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Division 1.5 INFORMATION ON THE TEST SUBSTANCE

United Kingdom

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Both radiolabelled and non-labelled test substances can be used in this test. 14C-labelling technique is recommended and labelling should normally be in the most stable part(s) of the molecule (see also section 1.4). For substances containing more than one aromatic ring, one or more carbons in each ring should preferably be 14C-labelled. In addition, one or more carbons on both sides of easily degradable linkages should preferably be 14C-labelled. The chemical and/or radiochemical purity of the test substance should be > 95 %. For radiolabelled substances, a specific activity of approx. 50 μCi/mg (1,85 MBq) or more is preferred in order to facilitate 14C measurements in tests conducted with low initial concentrations. The following information on the test substance should be available:

  • solubility in water [Method A.6],

  • solubility in organic solvent(s) (substances applied with solvent or with low solubility in water),

  • dissociation constant (pKa) if the substance is liable to protonation or deprotonation [OECD TG 112] (5),

  • vapour pressure [Method A.4] and Henry’s law constant,

  • chemical stability in water and in the dark (hydrolysis) [Method C.7].

When poorly water-soluble substances are being tested in seawater, it may also be useful to know the salting out constant (or ‘Setschenow constant’) Ks, which is defined by the expression: log (S/S’) = Ks Cm, where S and S’ are the solubility of the substance in fresh water and seawater, respectively, and Cm is the molar salt concentration.

If the test is carried out as a ‘suspended sediment test’ the following information should also be available:

  • n-octanol/water partition coefficient [Method A.8],

  • adsorption coefficient [Method C.18].

Other useful information may include:

  • environmental concentration, if known or estimated,

  • toxicity of the test substance to microorganisms [Method C.11],

  • ready and/or inherent biodegradability [Methods C.4 A-F, C.12, C.9, OECD TG 302 (5)],

  • aerobic or anaerobic biodegradability in soil and sediment/water transformation studies [Methods C.23, C.24].