Division 1.4 INFORMATION ON THE TEST SUBSTANCE

An analytical method, with adequate sensitivity for quantification of the substance in the test medium, should be available.

Information on the test substance which may be useful in establishing the test conditions includes the structural formula, purity, water solubility, stability in water and light, pK_a, K_ow, vapour pressure and biodegradability. Water solubility and vapour pressure can be used to calculate Henry’s Law constant, which will indicate if significant losses of the test substance during the test period are likely. This will help indicate whether particular steps to control such losses should be taken. Where information on the solubility and stability of the test substance is uncertain, it is recommended that these be assessed under the conditions of the test, i.e. growth medium, temperature, lighting regime to be used in the test.

When pH control of the test medium is particularly important, e.g. when testing metals or substances which are hydrolytically unstable, the addition of a buffer to the growth medium is recommended (see first paragraph in section 1.7.4). Further guidance for testing substances with physicochemical properties that make them difficult to test is provided in (11).