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Toxicity to microorganisms

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Description of key information

Moderately toxic sewage water treatment plant microorganisms

Key value for chemical safety assessment

EC50 for microorganisms:
116 mg/L

Additional information

The toxicity of Guanidine carbonate (CAS 593-85-1) to microorganisms was investigated in a GLP-compliant study (Weniger 1998) using activated sludge of a predominantly domestic sewage according to the OECD TG 209 (1984) protocol. The experiment is deemed valid, conclusive and thus suitable for assessment without restrictions.

The test organisms were in 3 replicate exposed to 5 nominal concentrations of the test item (19, 38, 75, 150 and 300 mg/L) versus two negative controls (tap water). As positive control substance 3,5-dichlorophenol (CAS 591-35-5) was used in 3 concentrations (5, 15 and 45 mg/L). The microbial inoculum was a preparation of activated sludge collected on the day of test. The concentration of the microbial inoculum was adjusted to 2 - 4 g of dry weight per litre which gives a final amount of 0.8 - 1.6 g dry weight per litre in the test medium. The inoculum was kept aerated before the test start.

After mixing the inoculum with synthetic sewage solution and appropriate amounts of control or test substance solutions the samples were aerated for a contact time of 3 hours at 20 °C. Negative controls were run as first and as last sample. After incubation the respiration rates were determined in closed bottles using an oxygen sensitive electrode. The inhibition of respiration was calculated from the respiration rates using the mean value of the negative controls as 100 %.

The effect levels were determined to be EC20 32 mg/L (95 % Cl 24 and 40 mg/L), EC50 116 mg/L (95 % CL 101 to 131 mg/L) and EC 80 > 300 mg/L.

In conclusion the test item was found moderately toxic sewage water treatment plant microorganisms.

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