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Sediment toxicity

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Description of key information

Three long-term sediment tests are performed with a diamine with a hydrogenated tallow alkyl chain.

It is considered to be justified to use these results also for other C10-18 diamines because in contrast to the difference in toxicity observed for the aquatic compartment only a limited difference is expected for the benthic compartment because the main exposure route for both the nematode and lumbriculus will be through uptake via food (comber et al., 2008) and because only a small difference in sorption to sediment for the diamines with different alkyl chains is anticipated.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater sediment:
86 mg/kg sediment dw

Additional information

For diamines, four test results are available regarding the sediment toxicity. Three long-term studies and one short-term study. The long term studies were performed with the hydrogenated diamine C16 -18 and were performed withLumbriculus variegatus and Caenorhabditis elegans. The long-term study with Caenorhabditis elegans showed no effects upto 1000 mg/kg dw. Two long-term tests withLumbriculus variegatus were performed applying two different spiking approaches. In the first test a solvent was used to spike the test substance on the sand fraction and in the second test the test substance was spiked onto the whole sediment in the water phase at a slightly elevated temperature. In the first test with solvent spiking, a significant difference in reproduction between the normal control and solvent control was observed. It was not clear why this difference was observed but considering to unrealism in using a solvent to spike the test substance it was decided to repeat the test using an environmentally more realistic solvent free spiking procedure of the whole sediment. For this second long-termLumbriculus variegatus a NOEC and EC10 for reproduction was observed of resp. 180 mg/kg dw and 86 mg/kg dw. The NOEC and EC10 based on dry weight of resp 360 and 237 mg/kg dw are higher probably because the moment of splitting of the worms is slightly influenced by the test substance.

The spiking procedure using a solvent to spike the sand fraction is unrealistic for cationic surfactants. Cationic surfactants which may enter surface water are normally sorbed to dissolved organic matter or suspended matter and may redistribute slowly to thermodynamically more favourable sites when available. Quartz sand has a very low CEC and no organic matter. The use of natural sediment spiked without using solvent is far more realistic and could allow a more evenly distribution of the test substance over the sediment. In addition it would allow the ingestion of the test substance more realistically. In addition the solvent apparently had a positive influence on the reproduction which limits the reliability of the result.

A similar toxicity is anticipated for organisms living in the benthic compartments for diamines with alkyl chain lengths ranging from C10-18 based on the fact that the main exposure route for sorbing substances is via ingestion (comber 2008) and limited difference in sorption to sediment because the main driver in alkyl-1,3 -diaminopropanes sorption is ionic interaction. Read-across of these sediment results to diamines with other alkyl-chain lengths is considered to be justified.