Chemical Dispersants Used in Bioremediating Oil Spills - Free Essay Example

Sample details Pages: 17 Words: 5065 Downloads: 2 Date added: 2017/09/11 Category Advertising Essay Did you like this example? UNIVERSITY OF PORT HARCOURT FACULTY OF SCIENCE DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY SEMINAR PRESENTATION ON CHEMICAL DISPERSANTS USED IN BIOREMEDIATING OIL SPILLS BY UPORO VICTOR BARIBEFE U2006/5581377 COURSE CODE: ICH 400. 2 COURSE TITTLE: UNDERGRADUATE SEMINAR COURSE LECTURER: MR. GODSON IWUOHA SEPTEMBER, 2010 Table of Contents CHAPTER 1 1. Don’t waste time! Our writers will create an original "Chemical Dispersants Used in Bioremediating Oil Spills" essay for you Create order 1 Introduction .. 2 1. 2 Background on the chemical composition of dispersants . 3 CHAPTER 2 2. History of Dispersants 6 2. 2 Dispersants Reformulation 7 2. 3 Function of dispersants . 7 2. 4 Current Dispersants 8 CHAPTER 3 3. 1 Mechanism of dispersion 12 3. 2 Toxicity of dispersants 5 3. 3 Analysis of the pros and cons to using dispersants at oil spills 17 CHAPTER 4 4. 1 Recommendations for the use of dispersants . 20 4. 2 Suggestions for future analysis and research .. 20 4. 3 References 21 CHAPTER 1 1. 1 INTRODUCTION Over the past couple of years, the use of chemical dispersants has become an increasingly common method to combat oil spills in water bodies. Chemical dispersants are substances applied to spilled oil that disperse oil into the water column rather than leaving it floating on the surface in a slick. When used appropriately, chemical dispersants can be an effective method of response to an oil spill. Following dispersant application, wave energy will cause the oil slick to break up into smaller oil droplets that are rapidly diluted and subsequently biodegraded by micro-organisms occurring naturally in the marine environment. Dispersing spilled oil into the sea by the use of oil spill dispersants can be an environmentally acceptable method of oil spill response. A â€Å"net environmental benefit† will be achieved if the damage that might be caused to marine life by dispersed oil is less than the damage that would have been caused if the oil had come ashore or drifted near to particularly oil-sensitive resources. This justification for dispersant use cannot, however, be imported into every oil spill scenario. Dispersing spilled oil in some circumstances might have the potential to damage marine life that exists in the close vicinity of a dispersing oil slick. Dispersed oil droplets and the chemical components in oil that are transferred into the sea have the potential to exert toxic effects, but only if the oil is present at high enough concentration for prolonged periods. This will only occur if there is not sufficient dilution of the dispersed oil and oil components into the sea. This report amongst other things aims to give an overview of the effectiveness of these oil spill dispersants in bio-remediating oil spills, the types and generations of dispersants available, their toxicity and preference of one mode/type over the other(s). . 2 BACKGROUND ON THE CHEMICAL COMPOSITION OF DISPERSANTS Dispersants are chemical formulations which reduce the surface tension of water allowing the oil to disperse into small droplets in the water column. The dispersants which are available on the market today comprise several components, the most important being a blend of two or three surfactants (surface active agents). Other components of dispersants include the solvent (the carrier of the surfactant) and additives. SURFACTANTS ( SURFACE ACTING AGENTS) The surfactant molecules are the key component of chemical dispersants. Surfactants bind to both oil and water to produce finely dispersed droplets of oil-surfactant molecules. The most common surfactants used are non-ionic (fatty acid esters and ethoxylated fatty acid esters) and anionic (sodium alkyl sulphosuccinate). Surfactants are made up of two parts: an oleophilic or rather lipophilic part (oil loving) and a hydrophilic part (water-loving). When dispersants are sprayed onto an oil slick, the solvent transports and distributes the surfactants through the oil slick to the oil/water interface where they re-arrange so that the oleophilic part of the molecule is in the oil and the hydrophilic part is in the water. This creates a sharp reduction in the surface tension of the oil/water interface and small oil droplets break away from the oil slick with the help of wave energy. Re-coalescence is minimised by the presence of the surfactant molecules on the droplet surface and the reduced probability of encountering other oil droplets as they move apart. There are several different basic chemistries of surfactants. An example of each class is as shown: (1. ) Ethoxylated fatty amines (Cationic) (2. ) Alkylphenol ethoxylate-based surfactants (non-ionic) These