Microplastics in the environment : development of a sample preparation method with further application and evaluation in fluvial and marine compartments

Plastics enter the environment via different sources and are transported and deposited there. They vary regarding polymer, density, colour, shape and size. Concerning the size, plastics are distinguished by their diameter in macroplastics, d ≥ 5 mm, and microplastics, d < 5 mm. Macroplastics, that enter the environment, are often the origin for microplastics due to degradation and fragmentation. Based on numerous environmental sampling and numeric modelling the fate of macro- and microplastics in the environment can be understood. Thereby, the entry is caused exclusively by anthropogenic action and the following transport is mainly by freshwater systems. Plastics in the environment accumulate due to the material’s durability on water surfaces and in soils and sediments which are therefore considered as temporary sinks. The final sink for plastic in the environment is the sea bed. To better understand the accumulation processes, more environmental sampling is necessary. For the following sample preparation, a separation method was developed based on the density independent extraction with canola oil in an efficient and cost-effective way using a plastic free separation unit. This method was extensively validated and could thus be identified as an equivalent separation technique which was applied on two different environmental areas. First, samples from marine water and sediment in the Northeast Atlantic were taken not only to prove the applicability of the separation method with canola oil but also to identify microplastic concentration there with microscopic analysis and polymer identification. The results showed a microplastic accumulation and furthermore an increase in microplastic concentration with increasing water depths and therefore distance to the coast. Second, fluvial sediments from a regional river catchment in North Rhine Westphalia were taken and analysed by microscope and infrared spectroscopy. The sampling included depth profiles in the river’s floodplains, composite samples from the river bed and surface samples outside the flooding area. The microplastic concentration was highest within the depth profile samples, followed by the river bed samples and the surface samples. Concerning the grain size, microplastic accumulated predominantly within fine sediment fraction. Furthermore, microplastic detection was set in a sedimentary context for the first time by using it to determine sedimentation rates. Additionally, a connection could be drawn between the polymers of the detected microplastic and the depth of the related sediment layer: the older the polymer, the deeper the layer in which it was found.With the knowledge about a temporal connection between microplastics and sediment deposition, a dating method for recent sediment layers can be developed in the future. In general, the detection of plastics can be seen as an indicator for a deposition after 1950, where the plastic mass production has started and enabled extensive environmental input. The understanding of entry, transport and accumulation of macro- and microplastics as well as the method validation of canola oil extraction and following application in marine and fluvial environments can be used variously as basics especially in upcoming microplastic research. With the consideration of microplastic detection as temporal marker for sediment deposition an additional groundwork for the development of a sediment dating method was set.