Once An Oil Spill Occurs

Published Date: 02 Nov 2017

Introduction

Oil spills are known to cause large amounts of environmental destruction. Many oil spills have occurred and have been recorded by the oil industry in the past. Some of the major spills that have occurred include the Santa Barbara channel platform blowout in 1969, the disaster of the Piper Alpha in the North Sea, the grounding of the supertanker Amoco Cadiz in 1978, the Exxon Valdez spill in Alaska in 1989, the Erika spill in France in 1999, and the Prestige in Spain in 2002 (Al-Majed et al., 2012). The most recent and largest oil spill to occur was the Deep Water Horizon oil spill, also known as the Gulf oil spill which occurred in United States waters (Al-Majed et al., 2012). The spill occurred on the 20th of April 2010 when the explosion of the Deep Water Horizon oil rig in the Gulf of Mexico occurred (Al-Majed et al., 2012). The oil spill itself lasted for almost three months where about five million barrels of crude oil were released into the Gulf of Mexico (Al-Majed et al., 2012). As about five million barrels of crude oil was released, both the ecosystem and environment were impacted as large populations of various species of animals were affected and were killed. After eight months since the initial occurrence of the spill, 320 miles of beaches and shoreline were affected and after an additional eight months, a total of 491 miles of shoreline were affected by the spill (Al-Majed et al., 2012).

One of the major challenges that come once these oil spills have occurred is in the cleanup efforts of these spills. Once an oil spill occurs, it undergoes a variety of different processes such as spreading, evaporation, emulsification, sinking, resurfacing, photo-oxidation, and biodegradation (Al-Majed et al., 2012). All of these processes make it difficult in the cleanup efforts of the oil and as a result the amount and extent of damage caused by the spill usually depend upon how quick the cleanup efforts are put into effect (Al-Majed et al., 2012). Some of the common current cleanup practices include in situ burning of the oil on water, mechanical tools such as booms and skimmers, synthetic sorbents, and the use of chemical dispersants (Al-Majed et al., 2012). The use of the mechanical techniques such as the use of booms and skimmers can vary and the effectiveness is highly influenced by the size of the spill, the location, and the environmental conditions in which the response is carried out in (Oil Spill Dispersants, 2005). The mechanical response usually is limited and is achievable to a certain degree (Oil Spill Dispersants, 2005). The more new non-mechanical techniques which were developed due to the limitations of the mechanical techniques include in-situ burning and the use of chemical dispersants (Oil Spill Dispersants, 2005). In-situ burning is a technique in which oil close to where the spill occurs is controlled and burned (Oil Spill Dispersants, 2005). When a spill occurs on open water, the oil from the spill has to be collected and has to be held either by fire-resistant booms or has to be trapped in ice in order to ensure that the oil can be ignited sustained while it is being burned (Oil Spill Dispersants, 2005). The technique of in-situ burning has its advantages compared to that of mechanical removal in that oil is rapidly removed and oil recovery, transport, storage, and disposal are not required (Oil Spill Dispersants, 2005). However, at the same time the disadvantages of this technique include black smoke which is released from the burning of the oil, difficulties in the collecting and containment of the large amounts of oil to burn, lowered effectiveness as the oil emulsifies and spreads, and sensitivity to weather conditions (Oil Spill Dispersants, 2005). In-situ burning has been conducted on thirteen actual oil spills in which in the United States in-situ burning was conducted once in 1989 during the Exxon Valdez oil spill where a fire-resistant boom was also used for the first time (Oil Spill Dispersants, 2005).

Compared to many of the other methods employed, the use of chemical dispersants can be a more effective means of accelerating the dispersion of the oil which in turn can help in accelerating the dilution and the biodegradation of the oil (Chapman et al., 2007). Dispersants are like detergents and they are usually sprayed on slicks of oil to remove the oil from the surface of the water so that it can be dispersed into the water column at a lower concentration (Demarco and Lessard, 2000). When this is done, this accelerates oil degradation through natural processes and it helps in reducing the impact of the oil spill on habitats or shorelines which are more sensitive to the oil spill (Demarco and Lessard, 2000). The chemical dispersants are made of surface active agents known as surfactants which are typically dissolved in one or more different solvents (Demarco and Lessard, 2000). These surfactants are made so that they have a chemical affinity for both the oil and the water (Demarco and Lessard, 2000). When they are applied to the oil that has spilled, these surfactants are designed so that they will align themselves so that lipophilic end of the molecule will attach itself to the oil and the hydrophilic part will extend out to the water (Demarco and Lessard, 2000). This mechanism of chemical dispersion helps to reduce the surface tension between the water and the oil allowing for the oil to disperse into (1-70 µm) droplets as shown in figure 1 (Demarco and Lessard, 2000).