surfactants usually include an alcohol as a solvent (isopropanol (X-77 ®, AG-98â„ ¢), butanol (R-11 ®, AG-98â„ ¢ (N)), glycol (AG-98â„ ¢ (N), Activator 90)), a silicone defoamer (polydimethylsiloxane), and water. (3. ) Alcohol ethoxylate-based surfactants (non-ionic) (4. ) Sodium alkyl sulphosuccinate (anionic) (5. ) Silicone-Based Surfactants. Also known as organosilicones, these are increasing in popularity because of their superior spreading ability. This class contains a polysiloxane chain. Some of these are a blend of non-ionic surfactants (NIS) and silicone while others are entirely silicone. The combination of NIS and a silicone surfactant can increase absorption into a plant so that the time between application and rainfall can be shortened. Examples: Sylgard ® 309 , Dyne-Amic ®, Silwet L-77 ® , etc. Blends normally include an alcohol ethoxylate, a defoamer, and propylene glycol. SOLVENTS Solvents must be used because the surfactants are often viscous or solid, and are either hydrocarbon-based or water-based. Modern dispersants are a blend of surfactants in a solvent. The solvent has two functions: * It reduces the viscosity of the surfactants which enables it to be sprayed and, * It promotes the penetration of the surfactant into the oil slick. ADDITIVES Another important component, the additive stabilizes and prevents the oil particle from breaking away from the border area between the oil and the water. These additives are also referred to as stabilizing agents. CHAPTER 2 2. HISTORY OF DISPERSANT Before 1970, chemical dispersants were degreasing agents that were developed to clean tanker compartments and engine rooms. The TORRY CANYON spill off Cornwall, England in 1967 resulted in the use of 6,000 barrels of chemical used to treat a spill of 85,500 barrels of oil. Many of these chemicals were degreasing solvents and were more toxic than the oil itself. The denser surfactants did not evaporate, mix with, or dissolve in water. Instead, they formed a stable â€Å"oil-detergent† emulsion that had a negative synergistic effect causing more harm to the environment than had they done nothing. There was a significant impact to the marine and coastal environment with resulting massive kill off of fish and intertidal invertebrates. Over 10,000 tons of detergents were sprayed on the floating oil. The result of the negative media attention was a poor public image of chemical dispersants. Future dispersant usage saw increasingly better results. In 1979 the Ixtoc 1 spill released more than 3. 5 million barrels of oil. Almost 500 aerial missions were flown applying the dispersant COREXIT 9527 to 1,100 square miles of slick. While dispersants were not used in the US waters, there was successful application of dispersants seen. 2. 2 DISPERSANT REFORMULATION While dispersant application was becoming increasingly more successful, dispersants were being reformulated to address concerns for efficiency and toxicity. COREXIT products are the principle US dispersants. In 1967 EXXON produced COREXIT 7664. This weak-water based product was the first that was specifically formulated for the marine environment. This product was not used during the TORREY CANYON. In 1972 EXXON produced the first â€Å"selfmix† concentrate, COREXIT 9527. This was the first product that could be applied by aircraft. In 1992 EXXON developed COREXIT 9500, which was effective on heavy, weathered and emulsified oils. (Exxon-mobil, 2004) By the third generation of formulas, dispersants consisted of surfactant with little solvent. These were designed to be mixed with water. 2. 3 FUNCTION OF DISPERSANTS Dispersants reduce the interfacial tension between the oil and water and helps the creation of small oil droplets, which move into the water column facilitating quicker natural biological breakdown (biodegradation) and dispersion. By decreasing the size of the oil droplets, and dispersing the droplets in the water column, the oil surface area exposed to the water increases and natural breakdown of the oil is enhanced. Dispersants are used to minimise the environmental impact of an oil spill. Dispersants do not eliminate the problem of an oil spill but are intended as a means of reducing the overall environmental impact of an oil slick at sea. Dispersant use accelerates the weathering and biological breakdown of oil at sea and reduces the impact of oil on sensitive foreshore environments. Oil Spill Dispersants are also highly effective in reducing exposure of sea birds to oil as most sea birds are oiled by slicks on the surface of the sea or in near shore coastal habitats. Dispersed oil is less sticky than undispersed oil, therefore the adhesion and absorption onto surfaces and sediments of dispersed oil is greatly reduced compared with the original oil slick. 2. 