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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

(96-h) LC50: 10-32 mg/l (18 mg/l as the geometric mean of the concentration range) mortality Brachydanio rerio, reliability 2

Key value for chemical safety assessment

Additional information

A 96-hour LC50 value of between 10 and 32 mg/l (18 mg/l as the geometric mean of the concentration range) and a NOEC of 10 mg/l have been determined for the effects of the test substance on mortality of Danio rerio (tested as Brachydanio rerio). The results are interpreted with reference to nominal concentrations of the test substance. However the test substance is susceptible to hydrolysis and it is likely that the test organisms were primarily exposed to a mixture of the parent compound and the hydrolysis products of the substance.

A functional group associated with ecotoxicity by a specific mode of action (thiocyanate) is present in both the registration substance and the silanol hydrolysis product, and the effects seen are attributed to this. It is therefore reasonable to conclude that both the parent and hydrolysis product could contribute equivalently to any effects observed. Daily renewal of test media was used and no undissolved material was observed at the test concentrations from which the LC50 is calculated. In the absence of analytical monitoring, it is not possible to estimate with confidence the concentrations of parent form or hydrolysis product in the test system. Therefore, since the LC50 is below the limit of solubility of either form, and if the contribution to toxicity is approximately equivalent, then the nominal LC50 should theoretically reflect the LC50 of either form alone. The bioavailability of the parent form (based on its log Kowof 3.1) is higher than that of the hydrolysis product (log Kowof -1.5).

It is therefore considered appropriate and conservative to use this result without adjustment as the starting point for deriving

·        PNECaqua (for registration substance)

·        PNECsoil and PNECsediment (for silanol hydrolysis product, by Equilibrium Partitioning method)