Microplastic Contamination Assessment In Marine Matrices Along Atlantic Coastline. Phase 1: Preliminary Analysis Along French Coast

Global plastic production is estimated at 368 million tons in 2019 (PlasticsEurope, 2020) and continues to increase, with 79% of plastic waste ending up in the environment (UNEP, 2020). Around 90% of this marine plastic pollution is made up of MicroPlastics (MPs) (Xanthos and Walker, 2017). These particles, smaller than 5 mm (Arthur et al., 2009), are considered one of the most harmful and persistent consequences of the marine plastic pollution (UNEP, 2023). Therefore, assessing contamination levels and understanding MPs distribution pathways are crucial. However, methodological inconsistencies introduce significant ambiguity and limit global understanding of this contamination (Rezania et al., 2025). To address this issue, the Interreg Free LitterAT project promotes harmonized protocols to sample and extract MPs from marine matrices to progress toward litter-free Atlantic coastal communities by preventing and reducing both macro- and microlitter. Some studies have assessed MPs contamination in these matrices but only in few French Atlantic local areas. However, none have realized an assessment within a coordinated timeframe and along the entire French Atlantic coast. Thus, for the first time, 25 stations were sampled along the French Atlantic coastline during the same period (February 2025). The results show than 100% of the sediment samples (16 stations) were contaminated by MPs, with concentrations ranging from 14 to 384 items/kg d.w, and an average of 158.3 ± 116.7 items/kg d.w. For mussel MPs contamination, samples of 14 out of 16 stations were contaminated, with concentrations ranging from 0.04 to 0.94 items/g w.w. and an average of 0.30 ± 0.26 items/g w.w. Both matrices were mainly contaminated by fibers (>70%) and fragments (>25%). This study (i) represents the first baseline of MPs contamination along the entire French Atlantic coastline and also at a European level, with future data from project partners. Moreover, this work will contribute to (ii) the harmonization of sampling and extraction MPs protocols within a Interreg FreeLitterAT framework, and (iii) to advance towards the validation of fluorescence-based method effectiveness compared to reference techniques.