Figure 1

In the end this process overall makes these little oil droplets highly accessible to the hydrocarbon degrading bacteria making it possible for the oil to be removed from the environment by natural processes (Demarco and Lessard, 2000). The small size of the droplets will significantly increase the area available to these hydrocarbon degrading organisms resulting in an increase in the rate of biodegradation (Demarco and Lessard, 2000). Also compared to that of the other cleanup methods, with the use of chemical dispersants, the disposal of the oil that is recovered is not required as it is biodegraded making it advantageous over other methods of cleanup (Demarco and Lessard, 2000).

Most of the chemical dispersants that are manufactured are proprietary and usually the complete composition of these dispersants is not publicly known (Wise 2011). Some manufacturers of these chemical dispersants include Nalco, BP, Shell, and Total Special Fluids (Wise 2011). There are also 19 other miscellaneous dispersants that are manufactured by other companies (Wise 2011). For the most part these dispersants have not widely been used and as a result extensive testing has not been widely attempted or studied (Wise 2011). In the Exxon-Valdez oil spill which occurred in Alaska in 1989 dispersants were used but only in small quantities and it was not until the Deep Water Horizon oil spill of 2010 in the Gulf of Mexico where the chemical dispersants were extensively used (Wise 2011).

As 757 million liters of crude oil were released into the Gulf of Mexico over a span of about 88 days, large amounts of chemical dispersants were used in order to reduce the amount of crude oil which could spread on coastlines and onto waters near the shore (Wise 2011). This use of these dispersants was the first large-scale application of the dispersants and almost at least 7.57 million liters were used (Wise 2011). Prior to the Deep Water Horizon oil spill, these dispersants had not widely been used and had not been studied (Wise 2011). The chemical components also were not known and as a result of the widespread application of these dispersants during the Deep Water Horizon oil spill, the United States Environmental Protection Agency (EPA) posted a full list of the chemical components of the dispersants that were used (Wise 2011). The two dispersants that were used within the Deep Water Horizon oil spill were manufactured by Nalco and were Corexit 9500 and Corexit 9527 (Wise 2011). The components of these dispersants consisted of: 1,2 propanediol, ethanol, butanedioic acid, 2-sulfo-1,4-bis(2-ethylhexyl) ester, sodium salt, sorbitan mono-(9Z)-9-octadecenoate, poly(oxy-1,2-ethanediyl) derivatives, 2-propanol, and distillates (petroleum) (Wise 2011). Corexit 9527 was the earliest dispersant that was used and it was applied by aerial application but was used in much smaller quantities compared to Corexit 9500 (Wise 2011). Corexit 9527 was later discontinued as it was considered to be too toxic (Wise 2011). Corexit 9500, however, was used in higher quantities and was applied through both deep water injection and aerial application (Wise 2011). Since Corexit 9527 is thought to be toxic, there are questions as to the effects these dispersants will have on the ecosystem and environment.

Current Research Question

Based on the components of these chemical dispersants, the toxicity and toxicological effects came into question as it is not known as to how they could impact animal species. The Material Safety Data Sheet (MSDS) for Corexit 9527 rates the compound as a moderate risk to human health whereas for Corexit 9500 the MSDS rates it as slight (Wise 2011). As the Nalco-manufactured dispersants Corexit 9500 and 9527 were used in the Deep Water Horizon oil spill, there are studies which are being conducted in order to assess the impact of the use of these dispersants on various species of animals.

