Sampling Strategies of Microplastic in Stormwater Runoff from Separate Drainage Systems

The occurrence of microplastic in terrestrial and water environments can be traced back to anthropogenic activities. Urban drainage systems play a role in transporting microplastic from urban sources into receiving waters or soils. The analysis (including sampling, sample preparation and detection) of microplastic are very complex and time-intensive, and sampling alone is the main contributor to uncertainty in the process. However, the lack of representative and comparable sampling strategies complicates the efforts to quantify emitted loads and to identify sources and pathways. Therefore, strategies for sampling microplastic in different wastewater compartments were developed and tested. The ongoing phase, however, focuses on sampling stormwater runoff in separate sewer systems. A new autonomous sampling concept for stormwater was designed and implemented to capture large sample volumes. The sample volume plays an important role with respect to the representativeness. Samples are then prepared, both in situ and in laboratory to produce five size fractions (1000, 500, 100, 50, 5 μm). Preliminary results show that urban drainage systems transport different loads of at least four microplastic types; namely polyethylene (PE), styrene-butadiene rubber (SBR)1, polypropylene (PP) and polystyrene (PS). High PE concentrations are detected in all stormwater samples, followed by SBR, a main tire wear constituent. SBR loads showed dependency to the number of dry-weather days prior to sampled rain events.