Microplasic measurements at the Danube river using a multi-level approach

Microplastics are already part of our environment - even in the most inaccessible and remote places we find plastic particles that also remain there due to their longevity. The finer the scale at which we analyse samples, the more particles we find. It also became clear in the recent years, that rivers transport microplastics and that they also represent a principal pathway for plastic transport from land to the sea.Initial measurements with benthic nets on the Austrian Danube have shown that the plastic particles are not only found on the surface, but are distributed unevenly with maximum concentrations partly near the bottom, partly on the surface and partly concentrated on one side of the river. Given the spatial and temporal distribution, a multipoint method seems inevitable and was chosen for further measurements, in which three measuring points each are distributed over the depths of several measuring verticals along a cross-section. Furthermore, it was found that the microplastic concentration also strongly depends on the discharge conditions and that by far the largest quantities of microplastics are mobilized and then transported during flood events.After the first comprehensive measurements on the Austrian Danube between 2014 and 2015, further samplings were carried out in Hungary, Serbia and at 3 locations in Romania over the recent years. Despite the limitations of the data set, regarding the longitudinal, cross-sectional and hydrological representation of the micro plastic transport in the Danube River, an attempt is made to describe its characteristics on a basin wide scale. The measurements, reaching from impounded sections in the Upper Danube all the way down to the Danube delta, have shown, that the concentrations fluctuate strongly longitudinally according also to the discharge level. Therefore, at least at certain times, the Danube – and river systems with their inundation areas in general – are not only pathways, but can also be regarded as a microplastic sink. However, to increases process understanding and derive reliable statements, more data are needed.