RuneScape Classic Wiki
RuneScape Classic Wiki
The main RuneScape Wiki has an article on: Poisoned Steel Spear
The Old School RuneScape Wiki also has an article on Poisoned Steel Spear.

A Poisoned Steel Spear is a poisonous spear which can be made by using weapon poison on a Steel Spear. It can be thrown or used while in melee combat.

They have no level requirements to wield, which may be a glitch, as the non-poisoned version requires 5 attack and 5 ranged to wield.