Sources, pathways and reservoirs of microplastics, plastic particles smaller than 5mm, remain poorly documented in an urban context. While some studies pointed out wastewater treatment plants as a potential pathway of microplastics, none have focused on the atmospheric compartment. In this work, the atmospheric fallout of microplastics was investigated in two different urban and sub-urban sites. Microplastics were collected continuously with a stainless steel funnel. Samples were then filtered and observed with a stereomicroscope. Fibers accounted for almost all the microplastics collected. An atmospheric fallout between 2 and 355 particles/m(2)/day was highlighted. Registered fluxes were systematically higher at the urban than at the sub-urban site. Chemical characterization allowed to estimate at 29% the proportion of these fibers being all synthetic (made with petrochemicals), or a mixture of natural and synthetic material. Extrapolation using weight and volume estimates of the collected fibers, allowed a rough estimation showing that between 3 and 10 tons of fibers are deposited by atmospheric fallout at the scale of the Parisian agglomeration every year (2500 km(2)). These results could serve the scientific community working on the different sources of microplastic in both continental and marine environments.

Studies about microplastics in various environments highlighted the ubiquity of anthropogenic fibers. As a follow-up of a recent study that emphasized the presence of man-made fibers in atmospheric fallout, this study is the first one to investigate fibers in indoor and outdoor air. Three different indoor sites were considered: two private apartments and one office. In parallel, the outdoor air was sampled in one site. The deposition rate of the fibers and their concentration in settled dust collected from vacuum cleaner bags were also estimated. Overall, indoor concentrations ranged between 1.0 and 60.0 fibers/m. Outdoor concentrations are significantly lower as they range between 0.3 and 1.5 fibers/m. The deposition rate of the fibers in indoor environments is between 1586 and 11,130 fibers/day/m leading to an accumulation of fibers in settled dust (190-670 fibers/mg). Regarding fiber type, 67% of the analyzed fibers in indoor environments are made of natural material, primarily cellulosic, while the remaining 33% fibers contain petrochemicals with polypropylene being predominant. Such fibers are observed in marine and continental studies dealing with microplastics. The observed fibers are supposedly too large to be inhaled but the exposure may occur through dust ingestion, particularly for young children.

International audienceThis study investigates the microplastic contamination of both urban compartments (wastewater and total atmospheric fallout) and surface water in a continental environment (Greater Paris, France). These first investigations on urban environment confirm the presence of microplastics in sewage, freshwater and total atmospheric fallout and provide knowledge on the type and size distribution of microplastics in the [100 µm-5 000 µm] range. For the first time, the presence of microplastics, mostly fibers, is highlighted in total atmospheric fallout (29-280 particles/m2/day). High levels of fibers were found in wastewater (260-320 x103 particles/m3). In treated effluent, the contamination significantly decreases to 14-50 x103 particles/m3. In River Seine, two sampling devices are used to collect both large and small microplastic particles: i) a plankton net (80 µm mesh) and ii) a manta trawl (330 µm mesh). Sampling with the plankton net showed a predominance of fibers with concentrations ranging from 3 to 108 particles/m3. A greater diversity of both microplastic shapes and types was encountered during manta trawl sampling but at much lower concentrations (0.28-0.47 particles/m3). This combined approach could be relevant and implemented in future studies to provide an accurate overview of microplastic distribution in freshwater

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