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EC number: 907-672-2 | CAS number: -
Table 1: Oxygen content, temperature and pH values during exposure phase (test item)
Test item concentration[mg/L]
Physico-chemical oxygen consumption control
Table 2: Oxygen content, temperature and pH values during exposure phase (reference compound)
Reference compound concentration[mg/L]
Table 3: Results of test item Dibutyl phenyl phosphate
Test item concentration(nominal)
Respiratory ratetest item
Respiratory rate - phys.-chem.O2consumption
Comments: Concentrations are given as nominal concentrations and were not confirmed by analytical methods. * The physico-chemical oxygen consumption has been determined at 1000 mg/L test item concentration. As no physico-chemical oxygen consumption was observed at that test item concentration this observation also holds true for the lower test item concentrations.
Table 4: Results of reference compound 3,5-Dichlorophenol
Reference compound concentration(nominal)
Respiratory ratereference compound
Comments: Concentrations are given as nominal concentrations and were not confirmed by analytical methods.
With the used method the effect of DBPP on microorganisms was assessed by measuring the respiration rate under defined conditions in the presence of different concentrations of the test item. The study was conducted in accordance with Council Regulation (EC) No 440/2008, Method C.11 ”Biodegradation: Activated Sludge Respiration Inhibition Test” (2008). This test method is equal to OECD Guideline 209 (1984).
To measure the oxygen consumption, 250 mL of sludge with the test item (or control or reference compound) was incubated for 3 h in 300 mL closed Erlenmeyer flasks and aerated through a glass tube at 50-100 L/h with clean oil-free air. For the measurement, the content of the Erlenmeyer flasks was completely transferred to 250 mL BOD bottles and oxygen content was measured with an oxygen meter (redox electrode) with writer.
Two controls without the test item were included in the test design, one at the start and the other at the end of the test series. Each batch of activated sludge was checked using 3,5-Dichlorophenol as a reference compound. Since some substances may consume oxygen by chemical reactivity, a physico-chemical oxygen consumption control was carried out additionally. In order to be able to differentiate between physico-chemical oxygen consumption and biological oxygen consumption (respiration), at least the maximum concentration of the test item was tested without activated sludge.
The respiration rate for each concentration was determined graphically from the linear part of the curve of the oxygen content versus time. The inhibitory effect of the test item at a particular concentration is expressed as a percentage of the mean of the respiration rates of two controls. An EC50 value was calculated from the respiration rates at different test item concentrations and for the reference compound the EC50 value was calculated using the statistics programme ToxRatPro Version 2.10. The EC50 of DBPP was > 1000 mg/L in the current test.
The key study was a respiration inhibition study (Richter, 2012) performed according to the current guidelines and GLP criteria. The determined EC10 value was 402 mg/L, this was used as starting value for the risk analysis.
The study was performed to assess the toxicity of Dibutyl phenyl phosphate to bacteria. The study was conducted in accordance with Council Regulation (EC) No 440/2008, Method C.11 ”Biodegradation: Activated Sludge Respiration Inhibition Test” (2008). This test method is equal to OECD Guideline 209 (1984). The activated sludge was exposed to Dibutyl phenyl phosphate at different concentrations. The respiration rate of each mixture was determined after aeration periods of 3 hours. Dibutyl phenyl phosphate showed 12.73 % respiration inhibition of activated sludge at a test item concentration of 1000 mg/L. Consequently, the EC50 is higher than 1000 mg/L. The calculated EC10 was 402 mg/L. The effect value relates to a nominal concentration, since no analytical monitoring was performed.
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