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Environmental fate & pathways

Biodegradation in soil

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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. Read-across data from similar fossil diesel fuels is used as a supporting information for CSA.

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Additional information

This substance is a complex mixture of hydrocarbons with different biodegradation properties in soil. Due to its chemical and physical properties, testing of this substance is not technically feasible. Literature shows that hydrocarbons with similar characteristics are not usually readily biodegradable, but have been demonstrated to be degradable when bioremediated with added nutrition and aeration. Weathering process can also affect the biodegradability and toxicity of petroleum hydrocarbons in soils by changing the hydrocarbon composition (Dorn & Salanitro 2000).

Van Gestel et al. (2001) aimed to investigate the effect of acute and chronic bioassays on ecological risk assessment of mineral oil in historically petroleum contaminated soil. As a part of the study, contaminated soil from harbour was bioremediated in pilot scale bioremediation plant. Bioremediation was done by stimulating microbes with nutrients and air flow. Oil concentrations and chemical characteristics were analysed using gas chromatograph and flame ionization detector.

After 12 weeks of incubation D50 values for samples 3, 5 and 11 were 48 d, 62 d and 56 d. Oil concentration degradation percentages for the same samples were 69 %, 54 % and 63 %, respectively. The number of MPNtotal bacteria and dehydrogenase activity of the oil-polluted soils did not show any correlation with oil concentrations in the soil samples. In general, soil bioremediation resulted in higher microbial biomass densities and decreased oil concentrations.

Dorn & Salanitro (2000) investigated how bioremediation on affects in the toxicity of oily soils by using bioassays. Two soil textures (Norrwood soil and mix of Norrwood/Baccto soil) were artificially contaminated with three different crude oils. 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. The light crude oil was similar to the renewable hydrocarbons of wood origin (diesel type fraction). Testing was conducted in a pilot plant consisting of stainless steel chambers, which were aerated during the incubation. Before starting the experiment, fertilizer solution was added to each oily soil. The results showed that the average highest degradation was 13 -81 % on all three oils in Norrwood/Baccto soil and 23 -31 % in the Norrwood soil.

On the basis of the literature, fossil diesel fuels similar to renewable hydrocarbons of wood origin are not readily biodegradable in soil, but when conditions are favourable to microbes and there are enough nutrients and air available, biodegradation is a potential fate process in soils.