Oil spills may originate in natural or anthropogenic causes.
Natural causes - such as oil that seeps from the bottom of oceans which enters the marine environment. Crude oil is formed during long periods of time through natural processes involving organic matter from dead organisms. Thus, oil exists in many environments and may be naturally spilled due to various factors (including climatic conditions, disturbance, etc.). Such natural oil spills may occur in oceans, due to eroding of sedimentary rocks from the bottom of the ocean (the effect may be similar with that of an accidental oil spill from human drilling in oceans such as the recent BP oil spill from the Gulf of Mexico).
Anthropogenic causes - including accidental oil spills (such as the recent BP oil spill in the Gulf of Mexico) as well as leaks and spills due to a large variety of human activities related to oil refining, handling and transport, storage and use of crude oil and any of its distilled products.
Thus, it is evident that a variety of sources for oil spills and a variety of ways the oil could be spilled exist. While various anthropogenic and natural sources of oil spill pollution determine the type and amount of oil spilled, as well as the location of the oil spill, the type of the oil spill pollution is important for the fate and transport of the spilled oil and its impact on humans and the environment. For example: a sudden oil spill involving large amounts spilled (thousands or even millions of gallons - such as that from an oil tanker failure or due to accidents in offshore drilling) could have disastrous effects due to the high concentrations of released contaminants and the difficulty to remediate such big spills. At the same time, an oil spill involving small but continuous releases such as those from leaking pipelines or road runoffs may have little visible effect (they are naturally attenuated usually due to microbial degradation as well as due to many chemical-physical processes).
The type, amount of oil discharged and its location will dictate the oil spill cleanup efforts, which could involve deployment of adsorbent booms, controlled burning, bioremediation, emulsification using detergents for increased degradation.
Even though numerous climate factors and natural disturbances can generate oil spills, the main causes of oil spill pollution are usually of anthropogenic origin. The most commonly encountered anthropogenic sources are the following:
Accidental spills may occur in various circumstances, most often during the following activities:
- Storage - oil and oil products may be stored in a variety of ways including underground and aboveground storage tanks (USTs and/or ASTs, respectively); such containers (especially USTs) may develop leaks over time
- Handling - during transfer operations and various uses
- Transportation - these could be large oil spills (up to million and hundreds of million gallons) on water or land through accidental rupture of big transporting vessels (e.g., tanker ships or tanker trucks). For example, the Exxon Valdez spill was a massive oil spill off the Alaskan shoreline due to ship failure which happened in late 1980’s– oil spill pollution residuals from that spill are still affecting our environment - or smaller oil spills, through pipelines and other devices also happens and their impact is mainly due to a large number of usually minor spills
- Offshore drilling - we have recently experienced the massive oil spill in the Gulf of Mexico, with its terrible consequences on the environment, marine life and humans as the spill continues since April 22, 2010, and it may take a while until a solution is implemented
- Routine maintenance activities - such as cleaning of ships may release oil into navigable waters. This may seem insignificant; however, due to the large number of ships even a few gallons spilled per ship maintenance could build up to a substantial number when all ships are considered
- Road runoff - oily road runoff adds up especially on crowded roads. With many precipitation events, the original small amounts of oil from regular traffic would get moved around and may build up in our environment
Intentional Oil Discharges
Intentional oil discharges are not necessarily malevolent. Most of them occur in the following circumstances:
- Through drains or in the sewer system. This include any regular activities such as changing car oil if the replaced oil is simply discharged into a drain or sewer system
- Indirectly through the burning of fuels, including vehicle emissions; they release various individual components of oils and oil products, such as a variety of hydrocarbons (out of which benzene and PAHs could pose serious health risks).