Agriculture Reference
In-Depth Information
14.4 Uptake and Accumulation of Engineered
Nanomaterials by Agricultural Crops
In addition to the impact of ENMs on the physiological health of agricultural crops,
their potential accumulation in agricultural crops, especially edible tissues, is an
important consideration because the accumulation of ENMs in these tissues could
become an important pathway for humans exposed to these ENMs. Current knowl-
edge on plant uptake and accumulation of ENMs is limited. The following section
will present a summary of the uptake and accumulation of ENMs by agricultural
crops, focusing again on four of the most agriculturally relevant ENMs.
14.4.1 Uptake and Accumulation of Multi-Walled Carbon
Nanotubes
Lin et al. (
2009
) investigated the uptake and translocation of carbonaceous
nanomaterials by rice plants (
Oryza sativa
) and found that fullerene nC
70
could
be easily taken up by plant roots and transported to plant shoots, but similar
phenomenon was not observed for MWCNTs. With a two-photon excitation micro-
scope, another group of researchers demonstrated that MWCNTs are primarily
adsorbed on root surface as individual and aggregated CNTs even though one or
both ends can pierce through root cap cell walls (Wild and Jones
2009
). Miralles
et al. (
2012
) exposed wheat and alfalfa to 2,560 mg/L of MWCNTs and used
electron microscopic techniques to examine the root tissues for possible internal-
ization, and the results showed no internalization of MWCNT. The accompanying
two-dimensional Raman mapping analysis confirmed that MWCNTs are predom-
inantly adsorbed onto the root surfaces of these plants without significant uptake
and translocation. However, using Fe
3
O
4
-functionalized MWCNTs, they did detect
CNTs in the epidermis of one wheat root tip, suggesting that internalization was
possible but unusual. Some recent studies also showed that MWCNTs could be
taken up by plant roots and transported to shoots. Researchers used photothermal
and photoacoustic techniques to confirm the presence of MWCNTs in tomato
leaves and fruits following their root exposure (Khodakovskaya et al.
2011
).
Other researchers also showed that CNTs entered into plant tissues through roots
and lined up with plant vascular tissues in roots and stems to enhance plant water
uptake (Tripathi et al.
2011
). However, these studies are largely qualitative. Using
14
C-radiolabeled MWCNTs, Larue et al. (
2012a
) demonstrated that MWCNTs
indeed can be taken up by wheat root and transported to leaves; however, the
quantity of MWCNTs accumulated in leaves is extremely small (0.0005 % of the
total MWCNTs added to the system) which did not induce any modifications on
plant photosynthetic activity or oxidative stress responses, suggesting that while
MWCNTs can be potentially taken up by crops, the actual accumulation in plant
tissues and potential transfer to food chain via crop consumption is very low.