Since Corexit 9500 was largely applied, studies that were conducted looked at the toxicity of the Corexit 9500 to marine life which includes various marine invertebrates and fish (Wise 2011). The endpoints of death, fish gill ion regulation, and effects on enzyme activities were examined (Wise 2011). As a reference in evaluating these studies, a concentration of 20 ppm of Corexit is equivalent to one drop in 2.5 liters of water (Wise 2011). In toxicology, there are certain parameters which are evaluated when studies are conducted. These parameters include the median lethal dose (LD), also known as LD 50% (LD50) or lethal concentration 50% (LC50) which is the dose that is required in order to kill half of the members of the tested population after the duration of a specified test and also the EC50 also known as the half-effective concentration which is the molarity that produces 50% of the maximal possible effect (Wise 2011). The LOEC, which is the lowest observable effect concentration and the NOEC which is the no observed effect concentration are also the other parameters that are evaluated (Wise 2011). When assessing the parameter LOEC it indicates that the lower the effective concentration of the compound, the more toxic the compound is; NOEC indicates the highest tested dose or concentration in which no adverse effects are found in the organisms which are exposed to the compound (Wise 2011).

With the studies that were conducted with Corexit 9500, two studies examined the ability of Corexit 9500 to induce death in crustaceans (Wise 2011). A species of shrimp (Americamysis bahia) and another species the kelp forest mysid (Holmesimysis costana) were specifically used within the study (Wise 2011). From the study the toxicity of the oil, dispersant, and oil plus dispersant were compared and it was found that continuous exposures to the media being tested were more toxic than declining exposures (Wise 2011). The oil media that was prepared with just the chemical dispersant alone appeared to be just as equally toxic as the oil test medium alone (Wise 2011). After exposure it was determined that in the Americamysis bahia the LC50 was 32 ppm with a NOEC of 18 ppm (Wise 2011). A dose from 18ppm-900ppm was used overall with the Americamysis bahia (Wise 2011). In the Holmesimysis costana a LC50 of 158 ppm was observed with a NOEC of 142.3 ppm and a dose ranging from 25ppm-500ppm (Wise 2011). The endpoints of these two studies were conducted to death and were done for a period of 96 hours (Wise 2011). With the kelp forest mysid (Holmesimysis costana) the researchers also conducted another study where they compared the toxicity of Corexit 9500 with Corexit 9527 and it was found from the data that Corexit 9500 was similar to Corexit 9527 (Wise 2011). They observed delayed mortality from this study and it was found that one third of the mortalities that were recorded occurred during the first 72 hours of exposure (Wise 2011).

There were also five other studies which observed the toxic effects of Corexit 9500 in different fish species. These fish species: tambaqui (Colossoma macropomum), inland silverside (Menidia beryllina), sheepshead minnow (Cyprinodon variegatus), crimson spotted rainbowfish (Melanotaenia fluviatilis), and rockfish (Sebastes schlegeli) were exposed to the Corexit 9500 in order to observe the effects (Wise 2011). With the tambaqui (Colossoma macropomum) species, various ratios of the Corexit 9500 and water were used in order to see the effects the Corexit 9500 would have on the gill ion regulation of this species of fish (Wise 2011). The gills of fish are involved in gas exchange as they are modified so that they help to increase the surface area that is available for the diffusion of carbon dioxide and oxygen (Evans et al., 1999). There are multiple processes and steps that are involved in the regulation of ions within the gill epithelium of fish and the purpose of this study was to see how Corexit 9500 may alter and affect ion regulation within the fish (Evans et al., 1999). The study involving gill ion regulation was conducted for a period of six hours with a 1:1200 or 1:1000 dose of the Corexit 9500 and water mixture (Wise 2011). After this species of tambaqui fish were exposed, it was found that the fish survived and no changes were observed after the six hours from which the fish were exposed to the Corexit 9500 (Wise 2011). Corexit 9500 had no effects on gill ion regulation of this species of fish; however even though no effects were observed with this species, other species may not respond in the same manner and further studies would need to be conducted in order to better observe gill ion regulation.

From the study conducted with the inland silverside (Menidia beryllina) researchers wanted to see the ability of Corexit 9500 to induce death within this species (Wise 2011). They also exposed this species to the Corexit for a period of 96 hours and measured the lethal concentration through continuous and declining toxicities of the corexit 9500 (Wise 2011). They determined a continuous LC50=79 ppm and a declining LC50=76 ppm (Wise 2011). The no observed effect concentration was also measured in addition to the lethal concentration and a continuous NOEC of 50 ppm was observed while a declining NOEC of 42 ppm was observed (Wise 2011). From this data that was obtained, it can be seen that there was little difference in the continuous and declining toxicities. The continuous and declining toxicities were very close as there was a continuous LC50 of 79 ppm with a declining LC50 of 76 ppm (Wise 2011). The NOEC observed was also close in range as well. A continuous NOEC of 50 ppm was observed with a declining NOEC of 42 ppm (Wise 2011). The species was able to tolerate a minimal dose of 50 ppm before they started seeing the effects of the dispersant.

