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EC number: 203-733-6
CAS number: 110-05-4
Respiration rate (mg O2/L min
In order to predict effects of di-tert-butyl peroxide
in biological wastewater treatment plants, an activated sludge
respiration inhibition test was performed, according to OECD 209
guideline and EU Method C.11.
The inoculum was an activated sludge, at 0.5 g dry
weight/L, collected from the RZWI Nieuwgraaf in Duiven plant which
predominantly treats domestic wastewater. Prior
to use, the activated sludge was diluted with tap water (1.5x) and
homogenized for two minutes.
The test substance was not soluble in water at the
nominal concentration of 1000 mg/l and therefore it was first dissolved
in dichloromethane and adsorbed onto silica gel in petri-dish for 30
min. The solvent was allowed to evaporate by placing the petri-dish in a
hood for 3 hours, and the entire contents were then transferred to the
test erlenmeyers. This method allowed a good contact between the
activated sludge and the test substance. Although no toxicity of the
silica gel was expected, a control with silica gel was carried out as
well. The diffusion of the test material during the 30 mn of exposure is
uncertain and according to the high volatility of the test substance
(vapour pressure is 42 hPa at 20°C) some may have evaporate when placed
in the hood during the preparation of the silica gel. The temperature
was 20°C and the pH ranged from 7.5 to 7.9. 2,4,5-trichlorophenol was
used as a reference substance during the test and show an EC50 of 10-20
mg/L which is within limits according to guideline (5 -30 mg/L). With
the test material, no effect was recorded, but as the exposure
concentration cannot be confirmed it is assumed that the highest
concentration tested is equivalent at the water solubility concentration
of di-tert-butyl peroxide. The EC50 therefore
is >171 mg/L based on water solubility of the test material.
The toxicity of the substance to activated sludge was tested in a reliable GLP study following OECD 209 and guidance on the testing of difficult substances. A 30 minute EC50 >1000 mg/L, which is above the water solubility, was observed. No effect up to the highest concentration tested of 1000 mg/L.
studies were available for this endpoint. Granditschet al.(1979)
tested toxicity of the substance on activated sludge following three
different methods but after 4 hours of exposure only and assessing the
concentration which killed 100% of the bacterial population. Ginkel and
Stroo (1989) assessed the toxicity of the substance to activated sludge
in a reliable GLP study following OECD 209 and guidance on the testing
of difficult substances. They calculated a 30 min EC50 nominal as >1000
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