Environmental Engineering Reference
In-Depth Information
ENPsreside(Guzmanetal. 2006 ; Benn and Westerhoff 2008 ). In turn, these factors
just mentioned, determine the fate of ENPs in water, as does the interactions the
ENPshavewithco-existingnatural/anthropogenicchemicalsandtheactionofnatu-
ralbiotic/abioticprocesseslikephotolysisandhydrolysis(Klaineetal. 2008 ). Such
interactions and transformations of the ENPs remain poorly understood. However,
someresearchershaveevaluatedtheaqueousbehaviorofENPs.Forexample,the
interaction of NOM with fullerene and CNTs caused disaggregation of their aggre-
gatesandincreasedstability(Kennedyetal. 2008 ). Similarly, NOM may influence
the characteristics of metal and metal oxide nanoparticles (nano-Ag, nano-Cu,
fullerene and iron oxide nanoparticle) at different pHs or at different ionic strengths
(Baaloushaetal. 2008 ; Diegoli et al. 2008 ;Gaoetal. 2009 ).Zhangetal.( 2008 )
reported rapid aggregation of metal oxide nanoparticles from electric double layer
compression that facilitated sedimentation. Before sedimentation the ENPs in the
water interacted with aquatic organisms. However, as stated before, much more
workisneededtobetterunderstandthefateofENPsintheaqueousenvironment.
4.3
Soil
Similar to aerosol nanoparticles, ENPs aggregate and are deposited in porous struc-
tures of soil ecosystems. Such aggregation and deposition is assessed by the high
diffusivity of aerosol nanoparticles. Size, surface characteristics and matrix con-
stituentsaremajorfactorthataffecttransportandfateofENPsinsoil(Darlington
et al. 2009 )(Table 4 ).Guzmanetal.( 2006 ) described three mechanisms for how
particles are transported in porous media: particle interception with media, gravita-
tional sedimentation and diffusion. The deposition of colloids in porous media is
givenbytheequation:
δ
δ
C
t vCDCKC
2
+
.
=
Where C is the particle concentration, t is time, v is the fluid velocity, D is diffusion
coeficientoftheparticles,andkisthedepositionratecoeficient(Guzmanetal.
2006 ).TheaboveequationcanbeusedtodeterminehowmanyoftheENPsinvolved
are undergoing diffusion. Lecoanet and Wiesner ( 2004 ) assessed the mobility of
threetypesoffullerenes(viz.,fullerol,nC 60 and SWCNTs), TiO 2 and SiO 2 at two
differentlowrates(Table 4 ). The highest mobility was observed for fullerol and
surfactant-modiiedSWCNTsinanunfracturedsandaquifer(10-14m),whereas
the lowest mobility was observed for nC60 (100 times lower than for fullerol).
SimilarlythetransportofdifferentENPs(viz.,CNTs,AgNPs,TiO 2 , ZnO, SWNTs,
andQDs)hasbeenstudiedbyusingsaturatedsoilorsandcolumns(Tianetal. 2010 ;
Jaisi and Elimelech 2009 ; Milani et al. 2010 ; Solovitch et al. 2010 ; Navarro et al.
2011 )(Table 4 ). The results for different nanoparticles have shown either aggrega-
tion or surfactant-induced transportation through the column.
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