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Toxicity to aquatic algae and cyanobacteria

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In a study conducted according to OECD Guideline 201 (Alga, Growth Inhibition Test), Pseudokirchneriella subcapitata were exposed to diisopropylbenzene concentrations for 72 h in closed system. The test was conducted using solvent (mixture of a dispersant of HCO40 and DMF). Analytical monitoring was done. 72 h EbC50 and NOEC were determined to be 1.6 mg/L and 0.31 mg/L (measured concentrations) and 72 h ErC50 and NOEC were found to be 2.7 mg/L and 0.69 mg/L (measured concentrations), respectively. All these values were above the solubility limits of the compounds.

This was confirmed by the ECOSAR prediction. The isomers m-DIPB and p-DIPB were processed through ECOSAR 1.11 for algae toxicity prediction for the target substance DIPB mixture of isomers. A QPRF was drafted in order to assess the 5 OECD principles regarding relevancy of the prediction. The estimated algae EC50(96h) and ChV exceed by nearly a factor 10 the water solubilities of the two isomers. Therefore it is considered that the isomers and the target substances have no effect on algae at saturation. The criteria of acceptability (log Kow and molecular weight) are respected and the functional group of the target chemicals belongs to the application domain of “Neutral SAR”. Moreover there are an important number of chemicals in the training set for the Neutral SAR and the coefficient of determination related to the QSAR equation is good. Therefore the prediction can be estimated as relatively reliable, all the more that experimental data on analogues of the target chemicals present in the training set are in agreement with the predictions for the target chemicals.

The algae study performed on the analog Diethylbenzene blend also strengthen the fact that no effect is to be expected for algae at DIPB solubility limit (72-ErC50 and NOEC at 1.21 mg/L and 0.547 mg/L respectively).

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