Environmental Effects of Oil Spill

When an oil spill occurs, many elements of the environment may be affected. Depending on the magnitude of the spill and its location, the effects can vary, ranging from minimal to serious ones. For instance, oil spills can have a major impact on the temporary animal and fish loss of habitat. Heavy oils may affect several organism functions like respiration, feeding, and thermo-regulation. At the same time, the entire ecosystem can change temporarily because of the chemical components and elements of the spilled oil that are toxic to the environment.

Usually, the oil spills occurring in a water environment (e.g., ocean or seas, or leaks from rigs ending up in water) are rapidly degraded as compared to oil spills on land or in the subsurface environment. However, if an aquatic oil spill is substantial enough (such as in the case of Exxon Valdez 1989 spill or the April 2010 BP spill in the Gulf of Mexico from offshore drilling) then the effects on marine life, birds, humans and ecosystems (including marshes and wetlands, as well as shorelines or gulf coasts) could be serious. In order to understand the type and magnitude of oil spill effects, we need to first understand the fate and transport of spilled oil.

The general fate and transport of spilled oil dictates its environmental effects and mainly involves:

the ability of oil to accumulate on top of water bodies forming oil slicks or non-aqueous phase liquids which are generally more resistant to degradation and natural attenuation than the dissolved compounds. From such oil slicks evaporation of many volatile components of oil spill is the dominant process when the oil slick is in contact with air, such as in marine spills
the dissolution of certain more soluble oil compounds happens in time along with some dispersion, diffusion, and advection
while the mechanisms (from above) contribute to the reduction of the oil spill and an increased efficiency of the oil spill cleanup, they also increase the mobility of oil resulting in potential spreading of the oil spill over large areas. These complicate Coast Guard cleanup measures taken in the case of marine spills, for example.
the persistence of many individual oil components makes them accumulate in the environment and living organisms.

The oil resulted from oil spills is transported throughout the environment in various forms, and has various characteristics that influence its effects over the environmental elements. Some of the main characteristics of the oil are briefly presented in the table below:

Main oil characteristics relevant to transportation	Oil Spill environment	Transportation of the spilled oil
Lighter (less dense) than water	Aqueous (e.g., marine)	Spilled oil will accumulate on top of water surface if the oil in the underwater spills (such as the one from offshore drilling) will move upward and settle on the surface of the water. Then, it may disperse over large areas in the marine environment due to the various water currents and waves.
Lighter (less dense) than water	Land or Subsurface	Spilled oil can reach groundwater bodies, in which case it will form a sheen on top of groundwater and will move at lower speeds.
Mixture of volatile compounds (e.g., hydrocarbons)	Aqueous (e.g., marine)	Spilled oil starts evaporating when in contact with air (when it reaches the top of the water), and so the air above the spill becomes polluted with various volatile oil components. Depending on their concentration, such air pollutants may travel by the wind and aerosols.
Mixture of volatile compounds (e.g., hydrocarbons)	Land or Subsurface	Volatilization is accentuated on land surfaces and in shallow subsurface depths, because spilled oil must be in contact with air in order for the volatilization to occur. Once evaporated, the volatile gaseous compounds usually travel upward through soil pores and, depending on the concentration, may reach the surface and accumulate in any existing structure (e.g., homes).
Mixture of compounds with different water solubility	Aqueous (e.g., marine)	Although oil accumulates on top of the water (as non-aqueous phase liquid), some oil compounds may dissolve (to some extent) in the water. If dissolved, such compounds integrate into the sea life.
Mixture of compounds with different water solubility	Land or Subsurface
Formation of oil slicks or sheens on water	Aqueous (e.g., marine)	Because oil and water are not miscible, oil slicks form whenever oil is spilled into the water. These slicks persist in the environment for a long time.
Formation of oil slicks or sheens on water	Land or Subsurface	The oil carried by rainwater in particulate matter forms may persist in the subsurface environments, including the top of groundwater, for decades.
Oil has a physical state (liquid) and biodegradable components	Aqueous (e.g., marine)	Some natural attenuation processes may reduce the amount of oil. This is due to a combination of evaporation, dissolution, and biodegradation of oil spill. In sea or river environments such natural attenuation processes are faster than those in subsurface environments, on land or in groundwater.
	Land or Subsurface
Oil composition involving the presence of individual components with environmental persistence and bioaccumulative potential (e.g., PAHs)	Aqueous (e.g., marine)	Some oil components may persist in the environment for longer periods of time, accumulating in sediments, sea life, and wildlife.

The effects of oil spills are not limited to the environment. There are immediate effects on humans, fish, animals, birds and wildlife in general, mainly due to:

direct contact with the spilled oil including breathing of volatilized oil components (hydrocarbons) from the spill;
direct contact with the environment polluted with spilled oil components (some of which may persist a long time), such as drinking polluted water or breathing polluted dust particles;
consumption of polluted food - at any level within the food chain, with a higher risk for food pollution at the higher levels of the food chain, i.e. humans and animals.