exposure medium. The following modifications have been proposed by Hund-Rinke
et al. (2016) for maintaining (more) constant exposure conditions in test systems:
• Conduct the OECD TG 202—acute immobilization of Daphnia magna test
(OECD 2004) at pH values enabling more stable dispersions of nanomaterials
and use a growth medium with very low ionic strength, e.g., very soft EPA
medium. This medium has been shown to allow normal growth and reproduction
of D. magna.
• In the OECD TG 210—fish, early-life stage toxicity test (OECD 2013) with
zebrafish, improve nanomaterial dispersion by using exposure chambers coupled
with water changes every 24 h.
• In tests using spiked soil or sediment, i.e., OECD TG 216—nitrogen transformation test (OECD 2000a); OECD TG 217—carbon transformation test (OECD
2000b); OECD TG 220—enchytraeid reproduction test (OECD 2016a); OECD
TG 222—earthworm reproduction test Eisenia fetida/Eisenia andrei (OECD
2016b); OECD TG 225—sediment-water lumbriculus toxicity test (OECD
2007), add nanomaterials to each replicate, to ensure homogeneity of spiking.
Exceptions can be made for low concentrations, where this modification can be
difficult to implement.
There has been a concern that some OECD test guidelines were not suited for the
detection of toxic effects, in the sense that they would underestimate the potential
toxicity of some nanomaterials. One way this underestimation could occur is by
reduction of the bioavailability of nanomaterials and their transformation products
due to sorption to organic matter or the elevated pH. Underestimation of the toxicity
of nanomaterials can also occur when the duration of the test is too short compared to
the slow transformation of nanomaterials in soil, which can be the source of toxic
chemical species. The following modifications proposed by (Hund-Rinke et al.
2016) may minimize the interference of the nanomaterials with the components of
the test media or the toxicity endpoints:
• OECD TG 201—freshwater alga and cyanobacteria, growth inhibition test
(OECD 2011): the chelating agent EDTA can interfere with metal nanomaterials
and a modified EDTA-free version of the OECD algal medium (OECD-M) for
Raphidocelis subcapitata is proposed.
• For the OECD TG 201 (OECD 2011), it is recommended to measure biomass by
determination of in vitro chlorophyll a, instead of optical density and in vivo
fluorescence measurements or cell counting by hemocytometry.
• OECD TG 216—nitrogen transformation test (OECD 2000a): for the testing of
ion-releasing metal nanomaterials, the pH of the soils should be at the lower end
of the range accepted according to the test guideline (pH 5.5). It is also proposed
to extend the duration of the test to 56 days, since some nanomaterials only show
effects after ageing, and to include multiple short-term measurements of the
potential ammonium activity, instead of single measurements at the start and
the end of the test.
28 Ecotoxicity of Nanomaterials Used for Remediation
581
et al. (2016) for maintaining (more) constant exposure conditions in test systems:
• Conduct the OECD TG 202—acute immobilization of Daphnia magna test
(OECD 2004) at pH values enabling more stable dispersions of nanomaterials
and use a growth medium with very low ionic strength, e.g., very soft EPA
medium. This medium has been shown to allow normal growth and reproduction
of D. magna.
• In the OECD TG 210—fish, early-life stage toxicity test (OECD 2013) with
zebrafish, improve nanomaterial dispersion by using exposure chambers coupled
with water changes every 24 h.
• In tests using spiked soil or sediment, i.e., OECD TG 216—nitrogen transformation test (OECD 2000a); OECD TG 217—carbon transformation test (OECD
2000b); OECD TG 220—enchytraeid reproduction test (OECD 2016a); OECD
TG 222—earthworm reproduction test Eisenia fetida/Eisenia andrei (OECD
2016b); OECD TG 225—sediment-water lumbriculus toxicity test (OECD
2007), add nanomaterials to each replicate, to ensure homogeneity of spiking.
Exceptions can be made for low concentrations, where this modification can be
difficult to implement.
There has been a concern that some OECD test guidelines were not suited for the
detection of toxic effects, in the sense that they would underestimate the potential
toxicity of some nanomaterials. One way this underestimation could occur is by
reduction of the bioavailability of nanomaterials and their transformation products
due to sorption to organic matter or the elevated pH. Underestimation of the toxicity
of nanomaterials can also occur when the duration of the test is too short compared to
the slow transformation of nanomaterials in soil, which can be the source of toxic
chemical species. The following modifications proposed by (Hund-Rinke et al.
2016) may minimize the interference of the nanomaterials with the components of
the test media or the toxicity endpoints:
• OECD TG 201—freshwater alga and cyanobacteria, growth inhibition test
(OECD 2011): the chelating agent EDTA can interfere with metal nanomaterials
and a modified EDTA-free version of the OECD algal medium (OECD-M) for
Raphidocelis subcapitata is proposed.
• For the OECD TG 201 (OECD 2011), it is recommended to measure biomass by
determination of in vitro chlorophyll a, instead of optical density and in vivo
fluorescence measurements or cell counting by hemocytometry.
• OECD TG 216—nitrogen transformation test (OECD 2000a): for the testing of
ion-releasing metal nanomaterials, the pH of the soils should be at the lower end
of the range accepted according to the test guideline (pH 5.5). It is also proposed
to extend the duration of the test to 56 days, since some nanomaterials only show
effects after ageing, and to include multiple short-term measurements of the
potential ammonium activity, instead of single measurements at the start and
the end of the test.
28 Ecotoxicity of Nanomaterials Used for Remediation
581