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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

The test item L-Cystine had no inhibitory effect on the respiration rate of activated sludge at all tested concentrations up to and including 1000 mg/L after the incubation period of three hours. 

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information

The inhibitory effect of the test item L-Cystine on the respiration rate of aerobic wastewater micro-organisms of activated sludge was investigated in a 3 hour respiration inhibition test according to the OECD Guideline for Testing of Chemicals, No. 209, adopted 2010. A range-finding test using the following three test item concentrations 10 mg/L, 100 mg/L and 1000 mg/L was performed. Single test vessel replicates were tested for the two lower concentrations, whereas for the highest test item concentration three replicates were prepared. As a positive control, the reference item 3,5 dichlorophenol was tested under identical test conditions, at concentrations of 3.2, 10 and 32 mg/L (all single replicates). Four blank controls, containing an equal volume of activated sludge and synthetic medium but no test or reference item were included in the range-finding test. The vessels were prepared in the following order: two blank controls, the reference item group (with ascending concentrations), the test item group (with ascending concen-trations) and at last again two blank control vessels. The results of the blank and positive control treatments confirmed suitability of the activated sludge and the method used. The validity criteria were fulfilled. The test item L-Cystine had no inhibitory effect on the respiration rate of activated sludge at all tested concentrations up to and including 1000 mg/L after the incubation period of three hours.The obtained 3-hour ECX- and NOEC-values were as follows: EC10 > 1000 mg/L; EC20: > 1000 mg/L; EC50: > 1000 mg/L; EC80: > 1000 mg/L; NOEC: ≥ 1000 mg/L. In conformity with the guideline, a definitive test was not necessary since in the range-finding test the test item showed no inhibition of the respiration rate at the highest tested concentration (performed as triplicate).