Seite - 193 - in Freshwater Microplastics - Emerging Environmental Contaminants?

otherorganismsiscloselyconnectedtoresearchintothetransportofplasticsbetween habitats (Sect. 3.1)and theenvironmental lifetimeof thisdebris (Sect. 3.3). While this chapter focuseson freshwater andmarineenvironments,plastisphere communitiesmayalsobeofsignificancetohumanhealth.Risksassociatedwith the human ingestion ofmicroscopic plastics have been identified [83], and investiga- tions of this topic could also be approached fromamicrobiological viewpoint. In particular, the human health implications of putative pathogens within plastic- associatedbiofilms (Sect. 2.3.1 and [13])merit further study. 3.3 InSituBiodegradability ofPlastics andPlastic-AssociatedCompounds The recent evidence for PET assimilation by I. sakaiensis [18] suggests that, although rates of plastic breakdown in the environment are extremely low (Sect. 2.3.2), several novel polymer-degrading taxa are likely to be presentwithin fresh- water andmarine ecosystems. Identifying such taxa and investigating their ability tobiodegradedifferentplastic types,additives,andpolymer-sorbedcompoundsare of primary importance to understanding the environmental residence times of plastic waste. Research in this area should focus on habitats functioning as sinks for theaccumulationofplastic, includingsediments[3–5,27].Toobtainacomplete understandingof the biodegradability of differentmaterials and compounds, there is aneed to combine laboratory-basedexperimentswithfield-basedmeasurements of plastic degradation in both freshwater andmarine environments.Moreover, as nanometer-sized plastic particles become released from the parent polymer as a result ofweathering [84], their biodegradation behaviorwill need to be compared with that of larger fragments that may support a comparatively complex biofilm community.Most research into plastic biodegradation has been based on indirect measurements such asmass loss [11], and a key challengewill be to conclusively demonstrate in situ assimilation of carbon from a given plastic type (or plastic- associated compound) [18]. The toxicity of any degradation products, or of com- pounds released from thepolymer,will also require investigation (Sect. 3.2). 3.4 Analytical andExperimentalAdvances inPlastisphere Research Research into plastisphere assemblages has focused on bacterial communities [44, 45].Little is knownabout plastic-associatedmicrobial eukaryotes in freshwa- ters, and there isaneed foranalyses targeting theseorganisms,not the least as they are known to occur onmarine plastics [48, 49]. Several advances have improved the suitability of metabarcoding for analyzing fungi, diatoms, and protists Microplastic-AssociatedBiofilms:AComparisonofFreshwater andMarine. . . 193