Ammonium 2-amino-4-(hydroxymethylphosphinyl)butyrate

Toxicity to aquatic algae and cyanobacteria

Description of key information

ECr50 (72 h) = 0.132 mg a.s./L (nominal) (Anabaena flos-aquae, EPA OPPTS 850.5400, OECD 201) (Banman et al., 2011)

ECr10 (72 h) = 0.0106 mg a.s./L (nominal) (Anabaena flos-aquae, EPA OPPTS 850.5400, OECD 201) (Banman et al., 2011)

Additional information

Six studies on the toxicity of glufosinate-ammonium to algae are available. All studies, with the exception of Hughes (1987), were conducted according to GLP and different international guidelines. Five species of freshwater algae (Anabaena flos-aquae (blue-green alga), Skeletonema costatum, Pseudokirchneriella subcapitata, Scenedesmus subspicatus, Navicula pelliculosa (diatom)) were tested.

The aim of the study by Banman et al. (2011a) was to determine the effects of glufosinate-ammonium techn. (purity 99.2%) on the growth of the blue-green alga Anabaena flos-aquae during a 96-hour exposure. The blue green algae were exposed under static conditions for 96-hours to nominal concentrations of 3.8, 12, 39, 125, and 400 µg a. s. /L and a control. The study was conducted according to OECD guideline 201 and similar guidelines. Measured glufosinate-ammonium concentrations ranged from 103% to 113% of nominal concentrations on day 0. At test termination (day 4), measured concentrations ranged from 101% to 111% of nominal. The biological endpoints are thus reported based on nominal concentrations. No physical abnormalities were observed in the control or in the treatment groups during the study. The 72-hour EC50 value for growth rate (ErC50) was determined to be 132 µg a. s. /L with ErC10 value of 106 µg a. s. /L, based on nominal concentrations.

The aim of the study by Banman et al. (2011b) was to determine the effects of glufosinate-ammonium techn. (purity 99.2%) on the growth of the saltwater diatom Skeletonema costatum during a 96-hour exposure. The saltwater diatom Skeletonema costatum was exposed under static conditions for 96 hours. Nominal (mean measured) concentrations were control, 3.13 (2.92), 6.25 (6.16), 12.5 (12.0), 25.0 (22), 50.0 (49), and 100 (93) mg a. s. /L. Measured glufosinate-ammonium concentrations ranged from 76% to 95% of nominal concentrations on day 0. At test termination (day 4), measured concentrations ranged from 97% to 102% of nominal. As the analytical findings at test termination confirmed the correct dosing and stability of the test item, the biological endpoints are reported based on nominal concentrations. No physical abnormalities were observed in the control or in the treatment groups during the study. The 72-hour EC50 value for growth rate (ErC50) was determined to be 52.4 mg a. s. /L with LOEC and NOEC values of 25 and 12.5 mg a. s. /L, respectively, based on nominal values.

Green algae (Pseudokirchneriella subcapitata) were exposed to glufosinate-ammonium (content 50.4 % w/w in a 50 percent aqueous concentrate) in a static system over a period of 72 hours (Ruhland, 2009b). Nominal concentrations were 6.25, 12.5, 25.0, 50.0 and 100 mg a. s. /L. In addition a water control was tested. Each vessel (Erlenmeyer flasks; 300 mL) served as one replicate filled with 150 mL test solution. At test initiation the cell density was 10000 cells/mL. The test was conducted with 3 replicates per treatment level. In the controls 6 replicates were tested. For analytical verification of the test item concentrations samples were taken at day 0 and day 3 from all concentrations. HPLC-MS/MS was used as analytical method. The limit of quantification (LOQ) was 2.0 µg/L. The range of linearity was 2.0 µg/L to 200 µg/L. Growth rates, observation on cell abnormalities and physical-chemical water parameters were assessed as indicated below in the result section. Analytical verification of test solutions revealed measured concentrations calculated as arithmetic mean: on day 0: 95 % to 101 % of nominal (average 97 %) and on day 3: 93 % to 110 % of nominal (average 101 %). Based on this biological results are reported as nominal. No cell abnormalities were observed. All validity criteria were fulfilled. The effect of glufosinate-ammonium on Pseudokirchneriella subcapitata can be quantified as a 72-hour-EC50 of 46.4 mg a. s. /L (95 % confidence limits: 25.6 – 159 mg a. s. /L). The highest concentration with no observed growth inhibition and no cell deformations could not be determined but was set to < 6.25 mg a. s. /L (significant effects were observed at the lowest test concentrations).

The effects on Selenastrum capricornutum of technical grade glufosinate-ammonium (Hoe 039866, purity 96.3% purity) were investigated over a 7-day period in accordance with US-EPA – FIFRA / Guideline 123-2 (Hughes, 1987). Test concentrations were 2.5, 5, 10, 20, 40 and 80 mg/L nominal plus control. The nominal initial cell concentration was 3000 cells/mL. Triplicate flasks were kept in an incubator at a temperature of 24 ± 2 °C. Initial pH ranged from 6.1 – 6.7. Biomass was determined by cell counts on days 3, 4, 5 and 7. The EC50 based on cell counts after 7 days was determined to be 37 mg/L. NOEC was estimated to 2.5 mg/L for Selenastrum capricornutum.

The effect of technical glufosinate-ammonium (GA; Hoe 039866, purity 96%) on the growth of green alga (Scenedesmus subspicatus) over 72 hours was investigated according to OECD Guidelines 201 in a study by Heusel (1994). Algal density was 104 cells/mL at test initiation and the nominal test concentrations were 32, 56, 100, 180, 320, 560, and 1000 mg/L, and an untreated control group. Test temperature was 25 ± 1 °C; the pH of the control was 7.9 at study start. Chemical analysis of the test substance concentration in the test water were made from the concentrations of 32, 180 and 1000 mg/L after 0 and 72 hours test duration by HPLC-analysis. The study was carried out with six replicates in the control and three replicates in each of the treated groups. Mean measured concentrations of glufosinate-ammonium in the tests systems were 104 - 110% of the nominal values. Test pH increased to a maximum of 9.9 in the control and the lowest test concentrations and to ca 8.5 at higher concentrations. Effects on mean growth rate (6% reduction) and area under the growth curve (26% reduction) compared to the control were seen at 180 mg/L and above. Hence, NOEC for Scenedesmus subspicatus was 100 mg/L. The 72 hours ErC50 and EbC50 were determined to be >1000 mg/L. The evaluation of the former RMS Sweden was, “The test was generally performed in accordance with the referred guidelines.The pH deviations were higher than recommended (according to the guidelines 1 unit allowed). However, these deviations should not seriously affect the results of this study.”

The effects of glufosinate-ammonium (purity 97% w/w) on a diatom alga, Navicula pelliculosa were investigated in accordance with OECD Guidelines 201 and US-EPA §123-2 by Sowig and Gosch (2001). Algal cultures with an initial cell density of 10 000 algal cells/mL were incubated in a synthetic medium at 25 ± 1 °C for 120 hours. Nominal test concentrations were 5.6, 10, 18, 32, 56 and 100 mg/L with four replicates each, plus control with eight replicates. Samples of the algal populations were removed daily from each test vessel and cell concentrations were determined after 24, 48, 72, 96 and 120 hours test duration. Algal morphology was also observed daily using a light microscope and counting chamber. Mean measured concentrations of the test substance were between 90 and 105% of the nominal values. No significant dose related effects on growth rate and area under the growth curve were observed during the study. Hence, the 120 hours ErC50 and EbC50 for Navicula pelliculosa were determined to >100 mg/L and the NOEC >= 100 mg/L.