Oil spills occur on a regular basis. A single vessel or refinery accident can become an ecological disaster. In 1989, the Exxon Valdez grounded on a reef, which ruptured several internal cargo tanks, causing nearly 11 million gallons of crude oil to leak into the surrounding waters. An explosion aboard the Deepwater Horizon, an oil drilling rig in the Gulf of Mexico, in April 2010, caused four million barrels of oil to escape from an undersea well before it could be capped months later. In October 2011, a cargo ship off New Zealand, the Rena, ran aground and released 1,700 tonnes of heavy oil and 200 tonnes of diesel fuel, affecting wildlife in the Bay of Plenty.
Occurring on large and small scales, oil spills pollute the environment with substances that birds and other wildlife cannot survive in. There are numerous ways to contain oil slicks. Sometimes, the oil can be retrieved so that all is not lost. Here are some of the leading methods used by spill response teams.
Spill Containment Booms
A boom is a floating barrier that is inflatable or solid. Made of plastic or metal, they are moored with anchors or land lines and designed to contain oil where it floats at the surface. Skimmers may pass within the contained area to collect the oil and deliver it to shoreside or vessel-based storage tanks. Deployment can be across inlets and stream outlets, so that oil from the ocean cannot reach marshlands and other habitats. These can prevent oil from reaching beaches, nesting habitats, or shellfish beds. Types of booms include:
Hard Boom: Essentially floating plastic, they have cylindrical floats above. On the bottom, they’re weighted down by a skirt under the water to deflect oil. Sometimes, the skirt can change the direction of the oil, especially if there are no strong currents or winds.
Sorbent Boom: Contains an absorbent material for the oil it is intended to contain. It is not as effective at containing a spill, as the skirt that hard booms have is not present.
Fire Boom: Used less frequently, this has a design that appears like metal plates topped by floating metal cylinders. The plates help in the same way that containment skirts do. This option is used when the intention is to burn up the spilled oil; the boom can contain it long enough for this to work.
Burning the Oil
Burning up the oil on site, or in situ, may be done on the ocean. After boats tow a fire-retardant boom to concentrate the spill, the oil on the surface is set afire to burn it up. This is typically done only under ideal conditions, such as in flat seas and calm winds. For it to work, the layer of oil needs to be thick enough, but crews need to monitor the surrounding air to be sure residue and smoke won’t be harmful to people, wildlife, or the surrounding environment. Burning is generally not done near any shorelines.
Dispersal with Chemicals
Chemical compounds can be released by boat or plane onto an oil slick. These apply a natural biodegradation process. Breaking up the oil into smaller droplets, the dispersants help to dilute the spill, so that evaporation and the actions of bacteria can further break it up. These must be used within a couple of hours of the initial spill to be most effective.
There are a few drawbacks to chemical dispersion. It can cause oil to disperse deeper into the water column, impacting coral, sea grass, and even sea life that may later be consumed by humans. Sea and weather conditions can also bring the chemicals to places where coastal habitats may be adversely affected. There can be negative effects on birds and wildlife, and beaches, tidal flats, and wetlands can sustain ecological damage. Dispersion is therefore not conducted in shallow water or close to shore, or anywhere near where people live. It’s ideally done in moderate sea conditions, in light winds, during the daytime.
In New Zealand, a dispersant called Corexit 9500 was used on the Rena oil spill. Considered less toxic than other dispersants, it consists of surfactants with a head that’s attracted to water molecules and a tail that repels water but attaches to oil and grease particles. The effect is to suspend oil droplets in the water. Crews spray the compound directly to oil spills on the water surface. It can also be sprayed from small aircraft or helicopters. In trial operations, the dispersant was more effective on fresh oil than that in the water for a few hours.
Oil Cleanup with Microorganisms
Some strains of bacteria can break down oil into carbon dioxide and fatty acids through biodegradation. Scientists have even identified types of bacteria that work more effectively depending on the depth and types of chemicals. For example, oceanospirillales has been studied in breaking up alkanes in deep water, and Cycloclasticus has been observed to effectively degrade toxic polycyclic aromatic hydrocarbons. The findings were made by US and UK scientists following the Deepwater Horizons spill.
Scientists have also found ways to speed up the natural process. Nitrogen, phosphorous, and other fertilizing nutrients can stimulate microorganisms to grow and flourish. The fertilizer, however, needs to be soluble in water. Other factors include how the compound is applied, either as a liquid or pellet, and the consistency of the ground.
However, from the discovery of natural enzymes within microbes to new DNA sequencing techniques, engineers have identified the types of microbes best suited for the type of oil spill. The discoveries are yielding promise in scientific communities that future oil spills will be contained and cleaned up faster than in the past.
Every Spill Is Different
Containment, burning, dispersal, and bioremediation are all ways that oil spills are cleaned up. Response crews still must consider the oil type, location, sea conditions, and weather when choosing a method. The factors involved mean every spill is different, and the same method of cleanup that works for one may not be effective for another. An oil spill can be cleaned up if the right method is used and expertise and resources are available within the first few hours.