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Including impacts of microplastics in marine water and sediments in life cycle assessment
Summary
This study developed new methods to measure the environmental impact of microplastics in both ocean water and seafloor sediments, filling a gap in how product environmental footprints are calculated. Previous assessments only considered microplastics floating in water but ignored those that settle into sediments where bottom-dwelling organisms live. Including sediment impacts gives a more complete picture of how plastic pollution from products affects marine life that may eventually enter the human food chain.
Microplastics (MPs) pose a threat to marine ecosystems. When released, MPs first reach the water column, where they can be ingested by pelagic species. MPs can then reach marine sediments, a potential sink, where they may affect sediment-dwelling species. However, current life cycle impact assessment (LCIA) methods do not consider the impact of MPs in sediments, providing an incomplete picture when comparing environmental profiles of products and services. This work builds on the MarILCA working group characterization factors (CFs) by computing updated physical effects on biota CFs that include both water and sediment compartments, as previous factors did not consider the latter. A simplified fate of MPs in the marine environment is modelled, combining fate in water and sediments and differentiating between MP polymers, sizes, and shapes. A combined exposure and effect factor for MPs in sediments (EEF sed ) is developed, calculated from a hazardous concentration for 20 % of species (HC20), derived from a species sensitivity distribution (SSD) of effect concentrations of 10 % (EC10) values. A methodology accounting for species feeding behaviour is proposed to derive ecosystem-level impacts via exposure through different compartments, expressed as the potentially affected fraction (PAF) of marine species. Combining the fate, EEF sed , and EEF w (water) yielded updated marine CFs including impacts on both water and sediment-dwelling biota. CFs were tested in a textile LCA case study. Sediments were found to be a sink for high-density MPs, with EEF sed (16 PAF m 3 /kg) significantly lower than the previously reported EEF w (1068 PAF m 3 /kg). Developed marine CFs range from 34 to 5.4 × 10 8 PAF m 3 d/kg and are available for use in environmental decision-making. • A simplified fate between marine water and sediments is modelled. • An exposure and effect factor for microplastics in sediments is proposed. • Characterization factors that include impacts in water and sediments are computed. • The characterization factors are tested in a textile LCA case study. • For high-density polymers, impacts are higher in sediments than in water.
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