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Toxicity to soil macroorganisms except arthropods

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Description of key information

This substance is a complex mixture of hydrocarbons with different biodegradation properties in soil. Testing of this substance is not technically feasible. Supporting information on literature for similar weathered fossil fuels (fresh and weathered) was discussed. For the purpose of hazard assessment, and the exposure assessment and risk characterisation of indirect releases, Soil PNECs for representative hydrocarbon blocks were calculated with a modelling tool (PETRORISK, see CSR sections 9&10).

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Additional information

This UVCB substance is a complex mixture of hydrocarbon compounds with variable physicochemical and ecotoxicological properties. Application of standard ecotoxicological tests to such UVCB substances includes a number of technical problems such as low water solubility and volatility of the substance. As supporting information the read-across studies on fossil fuel (fresh and weathered) contaminated soils are discussed.

Dorn P.B. and Salanitro J.P. (2000) aimed to examine the toxicity of soil spiked with crude oil before, during and after of 9 and 11 months of bioremediation in Norrwood and Norrwood/Baccto soils, respectively. Norrwood soil was silty loam obtained from cotton field near College Station, Texas, and contained 15 % clay, 60 % silt and 0.3 % organic carbon. The Baccto topsoil was commercially available sandy loam potting soil. Norrwood/Baccto soil mixture consisted 75 % from Norrwood and 25 % from Baccto soil (v/v) and contained 20 % clay, 56 % silt and 4.65 % organic content.Toxicity was examined by conducting 14-days LC50 tests using earthworms (Eisenia fetida). 

The crude oil used in this study had similar characteristics compared to renewable hydrocarbons of wood origin (diesel type fraction). The densities of the test crude oil and the renewable fuel are close to another (approx. 780 kg/m3 in Light-Gulf of Mexico and 804.4 -804.8 kg/m3 in the renewable hydrocarbons of wood origin) and they contain about the same amount of aromatics (6.4 % in Light-Gulf of Mexico and ca. 5.5% in renewable fuel). The test substance (Light-Gulf of Mexico) in the study by Dorn P.B. and Salanitro J.P. (2000) contains higher percentage of benzene than the renewable fuel (0.538 % in Light-Gulf of Mexico and < 0.1 % in the registering substance).

Initial diesel concentrations in soils were 4.2 g/kg (Norrwood soil) and 9.6 g/kg (Norrwood/Baccto soil) and after bioremediation 1 g/kg (Norrwood) and 1.2 g/kg (Norrwood/Baccto). Initial toxicity (t=0) in Norrwood soil was 22 % (LC50 as % soil) and in Norrwood/Baccto soil 36 % (LC50 as % soil). In Norrwood soil all animal survived (LC50 as % soil was 100 %) after 12 months of bioremediation, whereas in Norrwood/Baccto soil all animals survived after 3 months of treatment. Results showed that toxicity was lower in soil with higher organic matter.