Hydrocarbons, C5-C7, n-alkanes, isoalkanes, < 5% n-hexane

Short-term toxicity to fish

Description of key information

LC50 (96h) = 4.26 mg/L (OECD 203, measured, Oncorhynchus mykiss, read-across from pentane)

Additional information

There are no data available on the acute toxicity to fish of hydrocarbons, C5-C6, n-alkanes, isoalkanes, <5% n-hexane. However, there are reliable data available considered suitable for read-across using the analogue approach.

The target substance is a hydrocarbon solvent with carbon numbers in the range of C5 to C6. The main constituents of the mixed solvent consist of about 43% of C6 species and about 57% of C5 species. n-Hexane is only present in concentrations < 5% of the total volume.

Taking into account all available data, animal and human toxicity data as well as environmental fate and effects data show that source substances have a similar (eco-)toxicological and environmental fate properties as the target substance.

Therefore, read-across is performed based on an analogue approach (for details please refer to the analogue justification which is attached in section 13 of the technical dossier).

For a number of analogue substances the aquatic toxicity was estimated by a QSAR, 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 partition coefficients K(MW) that describe the partitioning of the hydrocarbons between the water and organism. The estimated freshwater 96 hour LL50 values based on mortality are as follows:

Hydrocarbons, C6, isoalkanes, < 5% n-hexane: 18.27 mg/L (Concawe 2009)

Hydrocarbons, C5-C7, n-alkanes, isoalkanes, n-hexane rich: 13.3 mg/L (Concawe 2009)

Hydrocarbons, C6, n-alkanes, isoalkanes, cyclics, n-hexane rich: 13.37 mg/L (Concawe 2009)

Pentane: 27.55 mg/L (Concawe 2009)

Experimental data are also available for hexane and pentane. In a 48h non-guideline study with Oryzias latipes exposed to hexane an LC50 of >1 mg/L was determined (Tsuji, 1986). A study according to OECD 203 with pentane was conducted by ExxonMobil Chemical (1997). Oncorhynchus mykiss were exposed for 96h under semi-static conditions. The LC50 was determined to be 4.26 mg/L.

Since in the study by Tsuji (1986) followed no guideline, the exposure period lasted only 48h and only a single concentration of 1000 µg/mL was tested, the LC50 greater than 1 mg/L is difficult to assesss and the test is used as supporting study only. The study conducted by ExxonMobil Chemical (1997) is a GLP guideline study, which would be rated RL1 if not used as read-across here. The LC50 of 4.26 mg/L determined therein based on measured data is the most critical value for this endpoint and thus chosen as key value.