Agriculture Reference
In-Depth Information
14.4.3 Uptake and Accumulation of Titanium Dioxide
Nanoparticles
Larue et al. (
2012b
) used microparticle-induced X-ray emission coupled with
Rutherford backscattering spectroscopy to quantify absorbed titanium and micro
X-ray fluorescence (uXRF) based on synchrotron radiation to determine the Ti
distribution in the roots and leaves of two agricultural crops: wheat and rapeseed.
They reported that both crop species could uptake and translocate TiO
2
NPs to
leaves after root exposure in hydroponic solutions and higher Ti content was
observed in rapeseed seedlings than wheat seedlings. Distribution of Ti in root
cross sections depended upon NP agglomeration state. These authors further inves-
tigated the impact of TiO
2
NPs
size and crystal structure impact on their uptake and
accumulation by wheat (Larue et al.
2012c
) and reported that TiO
2
NPs smaller than
36 nm were taken up by wheat roots and translocated to aboveground tissues.
TiO
2
NPs larger than 36 nm but smaller than 140 nm still accumulated in wheat
root parenchyma but do not reach stele and do not translocate. NPs above 140 nm
did not associate with wheat roots, likely precipitated to the bottom of growing
containers. Both crystal phases of TiO
2
NPs (anatase and rutile) were taken up by
wheat, and they maintained their phase structure in plant tissues. Jacob et al. (
2013
)
reported that exposure of wheat and beans to nutrient solution containing TiO
2
NPs
as a single source of Ti significantly increased root Ti sorption and uptake.
However, upward translocation was not reported for these two crops. The aggre-
gation state of Ti was not reported, but it is likely that they aggregated to sizes larger
than the reported threshold sizes by Larue et al. (
2012a
,
b
,
c
). Interestingly, these
researchers noticed that the presence of phosphorus significantly decreased the Ti
uptake by plants even though the mechanisms were not discussed.
Servin et al. (
2012
) also investigated the uptake and translocation of TiO
2
NPs by
cucumber with similar techniques as employed by Larue and colleagues, and their
study confirmed the transport of Ti from roots to leaves, and, in particular, they
found high concentrations of Ti in leaf trichomes, suggesting that trichomes are a
possible sink or excretory system for Ti. In consistent with the reports from other
groups, they found no biotransformation of Ti in plant tissues. Noticeably, they
reported that anatase TiO
2
NPs were primarily associated with root tissues and rutile
TiO
2
NPs were primarily associated with leaf tissues and trichome structure,
suggesting that rutile TiO
2
NPs might be easier to transport from roots to shoots
than anatase TiO
2
NPs. In a subsequent study by the same group, however, the
authors reported that both crystal phases of TiO
2
NPs could be transported from
roots to shoots. Using synchrotron-based techniques, these authors verified the
accumulation of TiO
2
NPs in cucumber fruits for the first time for both crystal
phases, suggesting a possible pathway of TiO
2
NPs transfer from soil into food
chain (Servin et al.
2013
). Once again, they confirmed that TiO
2
NPs in plant tissues
did not undergo any chemical reactions. These authors employed FTIR spectros-
copy to analyze the cucumber fruits and found that fruit macromolecules such as the
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