Thorium Headed Arrow

Thorium Headed Arrows were the second most powerful arrow in Kalimdor and the Eastern Kingdoms, right behind the Doomshot, until the addition of Wicked Arrows in patch 2.0.1. If one can overcome the expense of crafting Thorium Shells to trade for them, these arrows are quite useful for the span of three levels from 52-55, when Wicked Arrows become usable.

Source
Thorium Headed Arrows were a quest reward from the following repeatable quests: Each quest requires you to turn in 200 Thorium Shells.
 * given by Artilleryman Sheldonore in Ironforge
 * given by Bounty Hunter Kolark in Orgrimmar