Emilie Maria Falk Kallenbach:
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Microplastic is ubiquitous in the aquatic environment, however little is still known whether microplastic has a negative impact on freshwater macroinvertebrates and the potential risk of this for freshwater ecosystems. In this thesis, sources of microplastic to the freshwater environment are described, followed by a discussion of current methodological challenges and the need for a focus on method optimization and harmonization – which form the foundations of trustworthy and comparable data; a prerequisite for the management and risk assessment of microplastics. This is followed by a review of in situ studies of microplastic in freshwater macroinvertebrates, which is compared to results from exposure experiments. The current knowledge and its limitations are discussed. In general, it is evident from literature that observed effects of microplastic are reduced at environmental relevant concentrations or when studies are conducted in a natural environment. Finally, microplastic as a stressor is compared to other primary and documented stressors for freshwater macroinvertebrates. Based on this, which also includes my own findings as reported in papers I to IV, I conclude, that microplastic >50 µm at the current environmental concentrations are not likely to pose any risk to freshwater benthic macroinvertebrates, alone or in combination with other stressors.