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Toxicity to microorganisms

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Description of key information

Both, EC50 and NOEC of the test substance sulphamidic acid were found being > 200 mg/L for activated sludge based on respiration.

Key value for chemical safety assessment

EC50 for microorganisms:
200 mg/L
EC10 or NOEC for microorganisms:
200 mg/L

Additional information

A study was performed to determine potential inhibitory effects of the substance SULPHAMIDIC ACID at defined nominal concentrations on activated sludge respiration using the procedure given in the OECD Guideline for testing of chemicals No 209 and Method C.11 of Council Regulation (EC) No 440/2008. Alongside with the test substance, also the same effects of the reference substance (3,5-dichlorophenol) was determined, in order to validate the test. The 3 hour EC50 was recorded at the 5.41 mg/l for the reference substance showing the test system to be valid and sensitive.

Contrary to the reference substance, the test substance did not show any inhibitory effects (at chosen concentrations) on respiration of the activated sludge, thus no effective concentrations could have been calculated. It can be only stated that NOEC and EC50 value is higher than the highest concentration tested (i.e. > 200 mg/l).

Moreover, stimulation effects were observed in comparison to the control vessels. It means that chosen test substance concentrations increased respiration rate of the activated sludge in comparison with the control, which was a consequence of that microorganisms of the activated sludge behaved more active in the chosen concentrations. The test substance most likely provided to microorganisms some portion of nutrition notwithstanding to its moderately strong acid properties.

Activated sludge showed also a strong buffer capability during the exposure of test substance concentrations. The pH decreased very slowly with an increment of the test concentrations. The evidence of that is the pH measured in the solutions of each test substance vessels after 3 hours exposure. For the lowest test concentration (60 mg/l), the pH was measured at 8.06 and for the highest test concentration (200 mg/l), the pH values was determined at 7.68.