Thermal cracking oil from blends of rubber, fuel oils and paraffin waxes, steam-stripped

Short-term toxicity to fish

Description of key information

The acute toxicity to fish of the hydrocarbon fraction of the UVCB substance Thermal cracking oil from blends of rubber, fuel oils and paraffin waxes, steam-stripped, was calculated to be 0.44 mg/l (96 hour LD50) using the PETROTOX model, made available by CONCAWE, which uses the Hydrocarbon Block Model to predict the eco-toxicological endpoints. The hydrocarbon fraction of the oil was found to drive the aquatic toxicity of the substance as whole.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.44 mg/L

Additional information

The acute toxicity to fish 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. The 96 hour LD50 of the hydrocarbon fraction of the UVCB to fish was estimated to be 0.44 mg/l using PetroTox.

The hydrocarbon fraction of the oil equates to 93.5% of the oil; as such supporting information is provided for the remaining 6.5% of the oil. The potential toxicity to fish of the non-hydrocarbon components of the UVCB was determined via a literature search for applicable data on the substances. The only non-hydrocarbon components in the substance that have significantly greater toxicity than the hydrocarbon elements are the two nitriles, hexadecanitrile and eicosanitrile. These components make up a combined fraction of 1.7 % w/w of the substance. If the recommended assessment factors applied to the nitriles the toxicity of the overall substance will be mainly due to the nitriles. Therefore the PNEC of the substance will be based on the total nitrile content of the substance. Nitriles of chain length C20 or above are predicted to have such a low aqueous solubility that they would not display toxicity at saturation. However, as the substance is a UVCB, the conservative approach was taken to treat all nitriles of C18 or above chain length as octadecanitrile. Octadecanitrile being the longest chain nitrile predicted to display chronic aquatic toxicity at saturation.

The acute toxicity to fish of the nitrile fraction of the substance was calculated using the ECOSAR model (v 1.11), which was developed by the US EPA and uses a database of measured data to calculate the baseline ecotoxicity of organic compounds. The model calculates the baseline toxicity of a substance by assuming that the substance behaves as a narcotic and the toxicity is correlated to the partition co-efficient. It then highlights functional groups that have been shown to display excess toxicity. Neither nitrile contains functional groups that display excess toxicity and are therefore viewed as “neutral organics”. If a substance has a very high partition co-efficient, it is assumed that the substance is unlikely to be soluble enough for aquatic organisms to be exposed to the substance. Based on the model's partition-coefficient cut-off values, and the high log Kow (log Kow of hexadecanitrile was predicted to be 6.73, whilst the log Kow of octadecanitrile was predicted to be 7.71) it is concluded that the nitrile components of the oil (hexadecanitrile and octadecanitrile) have no acute effect on aquatic toxicity at saturation. It is therefore considered that the hydrocarbon fraction of the oil drives the acute toxicity to fish.