Determination of soil biodegradation half-lives from simulation testing under aerobic laboratory conditions: a kinetic model approach.

A kinetic model approach for determination of biodegradation half-lives from soil simulation testing is presented. The model describes transformation of the parent compound to metabolites and formation of bound (non-extractable) residues as well as mineralization in soil under aerobic laboratory conditions. Experimental data for several pesticide compounds from various soil simulation tests are used for fitting kinetic rate constants. Formation of bound residues, either from parent or metabolites or from both, can be described by first-order kinetics for all examined compounds. Correlation of kinetic rate constants of primary degradation and formation of bound residues from parent compound suggests a common mechanism, presumably co-metabolic microbial activity, for both processes. Inverse modelling allows for estimation of primary degradation half-life DegT50 instead of disappearance time DT50. Application of the DegT50 approach in PBT assessment might result in a different persistent classification for which the developed model delivers an appropriate evaluation tool.