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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Activated sludge toxicity test, OECD 209, EC50 (3h) > 10000 mg/L 

Key value for chemical safety assessment

EC50 for microorganisms:
10 000 mg/L

Additional information

The acute toxicity to microorganisms of the test substance was investigated in accordance with OECD guideline 209 and GLP compliance (Goodrich, 1994). Activated sludge was used in the static freshwater experiment with an exposure time to the test substance of 3 hours. The testing system consisted of two units: 1) a system used to expose the sludge inoculum to the test material and 2) a system to measure the rate of oxygen consumption of the sludge in a closed bottle. Initial test concentrations were 1, 10, 100, 1000 and 10000 mg/L. A control test system and 3,5 -dichlorophenol were run in parallel. The inoculum was exposed to the test material in 1-L flint glass bottles. Low-pressure oil-free air was delivered to each test vessel using a glass pipet. All of the test vessels were held in a Forma Scientific Model 3956 water-jacketed incubator in the dark during the three-hour exposure period. To measure the oxygen consumption after the exposure period, a Model 51 Yellow Springs Instruments (YSI) dissolved oxygen meter was used. The oxygen meter was fitted with a BOD bottle probe, with a standard sensitivity membrane and an external output to a Fisher Recordal (Model 5000) strip chart recorder. For this purpose, 300 mL of the sludge mixture were transferred into a BOD bottle containing a teflon-coated magnetic stir bar. The bottle was capped with the BOD bottle oxygen probe to eliminate air space and placed on a magnetic stirring plate. The sludge mixture was stirred at a constant rate and the consumption of oxygen over time was recorded on a strip chard recorder. The resultant respiration rates were respectively: 21.2, 30.7, 20.4, 19.9 and 23.8 mg O2/L * hr. These data are translated into percent inhibitions of 18.6 %, -17.9 %, 21.7 %, 23.6 % and 8.6 %, respectively. Because none of the test concentrations produced an inhibition greater than 50 %, an EC50 could not be calculated. Hence the EC50 is > 10,000 mg/L.