Seite - 192 - in Freshwater Microplastics - Emerging Environmental Contaminants?

This lack of data limits our ability to predict the ecological consequences and lifetimesof plastic pollution (Sects. 3.2 and3.3). 3.2 InteractionswithHigherOrganismsand theWider Environment Interactions between plastisphere communities and higher organisms have been recommendedasa topic for research inmarineenvironments [11,12],but theyalso require investigationwithin freshwaters.Manyorganisms includingfishes, gastro- pods, and zooplankton (e.g., Daphnia magna) ingest microplastics [2]. Indeed, nanopolystyrene has been found to negatively affect reproduction inD.magna, as well as population growth in the primary producer Scenedesmus obliquus [77].Effectsofplastic-sorbedchemicalshavebeenrarelystudied,but liver toxicity was observed in Japanesemedaka [78].A significant knowledge gap is the in situ analysis of microplastic present within freshwater organisms. Such analyses will need to consider how plastic-associated biofilms may amend the buoyancy of polymer particles and/or influence organismal behavior (e.g., selective feeding). Additionally, research is needed to investigate the pathogenicity of plastic- colonizing microbial taxa, as well as their ability to produce toxins. Oberbeckmann et al. [12] suggested that microplastics could carry pathogens encountered in the feces of marine organisms, and transport of human fecal bacteria on plastics has also been discussed [13]. There is a particular require- ment todeterminehowthisdebrisaffectsorganismsat lowtrophic levels, suchas invertebrates used for biomonitoring purposes [79, 80]. Impacts of plastisphere assemblages on processes such as nutrient cycling and primary production should also be investigated. Indeed, Bryant et al. [49] reported high densities of chlorophyll a and an increased abundance of nitrogen fixation genes (nifH, nifD, and nifK) on polymers in comparisonwith other sample types, leading the authors to suggest that plastic particlesmayconstitute autotrophic “hot spots” in seawater. Further to impactson thefitnessofplastic-ingestingtaxaandprocesses including elementalcycling,interactionsbetweenplastisphereassemblagesandotherorganisms may influence the distribution and fate of plasticwaste. For example,microplastics may become transported away from surface waters via encapsulation within fecal pellets [81]. Although this topic has not been investigated in freshwater ormarine environments, thegut bacteria ofmealworms (larvaeofTenebriomolitorLinnaeus) can degrade polystyrene [82], and certain aquatic organisms could harbormicroor- ganismscapableofmodifying the surfaceproperties ofplastics and/orbiodegrading them. Thus, investigating the interactions between plastisphere communities and 192 J.P.Harrison et al.