Bloontonium

 is a radioactive substance, making its debut in Bloons TD 5 and also makes subsequent appearances in games such as Bloons Super Monkey 2 and it has a big appareance on Bloons Monkey City. It is used in some weapons and it has varying effects on Bloons; ironically, weapons utilising Bloontonium can pop any type of non-Camo bloon. Bloontonium is produced at the Bloontonium Lab, an extreme difficulty track.

Upgrades that use Bloontonium

 * Dartling Gun's Depleted Bloontonium Darts
 * Monkey Ace's Ground Zero and Spectre
 * The Big One for the Mortar Tower
 * Robo Monkey for the Super Monkey
 * Glaive Lord's rotating glaives

Trivia

 * The only items that are references to Bloontonium in Bloons TD 5 are Depleted Bloontonium Darts and Bloontonium Lab.
 * Bloontonium is a pun on the word Plutonium (Pu).
 * There is speculation on whether Robo Monkey's darts contain Bloontonium, as they can pop Lead Bloons.
 * There is also speculation as to whether the Glaive Lord's glaives contain Bloontonium, as they too can pop Lead Bloons without the Red Hot 'Rangs upgrade.
 * On August 30, 2012, it revealed that bloons are made out of Bloontonium.
 * Bloontonium is a radioactive element and so often carries the radioactive hazard symbol on its container.
 * It is likely that the final boss in Bloons Super Monkey 2 contains Bloontonium.
 * Bloontonium is a currency in Bloons Monkey City, mostly used for Monkey vs Monkey.