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Toxicity to terrestrial plants

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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 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 fuels (fresh and weathered) contaminated soils are discussed.

A study by Trapp et al. (2001) determined 184-hour phytotoxicity using Salix viminalis and Salix alba to gasoline (95 ROZ). Test used transpiration, growth and water use efficiency as toxicity parameter. This study also included phytotoxicity tests using soil samples taken from former gas filling station.

Results showed that in laboratory tests fresh gasoline at concentration of 1000 mg/kg was fatal to Salix viminalis and Salix alba and the trees were dead after 184 hours. With concentration of 10000 mg/kg the lethal effect occurred even faster. One contaminated soil sample from the gas filling site contained 921 mg/kg gasoline range, which is similar to the concentration used in the artificial contamination test. Trees growing in this soil finally died, but slower than in soil with fresh gasoline. This indicated that the weathered gasoline had less toxic effect than fresh gasoline.

In the study by Dorn P.B. and Salanitro J.P. (2000), the toxicity of soils spiked with crude oil (Light-Gulf of Mexico) before and after 9 and 11 months of bioremediation in Norrwood and Norrwood/Baccto soils were examined. 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 21-days plant growth and germination inhibition tests using corn (Zea mays), wheat (Tritium aestivum) and oat (Avena sativa).

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 721.9-740.6 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. 6.1 % 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 ca. 0.45 % in the registering substance).

Results showed that in untreated soils, the plant seed germination was significantly decreased in all plants, but in bioremediated soils, seed germination was not significantly lower than in control soils. Plant growth was similarly reduced significantly in untreated soil, but although growth was enhanced in bioremediated soils, it was still lower compared to control soil.

In conclusion, gasoline in soil at concentration of 1000 mg/kg has been shown to be fatal to trees (Trapp et al. 2001), but weathering can decrease the ecotoxic effects. In study by Salanitro J.P and Dorn P.B. (2000), weathered light crude oil (1000 mg/kg) in bioremediated soil (total organic content 0.3 %) reduced plant weight of corn, wheat and oat 16, 32 and 50 %, respectively, compared to control. Based on their result and findings from literature, Salanitro J.P. and Dorn P.B. (2000) suggested that hydrocarbon phototoxicity cannot be predicted and varies widely with oil and soil type, concentration and species tested.

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