All the results noted above, for different projects, reject
the notion of ‘one size fits all’ implied in statements which
claim that nanoparticles are good for mankind because ‘they
help to increase agricultural production’. The lesson to be
learnt is that ‘just as a few swallows do not make summer’, a
few supportive research findings should not lead to euphoria
in the minds of those who may benefit from such revelations.
Corroboration of results using different methods may help to
remove any doubts about the authenticity of the results. The
above cautionary statements are not meant to demean or
discredit the findings of many research groups but rather to
encourage more research in a very crucial area, namely
exploiting the benefits of nanotechnology for better living
conditions for the world population of humans.
7 Phytoremediation
and Nanophytoremediation of nano-TiO 2
Soil and water pollution by ‘heavy metals’ is a problem that
has engaged and continues to engage the attention of many
research organizations globally. Among the light metals,
sodium is very much part of our daily lives in the form of
sodium chloride or table salt. This ubiquitous white crystalline compound has beneficial and non-beneficial properties. The latter is often highlighted because ‘high blood
pressure’ is attributed to high levels of sodium in the
bloodstreams of persons having this condition. However,
sufficient amounts of ions of sodium and chloride are also
very useful as an ingredient of ‘mouth wash and gargle’ for
reducing oral infections. Likewise ‘heavy metals’ also have
positive and negative features concerning their usages. In the
light of the above few remarks, about just one light element,
it is noted that titanium is on the borderline between light
and heavy metals in terms of the classification based on
density and atomic number, namely that heavy metal should
have a density of 5 g cm
−3 and an atomic number greater
than 23. Titanium has atomic number 22 and a density of
4.5 g cm
−3 . On this basis, titanium is said to be on the
borderline between light and heavy metals. In this chapter,
titanium metal is not the subject of discussion; titanium
dioxide in its nanoform is the focus. However, some aspects
of titanium would be useful in understanding the properties
of Ti(IV) which is the oxidation state of titanium in titanium
dioxide.
The electronic configuration of the element Ti is: [Ar]
3d
2 4s
2 . On the other hand, Ti(IV) has the electronic configuration of [Ar]3d
0 4s
0 . In electronic terms, this is a very
stable electronic structure, being that of an inert element,
namely argon. This implies that it would be energetically
unfavourable to add or remove electrons from Ti in oxidation state IV. This, in turn, implies that oxidation or
reduction will not occur readily. Stated differently, it could
be expected that Ti(IV)oxide, that is, titanium dioxide should
not be very reactive. The relatively large number of ‘safe’
uses or applications of titanium (IV) dioxide in macro- and
nanoforms, may be taken as indirect testimony to this simplistic analysis. Two applications in particular, namely the
addition of nanotitanium dioxide to foods (Ma et al. 2019)
and its inclusion in denture products (Alirahlah et al. 2018)
over many years without any reports of adverse effects,
suggests that nanotitanium is not reactive in these instances.
However, this is not to be interpreted that nanotitanium
dioxide is not toxic to humans.
7.1 Effect of Concentration of Toxicity
and the Role of Phytoremediation
One should be guided by the basic tenet of toxicology as
enunciated some 500 years ago by Paracelsus, a Swiss
physician and a chemist: ‘All things are poison and nothing
is without poison’. Since then this has been paraphrased to
read: ‘The dose makes the poison’. This implies that any
substance can be harmful if consumed in very high doses.
Even innocuous water, in exceedingly high doses, can be a
problem for the human body.
Faraji and Sepehri (2018) investigated the effect of adding n-TiO 2 on stress caused by presence of Cd. They used
n-TiO 2 at concentrations of 0, 500, 1000 and 2000 mg l
−1 in
the presence of sodium nitroprusside (SNP) to determine the
effect of Cd (as 0, and 100 mM CdCl 2 ) on germination and
growth of wheat seeds and seedlings. They found that the
sue of the pair of n-TiO 2 and SNP working in concert
reduced the stress due to Cd and thus promoted germination
and growth of wheat seeds and seedlings, respectively.
In the light of the information of the background given
above, it has to be conceded that the addition of large
quantities of nanomaterial to soil may disrupt the microbial
populations which serve desirable functions in soil conditioning. On the assumption that it is unnatural for high
concentrations of nanoparticles to be in the soil as pollutants,
plants have been used to uptake the nanoparticles of titanium
dioxide employing a strategy which has been described as
nanophytoremediation. Prior to the advent of nonophytoremediation, phytoremediation was in vogue some 50 years
ago for removal of pollutants from soil using selected plants
growing in the locality of the pollution (Judy et al. 2016) or
invasive plants from outside the site of the pollution (Prabakaran et al. 2019). The latter are generally viewed as being
destructive to established plants. Phytoremediation is a green
technology for removing pollutants from contaminated soil.