With the sheepshead minnow (Cyprinodon variegatus) species the same study was conducted as with that of the inland silverside (Menidia beryllina). With the use of the sheeshead minnow species of fish the following results were obtained: continuous LC50=180 ppm, declining LC50=670 ppm, continuous NOEC=107 ppm, and declining NOEC=305 (Wise 2011). The results obtained here were different compared to the results that were obtained with the inland silverside. The sheepshead minnow were better able to tolerate exposure to the Corexit 9500, however from the gathered data it can be seen that continuous exposure to the dispersant was more toxic than declining exposure.

The study involving the crimson spotted rainbowfish (Melanotaenia fluviatilis) was conducted a little differently from that of the previous two studies involving the inland silverside and sheepshead minnow. With the crimson spotted rainbowfish researchers were looking at the ability of Corexit 9500 to induce death in the early stages of the crimson spotted rainbowfish’s life as the early stages of this species life are the more sensitive stages (Wise 2011). From the data that was gathered after 72 hours of exposure there was an LC50 of 34.7ppm and after 96 hours an LC50 of 14.5 ppm (Wise 2011). Acute exposures resulted in the development of abnormalities within this species and when the researchers assessed Corexit 9500 and 9527 with this species, they found that Corexit 9500 alone was more toxic than Corexit 9527 as after 96 hours an LC50 of 20.1 ppm was observed with Corexit 9527 compared to the 14.5 ppm LC50 observed with the Corexit 9500 (Wise 2011).

In the study that was conducted with the rockfish (Sebastes schlegeli) the ability of Corexit 9500 to alter enzyme activities after a 72 hour exposure was observed. The concentrations of cytochrome P450 1A (CYP1A) and the levels of its catalytic activity, ethoxyresorufin O-de-ethylase (EROD), were exposed to water accommodated fractions (WAF) (Wise 2011). Water accommodated fractions are media that are prepared in the laboratory from the mixing of a low energy poorly soluble test material such as oil in the case of this study that was done (article 19). Water accommodated fractions at concentrations of 0.1% and 1% were used and when Corexit 9500 was added to these fractions with the oil their concentrations significantly increased (Wise 2011). From the study it was determined that with Corexit 9500 alone, there was no detectable CYP1A activity and no significant EROD levels (Wise 2011). However when Corexit 9500 was combined with the water accommodated fractions, CYP1A activity and EROD levels increased significantly after both 48 and 72 hours (Wise 2011). Based on these results, this shows that when the dispersant is added to the oil the level of exposure between these fish and the oil increases as their enzymatic activity increases.

As previously mentioned, Corexit 9527 was used in the Deep Water Horizon oil spill however it was later found that it was too toxic and its use was discontinued. Prior to its use in the Deep Water Horizon oil spill, Corexit 9527 had its first large scale application in the Exxon-Valdez spill in Alaska in 1989 (Wise 2011). As Corexit 9527 has been used previously there have been studies conducted in marine invertebrates, fish, birds, and rats (Wise 2011). A variety of different end points have been evaluated from death to behavior and immune responses.

One of the studies looked at a species of daphnia (Daphnia magna) which is a small planktonic crustacean and the ability of Corexit 9527 to induce death within this species (Wise 2011). In this experiment, bioassays were conducted and for this experiment bioassays for dispersants alone, for water-soluble fractions of crude oil, physical dispersions of crude oil and for the chemical dispersion of crude oil (Wise 2011). From this study, the results that were obtained showed that both the physical and chemical dispersed particles of oil were the main source of toxicity while the dissolved oil and the dispersants alone were not contributing to the toxicity as much (Wise 2011).

Species of anemones and corals were also investigated in a series three different studies. Reef corals (Montastraea franksi), coral (Acropora millepora), and snakelocks anemone (Anemonia viridis) were the species that were evaluated (Wise 2011). From these species, the reef corals (Montastraea franksi) were examined for the expression of P-glycoprotein, heat shock protein 70, and heat shock protein 90 after these species had been exposed to the dispersant Corexit 9527 (Wise 2011). From the experiment these reef corals that were exposed to Corexit 9527 showed a significant increase in both the P-glycoprotein gene expression and heat shock protein 70 gene expression (Wise 2011). Heat shock protein 90 gene expression did not change in these reef corals (Wise 2011). However, from this increase in gene expression from both the P-glycoprotein gene expression and heat shock protein 70 it indicated a general cellular stress response which shows that these reef corals were feeling the toxicological effects of Corexit 9527.

