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Fruits like mangoes can be ripened using agents like ethylene, acetylene or calcium carbide. Of these, the latter is dangerous and is banned in most countries. Wikipedia says it is because calcium carbide has traces of arsenic and phosphorus. Is there any other reason?

Will it still be unsafe if pure calcium carbide is used?

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    $\begingroup$ I have merged your two questions into one. I normally wouldn't do that, but in this case they seem too related to keep them apart and the current answer partly already addresses your second concern. $\endgroup$
    – Martin - マーチン ♦
    May 16, 2017 at 7:33
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    $\begingroup$ Thanks for the edit! I was under the impression double questions were not allowed. $\endgroup$
    – Ashwin
    May 16, 2017 at 7:38
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    $\begingroup$ If they are that closely related, I believe it's okay, and even better to ask them together. You are addressing the same people who are answering any way, and the whole process is not too broad to be considered together. When they are conceptually more loosely related, it's preferable to keep them separated. That's why I said I normally wouldn't do this, so your impression is right, this is an exception. $\endgroup$
    – Martin - マーチン ♦
    May 16, 2017 at 7:44
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    $\begingroup$ Presumably $\ce{CaC2}$ is only used to produce acetylene anyway by reacting with water. I suspect this refers to atmospheric water which isn't well-controlled so could lead to a build-up of acetylene. If the $\ce{CaC2}$ is used in an acetylene generator that presumably counts as using acetylene not $\ce{CaC2}$. $\endgroup$
    – Chris H
    May 16, 2017 at 8:44
  • $\begingroup$ My guess is that pure CaC2 is costlier to synthesize and people would use the industrial grade version which contains harmful chemicals. Thus it is banned, not due to chemical reasons. $\endgroup$
    – Ashwin
    May 16, 2017 at 9:02

2 Answers 2

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According to Anwar et al. the use of $\ce{CaC2}$ is discouraged due to

dangers of explosion and carryover of toxic materials like arsenic and phosphorus to consumers, thus making the healthy fruit poisonous. Since no technical knowledge is considered necessary for its anomalous use, higher quantity of calcium carbide needed to ripen immature fruit, makes them tasteless.

For references and more information, see: Anwar, R., A.U. Malik, M. Amin, A. Jabbar and B.A. Saleem, Int. J. Agri. Biol. 2008, 10, 35–41. Available at researchgate.net.

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    $\begingroup$ I have no idea what the second sentence of the quote is supposed to mean! $\endgroup$
    – David Richerby
    May 16, 2017 at 9:53
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    $\begingroup$ It is directly from the linked paper and seems to be badly written. This is what I understood. Since Calcium Carbide can be used by anyone, there is a chance that people will use a higher quantity as it should hasten ripening. This leads to the fruit becoming tasteless, in addition to it being poisoned. $\endgroup$
    – Ashwin
    May 16, 2017 at 11:56
  • $\begingroup$ Yeah, it's a bit poorly formatted, but I interpreted it as Ashwin did. People with little to no understanding on the effects of the chemical use large quantities of it, and end up spoiling the taste. $\endgroup$
    – Bdrs
    May 17, 2017 at 8:24
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Calcium carbide is typically used by traders who can't afford a proper infrastructure for fruit ripening (sealed storage locations and gas generators). Carbide stones are put in permeable packets (typically paper bags) and hanged above the fruit boxes, where they absorb water from the air to produce acetylene gas.

This leads to two issues:

  • the concentration of acetylene is uncontrolled, and given enough moisture can reach explosive levels
  • permeable bags release fine particles of reaction byproducts which land on the fruits

Of course, pure calcium carbide would be safe, at least from the nutrition perspective. You'd still have the risk of explosion though, and because carbide cannot be used safely for fruit ripening, nobody is producing it in food grade in the first place.

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  • $\begingroup$ Calcium carbide is in no way safe for consumption - it reacts with water to produce a gas and an alkali. $\endgroup$
    – gsurfer04
    May 16, 2017 at 18:17
  • $\begingroup$ Why does acetylene explode? @gsurfer04. I guess the other product of hydrolysis is Calcium Hydroxide. Is that bad for fruits? $\endgroup$
    – Ashwin
    May 17, 2017 at 4:18
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    $\begingroup$ @Ashwin (1) acetylene is a combustible gas which, like most such gases is explosive when mixed with air. As for (2), pure byproducts would be mostly harmless in small concentration (though CaO may still damage the fruit skin in some cases). But nobody bothers to produce pure carbide, so you're likely to get some arsenic along with CaO. $\endgroup$
    – Dmitry Grigoryev
    May 17, 2017 at 14:43
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    $\begingroup$ Again, chances of poisoning would be slim to none if everyone washed their fruits properly, but food is supposed to be safe in all cases. It's like keeping rat poison next to your salt dispenser: it doesn't make your salt poisonous, but is very unsafe nevertheless. $\endgroup$
    – Dmitry Grigoryev
    May 17, 2017 at 14:49
  • $\begingroup$ Nice analogy to make me understand. $\endgroup$
    – Ashwin
    May 18, 2017 at 4:34

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