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Sediment toxicity

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Description of key information

In a GLP-study according to OECD test guideline 225, the toxicity of the registered substance to sediment worms was determined as EC50 = 311 mg/kg soil dw and as NOEC = 154 mg/kg soil dw, respectively.

Key value for chemical safety assessment

EC50 or LC50 for freshwater sediment:
311 mg/kg sediment dw
EC10, LC10 or NOEC for freshwater sediment:
154 mg/kg sediment dw

Additional information

The effects of the test item on the oligochaete Lumbriculus variegatus in a water sediment system were determined according to an OECD Draft guideline (2006), which became test guideline 225. Test duration was 28 days after insertion of the test organisms. An NOEC/EC50 approach with spiking of sediment was conducted with 6 concentrations: 32.2, 70.0, 154.0, 322.0, 700.0, 1540.0 mg/kg soil dw. 60 worms were exposed per control and 40 worms per test item concentration (6 replicates and 4 replicates, respectively). Water quality parameters like temperature, pH, O2 - saturation and total hardness were determined to be within the acceptable limits.

The concentrations of the test item in the sediment were measured on days 0 and 28 and in the water layer on day 28. A GC-MS was used.

The measured concentrations of the test item in the sediment layer at the beginning of the exposure period were in the range of 47 - 76 %. Moreover, the measured concentrations in both stock solutions of 86 - 88 % in quartz sand confirmed well the target concentrations in the sediment.

At the end of the study the concentrations had decreased to 1 - 21 %. The measured concentrations of both the control and the lowest nominal test concentration (32.2 mg/kg soil dw) were below the LOQ at the test end. Degradation and adsorption to the sediment were expected to occur during exposure.

The contents of the water layer at the test end were negligible at the two highest test concentrations. At 32.2 - 322.0 mg/kg soil dw the test item concentrations were below the LOQ. All evaluations and effect levels were based on the nominal concentrations of the test item.

Mortalities and behavioural differences compared to the control group were observed at 700 and 1450 mg/kg soil dw after 28 days of exposure. At the end the mean number of living worms, incomplete worms as well as the mean dry biomass was significantly different compared to the control at 322.0 - 1540.0 mg/kg soil dw (ANOVA, Dunnett´s method, p<0.05) The validity criteria of the test guideline were met in all points:

- O2 - saturation > 5.4 mg/L at test end

- pH - value between 6 and 9 at test start and test end

- increase of average number of living worms in the control≥ 1.8

An EC50 of 311 (231 - 419) mg/kg soil dw and a NOEC of 154 mg/kg soil dw were derived from the results of this study. (NOACK, 2008)