Environmental Engineering Reference
In-Depth Information
and transport of ENPs in environmental systems. There is also a wealth of data
available on the behaviour and transport of natural colloids. Available data
indicate that, following release to water, nanoparticles (including carbon nano-
tubes, nanoscale zerovalent iron, titanium dioxide and fullerenes) will aggregate
to some degree (e.g., Fortner et al.
2005
;Guzmanet al.
2006
;Phenratet al.
2007
).
Aggregates may then settle out (Brant et al.
2005
). The degree of aggregation and
the size range of the aggregates is dependent on the characteristics of the particle
(i.e., type, size, surface properties and, for metal particles, the intrinsic magnetic
moment) and the characteristics of the environmental system (including pH,
ionic strength and dissolved organic carbon content) (Guzman et al.
2006
;Hyung
et al.
2007
; Phenrat et al.
2007
). The environmental behaviour of ENPs has also
been shown to be modified in the presence of biota (Roberts et al.
2007
).
Environmental transport studies indicate that NPs will exhibit differing mobi-
lities in the soils and waterbodies and in water treatment processes compared to
their corresponding parent form. Selected NPs have been shown to have the
potential to contaminate aquifers (Lecoanet et al.
2004
), and a portion may
pass through water treatment processes (e.g., Zhang et al.
2008
), although the
behaviour varies depending on nanomaterial type (Lecoanet et al.
2004
).
The behaviour of nanoparticles in environmental systems is, therefore,
highly complex and appears to be dependent on not only the particle type
but also the particle size. A number of modelling approaches have been pro-
posed for predicting behaviour in environmental systems (Mackay et al.
2006
);
however, these have yet to be fully evaluated. Moreover, the studies to date
have however generally looked at discrete processes, concentrated on a few
nanoparticle types and employed simple test systems.
Effects of ENPs in the environment
Alongside the fate investigations, studies have explored the uptake and
effects of nanoparticles on a range of environmental species and endpoints
(Oberdorster
2004
; Kashiwada
2006
; Lovern & Klaper
2006
; Oberdorster et al.
2006
)(
Table 5.1
). In the laboratory, aquatic organisms appear to rapidly accu-
mulate selected nanoparticles, including carbon black, titanium dioxide and
polystyrene (e.g., Lubick
2006
, Stone et al.
2006
).
Laboratory studies with microbes have reported effects of fullerenes on
microbial physiology (e.g., Fortner et al.
2005
; Fang et al.
2007
), whilst silver
nanoparticles have been shown to accumulate in bacterial membranes, ulti-
mately causing cell death (Sondi & Salopek-Sondi
2004
). In some cases, there is
however a mismatch between laboratory studies and studies to assess impacts
in the real environment. For example, under realistic exposure conditions,
fullerenes have little impact on the structure and function of the soil microbial
communities and microbial processes (Tong et al.
2007
).
The available data indicate that nanoparticles have low acute toxicity
to aquatic organisms (e.g., Lovern & Klaper
2006
; Oberdorster et al.
2006
;