4 CURRENT DISPERSANTS Over time, dispersants have developed over what one usually divides into three generations. The first generation of dispersants that came out on the market were hydrocarbon-based and were made of aromatic hydrocarbons, which gave rise to toxic effects. The second generation of dispersants that developed, the so-called ‘conventional dispersants’, contained no aromatic hydrocarbons and are used today in seas where they are applied directly from vessels without dilution. Conventional dispersants are starting to be replaced by the third generation of dispersants, the so-called ‘concentrated dispersants’ because these are easier to handle during clean-up operations. Concentrated dispersants are diluted with water before application, such that the volume problem on vessels and aircrafts decreases. Third generation dispersants are usually divided into two types based on their solvent agent – water-based or hydrocarbon-based. Hydrocarbon-based dispersants The solvent is a hydrocarbon with a low or no aromatic content. These dispersants typically contain between 15-25% surfactant and are intended for neat application to oil. They should not be pre-diluted with sea water since this renders them ineffective. They also require a high application rate of between 1:1 to 1:3 (dispersant to oil). Hydrocarbon-based dispersants are less effective and may be more toxic than concentrate dispersants and, as a consequence, in many countries are not now commonly in use. Concentrate or self-mix dispersants These dispersants contain a blend of different surfactants with both oxygenated and hydrocarbon solvents. They contain a higher concentration of surfactants (25% to 65%) and can be applied either undiluted (neat) or pre-diluted with sea water although it is more common to apply them undiluted. A typical dosage ranges between 1:5 to 1:30 (undiluted dispersant to oil). Water-based concentrated dispersants have a comparatively low toxicity, but require a longer time to disperse oil than ready-mixed products. Due to this time lag, there is a risk of using too much water-based dispersant before the process is complete. The hydrocarbon-based products have a higher toxicity than water-based products but require a lower dose with application. The manufacturers therefore claim that the toxicity levels of both types of products are low. A summary of dispersants used today is provided below (Table 1). Table 1. The table summarises the dispersants used today, application methods and dosages. Standard name| Generation| Type| Application method| Solvent| Dosage(dispersant/oil)| ConventionalDispersants| Second| 1| Not diluted on ships. | No aromatic hydrocarbons| 30-100%| Concentrated dispersants| Third| 2| Diluted on ships. | Water-based (e. g. glycol ether)| 5-15% (concentrated products)| | | 3| Not diluted on ships or airplanes. | Hydrocarbon based. | | The water-based dispersants’ solvent is made up of alcohol, glycols and glycol ethers (mostly ethanol, isopropane, ethylene glycol and propylene glycol) to increase its ability to mix with oil and lower the freezing point. Surfactants make up over 20% of these dispersants. The dispersant is applied from ships and diluted before application. Water-based dispersants require a relatively long time to complete dispersion. It has been argued that exceeding the dosage of these substances is common because people’s expectations for oil dispersion are too high. The most important limitation is their sensitivity for extreme temperatures. At high temperatures, there are security risks as certain solvents used in products are fire-hazardous. The most critical temperature area, though, is under 0 °C, because the risk for refreezing in the spreading device is high. The development of concentrated hydrocarbon-based dispersants, also known as self-mixing dispersants, has made the dispersion of oil on the sea surface much faster and easier. Self-mixing dispersants are spread from aircrafts, which means a doubling of the capacity. At present the following oil spill dispersants have been approved under the National Plan guidelines. Their Trade Names are listed below: * Tergo R-40 * Ardrox 6120 * BP-AB * Corexit 9500 * Corexit 9527 * Corexit 9550 * Shell VDC * Shell VDC+ * Slickgone NS * Slickgone LTSW. Composition of common dispersants Corexit 9527 The proprietary composition is not public, however the manufacturers own safety data sheet on Corexit EC9527A says the main components are 2-butoxyethanol and a proprietary organic sulfonate with a small concentration of propylene glycol. Corexit 9500 In response to public pressure, the EPA and Nalco released the list of the six ingredients in Corexit 9500, revealing constituents including sorbitan, butanedioic acid, and petroleum distillates. Corexit EC9500A is mainly comprised of hydrotreated light petroleum distillates, propylene glycol and a proprietary organic sulfonate. Environmentalists also pressured Nalco