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The Petrotox estimated freshwater fish 96 hour LL50 value is 34.05mg/l based on mortality. The Petrotox estimated freshwater fish 28-day NOELR (No Observed Effect Loading Rate) value is 7.618 mg/l for 2-methylbutane, based on growth. This is supported by a read across LC50 (96 hour) of 4.26 mg/l based on mean measured concentrations for n-pentane. Acute toxicity data for fish of an LC50 (96 hour) of 4.26 mg/l, based on mean measured concentrations, has been read across within the category from n-pentane and supported by QSAR estimate of12.8 mg/l.

The Petrotox estimated freshwater invertebrate 48 hour EL50 value is 59.44mg/l based on mobility. The Petrotox estimated freshwater invertebrate 21-day NOELR (No Observed Effect Loading Rate) value is 13.29 mg/l for 2-methylbutane, based on reproduction. The supporting study for acute toxicity of 2-methylbutane to aquatic invertebrates is Adema and Bakker (1986). This is equivalent to OECD 202, using a static, closed system with low headspace, a standard test species (Daphnia magna) as well as two marine crustaceans, Chaetogammarus marinus and Mysidopsis bahia. C marinus LC 50 (96 hours) = 3.2 mg/l (initial measured concentration) and M bahia = 3.2 mg/l (initial measured concentration). The 48hr EC50for Daphnia magna reported was 2.3mg/l, based on initial measured concentrations. The true EC50 value maybe higher since loss of the starting material was determined 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.

The Petrotox estimated algal, 72-hr EL50 value for this substance is 25.12mg/L based on growth inhibition.The estimated algal, 72-hr NOEL value for this substance is 5.62mg/L based on growth inhibition. This is supported by read across within the category from n-pentane, which gives an EC50 based on growth rate of 10.7 mg/l and a NOEC of 2.04 mg/l.An alga NOEC of 2.04 mg l-1has also been read across from n-pentane.

The Petrotox estimated protozoan, Tetrahymena pyriformis, 48-hr EL50 value 130.9 mg/l 2-methylbutane, based on growth inhibition. The estimated NOEL is 29.28 mg/l for 2-methylbutane, based on growth inhibition.

The result indicates that 2 -methylbutane 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.