• phytoextraction (where pollutant moves from root to
leaves which are generally removed and treated as waste
(Eissa et al. 2014)
• phytovolatilization (in which transpiration of the undesirable material occurs through leaves (Islam et al. 2013),
• phytofiltration (filtration by biomass of the plant (Limmer
and Burken 2016),
• phytostabilization (involves a reduction in movement of
pollutants (Mendez and Maier 2008),
• phytodegradation (degradation using enzymes He et al.
2017),
• rhizome degradation (degradation by microbes in the
rhizosphere Ouvrard et al. 2014).
The rhizosphere is the region of soil around the roots
where microbes exist to promote growth.
7.2 Studies on Phytoremediation
On the basis that the presence of titanium dioxide in soil has
not generally stunted growth of plants with some exceptions,
plans are afoot to manufacture nanotitanium specifically for
the protection of plants (Du et al. 2011). To test whether the
new products would be taken up by plants, red clover was
used in conjunction with a nitrogen-fixing bacterium (Moll
et al. 2016). This combination was subjected to contact with
two commercially available nanotitanium dioxides, namely
P25 and E171. A control comprising macrotitanium dioxide
was used as a control. It was found that E171 and the
macrotitanium dioxide suppressed the growth rate of the
bacterium while P25 produced no changes. The effect on red
clover was that the shoot lengths decreased. The analysis
showed that the nanoparticles had clustered to give units
with dimensions greater than 100 nm and thus no longer
nanoparticles (Moll et al. 2016).
As stated earlier, nanotitanium in the soil does not pose a
serious problem to humans or lower life forms. On the
contrary, nanotitanium aids in the uptake of heavy metals
which are considered to be toxic to humans. The following
study (Cai et al 2017) is a good illustration of this role of
nanotitanium dioxide in plants. Since it is known that different types of nano-TiO 2 exhibit different properties, four
types of nano-TiO 2 were chosen, namely anatase, pure rutile,
hydrophilic or hydrophilic rutile and macrorutile. The study
(Cai et al 2017) aimed to assess the effect of the presence of
nanotitanium on the uptake and bioaccumulation of Pb by
one variety rice, namely Oriza sativa from the soil which
had a very high concentration of Pb which associated with
toxic properties. The results showed that nano- and
macroforms of titanium dioxide had the effect of reducing
the uptake of Pb by rice seedlings by up to 80% depending
on the actual type of titanium dioxide used. In another study
in which oxides of Ti and Iron were involved, the effect of
these in their positive and negative forms was assessed for
their influence on the growth of roots of soybean and the
associated soil microbes (Burke et al. 2015). Plants of soybean were grown in a greenhouse while receiving feeds of
nanoparticles over six weeks. Then root growth and amount
of nutrient were measured. For the root, the DNA method
was applied to determine the extent of fungi and microbe
formation. It was found that the charge of the nanoparticle
played a significant part in growths investigated. Overall,
nanoparticles of titanium dioxide proved to be less effective.
8 Summary and Conclusion
As noted in different sections of this chapter, the interaction
of nanotitanium dioxide is influenced by several factors: the
salient ones being a type of nanoparticle, the size, the shape,
coating and microorganisms in the soil surrounding the roots
of plants and toxicity of the nanoparticles towards plants.
Furthermore, other factors such as ionic strength, pH and
composition of the soil, including the presence of natural
organic matter, on which the plants grow, should be taken
into account when assessing the influence of nanoparticles of
TiO 2 on the growth of plants. Regarding the type of
nano-TiO 2 , the source of the macrotitanium dioxide may be
important, that whether it is a pure form of one of the crystal
phases (rutile and anatase) in which TiO 2 exists or as a
mixture of these two forms. The size and shape of the
nanoparticles are crucial as they need to small enough as
well as have a suitable shape for penetrating the cell walls of
plants. It is worth noting that roots of plants have structures
which allow ingress of nutrient matter but block what is
detected to be ‘invasive’ particles. In a simplistic sense, the
nanoparticles also have to contend with microorganisms
which reside in the soil around the roots. It is clear from the
foregoing points about the factors affecting interactions of
nano-TiO 2, that there is much more to learn about the
interactions of nanotitanium dioxide with plants than is
known at present.
Acknowledgements The authors are grateful to the Natural Science
Foundation of Hainan Province (2019RC166, 2019RC110) and
National Natural Science Foundation of China (21965011) for financial
support. Authors also acknowledge Durban University of Technology,
South Africa, and Eskom Holdings, South Africa for financial support.
Dr Vasanthakumar acknowledges the Postdoctoral Funding of Hainan
Province, China.
