Environmental Engineering Reference
In-Depth Information
The fate of ENPs in soil is similar to its fate in other systems, in that behavior in
the medium depends on the physico-chemical characteristics of both the nanopar-
ticles and the soil. The fate of nanoparticles in the soil system is affected by the
transformation mechanisms. For example, metallic ENPs have a higher surface area
that favors easy sorption to soil particles, which renders them immobile. Alternately,
nanomaterials easily insert themselves into smaller spaces of soil particles or travel
larger distances before becoming trapped in the soil matrix. Soil microorganisms
arecapableofabsorbinganddegradingthereleasednanoparticles(Wiesneretal.
2006
).RiceUniversity'sCentreofBiologicalandEnvironmentalNanotechnology
Studies deduced that nanoparticles tend to bind to contaminating substances like
cadmium and petrochemicals already present in the environment. This means that
nanoparticlesactasacarrierofpollutantstogroundwaterresources(Colvin
2002
).
Thenanomaterials(ZVI)thatareusedinpollutantremediationmusttravelthrough
soil; as they move through the soil it is likely that they interact with various soil
constituentsin(Greg
2004
; Zhang
2003
). Another confounding factor when study-
ing the fate of ENPs in soil is that natural nanoparticles are also present that could
distort test results of the ENPs targeted for study. Clearly, much more work is
needed to elucidate the transport mechanisms for ENPs in the environment.
5
Toxicity of the ENPs
As yet, few studies have been performed that adequately address how toxic the
ENPsmaybe.Wesummarizebelow,andinTable
5
and Fig.
3
the results of the few
studies that have been performed to test the toxicity of the ENPs. The organisms
tested to date include microbes, such as bacteria, protozoans, invertebrates, and
nematodes, earthworms, fish and mammals.
5.1
Microbes
5.1.1
Bacteria
Escherichia coli
and
Bacillus subtilis
have been used as model organisms to test the
toxicity of pristine nano C
60
. Results indicate that the minimum inhibitory concen-
tration(MIC)ofnanoC
60
for
E. coli
ismuchless(0.5-1.0mg/L)thanfor
B. subtilis
(1.5-3.0mg/L).Minimumbactericidalconcentration(MBC)valuesfor
E. coli
and
B. subtilis
ranged from 1.5 to 3 mg/L and 2-4 mg/L, respectively (Table
5
).
Comparingthetoxicityofnanoformswithotherbulkmaterialslikecarboxyfuller-
eneandbenzenehaveshownthatthenano-C
60
toxicity is slightly higher. Bacteria
also appear to associate with nano-C
60
, and repeated washing could not remove it
frombacterialcells(Lyonetal.
2005
).
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