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In particular, how do a methylene more (in the case of the pentane) and a methylene less (in the case of the octane) make the difference in harmfulness to the environment in comparison with, respectively, the butane and the nonane?

I saw that butane and nonane are not classified as dangerous, but I have just done a research and it turns out nonane is harmful to fish, just like octane, but the difference is that the nonane becomes aqueous more difficult because of its low solubility. But I read that its soluble part is still dangerous for aquatic life. Then the question is: Shouldn't it be classified as dangerous anyway?
The propane, as well, appears to be harmful to the fish, while I can find nothing but "not classified as dangerous", as for the butane. Is LDC3's answer the explanation?

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  • $\begingroup$ Propane and butane are gases at normal temperatures so they will evaporate into the atmosphere before getting into the water supply. The water solubility goes down with hydrocarbon size so many higher hydrocarbons will also not be available in large enough quantities in the water to cause harm. Being a hazard is a product of availability as well as the inherent toxicity if ingested. Hence the results. $\endgroup$
    – matt_black
    Apr 21, 2019 at 14:58

2 Answers 2

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GHS09

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.

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  • $\begingroup$ I see, thank you. Indeed, I had just found out that the soluble part of the nonane still harms aquatic life. Then, shouldn't it be classified as dangerous anyway? I think this could cause misconceptions. How about the butane? Is it indeed because it wouldn't accumulate? $\endgroup$
    – Vincenzo Oliva
    May 23, 2015 at 18:40
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    $\begingroup$ @VincenzoOliva Concerning chronic aquatic toxicity, only substances of Category 1 (H410) and Category 2 (H411) show the ‘environment’ pictogram. No pictogram is used for Category 3 (H412) and Category 4 (H413, e.g. nonane). With regard to butane, I am inclined to follow LDC3's explanation. $\endgroup$
    – user7951
    May 23, 2015 at 19:10
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Butane is a gas at STP, so it would not accumulate in one location.

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