Microplastic abundance in atmospheric deposition within the Metropolitan area of Hamburg, Germany

Only few studies investigated the input of microplastic particles via the atmosphere, so far. Here, we present results on microplastic concentrations in the atmospheric deposition in the metropolitan region of Hamburg. In total, six investigation sites were equipped with three bulk precipitation samplers each and sampled biweekly over 12 weeks (12/17-03/18). Three sites were located in a rural area south of Hamburg comprising one open field site and two throughfall sites under beech/oak and Douglas fir forest canopy, respectively. Three further sites were selected within the city following a transect from north to south representing urban sites of varying degrees concerning population, traffic and industrial pressures. Particles and fibers were counted under UV light within a photo box and under a fluorescence microscope (Axio Lab A.1, Zeiss). Results show that microplastic particles are ubiquitous at all sites. A median abundance between 136.5 and 512.0 microplastic particles per m²/day has been found over the sampling period. This equals a mean microplastic abundance of 275 particles/m²/day μRaman spectroscopy showed that polyethylenes/ethylvinyl acetate copolymers are dominating significantly (48.8 and 22.0%, respectively), 16 particles analyzed (14.6%) were identified as contamination from PE (polyethylene) samplers. In contrast to other studies, fragments were significantly dominating compared to fibers. The spatial distribution comparing the urban sites concentrations followed in the order from high to low: "north" (Henstedt-Ulzburg, low population density, suburb) - "center" (University; large population density) - "south" (Wilhelmsburg, middle population density, port and industrial facilities) with highly varying concentrations within the time series. Surprisingly, the rural sites in the southern part of Hamburg showed highest concentrations (Douglas fir > open field > beech/oak). This finding is most likely a result of factors such as the comb out capacity of the different forest types and/or direct input pathways from the agricultural areas and the nearby highway.