Division 1.3 APPLICABILITY OF THE TEST

This simulation test is applicable to non-volatile or slightly volatile organic substances tested at low concentrations. Using flasks open to the atmosphere (e.g. cotton wool plugged), substances with Henry’s law constants less than about 1 Pa·m³/mol (approx. 10^–5 atm·m³/mol) can be regarded as non-volatile in practice. Using closed flasks with a headspace, it is possible to test slightly volatile substances (with Henry’s law constants < 100 Pa·m³/mol or < 10^–3 atm·m³/mol) without losses from the test system. Loss of ¹⁴C-labelled substances may occur, if the right precautions are not exercised, when the CO₂ is stripped off. In such situations, it may be necessary to trap CO₂ in an internal absorber with alkali or to use an external CO₂ absorber system (direct ¹⁴CO₂ determination; see Appendix 3). For the determination of biodegradation kinetics, the concentrations of the test substance must be below its water solubility. It should be noted, however, that literature values of water solubility may be considerably higher than the solubility of the test substance in natural waters. Optionally, the solubility of especially poorly water-soluble test substances may be established by use of the natural waters being tested.

The method can be used for simulating biodegradation in surface water free of coarse particles (pelagic test) or in turbid surface water which, e.g. might exist near a water/sediment interface (suspended sediment test).