Since glufosinate-ammonium is stable towards photolysis and hydrolysis, the degradation is concluded to be mainly microbially mediated under aerobic conditions. The available study on anaerobic degradation in soil was not of sufficient quality for assessment of the fate of GA under anaerobic conditions. The metabolic pattern of glufosinate-ammonium (AE F039866, GA) under aerobic conditions was similar in all soils tested. The initial metabolites were sometimes detected at low levels after deamination or acetylation of the amino group, but neither of these metabolites were consistently found nor detected in higher amounts. Therefore these metabolites are regarded as transient, rapidly undergoing further transformation after decarboxylation and deacetylation/deamination to MPP, MPF and CO2. Another possibility for GA degradation that might be considered is the deamination to an unstable intermediate that would undergo oxidative and decarboxylative processes to form the methylphosphinico-acetic acid MPA. AE F061517 (3-methylphosphinico-propionic acid, MPP) and its derived metabolite AE F064619 (2- methylphosphinico-acetic acid, MPA) were identified as the first soil metabolites of glufosinate. The next substance in the homologues row of acids, the methylphosphinico-formic acid (P-Y, MPF), was only found in minor (<10% of applied) amounts, and is probably rapidly decarboxylated. The methylphosphonic acid AE F130948 was in one study observed as the last metabolite in the degradation pathway, immediately before mineralisation to CO2, methane and orthophosphate (refer to Stumpf, Schink and Schmidt, 1995a). It was demonstrated that pure N-acetyl-glufosinate (AE F099730, NAG) applied on soil degrades rapidly to glufosinate (as AE F 057740, L-glufosinate) and that further degradation follows the metabolic pathway of glufosinate in soil. Also, glufosinate and N-acetyl-glufosinate residues, incorporated indirectly via plant material into soil, show the same metabolic pattern in soil as the pure test substances. Thus, the risk for accumulation of glufosinate and its plant metabolite by incorporation with plant material in soil is expected to be low. The degradation rate of glufosinate-ammonium was investigated in 5 different soils, with resulting laboratory DT50 values ranging between 5 and 10 days at 20 - 22 C and 40% mwhc (mean 7.1 days in five soils, 10 data). At lower temperature, e.g. 10 C, DT50 was three times higher than the comparable value at 20 C (Q10 = 3). The major metabolites in soil were identified as MPP and MPA, with MPP reaching a maximum level of 47% of applied radioactivity after 7 days and MPA 26% of applied after 14 days in a study with GA.