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Endpoint summary

Additional information

Biodegradation in water

Two biodegradation studies were conducted on the substance: OECD 301F "Ready Biodegradability; Manometric Respirometry Test" and OECD 301B "Ready Biodegradability: CO2 Evolution Test". Both studies were done according to GLP. The OECD 301B -study was considered as a key study. According to this key study, the test substance attained 33 % degradation after 28 days and was therefore could not be considered as readily biodegradable.

The exposure assessment and risk characterisation for the UVCB substance was conducted by using the PETRORISK model. This model uses the information on the biodegradation of the hydrocarbon blocks which have been identified from the substance. Therefore, the biodegradation potential was also estimated with the BIOWIN v4.10 model, which is part of the EPISUITE tool. The probability of biodegradation was estimated for the ten most abundant individual structures of the substance according to the available analytical information.

BIOWIN estimates the probability biodegradation of an organic compound in the presence of mixed populations of environmental microorganisms. Of the ten most abundant individual structures, nine were estimated to be readily biodegradable, and the time required for ultimate degradation for these components were estimated to be days to weeks (5 components), or weeks (4 components).

The key value for CSA was selected based on the result from the OECD 301B biodegradation study conducted for the substance and from the estimated biodegradation of the hydrocarbon blocks of the substance. The substance was considered as not readily biodegradable.

Based on the results of both the studies, the test substance can be concluded as not readily biodegradable in water.

Biodegradation in soil

This substance is a complex mixture of hydrocarbons with different biodegradation properties in soil. Due to its chemical and physical properties, testing biodegradability of this substance in soil is not technically feasible. Therefore, the supporting read-across data on fossil fuel with similar physical-chemical properties and composition was used for CSA to evaluate the biodegradation in soil.

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 a 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 the effect of bioremediation on toxicity of oily soils to plants, bacteria and invertebrate. As a part of the study, rate of bioremediation of two different soil textures (Norrwood soil and mix of Norrwood/Baccto soil) contaminated with three different crude oils were determined. 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 was similar compared to renewable hydrocarbons of wood origin. Testing was conducted in 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 on average highest 13-81 % degradation on all oils in Norrwood/Baccto soil and 23-31 % degradation for all oils on Norrwood soil.

The studies show that hydrocarbons with similar characteristics have been demonstrated to be biodegradable in soil, 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).