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Petrotox was used to derive data for the toxicity of n-pentane to aquatic invertebrates, fish and algae. 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.Measured data are also available for n-pentane for fish, invertebrates and algae. The lowest acute LC50or EC50value for n-pentane was usingDaphnia magnawith an EC50of 2.7 mg.l-1. 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 supporting study (Adema and Bakker 1986) follows equivalent guidelines to OECD 201. In this aquatic invertebrates study, three species were used,Daphnia magnaand two marine curstaceans,Chaetogammarus marinusandMysidopsis bahiawere used in the study. The reported LC50(96 hours) for bothC.marinusandM.bahiawas 3.6 mg/l (based on the initial measured concentration). The effect concentration forDaphnia magnawas the most conservative and so was selected for further assessment.TheDaphnia magnaEC50(48 hours) for n-pentane = 2.7 mg/l (based on initial measured concentration). The true EC50may be higher than the reported value due to loss via volatillisation during the test. This point is highlighted in the report itself. However the study was selected as key study in the EU Risk assessment report for n-pentane and can be considered acceptable for assessment. In the EU RAR, the original data is reanalysed and they state that using mean exposure concentration would probably give somewhat lower values by a factor of 0.88 -0.51. The Adema report does not allow exact recalculation but based on the available information the EC50/LC50would be 2.4, 1.4 and 1.8mg/l for D. magna, C.marinus and M.bahia respectively.

The results indicate that n-pentane would not meet the criteria for toxic in the PBT assessment. However, the 48 hr EC50of 2.7 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.