Trifluralin is degraded steadily under aerobic conditions. No major metabolites are formed. Up to seven minor metabolites at levels 4.6% AR each have been identified. Several other minor components were also seen but these did not exceed 7.9% AR in total and were not identified. Degradation proceeds via three competing pathways, i.e. oxidative dealkylation of N-propyl and reduction of nitro groups to form TR-2 and TR-5, dimeric condensation to form azoxy-benzene compounds such as TR-28, and cyclisation to form benzimidazoles such as TR-11, TR-13 and TR-15, with ultimate incorporation into the soil structure and mineralisation to carbon dioxide. NER levels increased to between 33.5 and 54.1% AR by 364 days and was mostly associated with the humin soil fraction in the majority of the soils. The level of evolved carbon dioxide is estimated to be between 18.5 and 32% AR by 364 days. Some volatilisation of trifluralin from soil following incorporation occurred, but this was not significant at <10% AR over the study period (364 days).