Environmental Engineering Reference
In-Depth Information
substances, their changes in oxidation state, their bioaccumulation, the molecular interactions that they are able to generate,
and other indirect effects. Solubility is important, as it affects the bioavailability of a material. Further transformation of an
NM prior to and after interacting with a biological system has to be considered, because an innocuous material may become
toxic and vice versa [14].
30.2
thE BiosystEm—nanomatErial intEraction
The chemical and physical properties of bulk materials can vary greatly with respect to their nanostructured forms. They may
become toxic and harmful, in contrast to being inert in their macroscopic form. The potential toxicity of NMs has been recog-
nized by several authors [3, 10, 15-22]. A better understanding of the risks associated with specific NMs may reduce environ-
mental damage or adverse health effects to the living beings in an ecosystem [23, 24]. Interpretation of toxicity may be a
complex issue, as sometimes the synthetic methodology may affect the results because the processing of the material may
incorporate additives, surfactants, and solvents that are not completely removed from the final products, especially if their
physical, chemical, and biological interactions are not known in detail. For example, C 60 was initially considered to be toxic,
but later studies indicate that such toxicity was related to residual tetrahydrofuran (THF) used in the processing of the material
[25]. Then, biological activity may depend on other components present in the chemical formulation of the material. Commercial
sources of NMs do not often provide information regarding the synthesis or the use of stabilizing/capping agents, so a careful
characterization a priori is highly recommended.
Interactions between nanostructured materials and biological systems may occur in several ways, being simple or very com-
plex. As the scale of biologically relevant objects such as membrane structures, biomolecules (enzymes, proteins, dNA, RNA,
antibodies), virus, bacteria, or eukaryotic cells is comparable in several kinds of NMs, there exist different unknown potential
levels of complex interactions. Toxicity is a complex event in vivo and currently it is difficult to monitor systemic and
physiological effects in vitro , so most assays determine effects at the cellular level. Most assays oversimplify the events they
measure and are selected because they are cheap, easy to quantify, and reproducible (Fig. 30.5).
Micro
Nano
Molecule
10 -10 m (0.1 nm)
Parasite
10 -2 m
(1 cm)
Fly
Plant cells
DNA
10 -4 m (100 µm)
10 -9 m (1 nm)
Human cells
10 -5 m (10 µm)
Nanoparticles
10 -6 m (1 µm)
Virus
10 -7 m (100 nm)
Bacteria
figurE 30.5
Comparative size scales of nanomaterials and biological systems.
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