Release, Transport and Toxicity of Engineered Nanoparticles - Reviews of Environmental Contamination and Toxicology - page 12

4 Fate and Transport of Engineered Nanoparticles

in the Environment

After ENPs are released to the environment, they may remain as they are, or their
makeupandcharactermaybealteredbytheactionoftheenvironment.Theirsur-
face characteristics, structure and reactivity may be altered during transport into or
withintheenvironment.Moreover,thephysico-chemicalcharacteristics(e.g.,pH,
ionic strength, presence of organic matter) of various environmental media may
affect the transport of ENPs. Below we describe the studies that have been con-
ducted to discover how ENPs move and are affected by environmental media.

4.1 Air

MadlerandFriedlander( 2007 ) described how nanoparticles are transported in air
(Table 4 ).Theycomparedthetransportoftheseverysmallentities(ENPs)asbeing
similar to how fluids are transported. In the absence of external forces, Brownian
diffusion is the main transport mechanism by which nanoparticles move in gaseous
atmospheres.MadlerandFriedlander( 2007 )derivedanequationofparticlediffu-
sivity(D)thatisgivenasfollows:

2 2 2

κ
ζ
Where D is particle diffusivity, x is direction coordinate, t is time, u is velocity, m is
mass of the particle, ʶ is the friction coeficient, ʺisBoltzmannconstantandTisthe
translationalenergyofagasmolecule.Asdescribedbythisequation,particletrans-
port is related to the frictional coefficient that depends on drag force and velocity
between particle and fluid. However, this relation may not be accurate for determin-
ing particle diffusivity through air.

um T
====

x ut

t

D

2 βζ t

Table 4 Factors that facilitate the transport of ENPs in ecosystems
Ecosystem

Behavior of nanoparticles Reference

Air(Abiotic
interaction)

a. Diffusion a. Friedlander( 2000 ), Madler

andFriedlander( 2007 )

b. Brownian coagulation b. LallandFriedlander( 2006 )

c. Agglomeration c. Bandyopadhyayaetal.( 2004 )

Water a. Aggregation a. Guzmanetal.( 2006 )

b. Interaction with natural organic matter b. Ghoshetal.( 2008 )
c. Adsorption c. Kelleretal.( 2010 )

Soil a. Depend on charge a. Darlingtonetal.( 2009 )

b. Aggregation b. Solovitchetal.( 2010 )
c. Interaction with organic molecules c. JaisiandElimelech( 2009 )
d. Degradation and surface modification d. Navarroetal.( 2011 )