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Toxicity to microorganisms

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Description of key information

The effect of the test substance, Benzyl Trimethyl Ammonium Chloride (BTMAC) on activated sludge microorganisms maintained in an aerobic environment was assessed by the Activated Sludge Respiration Inhibition Test (OECD Guideline 209). 

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L

Additional information

The effect of the test substance, Benzyl Trimethyl Ammonium Chloride (BTMAC) on activated sludge microorganisms maintained in an aerobic environment was assessed by the Activated Sludge Respiration Inhibition Test (OECD Guideline 209). The test contained control, reference and treatment groups. The control replicates were used to determine the background respiration rate of the sludge and were not dosed with the test or reference substance. The reference group was dosed with 3,5-dichlorophenol, a known inhibitor of respiration, at concentrations of 3, 15 and 50 mg/L. The treatment group was dosed with Benzyl Trimethyl Ammonium Chloride (BTMAC) at concentrations of 1, 10, 100, and 1000 mg/L. An abiotic control was dosed with the test substance at a concentration of 1000 mg/L to discriminate between abiotic uptake by the test substance and microbial respiration. After an exposure period of three hours, the respiration rates of the test solutions were determined using a YSI Model 50B-115 Dissolved Oxygen Meter.

The respiration rates in the two controls were 41.1 and 49.7 mg O2/L/hr. Both controls had respiration rates above 30.0 mg O2/L/hr, which is the low limit based on the validity criteria for mixtures with 1.50 g dry weight of suspended solids per liter. The coefficient of variation of the two control respiration rates was 13.3%, and was within the 30% limit established for the test. The validity of the test was further supported by the results from the 3,5-dichlorophenol reference group, which resulted in an EC50value of 19.8 mg/L, with 95 percent confidence limits of 15 mg/L and 50 mg/L. The EC50for the reference substance was within the 2 to 25 mg/L range considered acceptable for the test.

An inhibitory dose response effect was observed for the treatment group; however, the EC50value for Benzyl Trimethyl Ammonium Chloride (BTMAC) is greater than 1000 mg/L, the highest concentration tested. The abiotic treatment mixture dosed with 1000 mg/L of Benzyl Trimethyl Ammonium Chloride (BTMAC) had a respiration rate of –0.6 mg O2/L/hr showing there was no chemical

uptake of oxygen by the test substance.