Progress towards monitoring of microlitter in Scandinavian marine environments

Four different case studies were carried out to determine dominating microlitter types from urban environments to the regional Scandinavian seas (eastern North Sea). The sampling was both from sediment near sources (urban runoff and road dust sediment), and further out from coastal sediments. The sea surface layer and subsurface samples was taken in two different gradients, in the Oslo and Roskilde fjords, where also blue mussels were sampled. Best available technologies for sampling each compartment was used and evaluated, and while the water samples was analysed as collected, the sediment and biota samples needed some pretreatment of chemical digestion and/or heavy density liquid floatation or elutriation.

In order to develop visual identification as objective as possible, a visual and physical observation scheme was proposed. The visual identification scheme should be complemented with spectroscopic identification to different degrees depending on the size fractions.Spectroscopic identification is still often a quite time-consuming process, meaning that for monitoring purposes it is not currently advisable to aim to identify all particles during monitoring studies. Until fully or partly automated spectroscopic methods are available they are still important tools for verification of representative types of particles in samples above 100 μm.

The amount of particles that should be identified to provide adequate compositional information would be dependent on the aim of the study as well as the type and composition of the samples. However, in order to do monitoring and include sample composition in the results a minimum of 100 of the fewest particles should be counted in a sample to achieve 10% standard deviation in terms of counting statistical uncertainty.The field is however rapidly evolving, and automated procedures are already being published. For research purposes and more detailed monitoring and screening studies spectroscopic methods can aside from providing particle identification also give clues on additives and level of degradation.The most common types of microlitter found varied between studies but common trends could be identified between the road tunnel sediment and the urban creek sediment that these contained black particles resembling tire rubber from both visual and tactile tests, and also asphalt, charcoal, oil/tar particles and road marker particles. In the coastal water samples the surface layer was dominated by polystyrene foam particles and polyethylene fragments and films.

In the subsurface water samples fibres, films and fragments of plastic was most common. In both the Gothenburg urban creek sediment and Oslo fjord surface water samples particles that could be related to artificial sports turf (polyethylene green grass and clear cut, tire granulate) was observed. The microlitter in mussels was dominated by fibres. The approach of using gradient studies, and include both near source sampling as well as recipient gradient sampling, was concluded to be very suitable to determine sources and fate.