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Toxicity to microorganisms

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Description of key information

The 72 hour LC50 of the hydrocarbon fraction of the UVCB to SSTP microorganisms was estimated to be 3.21 mg/l using PetroTox. The 72 hour NOEC was predicted to be 0.67 mg/l.

Key value for chemical safety assessment

EC50 for microorganisms:
3.21 mg/L
EC10 or NOEC for microorganisms:
0.67 mg/L

Additional information

The acute toxicity of the hydrocarbon fraction of the UVCB substance Thermal cracking oil from blends of rubber, fuel oils and paraffin waxes, steam-stripped, was calculated using the PETROTOX model, made available by CONCAWE, which uses the Hydrocarbon Block Model to predict the eco-toxicological endpoints. The default systems parameters of PETROTOX are designed to mimic the design of typical experimental systems. Therefore the simulations were performed assuming a 10% headspace volume to account for volatilization of some components. Additionally the particulate organic carbon loading was set at 2 mg/L for algae and SSTP organisms, whereas it was left at 0 mg/L for the fish and daphnia models. It is assumed that the presence of organic carbon would result in the absorption of some of the test substance and hence lower the bioavailability. This approach was consistent with the initial validation of the model. The output of the PETROTOX model gives “Toxic Unit” (TU) values at different loadings that are converted to an LD50. This acute toxicity value is then converted to the chronic NOEL using standard acute to chronic ratios. The 72 hour LC50 of the hydrocarbon fraction of the UVCB to SSTP microorganisms was estimated to be 3.21 mg/l using PetroTox. The 72 hour NOEC was predicted to be 0.67 mg/l.

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