Environmental Engineering Reference
In-Depth Information
produces reactive oxygen species under similar conditions (Pickering and Wiesner,
2005). Data on potential toxicity of nanomaterials on terrestrial species (plants,
soil invertebrates or micro-organisms) is increasing rapidly (Handy et al. , 2008 ),
but there is a growing need for information on more realistic conditions as well
as descriptive and, eventually, predictive models of nanomaterials impacts on
organisms.
There are several reviews on the toxicity of nanomaterials (Borm et al. , 2006a )
such as carbon nanomaterials (Hurt et al. , 2006), carbon nanotubes (Donaldson
et al. , 2006 ; Lam et al. , 2006) and quantum dots (Hardman, 2006). Nanomaterials
may pose risk to human health and to the environment but only a few specifi c
nanoparticles have been investigated in a limited number of test systems and extra-
polation of this data to other materials is not possible. Manufactured nanomaterials
with new chemical and physical properties are being produced constantly and the
toxicity of these is unknown. Therefore, despite a small but increasing database on
the behaviour and effects of nanoparticles in the environment, no overarching and
predictive models exist and their development is an urgent and active area of
research. The (eco)toxicity of nanoparticles is further discussed in Chapter 7 .
1.8.1.2
Nanomaterials as Carriers of Coexisting Contaminants
In the environment, contaminants are often bound to natural solid phases including
nanoparticles (Lead et al. , 1999 ; Lyven et al. , 2003). Nanomaterials have the capacity
to bind substantial fractions of contaminants such as trace metals and organics.
Carbon nanotubes have been shown to sorb a variety of organic compounds (Long
and Yang, 2001) and metals such as copper (Liang et al. , 2006) and rare earth metals
(Liang et al. , 2005). Fullerenes will sorb organic compounds such as naphthalene
(Cheng et al. , 2004) and can be used for the removal of organometallic compounds
(Ballesteros et al. , 2000). Zero-valent iron oxide nanoparticles have been applied
for the remediation of organic contaminants (Obare and Meyer, 2005; Zhang, 2003).
Nanoporous ceramic sorbents have been used for the immobilization of cationic
metals (Mattigod et al. , 2006). It is possible that in this form contaminants may be
more bioavailable and may be taken up through cell membranes more readily,
although few studies are available (Navarro et al. , 2008). The use of nanoparticles
as drug delivery vehicles points to this being a potential problem.
1.8.1.3
Effect on Micro - Ecosystems
There are few studies demonstrating the indirect (nonbiological) impact of nano-
particles on environmental systems, although this remains a concern (Buffl e, 2006 ).
For instance, zero-valent iron nanoparticles have been used for the remediation of
soil and aquifers contaminated with halogenated hydrocarbons and heavy metals
(Zhang, 2003). However, as oxygen and other oxidizing materials are consumed,
moderate to strong reducing/anaerobic conditions were created. Although this
study did not examine consequences, it is likely that changes in, for instance,
microbial ecology will have occurred.
Aggregation and sedimentation of nanomaterials can be responsible for the
scavenging of colloids from the water column to the sediment (Baalousha et al. ,
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