Environmental Engineering Reference
In-Depth Information
Regarding this last point, an often ignored aspect is that when an NM sticks to an organism interface, it starts dissolving, yielding
a tremendously high local metal ion concentration. This is ascribed not only for cell walls or membranes but also for fish gills,
mollusk filtration mechanisms, and digestive tubes. The potential damage of highly concentrated point sources cannot be
neglected, especially when considering chronic effects on the organism's health.
32.3
recommenDatIons/gUIDelInes
In this section, it is assumed that the metal-containing NMs and their uses are known, thus defining the environmental
compartment where they are ultimately released. A proper literature survey should then be performed to choose the relevant test
organism(s). The guidelines to be followed for an environmentally relevant toxicological experimental protocol for metal-
containing NMs are based on a four-tier approach (Fig. 32.3):
1. Exposure solution. The physicochemical conditions of the exposure solution should mimic as far as possible those of the
environmental compartment. Care should be taken to avoid the starvation of the test organism. In the speciation and
toxicological assays, the following parameters need to be either fixed or varied in a controlled way: temperature, pH,
ionic strength, light, other metals, and organic ligands including NOM. In certain specific cases, other parameters might
also be important, for example, dissolved oxygen.
2. Speciation. These studies should be used to define the experimental conditions for toxicological assays, whether for
short-term (acute effects) or long-term (chronic effects) experiments. The most important parameter that needs to be
defined is the NM concentration. The lowest NM concentration should always coincide with the detection limit of the
available techniques since they are likely larger than their environmental concentration. The upper limit should be chosen
by analogy to the metal ion concentrations used in studies of acute effects. To accomplish this aim, it is necessary to mon-
itor the following aspects in the exposure media during the relevant time period: (i) NM dissolution and (dis)aggregation,
(ii) free metal concentration, and (iii) NM interaction with other components of the matrix.
Tier 1.
Exposure solution
• Dissolution
• (Dis)aggregation
• Free metal
concentration
• Interaction with the
matrix
Tier 2.
Speciation
• Control
• NMs contaminated
solution
• Metal (salt)
contaminated
solution
Tier 3.
Toxicological assays
• Interaction NMs vs.
Organism
• Internalization
• Specific
toxicological effects
Biological response
evaluation
Tier 4.
fIgUre 32.3 Schematic outline of the underlying structure of an environmentally relevant toxicological experimental protocol for
metal-containing NMs.
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