The coral (Acropora millepora) were evaluated for abnormalities in growth and reproduction after being exposed to the Corexit 9527 (Wise 2011). It was reported that after exposure of the corals to 10 ppm of Corexit 9527 caused significant impairment of fertilization and 5 ppm of the dispersant inhibited larval metamorphosis leading to an impairment of growth (Wise 2011). The researchers also noted that the dispersed oil was slightly more toxic to fertilization than just the dispersant alone (Wise 2011).

In the study with the snakelocks anemone (Anemonia viridis) the sub-lethal effects of Corexit 9527 were studied in which this species were exposed to Corexit 9527 for 48 hours and their ability to recover 72 hours after exposure was evaluated (Wise 2011). Doses of 0, 10, 20, 40, 80, or 160 ppm were given and it was found that the individuals who were exposed to 20 ppm would not respond to stimuli (Wise 2011). The concentration of Corexit 9527 above 80 ppm caused tissue decomposition and 89% of the anemones that were exposed to concentrations above 30 ppm were not able to recover (Wise 2011). Overall Corexit 9527 was found to be lethal to this species (Wise 2011).

Studies were also conducted within species of crustaceans with Corexit 9527. Six studies were conducted and they examined the effects of Corexit 9527 on prawns (Macrobrachium rosenbergii), brine shrimp (Artemia), copepods (Pseudocalanus minutus), mysid, rotifer (Brachionus plicatilis), and mud shrimp (Corophium volutator) (Wise 2011). With the prawns (Macrobrachium rosenbergii) the study done was conducted to see the effect of Corexit 9527 on the egg hatching rate of this species (Wise 2011). A flow through bioassay technique was used and from this technique when the fertilized eggs are detached from the mother, they have the ability to hatch artificially (Wise 2011). The control rate of the eggs hatching was 95.55% however with increasing concentrations of Corexit 9527 this rate was drastically reduced (Wise 2011). An EC50=80.4 ppm was observed with this species with there being no hatchability observed at concentrations above 250 ppm (Wise 2011). For this species they found that the recommended concentrations of Corexit 9527 stay below 40mg/L so that the dispersant is not lethal (Wise 2011).

In the species of brine shrimp (Artemia) they conducted six experiments and conducted them for two days in which they found that the LC50 to be 52 ppm with the EC50 ranging from 42 to 72 ppm (Wise 2011). They did not however, combine the results from the six experiments for an overall LC50 or an overall EC50 (Wise 2011). The same researchers who conducted the study on the brine shrimp species also conducted experiments on copepods (Pseudocalanus minutus) in which they found that Corexit 9527 was more toxic for copepods than brine shrimp (Wise 2011). They found that the copepods had an LC50 of 35.5 ppm after two days compared to the 52 ppm that was observed for the brine shrimp (Wise 2011).

In the mysid species a different group of researchers evaluated the ability of Corexit 9527 to cause death within the mysid species over a course of 96 hours (Wise 2011). Observations made regarding the species survival were recorded at 3, 6, 9, 12, and 24 hours in order to observe mortalities from spiked exposures (Wise 2011). They found that after 24 hours an LC50 of 65 ppm was observed and after 96 hours an LC50 of 27.1 ppm was observed (Wise 2011). An EC50 of 4.9 ppm was seen after the first 15 minutes of exposure indicating that 4.9 ppm of the dispersant was needed in order to produce 50% of the maximal effect within this species (Wise 2011).

