Microbial breakdown of aclonifen leads to the formation of non-extractable soil bound residues, which accounted for a maximum of 41 to 64 % of the applied aclonifen, and ultimately to carbon dioxide with very few intermediate products observed. Levels of carbon dioxide accounted for a maximum of 5 % of the applied radioactivity by the end of the aerobic studies. In older studies extractable degradation products were characterised as being multiple polar components. In more recent studies, these extractable degradation products were shown to be the result of binding to aqueous soluble soil colloids. Aclonifen and its degradation products formed in the soil bind strongly to the soil matrix. Supplementary investigations into the extractability of possible soil metabolites (RPA 407074, RPA 407291, RPA 508285 and RPA 407288) found the extractability of these metabolites to be very low with the exception of RPA 407074. This hydroxylated metabolite was detected occasionally in aerobic soil at a maximum of 1.5 %. RPA 407291, RPA 508285 and RPA 407288 were not observed at all in laboratory aerobic soil degradation studies. No cleavage of the diphenyl ether linkage was observed in soil metabolism studies. Cleavage of aclonifen or its minor soil metabolite RPA 407074 would lead to the formation of RPA 508285 and phenol (or hydroquinone from cleavage of RPA 407074). RPA 508285 was not observed in soil metabolism studies but would, however, very rapidly have formed unextractable soil residues by binding to soil organic matter. Phenol and hydroquinone are both natural soil constituents. Their fate and behaviour in soil has been evaluated and confirms they are rapidly metabolised in soil ultimately to carbon dioxide with DT50 values of less than 1 day.