Civil Engineering Reference
In-Depth Information
metals contained within the QDs core. These heavy metals may include
cadmium, lead, and zinc and are extremely toxic to both mammalian cells
and bacteria. Experiments performed on human cells indicate that cytotox-
icity results from ROS damage to organelles and infl ammation caused by
the release of cytokines. Quantum dots can accumulate in the spleen, liver,
and kidneys in mice, creating localized toxic effects. In microorganisms,
other toxicity mechanisms include growth inhibition, lipid peroxidation,
oxidative stress. In addition to the cellular toxicity caused by the heavy
metal core, some shell materials have also been identifi ed as toxic. Gene
expression studies in algae show that toxic responses to intact QDs differ
signifi cantly from responses to internal ions: in eukaryotic cells, oxidative
stress, damage to nucleic acids contribute to cytotoxicity independently of
the release of internal heavy metal ions from their core. Additionally, QD
toxicity experiments on mice neural cells demonstrate impaired calcium
infl ux and exocytotic mechanisms.
7.3
Lifecycle of nano-enabled structures
Manufactured nanomaterials may be released into the environment over
the entire lifecycle of the structure, from the time of construction, through-
out the use of the structure, and after demolition and disposal. It is impor-
tant to realize that these materials may transform over time via physical,
chemical, or biological processes.
It is important to recognize that much research needs to be conducted to
fi ll in the knowledge gaps regarding aging MNMs in structures. Few studies
currently published have investigated long-term physical and chemical
changes of imbedded MNMs and the associated hazards. For example, if an
MNM is imbedded into a concrete fl oor or pavement, continual traffi c and
abrasion will inevitably cause the release of nanomaterials.
7.3.1 Manufacturing of nanomaterials and
use in construction
One of the common human exposure routes for nanomaterials is through
inhalation. This threat is prevalent largely during the periods of manufac-
turing and construction due to the high levels of airborne or aerosolized
particles. Though unintentional, carbon fullerenes may be aerosolized
during the aqueous suspension process, which might require sonication.
These and other types of nanomaterials can become airborne when exposed
to open air for weighing. Sepiolite nanoclay, which may be used as fi ller in
construction nanocomposites, is lost to the air during mining, transporta-
tion, and the manufacturing process.
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