With the study done involving the rotifer (Brachionus plicatilis) species the researcher conducting the study used a model in which he conducted his experiment simulating the conditions of an oil spill in the San Francisco Bay where copper levels are 5 µg/L (Wise 2011). He examined the effect of multiple stressors on heat shock protein 60 within these species where they were exposed to a crude oil/Corexit 9527 fraction or Corexit 9527 alone (Wise 2011). These rotifers were either first exposed to 5 µg/L of copper for 24 hours and then to the oil/Corexit 9527 fractions for another 24 hours or directly to the oil/Corexit 9527 fractions (Wise 2011). Heat shock protein 60 specific antibodies along with chemiluminescent were used in order to measure the heat shock 60 protein as a percentage of the control values (Wise 2011). Significant levels of the heat shock protein 60 were observed in both the oil/dispersant and dispersant only preparations of the mixture (Wise 2011). A four to five fold increase was observed in the oil/dispersant and dispersant only mixtures and the rotifers that had been exposed to the copper prior to exposure to the oil and the dispersant maintained elevated levels of the heat shock protein 60 which did not change significantly (Wise 2011). From this experiment it was determined from the changes in the gene expression with exposure to Corexit 9527 that toxicological effects can arise within this species. However when exposed to copper this species is able to better tolerate the dispersant as little effects were observed. More studies are needed in order to determine exactly what effect copper has in relation to the effect of Corexit 9527 as little to no effects were observed in this study.

In the species mud shrimp (Corophium volutator) the researcher looked at Corexit 9527 and its ability to induce death within this species of mud shrimp (Wise 2011).He found that when these mud shrimp had been exposed to Corexit 9527 for a period of 24 hours after exposure to 375 or 500 ppm the number of individuals within these groups greatly declined. Those that were exposed to 125 ppm showed normal swimming and normal burrowing however once exposure had been increased to 175 ppm these mud shrimp were stressed and when exposure was increased above 175 ppm these mud shrimp could not recover (Wise 2011). From this experiment an LC50 of 159 ppm with a NOEC of 125 ppm, with any concentration above 175 ppm resulting in no recovery (Wise 2011).

Studies involving species of mollusks and Corexit 9527 were also conducted (Wise 2011). Five studies were conducted with these mollusk species and the species in which the studies were conducted on consisted of mussels (Mytilus edulis), bay scallops (Argopecten irradians), oyster drill (Urosalpinx cinerea), and littleneck clam (Protothaca staminea) (Wise 2011). With the mussels (Mytilus edulis) two studies were conducted in which they measured the toxicity of Corexit 9527 to this species of mussels. They found from the experiments conducted that this species of mussels were the least sensitive of all species tested (Wise 2011). From the results no reliable LC50 was obtained as at 500 ppm they only observed a 2.6% decrease of feeding in the treated groups compared to that of the control groups (Wise 2011). They also observed that these mussels were slow to close when they were touched. Since no reliable LC50 was observed Corexit 9527 had very little effect on these mussels as they were able to tolerate the Corexit exposure. Another study involving these mussels looked at the short term effects consisting of water soluble fractions of Corexit 9527 and diesel oil on cellular immune responses (Wise 20110).These mussels were exposed to Corexit 9527 for two days and were injected with zymosan (foreign particles) to induce inflammation (Wise 2011). From this study it was found that these mussels which were exposed to Corexit 9527 then injected with the foreign particles all ended up dying which shows that immune responses are compromised as a result of being exposed to Corexit 9527 (Wise 2011).

In the experiment with the bay scallops (Argopecten irradians) predator and prey recognition was being evaluated in which short term acute exposure to oil, dispersant, or oil-dispersant mixtures was investigated where the bay scallops (Argopecten irradians) and two other predators, the oyster drill (Urosalpinx cinerea) and the common starfish were exposed (Wise 2011). From the results that were determined it was noted that the predators and prey had different lethal susceptibilities. It was found that the bay scallops were the most sensitive to dispersant and dispersant mixed with the oil (Wise 2011). The starfish were found to be sensitive to just the dispersant alone and the oyster drill were the least sensitive (Wise 2011). Sub lethal concentrations of the dispersant and dispersant mixed with oil reduced the ability of scallops to recognize the drills and starfish and as the temperature was increased the degree of the effect also increased (Wise 2011). An overall slowness in the feeding response of the predators was observed within this study with exposure to the oil, dispersant, or an oil-dispersant mixture.

In the study involving the littleneck clam (Protothaca staminea) field and laboratory experiments were carried out to determine the effects of Alberta crude oil and Corexit 9527 on larval settlement, survival, siphon activities, and behavior of these littleneck clams (Wise 2011). The littleneck clams were exposed to 10 or 100 ppm of Corexit 9527 where they were treated twice a day for a period of five hours for five days with a five day recovery period in order to induce death (Wise 2011). The larval samples which were in petri dishes were also exposed to 10 or 100 ppm of Corexit 9527 but were exposed for a period of five minutes, five times for five days (Wise 2011). It was found from this study that crude oil itself was less toxic compared to Corexit 9527 and the highest toxicity was obtained when Corexit 9527 was mixed with the crude oil. No mortality was observed at 10 ppm however with 100 ppm for both the small and larger sized clams a lethal toxicity of 2-3 days was seen (Wise 2011).

