Spatial distribution of anthropogenic particles and microplastics in a meso-tidal lagoon (Arcachon Bay, France): A multi-compartment approach.

Assessment of microplastic (MP) contamination is still needed to evaluate this threat correctly and tackle this issue. Here, MP contamination was assessed for a meso-tidal lagoon of the Atlantic coast (Arcachon Bay, France). Sea surface, water column, intertidal sediments and wild oysters were sampled. Five different stations were studied to assess the spatial distribution of the contamination. Two were outside of the bay and three were inside the bay (from the inlet to the back). A distinction was made between all anthropogenic particles (AP, i.e. visually sorted) and MP (i.e. plastic polymer confirmed by ATR-FTIR spectroscopy). The length of particles recovered in this study ranged between 17 μm and 5 mm. Concentration and composition in sea surface and water column samples showed spatial variations while sediment and oyster samples did not. At outside stations, the sea surface and the water column presented a blended composition regarding shapes and polymers and low to high concentrations (e.g. 0.16 ± 0.08 MP.m-3 and 561.7 ± 68.5 MP.m-3, respectively for sea surface and water column), which can be due to coastal processes and nearby input sources. The inlet station displayed a well-marked pattern only at the sea surface. High AP and MP concentrations were recorded, and fragments along with polyethylene overwhelmed (respectively 76.0 % and 73.2 %). Higher surface currents could explain this pattern. At the bay back, AP and MP concentrations were lower and fibers were mainly recorded. Weaker hydrodynamics in this area was suspected to drive this contamination profile. Overall, fragments and buoyant particles were mainly detected at the sea surface while fibers and negatively buoyant particles prevailed in other compartments. Most of the studied samples presented an important contribution of fiber-shaped particles (from 31.5 % to 94.2 %). Finally, contamination was ubiquitous as AP and MP were found at all stations in all sample types.