to reveal to the public what concentrations of each chemical are in the product; Nalco considers that information to be a trade secret, but has shared it with the EPA. Propylene glycol is a chemical commonly used as a solvent or moisturizer in pharmaceuticals and cosmetics, and is of relatively low toxicity. An organic sulfonate (or organic sulfonic acid salt) is a synthetic chemical detergent that acts as a surfactant to emulsify oil and allow its dispersion into water. The identity of the sulfonate used in both forms of Corexit was disclosed to the EPA in June 2010, as dioctyl sodium sulfosuccinate. Often referred to as docusate sodium, this chemical is the active ingredient in several stool-softener laxatives. Sorbitan (3S)-2-(1,2-Dihydroxyethyl)tetrahydrofuran-3,4-diol| | Sorbitan is a mixture of chemical compounds derived from the dehydration of sorbitol. The mixture can vary, but usually consists of 1,4-anhydrosorbitol, 1,5-anhydrosorbitol and 1,4,3,6-dianhydrosorbitol. Sorbitan is primarily used in the production of surfactants such as polysorbates. Sorbitan esters ( also known as Spans ) are lipophilic non ionic surfactants that are used as emulsifying agents in the preparation of emulsions, creams, and ointments for pharmaceutical and cosmetic use. When used alone they produce stable water-in-oil emulsions but they are frequently used with a polysorbate in varying proportions to produce water-in-oil or oil-in-water emulsions or creams with a variety of different textures and consistencies. Sorbitan esters are also used as emulsifiers and stabilisers in food. Toxicity The relative toxicity of Corexit and other dispersants are difficult to determine due to a scarcity of scientific data. The manufacturers safety data sheet states No toxicity studies have been conducted on this product, and later concludes The potential human hazard is: Low. According to the manufacturers website, workers applying Corexit should wear breathing protection and work in a ventilated area. Compared with 12 other dispersants listed by the EPA, Corexit 9500 and 9527 are either similarly toxic or 10 to 20 times more toxic. In another preliminary EPA study of eight different dispersants, Corexit 9500 was found to be less toxic to some marine life than other dispersants and to break down within weeks, rather than settling to the bottom of the ocean or collecting in the water. None of the eight products tested are without toxicity, according to an EPA administrator, and the ecological effect of mixing the dispersants with oil is unknown, as is the toxicity of the breakdown products of the dispersant. Corexit 9527, considered by the EPA to be an acute health hazard, is stated by its manufacturer to be potentially harmful to red blood cells, the kidneys and the liver, and may irritate eyes and skin. The chemical 2-butoxyethanol, found in Corexit 9527, was identified as having caused lasting health problems in workers involved in the cleanup of the Exxon Valdez oil spill. According to the Alaska Community Action on Toxics, the use of Corexit during the Exxon Valdez oil spill caused people respiratory, nervous system, liver, kidney and blood disorders. Like 9527, 9500 can cause haemolysis (rupture of blood cells) and may also cause internal bleeding. According to the EPA, Corexit is more toxic than dispersants made by several competitors and less effective in handling southern Louisiana crude. On May 20, 2010, the EPA ordered BP to look for less toxic alternatives to Corexit, and later ordered BP to stop spraying dispersants, but BP responded that it thought that Corexit was the best alternative and continued to spray it. Reportedly Corexit may be toxic to marine life and helps keep spilled oil submerged. There is concern that the quantities used in the Gulf will create unprecedented underwater damage to organisms. Nalco spokesman Charlie Pajor said that oil mixed with Corexit is more toxic to marine life, but less toxic to life along the shore and animals at the surface because the dispersant allows the oil to stay submerged below the surface of the water. Corexit 9500 causes oil to form into small droplets in the water; fish may be harmed when they eat these droplets. According to its Material safety data sheet, Corexit may also bio accumulate, remaining in the flesh and building up over time. Thus predators who eat smaller fish with the toxin in their systems may end up with much higher levels in their flesh. Effectiveness The oil film will be dispersed in small droplets which intermix with the seawater. The oil is then not only distributed in two dimensions (on the surface) but is dispersed in three (in the water). In handling Louisiana crude Corexit EC9500A (formerly called Corexit 9500) was 54. 7% effective, while Corexit EC9527A was 63. 