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Short-term toxicity to fish

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The estimated freshwater fish 96 hour LL50 value is 27.55mg/l based on mortality. This is supported by  read across within the category from n-pentane. The 96 hour LC50 is 4.26 mg/l (95% C.I 3.60 - 5.04 mg/l) .

Key value for chemical safety assessment

Additional information

The aquatic toxicity was estimated using the Petrotox computer model, which combines a partitioning model used to calculate the aqueous concentration of hydrocarbon components as a function of substance loading with the Target Lipid Model used to calculate acute and chronic toxicity of non-polar narcotic chemicals. Petrotox computes toxicity based on the summation of the aqueous-phase concentrations of hydrocarbon block(s) that represent a hydrocarbon substance and membrane-water partitioning coefficients (KMW) that describe the partitioning of the hydrocarbons between the water and organism. The estimated freshwater fish 96 hour LL50 value is 27.55mg/l based on mortality.

This is supported by a measured result. The study (ExxonMobil Chemcal 1997) was conducted according to OECD Guideline 203 (Fish, Acute Toxicity Test) with some minor deviations to minimise volatilisation of the substance. During testing a decrease of 80 % of n-pentane concentration was observed and so a geometric mean was calculated from the fresh and used medium and a 95 % confidence limit was established. The study is otherwise considered reliable for assessment and the LC 50 (96 hours) for n-pentane is considered to be 4.26 mg/l (± 95 % C.I 3.60 - 5.04 mg/L).

The value is also supported by a published study (Morrow 1975), which reported no effects at the nonimal concentrations tested.. The study had no analytical confirmation of test concentrations and the method of application is likely to have resulted in losses of the test item due to volatilization given that aeration was provided and there was headspace. This study was also reviewed in the EU RAR and deemed unsuitable for assessment.

The hydrocarbon block method has been used for environmental risk assessment (see REACH guidance, R7, app.13-1). Aquatic PNECs for hydrocarbon blocks have been derived using the HC5 statistical extrapolation method and the target lipid model using representative structures. See Product Library tab in PETRORISK spreadsheet attached to IUCLID Section 13. Given the large database of freshwater organisms included in the target lipid model, an assessment factor of one has been applied to the HC5.