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Toxicity to microorganisms

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Description of key information

The test item L-Cysteine 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

EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information

The inhibitory effect of the test item L-Cysteine 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.

Based on the results of the range-finding test and in agreement with the sponsor a definitive test with the following nominal test item concentrations was performed: 10, 32, 100, 320 and 1000 mg/L, with three replicates per concentration.

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). Six blank controls, containing an equal volume of activated sludge and synthetic medium but no test or reference item were included in the definitive test. The vessels were prepared in the following order: two blank controls, the reference item group (with ascending concentrations),two further blank controls,the test item group (with ascending concentrations) and then two blank control vessels. NOEC: ≥ 1000 mg/L