The use of carrier solvents in regulatory aquatic toxicology testing: Practical, statistical and regulatory considerations

•Solvent carriers are discussed in terms of the practical, statistical and regulatory considerations.•Analysis using a database of 141 responses (endpoints) from 73 experiments.•Conditional strategy to control choice is recommended.•Wherever possible a solvent should not be employed or at least the concentration minimized.

Solvents are often used to aid test item preparation in aquatic ecotoxicity experiments. This paper discusses the practical, statistical and regulatory considerations. The selection of the appropriate control (if a solvent is used) for statistical analysis is investigated using a database of 141 responses (endpoints) from 71 experiments. The advantages and disadvantages of basing the statistical analysis of treatment effects to the water control alone, solvent control alone, combined controls, or a conditional strategy of combining controls, when not statistically significantly different, are tested. The latter two approaches are shown to have distinct advantages. It is recommended that this approach continue to be the standard used for regulatory and research aquatic ecotoxicology studies. However, wherever technically feasible a solvent should not be employed or at least the concentration minimized.