Environmental Engineering Reference
In-Depth Information
32
ImplIcatIons of the Use of nanomaterIals
for envIronmental protectIon: challenges
In DesIgnIng envIronmentally relevant
toxIcologIcal experIments
Rute F. Domingos
1
and José P. Pinheiro
2
1
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal
2
Centro de Biomedicina Molecular Estrutural (CBME)/IBB, LA, DQF/FCT, Universidade do Algarve, Faro, Portugal
32.1
IntroDUctIon
Deliberate application of nanomaterials (NMs) for environmental protection could result in intentionally diffuse inputs of these
engineered materials into the environment. The anticipated new or enhanced activity of these NMs will inevitably result in both
new risks and new benefits to human and environmental health.
The highly dynamic behavior of NMs in environmental systems
results in a set of chemical and physical transformations
such as dissolution, and/or size and shape changes, including homo-
(between particles of the same type) and heteroaggregation (between particles of different types), that will greatly affect their fate.
Due to NMs' inherent reactivity, stabilizers are usually added to improve their mobility by protecting the NMs' surface from
unwanted reactions, preventing the interparticle aggregation by charge repulsion and/or steric effects, and also serving as a
diffusion-controlled release carrier. The stabilizer is thus a barrier between the NM and the matrix where it is immersed.
Previously, the stabilizers used were low-molecular organic compounds such as carbonic acids, alcohols, and amides, and
natural polymers like gelatin, gum Arabic, agar-agar, starch, and cellulose [1]. Currently, synthetic polymers are more frequently
employed [2]. Charged polymers are more commonly used since the stabilization they provide is quite effective and yields
relatively stable core-shell entities that work well for their designed purpose. Due to their chemical stability, the commonest
acid groups used in stabilizers are sulfonic (-SO
3
−
) (polystyrene sulfonate (PSS)), carboxylic (-COOH) (like polyacrilic acid
(PAA)), and numerous combinations and variations such as block copolymers, and cross-linked configurations. Uncharged
stabilizers are less used and less relevant for our analysis since they tend to bind metal ions poorly or not at all. These include
polymers like polyvinil pirrolidone (PVP) and polyethylene glycol (PEG) that stabilize the particles mostly by steric effects.
The possible effects of stabilizers on the behavior of NMs showed that complex interactions are possible between several
different processes, affecting their physicochemical properties and consequently their fate. However, most of these interactions
have not yet been examined systematically.
It is vital to predict and validate the different forms of occurrence of nanoscale materials in the environmental compartments,
given that it is most likely that these forms have different mobility, bioavailability, and, consequently, different toxicological
effects.
The rigorous quantification of the dynamic contribution of various possible NM-containing species is extremely
necessary to accomplish this aim. In this chapter, several key questions that underlie the effort to understand how NMs behave
in natural systems and how they may impact the environment will be addressed: (i)
How do the NMs' properties and their
