Used oil is only a problem if mismanaged.
Because it is insoluble, persistent and may contain toxic chemicals and heavy metals, used oil that is spilled on the ground, poured down storm drains or disposed of with trash, can pollute surface water or groundwater. Oil spilled or dumped on land reduces soil productivity and may contaminate well water. Used oil can foul sewage treatment processes. Oil films on surface water block sunlight, impair photosynthesis and prevent the replenishment of dissolved oxygen, which can lead to fish kills. Used oil is a regulated waste in Connecticut.