and outlook

The research provides a comprehensive assessment of the physical impact of microplastics across marine, freshwater, and terrestrial ecosystems simultaneously. The findings indicate that CFs are primarily influenced by particle size, followed by polymer type and emission compartment. Larger particles generally have higher impacts due to their longer lifetime in the environment. While biodegradable polymers reduce environmental persistence through faster degradation, low-density polymers are more likely to be transported to marine environments where they exert prolonged effects. Future research is suggested to investigate how particle shape influences fate and bioavailability, as this study focused on spherical forms.