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7.3 Toxicity of Engineered Nanostructures
in Aquatic Environments
7.3.1 Nanotoxicity Investigations in Microalgae
and Microcrustaceans
Toxicity Assays with Pseudokirchneriella subcapitata
Among unicellular green algae used in the risk assessment of nanomaterials and
others chemicals agents (Li et al. 2016), the microalgae Pseudokirchneriella subcapitata (Chlorococcales, ex-Selenastrum capricornutum) is one of the most used
standard organisms in ecotoxicological evaluation (Jonsson and Aoyama 2009;
Machado and Soares 2014) because of its rapid reproduction and cosmopolitan distribution (Meena 2017; Oropesa et al. 2017).
The researchers usually grow this organism in culture medium in accordance
with the methodology recommended by the Organization for Economic Co-operation
and Development (OECD 1984, 2006) and United States Environmental Protection
Agency (USEPA 2002). For the tests, a control (without the test material) and at
least five concentrations of the nanomaterial, arranged in a geometric series, are
selected for the definitive test. The cell density in the inoculum is determined by
absorbance measurements at 750 or 684 nm in a spectrophotometer or in a microplate reader, once absorbance is proportional to the cell concentration. These determinations are conducted at 0, 24, 48, 72, and 96 h, but may be extended for 7 days.
Data are fitted using a linear regression model that generates the angular coefficient,
which gives algae growth rate, expressed as logarithm of absorbance per unit time.
The calculation of the concentration capable of inhibiting algal growth rate by 50%
on a given period (EC50) relies on the relative inhibition of growth rate as a function
of the nanomaterial concentration (Castro et al. 2018; OECD 1984).
The adverse effects of graphene oxide on the growth rate of P. subcapitata were
evaluated giving an EC50-72h equal to 66.60 (60.80–78.43) mg/L (Castro et al.
2018). This value is different from that calculated by Aruoja et al. (2009) for particulate nanomaterials like nano TiO 2 (EC50-72h = 5.83 mg Ti/L) and nano CuO
(EC50-72h = 0.71/ mg Cu/L) to the same algae, indicating a lower toxicity of large
carbon nanostructures than metals nanoparticles. Furthermore, the last authors
showed that the metal toxicity was enhanced in several times when in nanoformulation, comparatively to the bulk formulation (bulk TiO 2 EC50-72h = 35.0 mg Ti/L
and bulk CuO EC50-72h =11.55 mg Cu/L).
Polymeric nanoparticles have potential applications in the development of nanocarriers for delivering active compounds like drugs and pesticides (Lopes et al.
2014; Oliveira et al. 2018). Therefore, polymeric nanoparticles can be used to provide effective pesticide formulations which are less toxic to nontarget organisms
(Chauhan et al. 2017). In this context, Table 7.1 shows the results of a study in
which chitosan nanoparticles were loaded with the herbicide paraquat and added to
P. subcapitata cultures (Grillo et al. 2015). The influence of the aquatic humic
F. F. Pereira et al.
7.3 Toxicity of Engineered Nanostructures
in Aquatic Environments
7.3.1 Nanotoxicity Investigations in Microalgae
and Microcrustaceans
Toxicity Assays with Pseudokirchneriella subcapitata
Among unicellular green algae used in the risk assessment of nanomaterials and
others chemicals agents (Li et al. 2016), the microalgae Pseudokirchneriella subcapitata (Chlorococcales, ex-Selenastrum capricornutum) is one of the most used
standard organisms in ecotoxicological evaluation (Jonsson and Aoyama 2009;
Machado and Soares 2014) because of its rapid reproduction and cosmopolitan distribution (Meena 2017; Oropesa et al. 2017).
The researchers usually grow this organism in culture medium in accordance
with the methodology recommended by the Organization for Economic Co-operation
and Development (OECD 1984, 2006) and United States Environmental Protection
Agency (USEPA 2002). For the tests, a control (without the test material) and at
least five concentrations of the nanomaterial, arranged in a geometric series, are
selected for the definitive test. The cell density in the inoculum is determined by
absorbance measurements at 750 or 684 nm in a spectrophotometer or in a microplate reader, once absorbance is proportional to the cell concentration. These determinations are conducted at 0, 24, 48, 72, and 96 h, but may be extended for 7 days.
Data are fitted using a linear regression model that generates the angular coefficient,
which gives algae growth rate, expressed as logarithm of absorbance per unit time.
The calculation of the concentration capable of inhibiting algal growth rate by 50%
on a given period (EC50) relies on the relative inhibition of growth rate as a function
of the nanomaterial concentration (Castro et al. 2018; OECD 1984).
The adverse effects of graphene oxide on the growth rate of P. subcapitata were
evaluated giving an EC50-72h equal to 66.60 (60.80–78.43) mg/L (Castro et al.
2018). This value is different from that calculated by Aruoja et al. (2009) for particulate nanomaterials like nano TiO 2 (EC50-72h = 5.83 mg Ti/L) and nano CuO
(EC50-72h = 0.71/ mg Cu/L) to the same algae, indicating a lower toxicity of large
carbon nanostructures than metals nanoparticles. Furthermore, the last authors
showed that the metal toxicity was enhanced in several times when in nanoformulation, comparatively to the bulk formulation (bulk TiO 2 EC50-72h = 35.0 mg Ti/L
and bulk CuO EC50-72h =11.55 mg Cu/L).
Polymeric nanoparticles have potential applications in the development of nanocarriers for delivering active compounds like drugs and pesticides (Lopes et al.
2014; Oliveira et al. 2018). Therefore, polymeric nanoparticles can be used to provide effective pesticide formulations which are less toxic to nontarget organisms
(Chauhan et al. 2017). In this context, Table 7.1 shows the results of a study in
which chitosan nanoparticles were loaded with the herbicide paraquat and added to
P. subcapitata cultures (Grillo et al. 2015). The influence of the aquatic humic
F. F. Pereira et al.