Not only does used oil pose a serious threat to the environment, it also poses a threat to you. Used oil, if incorrectly disposed of, can make its way into rivers, lakes and streams. This in turn can affect your drinking water as well as the toxin levels in the ocean's.
Used oil also carries heavy metals and toxins as a result of the stresses it undergoes while it lubricates. If not correctly disposed of, these toxins and heavy metals can be released into the environment. Used oil contains arsenic, lead and chromium as well as cancer-causing PAHs.