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assumed to be uniformlymixed within each section, and the transport processes
advection, settling, and size-dependent resuspension from the sediment bedwere
taken into account.
Microplastic properties were defined by dimension and density. The study
assumed plastic particles were pristine, that is, effects of biofouling were not
takenintoaccount.Themodelshowedthat the transportofmicroplastics isstrongly
relatedtoflowregimes,especiallyfor thelarger (>0.2mm)particles.Thetransport
dynamics were more influenced by size than by density, which confirms the
findings by Besseling et al. [35, 36]. Average retention of particles was size
dependent, decreasing with decreasing particle size and starting with 90–100%
retention for particles>0.2mm.Particles<0.2mmwere lesswell retained, and a
large portionwas expected to endup in themarine environment. Theparticle size
range of the simulated particleswas 0.05–0.7mm; densities ranged from1,000 to
1,300kgm 3.Themodeldidnot includebiofouling,aggregation,orfragmentation.
These processes influence the hydrodynamic behavior and size distribution of the
particlesbutaccordingtotheauthorsshouldbebetterunderstoodbefore theycanbe
included in themodel.Nanoparticles are also not included in themodel yet [37].
Comparison of the Besseling (DUFLOW) and Nizzetto (INCA-Plastic)
Models Both the DUFLOW and INCA-Plastic models were in accordance with
their design criteria and study aim. TheNanoDUFLOWmodel seemsmore com-
plete as it includes aggregation, which has been shown to be a crucial process,
especially for submicronparticles [59, 60]. Themodel byBesseling et al. [35, 36]
also accounted for biofouling, which also has been shown to affect the settling
behavior of plastic particles.Given the study aim,Besseling et al. did not provide
long-termsimulations that accounted for the impacts ofweather conditions.How-
ever, in principle DUFLOW can accommodate point and diffuse sources like
WWTPs, tributaries [96], or runoff [111]. The latter processes were already
accounted for in the INCA-Plastic implementation byNizzetto et al., which is a
relevantmerit of that study.Bothmodeloutcomesagreeon the important effect of
particle size on retention and on a high retention for particles >0.2 mm. A
contrasting conclusion, however, is that the INCA-Plastic model predicted that
smaller particleswould be lesswell retained in the river and thus exported to sea,
whereas the NanoDUFLOW model reported an increased retention again for
particles smaller than 5 μm. This difference can be explained from the fact that
NanoDUFLOWaccounted for aggregation of these small plastic particles, which
allowed for the simulation of the increased sedimentation of these small plastic
particles captured in heteroaggregates. This emphasizes the need to include this
process. Ithasbeenshownthatbecauseheteroaggregationcapturesvirtuallyall free
nanosized particles, uncertainty with respect to the exact parameterization of
heteroaggregation is ofminor importance [73, 96, 112]. The conclusions of both
studies depend on themodeled scenario’s and parameters’ variability. Also labo-
ratory experiments have shown that processes like biofouling and aggregation
[57, 62, 84] and particle properties like density, size, and shape [52, 55] signifi-
cantly influenceparticle fate.
Modeling theFate andTransport of PlasticDebris inFreshwaters:Reviewand. . . 141
Freshwater Microplastics
Emerging Environmental Contaminants?
- Title
- Freshwater Microplastics
- Subtitle
- Emerging Environmental Contaminants?
- Authors
- Martin Wagner
- Scott Lambert
- Publisher
- Springer Open
- Date
- 2018
- Language
- English
- License
- CC BY 4.0
- ISBN
- 978-3-319-61615-5
- Size
- 15.5 x 24.1 cm
- Pages
- 316
- Categories
- Naturwissenschaften Chemie