Page - 11 - in Freshwater Microplastics - Emerging Environmental Contaminants?

6 Effects ofPlastics andMicroplastics onFreshwater Ecosystems Once in theaquaticenvironment, themobilityanddegradationofplasticswillgen- erateamixtureofparentmaterials, fragmentedparticlesofdifferentsizes,andother non-polymer degradation products. Accordingly, biotawill be exposed to a com- plexmixture of plastics and plastic-associated chemicals that changes in time and space. 6.1 UptakeandBiologicalEffects MPsmaybetakenupfromthewatercolumnandsedimentbyarangeoforganisms. This can occur directly through ingestion or dermal uptake most importantly through respiratory surfaces (gills). Previous investigations on freshwater zoo- plankton have included Bosmina coregoni that did not differentiate between PS beads(2and6μm)andalgaewhenexposedtocombinationsofboth[92].Thesame study also found thatDaphnia cucullata,when exposed toPSbeads (2, 6, 11, and 19 μm) in combinationwith algae cells of the same size, was observed to exhibit similar filtering rates for the three smaller size classes but preferred alga over the larger beads [92].Rosenkranz et al. [93] demonstrated thatD.magna ingests nano (20nm) andmicro (1μm)PSbeads. The authors note that both types ofPSbeads wereexcretedtosomeextent,but the20nmbeadswereretained toagreaterdegree within the organism. The extent to which organisms are exposed to physical stress because ofMP uptake depends on particle size, because particles larger than sediment or food particles may be harder to digest [94]. In addition, particle shape is also an important parameter, because particleswith amore needle-like shapemay attach more readily to internal and external surfaces. The indirect effects of MPs may includephysical irritation,whichmaydependonMPsizeandshape.Smallermore angular particlesmaybemoredifficult to dislodge than smooth spherical particles andcauseblockageofgillsanddigestive tract. Ina recentstudy, thechroniceffects of MP exposure toD. magnawere evaluated [21]. Exposure to secondary MPs (meanparticlesize2.6μm)causedelevatedmortality, increased inter-broodperiod, anddecreasedreproductionbutonlyatveryhighMPlevels(105,000particlesL 1). In contract, no effects were observed in the corresponding primary MP (mean particle size 4.1μm) [21]. There is someevidence suggesting that a trophic transfer ofMPmayoccur, for instance, frommussels tocrabs[27].ThebluemusselMytiluseduliswasexposedto 0.5 μm PS spheres (ca. 1 million particles mL 1) and fed to crabs (Carcinus maenas).Theconcentrationofmicrospheres in thecrabhaemolymphwas reported to be the highest after 24 h (15,033 particles mL 1) compared to 267 residual MicroplasticsAreContaminants ofEmergingConcern inFreshwater. . . 11