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Toxicity to microorganisms

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Justification: Column 2 criteria for aquatic microorganisms toxicity testing of ethylbenzene provide the following adaptations:

The study does not need to be conducted if:

·                   there is no emission to a sewage treatment plant, or

·                   there are mitigating factors indicating that microbial toxicity is unlikely to occur, for instance the substance is highly insoluble in water, or

·                   the substance is found to be readily biodegradable and the applied test concentrations are in the range of concentrations that can be expected in the influent of a sewage treatment plant.

Ethylbenzene is a volatile chemical with the low tendency to adsorb to solid matter (logKoc<4).

A screening level Sewage Treatment Plant (SRP) Fugacity Model was used by the registrant to assess the fate of ethylbenzene in the activated sludge sewage treatment plant (STPWIN programme). The model estimates the fate of a chemical present in the influent as it becomes subject to removal by evaporation, biodegradation or another degradation processes, sorption to sludge, and loss in the final effluent.

The model results suggest that most of ethylbenzene will be removed from the STP. Moreover, ethylbenzene will not absorb to sewage sludge. Therefore, it is considered that microbial toxicity due to exposure to ethylbenzene is not likely to occur within the STP.