Aquatic Toxicity Testing of Sparingly Soluble, Volatile, and Unstable Substances and Interpretation and Use of Data

Aquatic toxicity tests were originally designed for individual compounds that are soluble and stable in water. For sparingly soluble substances that are not toxic at the solubility limit, the issue is whether tests should be performed with insoluble test substance present. Based on a literature evaluation of the physiology of uptake, it was concluded that only the dissolved fraction is available for uptake and that the insoluble test substance may introduce artifacts that aggravate data interpretation. Therefore, toxicity tests should be conducted only up to the solubility limit. Testing of volatile, unstable, or adsorptive substances is complicated by the ability to keep exposure concentrations relatively constant. For these, appropriate test protocols including adequate design of the dosing systems must be employed. For test medium preparation, physical methods and, where necessary, use of low concentrations of certain solvents are recommended to support handling and speed of dissolution. However, recommendation is made against the use of dispersants. Water-accommodated fractions are recommended as one approach for dosing multicomponent substances. Interpretation of observed effects depends on appropriate test medium pre- paration, correct measurement and expression of exposure levels, and differentiation of true toxicity from indirect physical effects of the substance, or the toxicity of impurities.