4% effective. The EPA lists 12 other types of dispersants as being more effective in dealing with oil in a way that is safe for wildlife. One of those tested was Dispersit, which was 100% effective in dispersing Gulf oil and is less toxic to silverfish and shrimp than Corexit. Alternatives UK authorities have an approved list of products which must pass both sea/beach and rocky shore laboratory toxicity tests, following a review of approval procedures over a decade ago. Corexit did not pass the rocky shore test when submitted for renewal of its inclusion on the list, and was dropped. Although it has been omitted from the approved list since 1998, existing stocks which pre-date the removal may be permitted for use away from rocky shorelines, subject to prior approval. SLICKGONE NS Dasic Slickgone NS is one of the best selling Type 3 concentrate dispersants on the world market and has frequently been shown to be the most effective dispersant available for a wide range of different oils including those with a high wax content. Slickgone NS is extremely low in toxicity to marine organisms and is approved by many international approval organisations. SLICKGONE EW Dasic Slickgone EW is the latest member of the product range. Slickgone EW combines high efficiency and low toxicity with an exceptional ability to breakdown chocolate mousses (water in oil emulsions). Slickgone EW will continue to disperse efficiently those oils which have become too weathered to be amenable to conventional dispersants, therefore extending the window of opportunity for dispersant use. Unlike most dispersants, Slickgone EW is also effective on refined oils and bunker fuels making it a truly versatile dispersant for the 21st century. SLICKGONE LTSW Dasic Slickgone LTSW is a water based, hydrocarbon free, concentrate dispersant. It is highly effective at emulsifying crude oils, fuel oils and water in oil emulsions. It has extremely low toxicity and is internationally approved. CHAPTER 3 3. 1 MECHANISM OF DISPERSION Following an oil spill, some of the oil will disperse naturally into the water column. The extent to which this occurs depends on the type of oil spilt and the mixing energy. Oils with a lower viscosity are more amenable to natural dispersion than the ones with a higher viscosity. Natural dispersion takes place when the mixing energy provided by the waves and wind is sufficient to overcome surface tension at the oil/water interface and break the oil slick into droplets of variable sizes. The chemical dispersion process. A: Dispersant droplets containing surfactants are sprayed on to the oil. B: The solvent carries the surfactant into the oil. C: The surfactant molecules migrate to the oil/water interface and reduce surface tension, allowing D: small oil droplets to break away from the slick. E: The droplets disperse by turbulent mixing, leaving only sheen on the water surface. Generally, larger oil droplets will rapidly resurface and then coalesce to form an oil slick, but the smaller droplets will remain suspended in the water column where they will be diluted by turbulence and subsurface currents. The process of natural dispersion takes place in moderately rough seas with breaking waves and winds above 10 knots (5 m/s). Chemical dispersants aid the natural dispersion of oil by reducing the oil/water interfacial tension and, along with the natural motion of the sea, allow the break up of oil on the water into very fine droplets. Effectiveness of oil dispersion by chemical dispersants at sea is governed by a range of conditions and include the: * type and chemistry of the oil, * degree of weathering of the oil, * the thickness of the oil slick, type of dispersant, * droplet size and application ratio, * prevailing sea conditions (wave mixing energy), and * sea temperature and salinity Oil Spill Dispersant effectiveness varies greatly with oil type spilt and the degree of weathering of the oil. For example with increasing wind speed and wave action, the loss of light oil components increases. Evaporation becomes more significant, causing an increase in viscosity and density of th e remaining oil, and forming emulsions with water. The oil slick becomes thicker and heavier. It is generally accepted that for oils over 2000 cSt (Centistockes a measurement of the mobility of oil) viscosity, the effectiveness of oil dispersants decreases significantly. An oil that was easily dispersed may change quickly by wind and wave action into an oil which is not dispersable. To achieve an efficient dispersion, oil droplet size must be in the range of 1 ? m to 70 ? m with the most stable size being less than 45 ? m. Smaller droplets are better as they remain suspended in the water column where they will be diluted rapidly in the top few metres of the sea to below harmful concentrations. The increased surface area provided by the small droplets also enhances the opportunity for biodegradation of the oil. It is