Impacts, fate and trophic transfer of microplastics in the freshwater environment

Microplastics (1–1000 μm) are now ubiquitous in all environments, including freshwater systems. Plastics of different sizes and shapes have been reported to be present in river and lake samples from the water column and sediments. Some recent monitoring studies have reported the ingestion of plastic particles by different biota freshwater species. Also, microplastics are categorised as freshwater pollutants of emerging concern. Despite this, there are major unknowns regarding their potential toxic effects and their trophic mobility in freshwater ecosystems. In this study, the impacts, fate and trophic transfer of microplastics have been investigated on a primary producer and a consumer freshwater species. A key finding of this study is that different microplastics can be adsorbed onto the tissues of the aquatic plant Lemna minor. This led to the hypothesis that L. minor can act as a transfer vector of different microplastics. We tested the trophic mobility of microplastics in a mesocosms setting, from L. minor to the amphipod Gammarus duebeni. A detailed study on G. duebeni feeding showed that G. duebeni do not avoid the consumption of microplastic contaminated food. In addition to this, microplastics were found in the digestive tracts of G. duebeni that had ingested plant feed contaminated with plastics. Another key conclusion of this study is the finding that G. duebeni can rapidly fragment microplastics. It was observed that amphipods fragmented microplastics into different shapes and sizes, including plastic particles in the nanosized range. These results play a crucial role in the current understanding of plastic’s fate in the environment, which has largely been explained by slow physical processes until now. Another finding of this study is the accumulation of anthropogenic microfibers in G. duebeni digestive tracts. Plastic and non-plastic microfibers have been widely found in environmental samples. We tested the ingestion of two types of environmentally relevant fibers by G. duebeni. The finding that amphipods can accumulate anthropogenic fibers has wider implications on aquatic food webs, beyond plastic pollution. Lastly, this study concludes that microplastics had no apparent acute negative effects on L. minor or G. duebeni under the conditions tested. This finding agrees with previous literature. However, major questions still remain to be explored such as the effects of microplastics in the long term under environmental relevant concentrations or the effects of nanoplastics. Overall, the results presented here highlight the importance of microplastics in regard to plant adsorbance, the fate of plastics inside organisms and the trophic mobility of plastic particles in freshwater ecosystems.