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There are no measured acute toxicity data available for isoheptane on fish. Data are read-across to hydrocarbons, C7-C9, isolkanes based on a category-approach. A study with the latter substance was conducted according to OECD 203 (CEFIC 1995). The acute toxicity, as measured by mortality to rainbow trout (Oncorhynchus mykiss), was evaluated in freshwater by using water accomodated fractions (WAFs). Under the conditions of this study, the test substance, hydrocarbons, C7-C9, isoalkanes produced acute lethal toxicity to Oncorhynchus mykiss at 18.4 mg/L (CEFIC 1995) based on nominal loadings of the test substance in water.

The long-term toxicity to fish was calculated using the Petrotox computer model (v. 3.04), 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 28 -day NOELR value is 2.426 mg/L.

Data on the acute toxicity on freshwater and marine aquatic invertebrate species are read-across to 2,3,4-trimethylpentane (Adema & van den Bos Bakker 1987). The acute toxicity, as measured by immobilisation of Daphnia and mortality to Chaetogammarus and Mysidopsis, was evaluated in fresh- and saltwater by using water accomodated fractions (WAFs). The test substance produced acute toxicity to Daphnia and Mysidopsis at 2.4 mg/L, and to Chaetogammarus at 5.4 mg/L based on nominal loadings of the test substance in water. Data on the chronic toxicity are read-across to hydrocarbons, C7-C9, n-alkanes, isoalkanes, cyclics based on a category approach. A study of the chronic toxicity, as measured by survival, sublethal effects, reproduction, and length of first generation adults, conducted with Daphnia using WAFs (Wilbury Laboratories 2004) resulted in a NOELR of 1 mg/L.

 

Toxicity to algae and microorganis was estimated using the Petrotox computer model (v. 3.04). The estimated freshwater algae 72-h EL50 (Effect Loading Rate) and NOELR (No Observed Effect Loading Rate) values are 8.204 and 1.835 mg/L, respectively, based on biomass. The estimated protozoan, Tetrahymena pyriformis, 48-hr EL50 value is 42.756 mg/L based on growth inhibition.