important to remember that dispersants are manufactured primarily for use in the marine environment. Their efficiency will be optimum in waters with a salinity of around 30-35 parts per thousand (ppt) but will decrease rapidly in waters with a salinity below 5-10 ppt, especially when pre-diluted. Similarly, efficiency is also affected when salinity rises above 35 ppt. In freshwater, dispersant effectiveness is dramatically reduced because the surfactants tend to travel through the oil layer into the water column instead of stabilising at the oil/water interface. Nevertheless, some dispersants have been specially formulated for use in freshwater. In a confined freshwater system, other factors also need to be considered, such as whether there is sufficient water depth or exchange of water to achieve adequate dilution. 3. 2 TOXICITY OF DISPERSANTS Knowledge on the toxicity of dispersants comes largely from laboratory studies. Only in a few cases have systematic studies been carried out on the toxicity of dispersants at a spill. No common standard method for testing the effectiveness of dispersants has been developed yet, other than certain oil companies’ and institutes that have developed their own tests. This has made it difficult to compare different products on the market and has also resulted in wide variances in quality among products on the market. The need remains to develop a testing system that is accepted by all countries and is used for the approval of products based on the requirements of each country. se tests to measure the effectiveness of dispersants. Test results of approved first generation dispersants showed them to be highly poisonous on test organisms. Toxicity values around 1 mg/L (measured as 48 h LC50, the concentration that kills 50% of test organisms within 48 hours of exposure) were registered for many adult marine invertebrates. Examples of products that showed such valu es include BP 1002, Slickgone, Gamlen, Essolvene and Finasol SC. The most harmful component in dispersants is the solvent, with very high aromatic concentrations. Second generation dispersants showed lower toxicity values, often between 1 000 – 10 000 mg/L (48 h LC50) in adult organisms. Examples of such products include BP 1100X, some Corexits and Finasol OSR-2. (Lehtinen, 1981). The United States Environmental Protection Agency (EPA) has conducted toxicity tests on several of the dispersants they allow. Tables 4 through 7 summarise the toxicity of four different dispersants Corexit 9500, Corexit 9527, Dispersit 1000 and JD-109. The tests studied the toxicity of dispersants alone, dispersants with oil, and oil alone. The toxicity tests were carried out on the minnow Menidia beryllina (96-hours test) and the crustacean Mysidopsis bahia (48-hours). (EPA, 2001). In summary, the studies suggest that a mixture of oil and dispersant give rise to a more toxic effect on aquatic organisms than oil and dispersants do alone. Analyses of dispersants alone showed that Corexit 9500 and 9527 are the least harmful for aquatic organisms. Dispersit 1000 and JD-109 showed similar toxicity levels as the oil products. 3. 3 ANALYSIS OF THE PROS AND CONS TO USING DISPERSANTS AT OIL SPILLS An account of the pros and cons for the use of dispersants to combat oil spills n the sea is presented in Table 2. From an environmental point of view, the best method to control oil is naturally to remove the oil from the water using mechanical methods. When these methods do not work or there are other reasons for not using them, chemical dispersion of oil can be an alternative. If the decision is made to use dispersants instead of m echanical combat methods, one should keep in mind that chemically dispersed oil reduces the chances for later mechanical clean-up. Dispersants can only be used within a limited time period. The window for using dispersants at an oil spill is short. In addition, applying dispersants is only possible during daylight hours when one can still see the extent of the oil. In certain situations, using dispersants to combat oil spills in seas can be preferred as mechanical control actions are not always successful. Chemical dispersion prevents the oil from emulsifying. The advantage of chemical control is that it decreases the damage oil can cause on birds and marine mammals. In addition, the number of incidents where the oil slick affects beaches will also be reduced or prevented. In the case of an oil slick moving towards the coast, strategic use of dispersants can disperse the oil vertically towards deeper waters instead of it moving along the water surface towards shallower and more productive areas by the coast. If the oil is not sufficiently dispersed, there is even a risk that drops coagulate again and build a new film of oil. It is therefore important for the amount of mixing energy to be high for effective dispersion. Table 