Interaction of Nano-TiO 2 with Plants: Preparation and Translocation
81
leaves which are generally removed and treated as waste
(Eissa et al. 2014)
• phytovolatilization (in which transpiration of the undesirable material occurs through leaves (Islam et al. 2013),
• phytofiltration (filtration by biomass of the plant (Limmer
and Burken 2016),
• phytostabilization (involves a reduction in movement of
pollutants (Mendez and Maier 2008),
• phytodegradation (degradation using enzymes He et al.
2017),
• rhizome degradation (degradation by microbes in the
rhizosphere Ouvrard et al. 2014).
The rhizosphere is the region of soil around the roots
where microbes exist to promote growth.
7.2 Studies on Phytoremediation
On the basis that the presence of titanium dioxide in soil has
not generally stunted growth of plants with some exceptions,
plans are afoot to manufacture nanotitanium specifically for
the protection of plants (Du et al. 2011). To test whether the
new products would be taken up by plants, red clover was
used in conjunction with a nitrogen-fixing bacterium (Moll
et al. 2016). This combination was subjected to contact with
two commercially available nanotitanium dioxides, namely
P25 and E171. A control comprising macrotitanium dioxide
was used as a control. It was found that E171 and the
macrotitanium dioxide suppressed the growth rate of the
bacterium while P25 produced no changes. The effect on red
clover was that the shoot lengths decreased. The analysis
showed that the nanoparticles had clustered to give units
with dimensions greater than 100 nm and thus no longer
nanoparticles (Moll et al. 2016).
As stated earlier, nanotitanium in the soil does not pose a
serious problem to humans or lower life forms. On the
contrary, nanotitanium aids in the uptake of heavy metals
which are considered to be toxic to humans. The following
study (Cai et al 2017) is a good illustration of this role of
nanotitanium dioxide in plants. Since it is known that different types of nano-TiO 2 exhibit different properties, four
types of nano-TiO 2 were chosen, namely anatase, pure rutile,
hydrophilic or hydrophilic rutile and macrorutile. The study
(Cai et al 2017) aimed to assess the effect of the presence of
nanotitanium on the uptake and bioaccumulation of Pb by
one variety rice, namely Oriza sativa from the soil which
had a very high concentration of Pb which associated with
toxic properties. The results showed that nano- and
macroforms of titanium dioxide had the effect of reducing
the uptake of Pb by rice seedlings by up to 80% depending
on the actual type of titanium dioxide used. In another study
in which oxides of Ti and Iron were involved, the effect of
these in their positive and negative forms was assessed for
their influence on the growth of roots of soybean and the
associated soil microbes (Burke et al. 2015). Plants of soybean were grown in a greenhouse while receiving feeds of
nanoparticles over six weeks. Then root growth and amount
of nutrient were measured. For the root, the DNA method
was applied to determine the extent of fungi and microbe
formation. It was found that the charge of the nanoparticle
played a significant part in growths investigated. Overall,
nanoparticles of titanium dioxide proved to be less effective.
8 Summary and Conclusion
As noted in different sections of this chapter, the interaction
of nanotitanium dioxide is influenced by several factors: the
salient ones being a type of nanoparticle, the size, the shape,
coating and microorganisms in the soil surrounding the roots
of plants and toxicity of the nanoparticles towards plants.
Furthermore, other factors such as ionic strength, pH and
composition of the soil, including the presence of natural
organic matter, on which the plants grow, should be taken
into account when assessing the influence of nanoparticles of
TiO 2 on the growth of plants. Regarding the type of
nano-TiO 2 , the source of the macrotitanium dioxide may be
important, that whether it is a pure form of one of the crystal
phases (rutile and anatase) in which TiO 2 exists or as a
mixture of these two forms. The size and shape of the
nanoparticles are crucial as they need to small enough as
well as have a suitable shape for penetrating the cell walls of
plants. It is worth noting that roots of plants have structures
which allow ingress of nutrient matter but block what is
detected to be ‘invasive’ particles. In a simplistic sense, the
nanoparticles also have to contend with microorganisms
which reside in the soil around the roots. It is clear from the
foregoing points about the factors affecting interactions of
nano-TiO 2, that there is much more to learn about the
interactions of nanotitanium dioxide with plants than is
known at present.
Acknowledgements The authors are grateful to the Natural Science
Foundation of Hainan Province (2019RC166, 2019RC110) and
National Natural Science Foundation of China (21965011) for financial
support. Authors also acknowledge Durban University of Technology,
South Africa, and Eskom Holdings, South Africa for financial support.
Dr Vasanthakumar acknowledges the Postdoctoral Funding of Hainan
Province, China.
Interaction of Nano-TiO 2 with Plants: Preparation and Translocation
81