Table 2.

Overview of issues and considerations regarding preparation of samples of NMs in exposure media for aquatic ecotoxicity studies. Data from [18].

Issues	Considerations	Recommendations
Method of suspension (e.g., stirring, sonication, grinding, use of solvents and stabilizing agents)	Different suspension methods may significantly alter the NMs per se or the toxic properties of the NM.	Best scientific judgment should be used. If there is evidence of altered toxicity, the effects should be controlled or quantified.
Quantification of media quality (e.g., pH, ionic strength and concentration of dissolved organic matter)	Variability in NM properties (e.g., agglomeration/aggregation) depend significantly on media pH, ionic strength and concentration and form of dissolved organic matter.	Media quality determination should be made at intervals sufficient to determine their variability (both in stock suspension and test media); Physical-chemical characterization of NM should be made in the actual test media (whenever possible).
Physical-chemical characterization	Agglomeration/aggregation is likely to occur, which may alter the exposure due to reduced particle counts, surface area or loss of bulk concentration.	Particle size and/or agglomerate size distribution and material concentration must be assessed at intervals during the tests (or at a minimum immediately prior to and after media renewal). Measurements of particle size distribution using two or more methods are desirable. Characterization should be made in the test media in the presence of test organisms (and food if feeding is required).