Ammonium 2-amino-4-(hydroxymethylphosphinyl)butyrate

Endpoint summary

Description of key information

The substance is stable for hydrolysis and is considered as not readily biodegradable based on OECD 301 tests. Glufosinate-ammonium is photolytically stable in sterile aqueous solutions. Direct or indirect photolytic transformation in water therefore does not significantly contribute to the elimination of glufosinate-ammonium residues from the aquatic environment. No quantum yield was determined due to a lack of absorption of light by glufosinate-ammonium in the relevant wavelength range of visible light. Photodegradation of glufosinate-ammonium was studied on the surface of a sandy loam soil. No transformation products were formed being specific for photolytic degradation. Conclusively, photolytical transformation processes on soil surfaces do not play a role for the elimination of glufosinate-ammonium residues from the soil environment.

The degradation of 14C-glufosinate-ammonium was investigated under the conditions of two water /sediment studies. The degradation under conditions of a water/sediment study was also investigated following separate dosing of metabolite AE F061517 (MPP).

Route of degradation:

Glufosinate-ammonium was degraded via a similar route as found for aerobic soil, i.e. via oxidative deamination to AE F065594 (PPO) as a minor metabolite, followed by the formal but multistep loss of methylene groups each to result in AE F061517 (MPP, maximum 79.8% at day 14) and AE F064619 (MPA, maximum 19.9% at day 50) by oxidative processes. Alternatively, the transformation of AE F061517 (MPP) resulted via dehydrogenation (formal loss of hydrogen) in the formation of 3-[hydroxy(methyl)phosphoryl]acrylic acid (P-X, AE 0015081, maximum 12.5% at day 50). Metabolite N-acetylglufosinate (NAG) was observed at a maximum of 13.7% at day 1 thus demonstrating the transient character.

Rate of degradation:

Water/sediment studies were kinetically evaluated following the FOCUS kinetics guidance. For total systems the kinetic evaluation according to FOCUS guidance (Level P-I) resulted in geometric mean degradation half-lives of 8.7 days for glufosinate-ammonium and 219.4 days for MPP (AE F061517). For MPA (AE F064619) a DegT50 of 33.3 days was derived for total systems.

According to Echa guidance R.16, equation R.16 -9, the DT50 of glufosinate-ammonium for the whole system of 8.7 days at 20°C resulted in a half-life of 16.5 days or a degradation rate of 0.042 d-1 at 12°C.

Additionally the degradation of 14C-glufosinate-ammonium was investigated in a pelagic-water study at 20 °C. The half-life was estimated to be 54.3 days. This value is considered as worst-case figure due to the lack of microbial activity based on the absence of the sediment phase.