Division 1.4 INFORMATION ON THE TEST SUBSTANCE

Non-labelled or isotope-labelled test substance can be used to measure the rate of transformation although labelled material is preferred. Labelled material is required for studying the pathway of transformation and for establishing a mass balance. ¹⁴C-labelling is recommended, but the use of other isotopes, such as ¹³C, ¹⁵N, ³H, ³²P, may also be useful. As far as possible, the label should be positioned in the most stable part(s) of the molecule^f1. The chemical and/or radiochemical purity of the test substance should be at least 95 %.

Before carrying out a test, the following information about the test substance should be available:

1. (a)

   solubility in water (Method A.6);

2. (b)

   solubility in organic solvents;

3. (c)

   vapour pressure (Method A.4) and Henry's Law constant;

4. (d)

   n-octanol/water partition coefficient (Method A.8);

5. (e)

   adsorption coefficient (K_d, K_f or K_oc, where appropriate) (Method C.18);

6. (f)

   hydrolysis (Method C.7);

7. (g)

   dissociation constant (pK_a) [OECD Guideline 112] (13);

8. (h)

   chemical structure of the test substance and position of the isotope-label(s), if applicable.

Other useful information may include data on toxicity of the test substance to microorganisms, data on ready and/or inherent biodegradability, and data on aerobic and anaerobic transformation in soil.

Analytical methods (including extraction and clean-up methods) for identification and quantification of the test substance and its transformation products in water and in sediment should be available (see section 1.7.2).