Reaction mass of 2-[4-[(Hexahydro-2,4,6-trioxo-5-pyrimidyl) azo]phenyl]-6-methylbenzothiazole-7-sulphonic acid, compound with 2,2',2''-nitrilotris[ethanol] (1:1) and Lithium 2-[4-[(hexahydro-2,4,6-trioxopyrimidin-5-yl)azo]phenyl]-6-methylbenzothiazole-7-sulphonate

Toxicity to microorganisms

Description of key information

In a valid Activated Sludge Respiration Inhibition Test the 3-hour EC10 and the EC50 of the test item was determined to be > 1000 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

Key study

In a GLP-compliant Activated Sludge Respiration Inhibition Test according to OECD Guideline 209 and Commission Regulation (EC) No 440/2008-C.11, activated sludge (1.5 g/L dw) from a municipal wastewater treatment plant was exposed for 3 hours at 18.9 – 19.8 °C to test item concentrations of 1000, 500, 250, 125, 62.5 mg/L (nominal, 3 replicates for each test substance concentration). In addition, a negative control (6 replicates) and a positive control with the reference substance 3,5 dichlorophenol (2 replicates for each reference substance concentration) was performed. The test substance was added in the required amounts according to the test concentrations directly to the test vessels with 234 mL deionized water. Aliquots of the reference substance stock solution were dosed to the test vessels and made up with deionized water to a volume of 234 mL. 16 mL synthetic medium (100-fold concentrated OECD medium) were dosed to each test vessel with test substance and reference substance afterwards. To prepare the blank control assays 234 mL of deionized water and 16 mL synthetic medium were mixed. The pH-values in all test vessels were checked. An adjustment was not necessary. After addition of 250 mL of inoculum suspension (3 g/L dw) the incubation was started by aeration of the test vessels with pressured air. The vessels for the blank control assays were prepared to the same procedure without addition of test- or reference substance. After 3 hours incubation at 20 +- 2°C the mixtures in the test vessels were placed subsequently for oxygen measuring. The temperature was measured for seven times in a separate vessel filled with deionized water. The content of oxygen at the start of the measurements was > 7 mg/L (except in one replicate with a test concentration of 1000 mg/L: Start value ca. 6.5 mg O2/L). The consumption rate (mg O2/L*x minutes) of each test concentration and the blank controls were determined after 3 hours of exposure. The consumption rates (mg O2/L*h) were used to calculate the inhibition effects at particular test concentrations compared to the mean consumption rate of all controls. In result, the following effect concentrations were determined: 3-hour EC10 = >1000 mg/L, EC20 = >1000 mg/L, EC50 = >1000 mg/L, EC80 = >1000 mg/L. The EC50 of 3,5-dichlorophenol was 12.5 mg/L, indicating that the microorganisms responded normally to toxicant stress. All validity criteria of the guidelines were met (BASF SE, 2016).

Study disregarded due to major methodological deficiencies

In a study Pseudomonas putida strain DSM 50026 was exposed to the test substance (in formulation) to assess the inhibitory effect on bacterial respiration. The following nominal concentrations were used: 10000, 5000, 2500, 1250, 625, 313, 156, 78 and 39 mg/L. The test duration was 30 min. After this exposure period, the O2 consumption was measured. As a result, the EC10, EC50 and EC90 values were found to be greater than 10000 mg/L. As the amount of test substance in the preparation was less than 20%, this study was disregarded due to major methodological deficiencies (BASF AG, 1983).

Overall conclusion

Based on a valid and GLP-compliant Activated Sludge Respiration Inhibition Test according to OECD Guideline 209 and Commission Regulation (EC) No 440/2008-C.11 (BASF SE, 2016), the 3-hour EC10 and EC50 of the test item is considered to be >1000 mg/L.