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EC number: 203-674-6 | CAS number: 109-46-6
Total respiration was inhibited at each tested concentrations as described below:
Test item nominal concentration (mg/L)
Inhibition of total respiration (%)
This GLP OECD 209 study was carried out in order to determine the 3h-EC50 and 3h-NOEC of 1,3 -dibutythiourea on total respiration inhibition of activated sludge. The inoculum was obtained on 31 August 2015 from the activated sludge of the biological wastewater treatment plant from Abidos (France, 64) which handles predominantly domestic sewage. The sludge was prepared so as to obtain a 10 -L stock solution at a concentration of 3g/L of suspended solids (dry weight) diluted in Volvic water medium supplemented with a synthetic sewage feed.
At the start of the test, 16 mL of synthetic sewage feed were made up to 250 mL with ultra-pure water and 250 mL activated sludge inoculum with a sludge concentration of nominally 1.5 g/L (dry weight) were added to the first control vessels couple. Thereafter, at time intervals of about fifteen minutes, the procedure was repeated with test vessels couples in which the 16 mL of synthetic sewage were made up to 250 mL with the appropriate amounts of reference or test item diluted in ultra-pure water to obtain a volume of 250 mL. As for the controls, 250 mL of activated sludge inoculum (1.5 g/L) were then added. Fifteen minutes after the preparation of the last treatment, the second control vessels couple was prepared at last. The fifteen minutes interval was done so that the 10 min incubation period with O2 depletion monitoring could take place exactly 3 hours after start of incubation of each test vessel. The addition of the inoculum was considered as the start of the 3-hours incubation time period. All solutions were incubated at 20 +/- 2°C in darkness for 3 hours in a temperature controlled room. Solutions were mixed by stirring and aerated with clean, oil-free compressed air via narrow bore glass tubes at a rate of 0.5 to 1.0 liter per minute during 3 hours. At the end of the test incubation period, a well-mixed sample of each solution (following their order of preparation) were poured into a BOD bottle in which dissolved oxygen concentrations were measured at 1 min intervals for up to a maximum period of 10 min or until the oxygen concentration felt below 1 mg/L. The temperature was monitored throughout the test period. 1,3-dibutylthiourea did not cause any significant respiratory inhibition up to the highest tested concentration. The NOEC is therefore considered superior or equal to 100 mg/L. The 3h-EC50 for 3,5-dichlorophenol to activated sludge was 17.0 mg/L for total respiration. The test met all the validity criteria of the guideline.
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