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Sediment toxicity

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A sediment toxicity study was performed according to OECD Guideline 225 and in compliance with GLP. Groups of the oligochaete, Lumbriculus variegatus, were exposed to Hexyl Cinnamic Aldehyde in a static water-sediment system for 28 days. The study was performed by spiking the test item into artificial sediment with concentrations of 3.2, 10, 32, 100, 320 and 1000 mg/kg sediment dry weight and a further equilibration period of 7 days. Six replicates (10 worms/vessel) per control, solvent control and test item concentration were set up for biological investigations. A recovery phase of a further 28 days was also carried out by placing the groups (in duplicates) into clean sediment.

The concentrations of Hexyl Cinnamic Aldehyde in the sediment and the overlying water were analytically verified for all test item concentrations on Days 0 (worm insertion), 14 and 28 via HPLC-DAD. Additionally on Day -7 (Day of application), the test item concentration in the spiked sediment was verified at 1000 mg/kg treatment and the control.

The measured concentration of the test item in the spiked sediment (1000 mg/kg sediment dry weight) on day of application (Day -7) was 92 % of the nominal value. The measured concentrations of Hexyl Cinnamic Aldehyde in the sediment at the beginning of the test (Day 0, after equilibration) were in the range of 26 - 81 % of the nominal values with the highest losses at low concentrations and the lowest losses at high concentrations. At the end of the exposure period (Day 28) the measured concentrations further decreased to < LOQ in the lowest 2 concentrations, just 2% of the nominal in concentrations from 32 to 320 mg/Kg dw and 13 % of the highest concentration at 1000 mg/Kg dw. In the aqueous layer the concentrations were constantly <LOQ during the test. This provides further evidence that the substance would be rapidly removed in the sediment compartment and unlikely to be transferred to the pelagic compartment.

Effects on worms were limited during the study. No significant mortality was observed (>10%) at any concentration. However the total number of worms was substantially lower at 100, 320 and 1000 mg/Kg dw. The EC50 based on biomass was determined as 659 mg/Kg dw. Nevertheless, this effect was suspected to be due to palatability issues related to the high concentrations. At the highest concentration of 1000 mg/Kg dw, the worms refused to burrow and in the recovery study complete reversibility of the effects were demonstrated.

The Authors consider that the NOAEC was therefore 1000 mg/Kg dw, however as effects were noted down to 100 mg/Kg dw during exposure the NOEC of 32 mg/Kg is retained for this study.