28.1 Introduction
Ecotoxicology for evaluating possible negative effects of nanomaterials
(nanoecotoxicology) has some special features; while traditional ecotoxicology
aims at measuring possible negative effects of more or less soluble chemicals or
dissolved elements, nanoecotoxicology aims at measuring the toxicity of particles. In
addition, nanoecotoxicology has its main focus on those effects that are unique to
nano-sized particles, as compared to larger particles or solutes. For this reason,
experiments in nanoecotoxicology usually compare the results with effects caused
by larger particles with similar composition. Another common comparison is that to
the effects of dissolved ions of the same elements constituting the nanoparticles
tested, since many metal-based nanoparticles may partly dissolve, and the toxic
effects can be due to their soluble ionic component. These so-called control treatments are not always easy to establish, or they may result in imperfect comparisons,
as larger-scale particles (often referred to as “bulk material”) may behave quite
differently due to their larger size, and soluble salts of elements found in many
nanomaterials may not exist, or may precipitate during the tests (Kahru and
Dubourguier 2010; Handy et al. 2012a; Sørensen et al. 2015).
Exposing organisms to nanomaterials requires stable suspensions of these
nanomaterials. This is typically obtained through the use of surface-active agents
reducing the attractive forces between particles (Labille and Brant 2010), causing
them to remain suspended in water or other media for a period of time that would
permit absorption or other interactions causing harm to the test organism. These
surfactants may themselves affect the test organisms, and thereby the test outcome.
Control treatments used for comparisons should therefore take this into account.
28.2 Toxicity of Particles
Particle toxicity can be rather different from toxicity of soluble substances or ions.
This is due to the strong barriers against the uptake of particles that most organisms
possess. Ions enter organisms through channels (transporters) in the cell membranes, which can discriminate the uptake based on characteristics like charge
and size. Organic molecules may either pass through uptake channels for organic
nutrients or cross bilayer membranes due to their hydrophobicity. Nanoparticles fit
none of these routes of transport, and are therefore relegated to entering cells by
random “back doors”, like compromised cell membranes or accidental passive
uptake. The size of the particles in question is then of course of major importance
for such uptake. Most nanoparticles used for remediation are found among the
larger nanoparticles, typically >50–200 nm. To put this in perspective, a 20 nm
silver nanoparticle would contain 750,000 atoms (Oughton et al. 2008), each atom
approximately twice as big as, e.g., a zinc ion that enters cells through ion channels.
574
C. Coutris et al.
Ecotoxicology for evaluating possible negative effects of nanomaterials
(nanoecotoxicology) has some special features; while traditional ecotoxicology
aims at measuring possible negative effects of more or less soluble chemicals or
dissolved elements, nanoecotoxicology aims at measuring the toxicity of particles. In
addition, nanoecotoxicology has its main focus on those effects that are unique to
nano-sized particles, as compared to larger particles or solutes. For this reason,
experiments in nanoecotoxicology usually compare the results with effects caused
by larger particles with similar composition. Another common comparison is that to
the effects of dissolved ions of the same elements constituting the nanoparticles
tested, since many metal-based nanoparticles may partly dissolve, and the toxic
effects can be due to their soluble ionic component. These so-called control treatments are not always easy to establish, or they may result in imperfect comparisons,
as larger-scale particles (often referred to as “bulk material”) may behave quite
differently due to their larger size, and soluble salts of elements found in many
nanomaterials may not exist, or may precipitate during the tests (Kahru and
Dubourguier 2010; Handy et al. 2012a; Sørensen et al. 2015).
Exposing organisms to nanomaterials requires stable suspensions of these
nanomaterials. This is typically obtained through the use of surface-active agents
reducing the attractive forces between particles (Labille and Brant 2010), causing
them to remain suspended in water or other media for a period of time that would
permit absorption or other interactions causing harm to the test organism. These
surfactants may themselves affect the test organisms, and thereby the test outcome.
Control treatments used for comparisons should therefore take this into account.
28.2 Toxicity of Particles
Particle toxicity can be rather different from toxicity of soluble substances or ions.
This is due to the strong barriers against the uptake of particles that most organisms
possess. Ions enter organisms through channels (transporters) in the cell membranes, which can discriminate the uptake based on characteristics like charge
and size. Organic molecules may either pass through uptake channels for organic
nutrients or cross bilayer membranes due to their hydrophobicity. Nanoparticles fit
none of these routes of transport, and are therefore relegated to entering cells by
random “back doors”, like compromised cell membranes or accidental passive
uptake. The size of the particles in question is then of course of major importance
for such uptake. Most nanoparticles used for remediation are found among the
larger nanoparticles, typically >50–200 nm. To put this in perspective, a 20 nm
silver nanoparticle would contain 750,000 atoms (Oughton et al. 2008), each atom
approximately twice as big as, e.g., a zinc ion that enters cells through ion channels.
574
C. Coutris et al.