Once the oil is in the water there are really no good options for dealing with a spill, none of the options available are fully effective and each has negative impacts. Once a spill occurs, we are left with no choice but to find the lesser of damages. The bottom line is that with continued oil production, spills are inevitable and we simply do not have effective and safe methods for cleaning them up.
Burning of Slick
Unfortunately, burning off of the oil is a no-win situation. Burning of the oil can result in large, toxic plumes of smoke that can result in respiratory problems and eye, nose, throat and skin irritations in both wildlife and humans. Birds may become disoriented in the smoke. But, compared to leaving the oil in place, burning seems to be the lesser of two evils as it will remove large amounts of oil that could otherwise result in immediate and long-term impacts to wildlife in the area. Impacts on wildlife can include skin irritations, organ damage, reproductive failures, developmental abnormalities and death. Even after the burn there will still be oil remaining in the marine environment as there is no truly effective way of cleaning up a spill.
Dispersants are usually comprised of a surfactant, a solvent and stabilizing compound. The level of toxicity depends on the specific surfactant and solvent contained in the dispersant as well as the environmental conditions under which it is applied. The toxicity of dispersed oil is primarily due to the toxic components of the oil itself.
The toxicity of dispersants has been reduced considerably over the years. The primary ecological concern associated with dispersants is their ability to enhance the effective toxicity of oil via the dispersion process.
Dispersants do not actually reduce the total amount of oil entering the environment rather they change the properties of the oil so that it is transported differently through the water. Dispersant is used to increase the amount of oil that mixes into the water column, thereby reducing the amount on the surface and decreasing the chances of shoreline contamination. While transferring oil from the water surface into the water column can decrease the exposure for surface dwelling organisms, such as seabirds, marine mammals and sea turtles, it increases the possibility of exposure for species within the water column and benthos, such as fish, eggs and larvae, and shrimp, oysters and corals.
Dispersed oil particles tend to remain in the upper layers of the ocean and as they approach inshore areas, increasingly impact benthic habitats and benthic animals. Dispersed oil particles tend to assume a less visible, more persistent (i.e. not easily cleaned-up) and pervasive presence in the environment, with increased opportunities for long-term ecological impacts, particularly in coastal areas.
The choice to use dispersants is a choice to increase the amount of oil in one part of the ecosystem (water column and seafloor) while decreasing it the amount from another (coasts). The decision to use dispersants is a trade-off between decreasing the risk to water surface and shoreline habitats while increasing the potential risk to organisms in the water column and on the seafloor.
Sensitivity to dispersants and dispersed oil can vary significantly by species and life stage. Embryonic and larval stages appear to be more sensitive than adults to both dispersants.
Oil droplets can physically affect exposed organisms, for example by smothering through the physical coating of gills and other body surfaces. For some organisms, dispersed oil droplets may also be an important route of exposure, through either oil droplet/gill interactions or ingestion of oil droplets.
Oil droplets may be ingested by many suspension-feeders. The general size of the oil droplets is similar to the preferred food size of many of these organisms, including common zooplankton, such as copepods. Oysters, amphipods and polychaetes are also known to select food particles that correlate with the size of dispersed oil droplets.
Dispersants are not generally used when corals, sea grass, and fish spawning areas can be affected by dispersed oil and the dispersants. However, that may not have been true in the case of the Deepwater Drilling Disaster since it occurred in a recognized fish spawning area.
Microdroplets, formed by the effective use of dispersants, are efficiently accumulated by suspension feeders such as clams, barnacles, some kinds of zooplankton, and deepwater corals. Zooplankton may ingest oil droplets which become mixed with inorganic material from other prey and ejected as oily fecal pellets that sink to the seafloor, where they may be scavenged by deepwater corals. These corals are abundant in the vicinity of the Deepwater Horizon, and the effects of oil microdroplets or of oily fecal pellets derived from them on these corals is not at all well known. This is probably the most serious threat associated with wellhead application of dispersants.
Accumulation of oil microdroplets by suspension feeders is especially worrisome when dispersants are applied to oil near the coast. Biological productivity in general increases dramatically as the coast is approached, and many suspension feeders such as oysters are commercially important. But these risks must be weighed against impacts that arise from no response, and are especially acute when sensitive and vulnerable habitats such as coastal marshes are threatened. Oil cannot be removed from these habitats without serious collateral damage, and if left in place may continue to kill fish and wildlife for years and possibly decades. From this perspective, another distinct advantage of dispersants is the option to choose, to some extent, where toxicity occurs.
Typically contain 15-25% surfactant and require high application rates of between 1:1 to 1:3 (dispersant to oil). Sea water renders these dispersants ineffective and should not be pre-diluted. Less effective and more toxic than concentrate dispersants.
Concentrate or self-mix dispersants
Contain 25%-65% surfactant mixed with hydrocarbon and oxygenated solvents, and are typically more effective when applied undiluted. Typical application ratios are 1:5 to 1:30 (dispersant to oil).
Natural “weathering” makes the oil more difficult to disperse through time; consequently, the window of opportunity for effective dispersant application is early, usually within hours to 1–2 days after a release under most conditions. Wave energy is required for successful application of dispersant, however too much wave energy can prevent contact between dispersant and oil.
Dispersant effectiveness generally decreases as oil viscosity increases, and are largely ineffective for oils with initial viscosity above 10,000 cST. Fresh light to medium crude oils (group 2 or 3 oils) can typically be dispersed. Oils that cool and become highly viscous after the spill (pour point 10-15 C below sea temperature) are difficult to disperse. Loss of volatile compounds leads to an increase in viscosity after spill occurs.
Vessel Spraying – Most frequent method. Convenience, ease and cost advantages.
Aerial Spraying – Allows for rapid response and high treatment rates.
Shoreline Application - Generally restricted to areas of low environmental concern.