Different types of nanomaterials may affect organisms differently. This is yet
another aspect to consider when choosing how a given nanomaterial is tested with
respect to ecotoxicity. For approval of new nanomaterials or for conducting risk
assessments, a set of minimum three tests with contrasting organisms must be carried
out (Baun et al. 2009).
28.3 Choice of Test Organisms
The choice of test organisms is important for several reasons, and may ultimately
determine the outcome of a testing scheme. First, the choice of organisms must be
relevant for the matrix to be treated. If nanomaterials for treating polluted soil are to
be tested, soil organisms should be chosen. Similarly, freshwater and marine organisms are relevant to their native habitats. Within these three major organism habitats,
there may be some overlap, or it may be relevant to include organisms from two
groups as a remediation situation can affect more than one matrix: treated soil may
lead to nanomaterials ending up in nearby ponds and streams, or streams and rivers
may reach brackish or saltwater habitats.
When choosing test organisms within these major groups, there are at least three
key aspects to consider:
• How contact with the tested material may occur
• Which endpoints are available to assess effects
• Which trophic level the organism belongs to (and how this will affect exposure).
Ecotoxicity can be strongly affected by the mode of exposure. Dermal contact is
commonly affecting an organism less than ingestion or interference with respiratory
organs. This distinction is less relevant for, e.g., microorganisms and plants, but even
for microorganisms and plants that have no intestines, internalization may occur and
cause different toxicity than surface contact. In many cases, the nature of the
organism’s natural habitat and the test design will determine the mode of exposure.
Plants may, e.g., be exposed in an aqueous suspension (seed germination tests and
hydroponic plant cultures), or in solid matrices with more or less resemblance to a
real soil at a site to be treated (El-Temsah and Joner 2012b). While exposure in
aqueous suspensions may say something about the inherent toxicity of the
nanoparticles tested, it will give a far higher exposure than equivalent tests using
soil, and should thus include appropriate exposure estimates when questions of risks
are addressed. When testing toxicity of nanoparticles to plants or soil organisms
using soil as an exposure medium, the choice of a test soil is also decisive, as the
relative amount of different soil constituents may vary considerably and affect both
bioavailability of particles and whether plants or soil organisms thrive in them.
Using a soil with a minimum of soil organic matter will go a long way to ensure
that plants germinate and grow in them, or that earthworms are active in ingesting
576
C. Coutris et al.
another aspect to consider when choosing how a given nanomaterial is tested with
respect to ecotoxicity. For approval of new nanomaterials or for conducting risk
assessments, a set of minimum three tests with contrasting organisms must be carried
out (Baun et al. 2009).
28.3 Choice of Test Organisms
The choice of test organisms is important for several reasons, and may ultimately
determine the outcome of a testing scheme. First, the choice of organisms must be
relevant for the matrix to be treated. If nanomaterials for treating polluted soil are to
be tested, soil organisms should be chosen. Similarly, freshwater and marine organisms are relevant to their native habitats. Within these three major organism habitats,
there may be some overlap, or it may be relevant to include organisms from two
groups as a remediation situation can affect more than one matrix: treated soil may
lead to nanomaterials ending up in nearby ponds and streams, or streams and rivers
may reach brackish or saltwater habitats.
When choosing test organisms within these major groups, there are at least three
key aspects to consider:
• How contact with the tested material may occur
• Which endpoints are available to assess effects
• Which trophic level the organism belongs to (and how this will affect exposure).
Ecotoxicity can be strongly affected by the mode of exposure. Dermal contact is
commonly affecting an organism less than ingestion or interference with respiratory
organs. This distinction is less relevant for, e.g., microorganisms and plants, but even
for microorganisms and plants that have no intestines, internalization may occur and
cause different toxicity than surface contact. In many cases, the nature of the
organism’s natural habitat and the test design will determine the mode of exposure.
Plants may, e.g., be exposed in an aqueous suspension (seed germination tests and
hydroponic plant cultures), or in solid matrices with more or less resemblance to a
real soil at a site to be treated (El-Temsah and Joner 2012b). While exposure in
aqueous suspensions may say something about the inherent toxicity of the
nanoparticles tested, it will give a far higher exposure than equivalent tests using
soil, and should thus include appropriate exposure estimates when questions of risks
are addressed. When testing toxicity of nanoparticles to plants or soil organisms
using soil as an exposure medium, the choice of a test soil is also decisive, as the
relative amount of different soil constituents may vary considerably and affect both
bioavailability of particles and whether plants or soil organisms thrive in them.
Using a soil with a minimum of soil organic matter will go a long way to ensure
that plants germinate and grow in them, or that earthworms are active in ingesting
576
C. Coutris et al.