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

Toxicity to aquatic algae and cyanobacteria

Description of key information

EC50 (72h, growth rate) = 10.7 mg/L (OECD 201, measured, Scenedesmus capricornutum, read-across from pentane)
NOEC (72h, growth rate) = 2.04 mg/L (OECD 201, measured, Scenedesmus capricornutum, read-across from pentane)

Additional information

There are no data available on the toxicity to aquatic algae 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 72 hour EL50 and NOELR values based on growth rate are as follows:

Hydrocarbons, C6, isoalkanes, < 5% n-hexane: EL50 = 13.56 mg/L (Concawe 2009)

Hydrocarbons, C6, isoalkanes, < 5% n-hexane: NOELR = 3.034 mg/L (Concawe 2009)

Hexane: NOELR = 2.077 mg/L (Concawe 2009)

Hydrocarbons, C5-C7, n-alkanes, isoalkanes, n-hexane rich: EL50 = 9.947 mg/L (Concawe 2009)

Hydrocarbons, C5-C7, n-alkanes, isoalkanes, n-hexane rich: NOELR = 2.225 mg/L (Concawe 2009)

Hydrocarbons, C6, n-alkanes, isoalkanes, cyclics, n-hexane rich: EL50 = 9.902 mg/L (Concawe 2009)

Pentane: EL50 = 20.33 mg/L (Concawe 2009)

Pentane: NOELR = 4.549 mg/L (Concawe 2009)

Experimental data are also available for hexane and pentane. In a study with Chlorella pyreniodosa exposed to hexane a nominal EC50 of 2.66% v/v based on growth rate was determined (Stratton & Smith, 1998). A study on pentane with Scenedesmus capricornutum was conducted by ExxonMobil Chemical (1997). The measured EC50 values were determined to be 10.7 mg/L and 7.51 mg/L for growth rate and biomass, respectively. NOECs for growth rate and biomass were reported as 2.04 mg/L and 1.26 mg/L, respectively.

Of the studies providing experimental results, ExxonMobil Chemical (1997) was conducted according to GLP and OECD guideline 201. An EC50 of 10.7 mg/L and a NOEC of 2.04 mg/L for growth rate were reported as the most critical experimental values, which are supported by a number of calculated EL50 values in the same range (Concawe 2009), and thus this study is chosen as key.