The environmental fate of paclobutrazol was investigated in a number of laboratory studies using either triazole or methine labelled material. Results of the laboratory aerobic route and rate of degradation carried out at 20, 21 or 25°C are available for six different soils. The major metabolite was identified as (2RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1H- 1,2,4 triazol-1-yl) pentan-3-one (CGA 149907) which peaked at 19% AR after 12 months at 20°C in loam soil. CGA 149907 is degraded in soil, via cleavage of the 1H- 1,2,4-triazole moiety (CGA 71019). 1,2-4 triazole was only observed at a maximum 3% AR. Degradation of 1,2-4 triazole was reported by the Notifier to proceed via CGA 142856 (1,2,4-triazol-1-yl acetic acid, triazole acetic acid) and NOA 457654 (3- hydroxy-1H-1,2,4-triazole, hydroxy triazole). NOA 457654 was identified in its keto form at a low level in a soil column leaching study but was not observed in any of the soil metabolism studies. Several other minor metabolites were observed from the degradation of 14C-triazole labelled paclobutrazol but none were present at greater than 10% AR and probably were present at a maximum of approximately 5%. Unextracted (bound) residues from the 14C-triazole radiolabel increased with time and accounted for up to 37% AR, whilst amounts of CO2 evolved remained low, suggesting that 1,2-4 triazole and/or its degradates are preferentially incorporated into the soil matrix. There were no significant metabolites formed in soil studies from paclobutrazol radiolabelled in the 14C-methine position (maximum of 4% AR). Unextracted (bound) residues accounted for a maximum of 7% AR from the methine radiolabel. Levels of 14CO2 evolved in the 14C-methine study reached a maximum of 12% after 12 months. The Notifier has reported that there is a strong relationship between concentration of active substance applied and degradation rate. The Rapporteur has noted that there appears to be an inverse relationship between pH and degradation rate of paclobutrazol. The Rapporteur considered that the exact relationship between application rate / pH and degradation rate could not be fully elucidated from the data available given the small range of doses tested. Overall the RMS considered the use of mean degradation data to be applicable in the exposure assessments.