Floating Microplastics in the Northwestern Mediterranean Sea: Temporal and Spatial Heterogeneities

Abstract

Mediterranean sea is one of the most sampled areas for floating microplastics (MPs). However, only few investigations have been conducted at small spatial and temporal scales in coastal areas. To fill this gap, MPs (< 5 mm) were collected off the mouth of two contrasted rivers: the Rhône River, the largest source of freshwater and sediments into the Mediterranean Sea, and a typical small Mediterranean coastal river, the Têt River. Close surface seawater transects were performed using a manta trawl (>300 μm), at different seasons in the Rhone area and every month during one year in the Têt area. After removal of organic matter, MPs were examined under a dissecting stereo microscope. Preliminary results show highly variable MP concentrations even at small scale. Indeed, concentrations ranged from 0.05 to 0.6 items.m−3 for the Têt area with an average of 0.2 items.m−3 and from 0.1 to 0.5 items.m−3 with an average of 0.3 items.m−3 for the Rhône area. Concentrations can change by a factor of 4 between two consecutive days at the same location and by a factor of 3 between two consecutive trawls on the same day. Fibers are the most abundant shape (40–90%), followed by fragments (0–50%). Foams and films are less represented (0–20%). FTIR analysis indicates that fragments and films were mostly polyethylene (PE) and polypropylene (PP), while foams were essentially made of polystyrene (PS). Fiber analysis is ongoing. Occasional presence of lint composed of hundreds of fibers can partly explain the high differences observed at small scales, as well as fast changing river inputs. These extended observations of floating MPS in the NW Mediterranean coastal environment underlines the necessity of performing replicate sampling to get a better insight into the spatial and temporal distribution patterns of these worrying pollutants.