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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 29.3mg/l based on mortality.

Measured data has been used to support the Petrotox values and where no measured data were available for cyclopentane, read across within the category has been applied. Acute toxicity data was available for n-pentane for fish, invertebrates and algae and an acute toxicity study was available for 2-methylbutane usingDaphnia magna. The lowest acute LC50or EC50value was for 2-methylbutane usingDaphnia magnawith an EC50of 2.3 mg.l-1. A similar EC50of 2.7 was also reported for n-pentane. An alga NOEC of 2.04 mg l-1was also reported. However, this value was not deemed suitable for use for further assessment despite being the lowest endpoint reported as, in accordance with the guidance, ‘In general an algal EC10or NOEC should not be used unsupported by long term EC10or NOECs of species of other trophic levels’. In addition, this long term result was not from the species with the lowest L(E)C50and so it cannot be regarded as protective of other more sensitive species using the assessment factors available.

The result indicates that cyclopentane would not meet the criteria for toxic in the PBT assessment. However, the 48 hr EC50of 2.3 mg/l reported forDaphnia magnawould result in a GHS classification of acute category 2 with the hazard phrase ' toxic to aquatic life'.


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.