Agriculture Reference
In-Depth Information
exposure concentration has not been established. Growing conditions, exposure
methods, and plant species also affect the interactions of ENMs with agricultural
crops. It appeared that natural soil reduced the negative (maybe positive as well)
effect of ENMs on agricultural crops and foliar exposure seemed to be less
detrimental to plants than root exposure. It could be argued that the differential
responses of foliar and root exposure may just be an age issue of plants. When
plants are ready to be foliar treated, they have grown stronger and more effective to
defend the hazardous effects of ENMs compared with most root exposure studies:
plants were exposed to ENMs at the beginning stage of their life cycle (e.g., seed
germination stage). Further investigation is needed to confirm this hypothesis. In
addition, the investigations on the ENM impact of crop development are predom-
inantly based on short-term studies, leaving the long-term impact of ENMs at
environmentally relevant concentrations still unaddressed.
The uptake and accumulation of ENMs by agricultural crops appeared to be
certain. But the extent of accumulation and the subsequent distribution and stability
of ENMs in plant tissues after plant uptake appeared to vary greatly between
different ENMs. Even though MWCNTs can be taken up by plant roots and
translocated to shoots, the upward transport and the actual accumulation of
MWCNTs in aboveground tissues seem to be very limited and are unlikely to
cause any serious concern on food safety. AgNPs uptake and accumulation are
still controversial, and more mechanistic study to distinguish AgNPs vs. Ag ion
uptake needs to be conducted. One thing seems to be certain that irrespective of the
exposure form of Ag, many plants are capable of storing AgNPs in their tissues.
Plant uptake, transport, and accumulation of TiO
2
NPs are broadly reported and
could be a concern considering that several studies confirmed their detection in the
edible tissues. The uptake and accumulation seemed to be mainly governed by their
size, and both crystal phases of TiO
2
NPs can be accumulated by agricultural crops.
The upward transport of these two different crystal structures may differ, but more
studies seem to be needed. CeO
2
NPs can also be taken up and accumulated in plant
tissues in most conditions, but the fate (e.g., maintain the nanoparticle structure or
undergo chemical reactions) following their uptake is not fully understood. The
mechanisms regarding the entrance of ENMs in plant tissues are still poorly
understood.
ENMs also affect the agricultural systems through their alteration of the uptake
and accumulation of coexisting environmental chemicals and necessary macronu-
trients and micronutrients. Studies on these areas are severely lacking. In summary,
ENMs have profound impact on agricultural crops. Even though some insights have
been obtained, substantial efforts are needed to understand the full implications of
ENMs on agricultural health.
Acknowledgement Dr. Ma acknowledge the financial support of the USDA-AFRI (#2011-
67006-30181) and (#2012-67005-19585).
