Life cycle impact assessment framework for assessing physical effects on biota of marine microplastics emissions

PurposeThe international working group MariLCA has proposed a framework aiming towards integrating the impacts of plastic pollution in life cycle impact assessment (LCIA). Filling one of the identified mechanisms, this paper proposes a harmonized LCIA framework for the development of mechanistic fate factors (FFs) and consequently characterization factors (CFs) for microplastics (MPs) emissions in the marine environment, for the proposed impact category "Physical effects on biota."MethodsBased on a literature review, fate mechanisms and environmental factors influencing MPs in the marine environment are identified. Dominant fate mechanisms are determined, based on which the marine environment is divided into homogeneous sub-compartments. Following on this framework and multimedia fate models adopted in LCIA, rate matrices for different types, shapes, and sizes of MPs are constructed. Fate matrices are obtained by negatively inverting rate matrices. Similar to emission-related impact categories, CF matrices are constructed by multiplying FF matrices with exposure-effect matrices.Results and discussionThe marine environment is divided into marine sub-compartments at two different scales: continental and global. Marine sub-compartments include beach, water surface, water column, and sediments at the continental scale and water surface, water column, and sediments at the global scale. Due to the dependency of MPs fate on their physiology (shape, size, and density), different rate and fate matrices can be obtained. Mechanistic characterization factors for water surface and water column sub-compartments are obtained by multiplying the fate matrix with already existing exposure-effect factors for aquatic ecosystem. However, in order to develop CFs for beach and sediments sub-compartments, this framework suggests the development of new exposure and effect factors specific to these sub-compartments.ConclusionSince LCA is known as a holistic approach, marine litter should be integrated in its impact assessment. This proposed framework fills one of the gaps of MariLCA's framework that aims towards integrating plastic litter in LCIA by proposing fate and CF matrices for different types of microplastics emitted to the marine environment.