Chemistry - Why is use of calcium carbide as an artificial fruit ripening agent banned?

Solution 1:

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.

Solution 2:

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.