Agriculture Reference
In-Depth Information
14.2 Engineered Nanomaterials
As mentioned above, ENMs refer to artificial materials with their size smaller than
100 nm in at least two dimensions. Within the nanoscale, a reduction of the size will
lead to exponential increase of specific surface area, and from the environmental
health point of view, ENMs smaller than 20-30 nm in diameter are the ones of most
concern (Auffan et al.
2009
). For some metallic NMs such as silver nanoparticles
(AgNPs) and zinc oxide nanoparticles (ZnONPs), the increase of specific surface
area results in significant increase of the dissolution rate and markedly change the
interactions of ENMs with surrounding environment (Liu and Hurt
2010
; Reed
et al.
2012
). The altered dissolution rate could either be a boon or a doom to the
agricultural industry. For instance, the rapid dissolution rate of ZnONPs has been
explored to increase the Zn releasing efficiency of Zn fertilizer (Milani et al.
2012
),
but a separate study found that rapid dissolution rate of Zn ion was directly
associated with the enhanced toxicity of ZnONPs (Miao et al.
2010
).
ENMs with similar size but different shape exhibit considerably different optical
properties due to the variations of collective oscillations of a nanoparticle
s free
electrons into resonance, defined as localized surface plasmon resonance (Nehl and
Hafner
2008
). The variation on optical property and other properties such as
physical contact angles with biological systems has direct consequences on their
toxicity to plants. Our previous studies showed that plate-shaped AgNPs are more
hazardous to lettuce growth than wire-shaped AgNPs at the same concentrations
(Fig.
14.1
). Lettuce exposed to plate-shaped AgNPs also showed smaller and less
healthy roots. Due to the
van der Waals
forces, naked ENMs often attract to each
other and aggregate in liquid solutions. As a result, these materials are typically
passivated with different materials to electrostatically or sterically stabilize them in
liquid solutions. Numerous studies have indicated that surface coating materials
dictate the surface chemistry and interactions of ENMs with biological systems
(Albanese et al.
2012
). Evidences are also abundant that these physicochemical
'
2.5
2
1.5
1
Fig. 14.1 Accumulative
biomass of lettuce plants
grown hydroponically in
solutions containing
different shapes of AgNPs.
The AgNPs were coated
with PVP. The reported
values are the average of six
replicates,
n
0.5
0
0
5
10
Days
Control
Plate-shaped AgNPs
Wire-Shaped AgNPs
ΒΌ
6
