Abstract |
The effect of the test substance on activated sludge microorganisms was assessed by the Activated Sludge Respiration Inhibition Test Method (OECD Guideline 209). The test contained a control, reference and treatment groups. The control group was used to determine the background respiration rate of the sludge and was 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 test substance was dosed at 1, 3, 10, 30, 100, 300, and 1000 mg/L. After an exposure period of 3 hours, the respiration rates of the test solutions were measured using a dissolved oxygen meter. The respiration rates in the two controls were 41.2 and 48.4 mg O,/L/hr, or a difference of 14.9%. The difference in control respiration rates was within the 15% difference 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 EC50 of 8.6 mg/L. The EC50 was within the 5 to 30 mg/L range considered acceptable for the test. |