Comparative analysis of microplastics detection methods applied to marine sediments: A case study in the Bay of Marseille

Abstract

An intercomparison exercise on “microplastics in sediment” was carried out by five laboratories using samples collected in the Bay of Marseille in September 2021. The results from different extraction and identification methods varied depending on the type and size classes of MPs, and was better than 80 % for the size class >300 μm and for the fragments. The variability in recovery rates can be attributed to the choice of reagents and extraction protocols. Recovery rates per laboratory were between 47 % and 113 % and the use of ZnCl 2 and NaI increased recovery rates by an average of 70 %. The lowest recovery rates (47 and 53 %) were attributed to the reference methods (FTIR and LDIR), conversely the highest (80 and 87 %) were attributed to identification by Nile Red. The average ranged between 23 and 53 items /50 g d.w. with decreases offshore and at greater depth. • Harmonizing protocols and methods appear essential to achieve data comparability. • Differences results may arise from the extraction and identification methods applied depending on the nature of MPs. • Positive control samples and intercalibration exercises are recommended to increase the quality of MP monitoring. • Despite the methodological differences, all the partners observed higher MP contamination in the Park compared to Marseille.