45
filtration should be also applied to personal protective equipment. Another point
need to be considered is the case of leakage of nanomaterials or chemicals. Since
some products such as baby bottles, pacifiers, and healthcare products containing
nanosilver for antimicrobial activity (Chaudhry 2012) are intended for use by specific groups such as children and other vulnerable groups, the exposure assessment
for these groups is also an urgent need. Although scarce, evidence from animal studies suggests that some nanoparticles might be toxic to vulnerable subgroups, such
as fetuses. For instance, mice treated with titanium dioxide nanoparticles of 35 nm
size have shown to have smaller uteri and smaller fetuses than untreated control
after pregnant mice had been injected intravenously. Also nanoparticles were found
in the placenta, fetal liver, and fetal brain (Yamashita et al. 2011).
Since the data are limited, systematic data collection of short-term and long-term
exposure, manufacturing conditions, level of production, industrial applications,
consumer products, and environmental fate and distribution is an urgent need
(Hansen 2012).
However, there is no consensus on the best metric in terms of risk assessment; it
has been agreed that comprehensive investigation should be performed to express
nanomaterial in a metric such as number, surface area, or mass. Seaton et al. have
discussed which metric is the most suitable for human exposure to nanoparticles
(Seaton et al. 2010). The conventional dose metric is based on gravimetric measurements. For nanoparticles, it seems that particle number is more proper than particle
mass. However, if particles are not uniform in terms of size, it will be complicated
to compare concentrations.
It has been observed that there is a relation between toxicological response and
dose by mass for some materials such as C60 and carbon nanotubes. However, it has
been observed that mass concentration is not the most significant metric of exposure
assessment. Owing to the lack of information related to the mechanism of nanoparticle actions and technical deficiencies, providing a suitable metric is difficult
(Poland 2012). Besides mass-dependent toxicity, studies have shown that physical
and chemical properties might also have toxicological effects (Loft 2012). It is recommended that the surface area of low-soluble nanomaterials is a better indicator of
inflammation (Howard 2012). It has been claimed that particle number was the best
metric for risk assessment while the number of functional groups has been suggested in others. The reason for varied metric suggested is the lack of information
about nanomaterials and methods used. Also there is considerable debate about
whether the current health and safety protocols, guidelines, animal models are feasible to make risk assessment for human (Kearns 2012).
It was suggested that case-by-case risk assessment should be carried out in order
to take specific properties of specific nanomaterials into account (Kobe 2012).
However, nano world has a large population in terms of structure, material, sizes,
and physical and chemical variety, etc. All these parameters should be considered
for risk assessment. Each of these parameters and the interactions between them
make case-by-case risk assessment almost impossible unless the parameter determining outcome is not fully clear. Thus renewed methods and tools are necessary
for assessment of potential risk of nanomaterials. Unfortunately, such detailed
2 Nanomaterials and Human Health
filtration should be also applied to personal protective equipment. Another point
need to be considered is the case of leakage of nanomaterials or chemicals. Since
some products such as baby bottles, pacifiers, and healthcare products containing
nanosilver for antimicrobial activity (Chaudhry 2012) are intended for use by specific groups such as children and other vulnerable groups, the exposure assessment
for these groups is also an urgent need. Although scarce, evidence from animal studies suggests that some nanoparticles might be toxic to vulnerable subgroups, such
as fetuses. For instance, mice treated with titanium dioxide nanoparticles of 35 nm
size have shown to have smaller uteri and smaller fetuses than untreated control
after pregnant mice had been injected intravenously. Also nanoparticles were found
in the placenta, fetal liver, and fetal brain (Yamashita et al. 2011).
Since the data are limited, systematic data collection of short-term and long-term
exposure, manufacturing conditions, level of production, industrial applications,
consumer products, and environmental fate and distribution is an urgent need
(Hansen 2012).
However, there is no consensus on the best metric in terms of risk assessment; it
has been agreed that comprehensive investigation should be performed to express
nanomaterial in a metric such as number, surface area, or mass. Seaton et al. have
discussed which metric is the most suitable for human exposure to nanoparticles
(Seaton et al. 2010). The conventional dose metric is based on gravimetric measurements. For nanoparticles, it seems that particle number is more proper than particle
mass. However, if particles are not uniform in terms of size, it will be complicated
to compare concentrations.
It has been observed that there is a relation between toxicological response and
dose by mass for some materials such as C60 and carbon nanotubes. However, it has
been observed that mass concentration is not the most significant metric of exposure
assessment. Owing to the lack of information related to the mechanism of nanoparticle actions and technical deficiencies, providing a suitable metric is difficult
(Poland 2012). Besides mass-dependent toxicity, studies have shown that physical
and chemical properties might also have toxicological effects (Loft 2012). It is recommended that the surface area of low-soluble nanomaterials is a better indicator of
inflammation (Howard 2012). It has been claimed that particle number was the best
metric for risk assessment while the number of functional groups has been suggested in others. The reason for varied metric suggested is the lack of information
about nanomaterials and methods used. Also there is considerable debate about
whether the current health and safety protocols, guidelines, animal models are feasible to make risk assessment for human (Kearns 2012).
It was suggested that case-by-case risk assessment should be carried out in order
to take specific properties of specific nanomaterials into account (Kobe 2012).
However, nano world has a large population in terms of structure, material, sizes,
and physical and chemical variety, etc. All these parameters should be considered
for risk assessment. Each of these parameters and the interactions between them
make case-by-case risk assessment almost impossible unless the parameter determining outcome is not fully clear. Thus renewed methods and tools are necessary
for assessment of potential risk of nanomaterials. Unfortunately, such detailed
2 Nanomaterials and Human Health