Division 1.2 DEFINITIONS

Test substance: any substance, whether the parent compound or relevant transformation products.

Transformation products: all substances resulting from biotic or abiotic transformation reactions of the test substance including CO₂ and products that are in bound residues.

Bound residues:”Bound residues” represent compounds in soil, plant or animal, which persist in the matrix in the form of the parent substance or its metabolite(s)/transformation products after extraction. The extraction method must not substantially change the compounds themselves or the structure of the matrix. The nature of the bond can be clarified in part by matrix-altering extraction methods and sophisticated analytical techniques. To date, for example, covalent ionic and sorptive bonds, as well as entrapments, have been identified in this way. In general, the formation of bound residues reduces the bioaccessibility and the bioavailability significantly (12) [modified from IUPAC 1984 (13)].

Aerobic transformation: reactions occurring in the presence of molecular oxygen (14).

Anaerobic transformation: reactions occurring under exclusion of molecular oxygen (14).

Soil: is a mixture of mineral and organic chemical constituents, the latter containing compounds of high carbon and nitrogen content and of high molecular weights, animated by small (mostly micro-) organisms. Soil may be handled in two states:

1. (a)

   undisturbed, as it has developed with time, in characteristic layers of a variety of soil types;

2. (b)

   disturbed, as it is usually found in arable fields or as occurs when samples are taken by digging and used in this test method (14).

Mineralisation: is the complete degradation of an organic compound to CO₂ and H₂O under aerobic conditions, and CH₄, CO₂ and H₂O under anaerobic conditions. In the context of this test method, when ¹⁴C-labelled compound is used, mineralisation means extensive degradation during which a labelled carbon atom is oxidised with release of the appropriate amount of ¹⁴CO₂ (14).

Half-life: t_0.5, is the time taken for 50% transformation of a test substance when the transformation can be described by first-order kinetics; it is independent of the concentration.

DT₅₀ (Disappearance Time 50): is the time within which the concentration of the test substance is reduced by 50%; it is different from the half-life to.5 when transformation does not follow first order kinetics.

DT₇₅ (Disappearance Time 75): is the time within which the concentration of the test substance is reduced by 75%.

DT₉₀ (Disappearance Time 90): is the time within which the concentration of the test substance is reduced by 90%.