What makes pentane, hexane, heptane, and octane dangerous, while butane and nonane aren't?
Pentane, hexane, heptane, and octane are labelled with the ‘environment’ hazard pictogram (GHS09) since they are considered toxic or very toxic to aquatic life with long-lasting effects (H411 or H410) because of their toxicity to the water flea Daphnia magna in standardized tests.

Nevertheless, nonane is not completely harmless; it still may cause long-lasting harmful effects to aquatic life (H413). However, a pictogram is not required for this hazard category.

According to a comparative study, the toxicity of these substances is mainly determined by their solubility in water and their organism–water partition coefficient.