2. Pros and cons for the use of dispersants at oil spills. Pros| Cons| The oil does not remain on the water surface * Often the method that produces the fastest results * Compared to other methods, dispersants are more effective in weather conditions that create fast mixing of water * Easy to apply * Prevents the oil from emulsifying * Grinds up the oil making natural decomposition easier * Seabirds and marine mammals can be saved * Prevents oil contamination of beaches| * Builds an oil cloud underwater and can product harmful effec ts for aquatic organisms that would otherwise not have been affected by the oil * Not always effective on all oil types * Limited window of time for use (relatively short) * Application is only possible when the oil slick is visible * Must be used where water masses are large for effective dilution * Mixing of oil and dispersants can be more toxic than each part individually * Few studies looking at long-term effects in the field * If the oil is not sufficiently dispersed, drops can coagulate again * Oil drops can settle * During beach clean-up, dispersants can increase the penetration of oil into the sedimentation * Few field studies on the effects of bioaccumulation| CHAPTER 4 4. 1 RECOMMENDATIONS FOR THE USE OF DISPERSANTS Based on the knowledge garnered on dispersants and their effects, one can recommend their use on Nigerian waters. This is based on the deciding factors for effective dispersion – water temperature, salinity, and amount of mixing energy. Before dispersants can be recommended at all, more studies need to be conducted looking at the spread and bioaccumulation of dispersants at sea and what effects they can give rise to. 4. 2 SUGGESTIONS FOR FUTURE ANALYSIS AND RESEARCHS Over the course of this research, gaps in current knowledge were identified. The main areas that need future research are the spread of dispersants and how dispersion products and dispersed oil bio-accumulate. The long-term effects of dispersants need to be studied. In order to adequately understand the effects of oil dispersants on aquatic systems, the following studies should be undertaken: †¢ Long-term effects of dispersed oils on aquatic organisms †¢ Bioaccumulation of dispersants and dispersed oil †¢ Is there a risk that dispersed oil may coagulate again? †¢ Analysis of the environmental effects of dispersants used on past oil spills †¢ Analysis of the use of sinkers, beach cleaning agents, etc. 4. 3 REFERENCES 1. Belore, Randy. â€Å"The History of Chemical Dispersants in the United States. † Petroleum Association of Japan Esymposium, 2004. 2. Bonn Agreement, 2001. Counter pollution manual: Chapter 20. Homepage 2001-02-26:https://www. bonnagreement. org 3. Chemicals Meant To Break Up BP Oil Spill Present New Environmental Concerns. ProPublica. https://www. propublica. org/article/bp-gulf-oil-spill-dispersants-0430. Retrieved 2010-05-07. 4. Considering Dispersant Planning Caps. U. S. Coast Guard, 1998. https://www. uscg. mil/vrp/reg/disperse2. shtml#potential Dispersants. 5. Danish EPA (Environmental Protection Agency), 2001. National structure – Spill notification point and response authority for clean-up operation at sea. 6. Dispersant Pre-approval status throughout the U. S. U. S. Coast Guard, 2004. https://www. uscg. mil/vrp/reg/disperse. shtml 7. Elmgren, R. , Hansson, S. , Larsson, U. , Sundelin, U. och Boehm, P. D. 1983. The â€Å"Thesis† Oil Spill: Acute and Long-Term Impact on the Benthos†. Marine Biology 73, pp. 51-65. 8. Environment Canada, 2001. Oil spill dispersants. Environment Canada’s homepage 2001-05-14: https://www. atl. ec. gc. ca/epb/envfacts/oil 9. ExxonMobil, 2004 https://www. prod. exxonmobil. com/scitech/leaders/capabilities/ mn_downstream_safety_dispersants. html 10. Jamie Anderson (May 23, 2010). BP to persist with Corexit 9500 dispersant. themoneytimes. com. https://www. themoneytimes. com/featured/20100523/bp-persist-corexit-9500-dispersant-id-10114389. html. Retrieved June 26, 2010. 11. Juliet Eilperin (2010-05-20). Post Carbon: EPA demands less-toxic dispersant. Washington Post. https://views. washingtonpost. com/climate-change/post-carbon/2010/05/epa_demands_less_toxic_dispersant. html. Retrieved 2010-05-20. 12. Ministry for the Environment and Energy’s homepage 2001-05-09: https://www. mst. dk/ DeCola, Elise G. 1999. Dispersed Oil Toxicity Issues, A National Research Council. â€Å"Using Oil Spill Dispersants on the Sea. † 1989. 13. National Contingency Plan Overview. U. S. Environmental Protection Agency, Oil Program, 2004. https://www. epa. gov/oilspill/ncp 14. National Contingency Plan Product Schedule. Environmental Protection Agency. https://www. epa. gov/emergencies/content/ncp/product_schedule. htm. Retrieved 2010-05-21. 15. Paul Quinlan (2010-05-24). Secret Formulas, Data Shortages Fuel Arguments Over Dispersants Used for Gulf Spill. New