Agriculture Reference
In-Depth Information
properties of ENMs have a pronounced impact on the stability of ENMs in the
environment and consequently their toxicity to the biological systems (Yang
et al.
2009
; Simon-Deckers et al.
2009
). Previous studies including our own
research indicated that surface coating and surface charge strongly affect the
phytotoxicity of ENMs. According to our preliminary data, polyvinylpyrrolidone
or PVP-coated AgNPs appeared more toxic to plants than citrate-coated AgNPs,
possibly because that PVP-coated AgNPs are more stable in solutions than citrate-
coated AgNPs (Tejamaya et al.
2012
).
The USEPA currently organizes ENMs into four categories according to their
composition and structures: carbonaceous NMs, metallic NMs, dendrimers, and
composites. Carbonaceous NMs are the most abundant ENMs and primarily consist
of fullerenes and nanotubes. Metallic NMs include both elemental metallic NMs
(e.g., Au, Ag) and metal oxide NMs (e.g., TiO
2
, CeO
2
, ZnO). Dendrimers are
spheroid or globular nanostructures used in different industries deriving mainly
from its large voids inside and versatile functional groups on the surface.
Nanocomposites are combinations of different NMs or NMs with larger, bulk-
type materials. These materials are often added to auto parts and packaging
materials to enhance mechanical and thermal properties. ENMs with the most
agricultural relevance are primarily from the first two categories: carbonaceous
NMs and metallic NMs. The chapter will focus on four ENMs with the most
agriculture significance: multi-walled carbon nanotubes (MWCNTs), AgNPs, tita-
nium dioxide nanoparticles (TiO
2
NPs), and cerium oxide nanoparticles (CeO
2
NPs).
14.3
Impact of Engineered Nanomaterials on Agricultural
Crops
The impact of ENMs on agricultural crops was affected by a suite of factors such as
the properties and concentrations of ENMs, plant species, presence of dispersants
(e.g., surfactants or natural organic matters), and growth media. As a result, the
reported impact of ENMs on agricultural crops varied dramatically from their
enhancive impact to plant growth to inconsequential impact and inhibitive effect
(Ma et al.
2010a
,
b
; Remedios et al.
2012
). More details on the phyto-effect of
ENMs will be presented below. Again, due to the large body of information on the
interactions of ENMs with plants, the discussion will focus only on the four ENMs
most relevant to agricultural business.
14.3.1 Phyto-Effect of Multi-Walled Carbon Nanotubes
The impact of CNTs on plants varied from whether the CNT contained only one
layer of graphene sheet (SWCNTs) or more than one layer of the graphene sheet
