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Toxicity to soil microorganisms

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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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In study by Labud et al. (2007), sandy soil (organic carbon content 5.7 %) and clayey soils (organic carbon content 13.8 %) were spiked with 5 % and 10 % (w/w) of gasoline and incubated in glass pots under controlled conditions (50-70% WHC and room temperature) for 180 days. During the study Microbial Biomass Carbon was used to evaluate toxicity response to microbes.

Results for MBC after 180 days of incubation were 20 mg/kg (10 % gasoline) and 58 mg/kg (5 % gasoline) for sandy soil and 192 mg/kg (10 % gasoline) and 169 mg/kg (5 % gasoline) for clayey soil. Compared to control sample MBC values were reduced by 33% (5% gasoline) and 65 % (10 % gasoline) in sandy soil and 27 % (5 % gasoline) and 17 % (10 % gasoline) in clayey soil.

In general, results showed that in general gasoline had toxic effects on soil microbes. Toxic response was slightly higher to microbes in sandy soils than in clayey soils. This was probably because the difference between the soil properties. Clay and organic matter are known to absorb contaminants and decrease their concentrations in aqueous and gaseous phase, and they also decrease their transport and bioavailability.