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Sediment toxicity

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Description of key information

(28-d) NOEC ≥100 mg/kg dw Lumbriculus variegatus (read-across, reliability 2).
(28-d) NOEC ≥560 mg/kg dw Chironomus riparius (read-across, reliability 2).
(28-d) EC50 = 590 mg/kg dw Lumbriculus variegatus (read-across, reliability 2).
(28-d) EC50 >1000 mg/kg dw Chironomus riparius (read-across, reliability 2).

Key value for chemical safety assessment

EC50 or LC50 for freshwater sediment:
590 mg/kg sediment dw
EC10, LC10 or NOEC for freshwater sediment:
100 mg/kg sediment dw

Additional information

A test was performed with the sediment organismLumbriculus variegatus (Goodband and Mullee, 2012). 40-60 worms of Lumbriculus variegatus were exposed to formulated spiked sediment at nominal ‘dry weight’ concentrations of 10, 32, 100, 320 and 1000 mg/kg sediment. The study was carried out according to OECD test guideline 225 and in compliance with GLP. Analytical monitoring was performed, however analysis of ‘wet’ sediment was problematic, therefore measurements with sediment that was ‘pre-dried’ prior to analysis were also carried out.

Analysis of the pre-dried sediment at nominal concentrations of 100, 320 and 1000 mg/kg dw sediment (dried at 60°C for approximately 24 hours) gave measured concentrations of 68% to 78% of nominal and from 28% to 38% nominal on days -9 and 0, respectively. Analysis of the 1000 mg/kg ‘dry’ sediment on Day 28 showed a measured concentration of 51% of nominal. Results for the 10 and 32 mg/kg dw sediment test concentrations were variable since these were close to or below the limit of quantitation of the analytical method. The low recovery rates can be attributed to the difficult nature of the test substance; losses may have occurred due to volatilisation during media preparation, or due to non-extractable residues bound to the sediment phase.

Analysis of the overlying water on Days 0 and 28 gave measured concentrations less than the limit of quantitation of the analytical method. Results for the interstitial pore water were below the limit of quantitation on Days 0 and 28 at 10 mg/kg dw sediment and on Day 0 at 1000 mg/kg dw sediment. A measured interstitial pore water concentration of 7.1 mg/l was determined at 1000 mg/kg dw sediment on Day 28.

Based on survival, the 28-day EC50was determined to be 590 mg/kg dw sediment, and the NOEC was 100 mg/kg dw sediment. There were no significant differences in body weight compared to controls at any test concentration.

The toxicity of a sample of GTL Gasoil has also been determined by Harlan Laboratories (Goodband and Mullee, 2011) in a test with the sediment organism Chironomus tentans. The test was conducted in accordance with OECD Test Guideline 218.

Chironomus tentans were exposed to formulated spiked sediment nominal loading rates of 1000 mg/kg of test material over a period of 28 days, following a range finding test where no effects were recorded at 1000 mg/kg. The study was carried out according to GLP and analytical monitoring was performed. Analytical work on the ‘wet’ sediment was problematic, therefore analysis on the ‘dry’ sediment and wet sediment ‘pre-dried’ before analysis sediment was also carried out.

The test results, expressed as the EC50and NOEC values, showed that the sample was not toxic to sediment organisms at 1000 mg/kg over the time period tested.

Analysis of the ‘dry’ sediment on the day of preparation (Day -7) showed measured concentrations to be 93% of nominal. Analysis of the ‘pre-dried’ sediment showed the measured concentrations to be stable for the duration of the study. Analysis of the overlying and interstitial pore water on Days 0 and 28 gave measured concentrations below the limit of quantitation of the analytical method.

It should be noted that the tests were designed to evaluate the toxicity of single substances and not complex mixtures such as the test item 'Distillates (Fischer-Tropsch), C8-26-branched and linear' which is considered as an UVCB substance. This means that greater care should be taken in the interpretation of the data (see also 7.1.2.2).

 

The toxicity of a sample of GTL Base Oil Distillates has been determined by Harlan (Goodband, 2011) in a test with the sediment organism Chironomus tentans. The test was conducted in accordance with OECD Test Guideline 218.

Chironomus tentanswere exposed to formulated spiked sediment nominal loading rates of 100, 180, 320, 560 and 1000 mg/kg of test material over a period of 28 days. The study was carried out according to GLP and analytical monitoring took place. Analytical work on the ‘wet’ sediment was problematic, therefore analysis on the ‘dry’ sediment was also carried out.

The test results, expressed as the EC50and NOEC values, showed that the sample was not toxic to sediment organisms at 1000 mg/kg over the time period tested.

Analysis of the ‘dry’ sediment on the day of preparation (Day -7) showed measured concentrations to range from 90% to 111% of nominal. Analysis of the overlying and interstitial pore water on Days 0 and 28 showed measured concentrations to be <LOQ.

Conclusion

 

Long-term (28-d) sediment toxicity tests are available for two GTL-derived substances in the relevant carbon number range. For GTL Gasoil (C8-C26) tests were conducted up to 1000 mg/kg dw loading rate with Lumbriculus variegatus and Chironomus riparius. Based on the studies available, Lumbriculus variegatus appeared to be the more sensitive species, with an EC50of 590 mg/kg dw and NOEC of 100 mg/kg dw based on mortality. For Chironomus riparius, the EC50was >1000 mg/kg dw and NOEC ≥1000 mg/kg dw. For GTL Base Oil Distillates (C18-C50) a study with Chironomus riparius was conducted. In this study, the EC50was >1000 mg/kg dw and NOEC ≥1000 mg/kg dw for development. The EC50was >1000 mg/kg dw and NOEC = 560 mg/kg dw for mortality and emergence rate. The OECD test guidelines for long-term sediment toxicity are designed for monoconstituent substances rather than UVCB substances such as these, therefore interpretation of the results should be done with caution. However, the studies indicate that these substances are not toxic to sediment-dwelling organisms at high dose levels. The results cannot be used to derive a meaningful PNEC for Hydrocarbons, C18-C24, isoalkanes, <2% aromatics. It is not possible to derive a meaningful PNEC for the sediment compartment from these whole-substance data.

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