Dispersants help break up an oil slick into very small droplets - smaller in width than a human hair. These droplets are biodegraded by naturally occurring oil-eating microorganisms that live in the water.
When dispersants are used appropriately, they can help protect human health, minimize the environmental impact of oil spills and be an effective oil spill response strategy.
It is important to note that the use of dispersants is a complex and carefully regulated process. Their effectiveness depends on various factors such as the type of oil, weather and sea conditions, and the timing of the dispersant application.
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Oil spill dispersants are low toxicity chemical products specially manufactured to break down oil that has spilled into the sea. When dispersants are used appropriately, they help minimize ecological damage and impacts on coastal communities’ resources and businesses by enhancing the natural biodegradation processes that break down oil. This helps prevent oil from reaching sensitive coastal habitats and shorelines.
Dispersants can, in most situations, be quickly deployed and enable responders to treat much more of an oil slick than any other response technique. This can help reduce the potential impact of the spill on the environment. If the environmental conditions are right (see ‘When are dispersants effective?’ question and answer below), using dispersants greatly enhances the rate and extent of naturally occurring processes which can degrade, disperse and dilute the oil and helps to protect sea birds, wildlife and sensitive shorelines.
A dispersant contains special compounds that are designed to interact with the oil, allowing the motion of waves to break the oil into tiny oil droplets. The smaller droplets created in this process are rapidly diluted and are also able to be quickly degraded by naturally occurring microorganisms which ultimately remove the oil from the environment.
Dispersants can be applied by boat, plane, helicopters or by subsea injection. The application rate can vary widely depending on several factors. Experienced responders will carefully assess and monitor the application and will know how to adjust the dosage rate accordingly to achieve optimal dispersion efficiency.
Using dispersants will carry oil into the surface layers of the water, causing marine organisms to be exposed to the dispersed oil to a greater extent than if dispersants were not used. Experience and research have shown that concentrations will decline rapidly in open water due to dilution caused by currents and tides. An environmental assessment needs to be performed to evaluate the relative risks to different parts of the marine environment. Response decision makers will analyse the conditions and make an informed decision about the most appropriate solution.
For the public, there are no likely sources of exposure to dispersants or dispersed oil. Because dispersant operations are typically carried out several kilometres from shore, contact with dispersant spray itself or significant inhalation of fumes by those on shore is unlikely. In any case people should avoid contact with oiled areas and avoid handling items that have oil or oil-like sprays on them. Workers involved with the handling of dispersants should be professionally trained and wear protective equipment to avoid inhalation and contact with eyes and skin. It is worth noting dispersants can also reduce potentially harmful vapours in the vicinity of a spill and provide a safety benefit for any responders undertaking vessel-based activities in the immediate area, as well as minimizing the exposure of responders and local on shore communities to the oil.
Effectiveness depends on various factors such as the type of oil, weather conditions and the timing of the dispersant application. In the right conditions, dispersants can be the most effective response tool in the responder’s toolbox. There is a limited window of opportunity for their use and dispersants should be used as soon as possible after the oil is released. As time passes the oil composition changes making dispersant less effective because oil will become more viscous due to evaporation and emulsification. Dispersants work best with medium viscosity oils such as light crudes and products. Dispersants work best when there are current and wave actions which help to disperse the tiny oil droplets which dispersants create. Dispersants are relatively quick to deploy, and a large area can be treated quickly with small amounts of equipment and personnel. This also enables rapid response in remote locations where resources may not be available.
The use of dispersants is regulated through a combination of national regulation, international frameworks and guidelines. Regulations do vary between countries, but most only permit dispersants that have passed toxicity tests, as well as tests for dispersant effectiveness. Additionally, regulators can require ‘on-the-day’ approval to use dispersants that are already tested and approved.
Introduction to dispersants (source: API)
