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Short-term toxicity to aquatic invertebrates

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Description of key information

The estimated freshwater invertebrate 48 hour EL50 value is 51.15mg/l based on mobility. To support this value, the toxicity of cyclopentane to aquatic invertebrates was read across within the category from 2-methylbutane. The 48hr EC50 for Daphnia magna reported was 2.3mg/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 invertebrate 48 hour EL50 value is 51.15mg/l based on mobility.

As there was no measured data available, this value was supported by read across from 2 -methylbutane. The study (Adema and Bakker 1986) is equivalent to OECD 202, using a static, closed system with low headspace, a standard test species (Daphnia magna) and the standard exposure duration (48hrs). The results were based on initial measured concentrations. The 48hr EC50for Daphnia magna reported was 2.3mg/l for 2-methylbutane and 2.7 for n-pentane. Two marine crustaceans were also used in the study, Chaetogammarus marinus and Mysidopsis bahia. As the lowest EC50 was reported for 2-methylbutane, this was considered for further assessment. The tests with marine crustaceans were carried out with only one animal per container (10 individuals per concentration). LC50values for both species were based on the initial measured concentration. C marinus LC 50 (96 hours) = 3.2 mg/l (initial measured concentration) and M bahia = 3.2 mg/l (initial measured concentration). The most conservative effect concentration was for Daphnia magna with a 48 hour EC50of 2.3 mg/l and so this was used for further assessment to derive the PNEC.The true EC50 value maybe higher since loss of the starting material was determine to be about 50% during the 48hr exposure period. The version of the study reviewed lacked the annex containing key details on the test conditions and therefore these could not be reviewed and generally validated against OECD criteria.

There is no measured data available for cyclopentane and therefore a QSAR has been used to calculate a value. The calculated 48 hr LC50 has been estimated to be 4.659mg/l and the 96 hour LC50 has been estimated to be 3.483 mg/l for saltwater mysid shrimp. The ECOSAR model is a reliable and appropriate QSAR model to apply to cyclopentane as it is based on a related chemical dataset that calculates the toxicity of neutral organic hydrocarbons whose mode of action is non-polar narcosis. The endpoint calculated here is therefore a reasonable estimate of its baseline toxicity.

This result would not indicate that cyclopentane would meet the criteria for toxic in the PBT assessment. However, the 48 hour EC50 of 2.3 mg/l would result in a 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.