Theta storage tanks were the primary component of a Malon waste export vessel, designed for the containment of theta radiation, antimatter waste and other industrial byproducts during transport. The tanks were moderately radiation proof, but prolonged proximity to the tanks still led to radiation exposure. In the event of a tank breach or other high radiation leak, the tanks could be jettisoned into space.
In 2375, Fesek told Chakotay of a legend which claimed poisonous radiogenic waste creatures called Vihaar were created and lived in these tanks, causing damage to the ship. (VOY: "Juggernaut")