Biomedical Engineering Reference
In-Depth Information
PECs of nano-Ag, nano-TiO
2
, and nano-ZnO in sewage treatment effluents
could pose a risk for aquatic receptors. At the same time, it was admitted that
prediction of toxicological risk is complicated because of the lack of reliable
ecotoxicity data, especially for the nano-Ag and nano-ZnO.
Recently, many researches have dealt with silver contamination [27-36]. As
mentioned above, the antimicrobial effect of nanosilver is already exploited
in washing machines, and in a vast assortment of household products,
including wound dressing and even footwear. The increased use of nanosil-
ver has been the subject of many debates, especially for the environmental
defense community [28], concerning its effects on soil (or sediment) microbes
as well as on the biomass in wastewater treatment plants [29]. However, a
study conducted on nanosilver fate suggests that this NM may be detoxi-
fied when present in wastewater, by transformation into an innocuous form
(Ag
2
S) [36]. Still, fate issues remain to be identified for other NMs. Moreover,
it is not known if the biosolids coming from wastewater treatment plants
will exert toxic effects when dispersed on surface soil. The geochemical
cycles of carbon and nitrogen are largely dependent on microbial activity
and it has been reported that bacteria such as nitrifiers and denitrifiers are
highly sensitive to xenobiotics [31,37]. The possible effect of nanosilver act-
ing as a mutagen on the genetic diversity of exposed microbial populations
has been investigated, suggesting that nanosilver would influence neither
the genetic diversity nor antibiotic resistance, at least in a marine sediment
environment [32,33]. Because these results were obtained from short-term
exposure assays, the chronic exposure effects remain to be verified.
Likewise, the presence of carbonaceous or organic NP in industrial efflu-
ents and in leachates coming from landfill sites has been suspected to have an
impact on the aquatic environment. On the basis of mathematical modeling,
a recent study predicted that manufactured carbon nanoparticles (MCNPs)
would not contribute significantly to toxicity or to transport of cocontaminants
because the MCNPs should remain in a small fraction compared with black
carbon NP that resulted from other human activities (coal combustion) or even
from natural sources such as forest fires [38].
Nanotechnology has also been used in the defense sector for several appli-
cations, for example, using CNTs for various purposes, including smokes,
fogs, and obscurants [40-41]. Following the unintentional release of NMs
into the environment during their production, testing, and training activi-
ties, a series of environmental (transport, toxicity, and fate) studies have been
initiated [41].
Finally, very few studies have addressed the issue of particle emission
from coated materials. Significant transfer to the atmosphere takes place
when the surfaces coated by nano-TiO
2
are eroded by wind, UV light, or
direct contact by the users; therefore, particle emission should be evaluated
for materials coated with nano-TiO
2
[43]. Studies on surface preparation and
potential release of NMs from functional clothes and nanocomposite filters
are also recommended [43].