It has been classified, by those working in the field, into the
following six types:
80
K. G. Moodley and V. Arumugam
the notion of ‘one size fits all’ implied in statements which
claim that nanoparticles are good for mankind because ‘they
help to increase agricultural production’. The lesson to be
learnt is that ‘just as a few swallows do not make summer’, a
few supportive research findings should not lead to euphoria
in the minds of those who may benefit from such revelations.
Corroboration of results using different methods may help to
remove any doubts about the authenticity of the results. The
above cautionary statements are not meant to demean or
discredit the findings of many research groups but rather to
encourage more research in a very crucial area, namely
exploiting the benefits of nanotechnology for better living
conditions for the world population of humans.
7 Phytoremediation
and Nanophytoremediation of nano-TiO 2
Soil and water pollution by ‘heavy metals’ is a problem that
has engaged and continues to engage the attention of many
research organizations globally. Among the light metals,
sodium is very much part of our daily lives in the form of
sodium chloride or table salt. This ubiquitous white crystalline compound has beneficial and non-beneficial properties. The latter is often highlighted because ‘high blood
pressure’ is attributed to high levels of sodium in the
bloodstreams of persons having this condition. However,
sufficient amounts of ions of sodium and chloride are also
very useful as an ingredient of ‘mouth wash and gargle’ for
reducing oral infections. Likewise ‘heavy metals’ also have
positive and negative features concerning their usages. In the
light of the above few remarks, about just one light element,
it is noted that titanium is on the borderline between light
and heavy metals in terms of the classification based on
density and atomic number, namely that heavy metal should
have a density of 5 g cm
−3 and an atomic number greater
than 23. Titanium has atomic number 22 and a density of
4.5 g cm
−3 . On this basis, titanium is said to be on the
borderline between light and heavy metals. In this chapter,
titanium metal is not the subject of discussion; titanium
dioxide in its nanoform is the focus. However, some aspects
of titanium would be useful in understanding the properties
of Ti(IV) which is the oxidation state of titanium in titanium
dioxide.
The electronic configuration of the element Ti is: [Ar]
3d
2 4s
2 . On the other hand, Ti(IV) has the electronic configuration of [Ar]3d
0 4s
0 . In electronic terms, this is a very
stable electronic structure, being that of an inert element,
namely argon. This implies that it would be energetically
unfavourable to add or remove electrons from Ti in oxidation state IV. This, in turn, implies that oxidation or
reduction will not occur readily. Stated differently, it could
be expected that Ti(IV)oxide, that is, titanium dioxide should
not be very reactive. The relatively large number of ‘safe’
uses or applications of titanium (IV) dioxide in macro- and
nanoforms, may be taken as indirect testimony to this simplistic analysis. Two applications in particular, namely the
addition of nanotitanium dioxide to foods (Ma et al. 2019)
and its inclusion in denture products (Alirahlah et al. 2018)
over many years without any reports of adverse effects,
suggests that nanotitanium is not reactive in these instances.
However, this is not to be interpreted that nanotitanium
dioxide is not toxic to humans.
7.1 Effect of Concentration of Toxicity
and the Role of Phytoremediation
One should be guided by the basic tenet of toxicology as
enunciated some 500 years ago by Paracelsus, a Swiss
physician and a chemist: ‘All things are poison and nothing
is without poison’. Since then this has been paraphrased to
read: ‘The dose makes the poison’. This implies that any
substance can be harmful if consumed in very high doses.
Even innocuous water, in exceedingly high doses, can be a
problem for the human body.
Faraji and Sepehri (2018) investigated the effect of adding n-TiO 2 on stress caused by presence of Cd. They used
n-TiO 2 at concentrations of 0, 500, 1000 and 2000 mg l
−1 in
the presence of sodium nitroprusside (SNP) to determine the
effect of Cd (as 0, and 100 mM CdCl 2 ) on germination and
growth of wheat seeds and seedlings. They found that the
sue of the pair of n-TiO 2 and SNP working in concert
reduced the stress due to Cd and thus promoted germination
and growth of wheat seeds and seedlings, respectively.
In the light of the information of the background given
above, it has to be conceded that the addition of large
quantities of nanomaterial to soil may disrupt the microbial
populations which serve desirable functions in soil conditioning. On the assumption that it is unnatural for high
concentrations of nanoparticles to be in the soil as pollutants,
plants have been used to uptake the nanoparticles of titanium
dioxide employing a strategy which has been described as
nanophytoremediation. Prior to the advent of nonophytoremediation, phytoremediation was in vogue some 50 years
ago for removal of pollutants from soil using selected plants
growing in the locality of the pollution (Judy et al. 2016) or
invasive plants from outside the site of the pollution (Prabakaran et al. 2019). The latter are generally viewed as being
destructive to established plants. Phytoremediation is a green
technology for removing pollutants from contaminated soil.
It has been classified, by those working in the field, into the
following six types:
80
K. G. Moodley and V. Arumugam