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EC number: 203-347-8
CAS number: 105-95-3
Weight of Evidence approach; geometric mean between the two results (experimental and QSAR results):- 48h-EC50 = 4.65 mg/L.
Due to the unexpected and inconsistent loss
of substance observed in the static experimental study (EU Method C.2
with GLP statement), a weight of evidence approach with ECOSAR
estimation has been used to assess the acute toxicity of the substance
to aquatic invertebrates.
acute toxicity study, performed according to EU Method C.2 with GLP
statement, Daphnia magna were exposed to the substance at nominal
concentrations of 0 (blank control), 3.2, 5.0, 6.4, 10.0, 12.8 and 20.0
static conditions. Analytical monitoring of the concentrations was
performed at t = 0h and t= 48h. This
study is considered invalid because the test method used was not
appropriate, the substance was apparently lost rapidly during this
static test although similar final concentrations of the test substance
were found in all test solutions at the end of the study. This profile
would not be expected for a relatively low volatility substance tested
below the water solubility limit as is the case here. The EC50 value was
therefore recalculated with ToxRat Professional v2.10 using the initial
measured concentrations. The
recalculated 48h-EC50 for Daphnia magna was determined to be 8.09
mg/L (95% CL: 7.39 - 8.87 mg/L).
In addition, the short term toxicity
of the substance to daphnid was estimated using the ECOSAR v1.11 QSAR
model available from the U.S. EPA.
The estimation 48h-LC50 was 2.67 mg/L
(esters class), calculated from a measured log Kow value (4.3) and a
linear regression. The
substance falls within the applicability domain and therefore the
predicted value can be considered reliable.
To obtain a more reliable EC50 value, the
geometric mean between these two results was determined to be 4.65 mg/L.
Further investigation is ongoing on this
difficult substance in order to determine whether instability or
analytical issues account for the rapid loss observed under
ecotoxicological test conditions.
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