Engineered Nanomaterials as Emerging Contaminants in Water - Nanotechnologies for Water Environment Applications - page 569

ultimate disposition of NMs in the environment (e.g., ocean, ocean sediments, lake/river
sediments). The concepts required for addressing linked biogeochemical or
physicochemical processes and transport processes are discussed in Section 16.6.

Table 16.1 Summarize of processes potentially influencing NMs in aqueous
environmental settings.
Process

Representative Effects on NM Fate
in the Environment

Description

Aggregation Interactions of colloids with resulting low net

energies of repulsion will “stick” together into larger
colloids

Aggregated NMs may result in more rapid
sedimentation out of water columns

Biodegradation Bacteria (heterotrophic or autotrophic) gain

metabolic energy from a substrate (organic or
inorganic, respectively)

Organic capping ligands on quantum dots may
biodegrade and change the surface charge
characteristics of the metal core.

Bioaccumulation Passage of a pollutant up and through a food chain Partitioning of hydrophobic fullerenes in lipids may

biomagnify their detrimental effects in higher trophic
states

Dissolution Phase transformation from solid to dissolved in

water

Nano-silver partially dissolves into silver ion in water
(Benn and Westerhoff submitted)

Facilitated
transport

Dissolved pollutant sorption onto colloids affect
their fate and toxicity

In the presence of TiO2 NMs, compared to no TiO2,
higher levels of arsenic and cadmium were observed in
fish (Sun et al., 2007; Zhang et al., 2007)

Filtration Removal of colloids from water passing by fixed

collectors (i.e., sand) due to interception,
sedimentation or diffusion from streamlines
followed by chemical attachment to the collector

The velocity and ionic strength of water conveying
fullerenes and metal NMs affects their removal on
quartz collectors (Lecoanet et al., 2004; Lecoanet and
Wiesner, 2004)

Flocculation Processes (diffusion, fluid shear, differential

settling) that bring colloids into contact with each
other and when a fraction of the colloids aggregate
together

Rapid and slow mixing of metal oxide NMs causes
increasing particle sizes to form over time (Zhang et al.,
in-press-a)

Magnetism Attraction of oppositely charged paramagnetic

materials or aggregation in a magnetic field

Iron oxide NMs (5-12 nm) exhibit high magnetic
attraction (Mayo et al., 2007)

Nucleation Increased rate of crystal formation of a chemical

precipitate due to presence of “seed” colloid

Calcite seed particles increase rate of calcium
precipitation (Chao and Westerhoff , 2002)

Oxidation An increase in valence state, which may include

oxygen incorporation, that occurs via abiotic or
biotic reactions

Photo-oxidation of fullerenes incorporates oxygen-
containing functional groups which may change surface
chemistry (Lee et al., 2007)

Partitioning Division of pollutant between two phases Hydrophobic fullerenes partition from aqueous

solutions via non-specific uptake mechanisms in
hydrophobic lipid bilayers (Qiao et al., 2007)

Reduction A reduction in valence state that occurs via abiotic

or biotic mechanisms

Bacteria can adhere onto metal surfaces and, via
enzymatic processes, facilitate their dissolution
(Shashikala and Raichur, 2002; Stack et al., 2004)

Sedimentation Removal of particles from water as gravitational

forces exceed buoyant and drag forces

Increases in metal oxide NM diameter leads to more
rapid rates and extent of removal by sedimentation
(Zhang et al., 2008a)

Stabilization NMs suspended in water columns over long periods

are stable. Destabilized particles may rapidly
aggregate. The degree of stabilization is related to
the surface charge and surface properties of NMs.

Dissolved organic matter facilitates increased
“dissolved” concentrations of fullerenes in water
(Hyung et al., 2007)

Volatilization Transfer of material from water or solids into the air Oceanic whitecaps which are the largest source of

aerosol particles on earth, accounting for approximately
10 12 g of sea salt particles annually, and have diameters
of 40 to 120 nm (Bates et al., 1998; Lewis and
Schwartz, 2004)