Seite - 188 - in Freshwater Microplastics - Emerging Environmental Contaminants?

polyethylene (LDPE) byArcobacter spp. has also been shown to occur in coastal marine sediments [21].The studybyMcCormick et al. [45]was conducted imme- diatelybelowaWWTPoutfall,andit isunknownifwastewater-affiliatedmicrobial communities will persist further downstream. However, the presence of plastic- colonizingArcobacter spp. inboth freshwater andmarinehabitats [21,45] implies that certaingenera could surviveonpolymers as theyare transported fromWWTP tootherecosystems(Fig.2andSect.2.1). Indeed,Arcobacterspp.havebeenfound tobeprevalentmembersof the“landfillmicrobiome”intheUSA[51]andhavealso beendetected in sewage [52]. The objective ofLagarde et al. [46]was to examine the growth of amicroalga (Chlamydomonasreinhardtii)onplasticparticlesover time,determine theeffectof plastic type on algal growth, andmeasure particle aggregation.The authors found littleeffectofplastic (high-densitypolyethylene[HDPE]orpolypropylene[PP])on algalgrowth,butcontactwithpolymerparticles altered theexpressionofgenes for somesugarsused in extracellular polysaccharides.OnPP, algal biofilms increased particle aggregation, which was not observed for HDPE. Research has recently beenaimedat characterizing the sedimentation ratesofmicroplastics in freshwater andmarineenvironments [26,35,36].Lagardeet al. [46]add toourunderstanding of microplastic movement by showing that aggregation of plastic particles via biofilm attachment occurs differently among polymer types, which will affect their suspension or deposition. Future studies will benefit from extrapolating this approach to in situ analyses, as well as comparing findings betweenmarine and freshwater environments. For example, the types and sinking rates of algal microplastic aggregates within marine environments are known to be species specific [35], and similar interactions could affect the distributionofmicroplastics in rivers and lakes. Fig. 2 Scanning electron micrograph showinga biofilmattached to aHDPE fragment incubated in aerobicwastewater for 6months.Microplastics are likely to function as vectors for the transport of microbial taxa fromWWTP toother environments. The scale bar is 2μm(Credit: AlexanderS.Tagg) 188 J.P.Harrison et al.