Six major use pesticides (Atrazine, Dicamba, Isoproturon, Lindane, Paraquat and Trifluralin) with differing physico-chemical properties were evaluated for the significance of `bound' or non extractable residue formation. Investigations were carried out in purpose-built microcosms where mineralization, volatilisation, `soil water' extractable and organic solvent extractable residues could be quantified. Extractable residues were defined as those accessible by sequential extraction where the solvent used became increasingly non-polar. Dichloromethane was the `harshest' solvent used at the end of the sequential extraction procedure. C-14- labelled volatilised and (CO2)-C-14 fractions were trapped on exit from the microcosm. The pesticides were categorised into 3 classes based on their behaviour. (i) Type A (Atrazine, Lindane and Trifluralin) in which ring degradation was limited as was the formation of non-extractable residues; the remainder of the C-14-activity was found in the extractable fraction. (ii) Type B (Dicamba and Isoproturon) in which approximately 25% of the C-14-activity was mineralised and a large portion was found in the non-extractable fraction after 91 days. Finally, Type C (Paraquat) in which almost all of the C-14-activity was quickly incorporated into the non-extractable fraction. The implications of the data are discussed, with respect to the variability and significance of regulatory aspects of non-extractable residues. (C) 2004 Elsevier Ltd. All rights reserved.