As mostly all of the studies with Corexit 9500 and 9527 have involved marine wildlife, there are two studies conducted with Corexit 9527 which did not involve marine organisms. The first of the studies involved birds which examined mallards (Anas platyrhynchos) in which hatchability and neurologic behavior within this bird species was examined after exposure to Corexit 9527 over a period of 48 hours (Wise 2011). When the chemically dispersed oil was tested for the effects on the immune response of these birds it was noted that the mallards that received the highest concentration of Corexit 9527 which consisted of 5.0 mL/kg of a 1:10 dilution in double distilled water developed temporary disorders within the nervous system (Wise 2011). Reduced mobility and loss of motor coordination was observed however none of the mallards during the treatment died (Wise 2011). With hatchability they used the same concentration of Corexit 9527 as was done in the study with the immune response over a period of 48 hours on breeding mallard ducks and it was determined that the exposure did not affect hatchability (Wise 2011). Another study conducted which also involved these mallards looked at resistance to bacterial infection where the mallards were exposed to Pasteurella multocida. It was found in this study that the mallards that received 4.0 mL/kg of 50:1 oil/Corexit 9527 mixture daily for a period of 28 days were significantly affected as resistance to Pasteurella multocida was significantly lowered (Wise 2011).

The other study conducted with Corexit 9527 involved rats where the toxicity of Corexit 9527 to the intestinal metabolism and the microbacteria of the Fischer 344 rats was examined (Wise 2011). These rats used within this study were treated over a period of five weeks with oil, dispersant, or oil dispersant mixture (Wise 2011). Within the cecum and small and large intestines, the impact on intestinal microflora and three microbial intestinal which are linked to bioactivation were determined (Wise 2011). Body and tissue weights along with urine mutagenicity examined with exposure (Wise 2011). When these Fischer 344 rats were exposed to undiluted Corexit 9527 it was found to be lethal to the rats whereas oil alone generally was not toxic (Wise 2011). With dilution, depending on the dilution amount, weight changes within these rats was observed and at the end of the study they found that body and tissue weights were not affected at the doses which had been administered (Wise 2011). In urine mutagenicity, S. typhimurium was used and it was noted that Corexit 9527 was toxic to S. typhimurium strains TA98, TA100, TA1535, TA1537, and TA1538 with dilutions up to 1:1000 (Wise 2011). The oil was not mutagenic in strains TA98 and TA100 with there being no urine mutagens detected by these two strains (Wise 2011). Within the small intestine, large intestine, and cecum the levels of azoreductase, β-glucuronidase, and nitroreductase were measured where all the activity levels of these enzymes were overall lower within the small intestine than they were in the large intestine or cecum at the same time in which they were measured (Wise 2011). An increase in azoreductase occurred in control animals within all tissues that were examined and β-glucuronidase activity was elevated within the large intestine in three week controls with no noticeable changes in cecal β-glucuronidase (Wise 2011) Compared to that with the controls in the activity of these enzymes, oil or dispersant treated rats after a period of three weeks had mixed results with reduced activity being observed after three weeks with elevated activity at five weeks (Wise 2011). Once the dispersant was combined with the oil, at three weeks the reduction in activity observed was close to that of the dispersant alone (Wise 2011). Nitroreductase activity after one week in the small intestine and cecum was unaffected with elevated activity observed in the large intestine in rats which were treated with the oil or dispersant alone and when oil was administered in combination with the dispersant, similar activity was observed as it was with the oil or dispersant alone (Wise 2011). On the fifth week of just oil treatment alone, enterobacteria and enterococci from the ceca of treated rats were eliminated but in combination with the oil and dispersant a protective effect was observed and the enterobacteria and enterococci were apparent within the ceca of these rats (Wise 2011). Overall it was noted that prolonged exposure of mammals to oil, dispersant, or the combination of both has a dramatic impact on intestinal metabolism which can lead to alterations on intestinal microflora and microbial intestinal enzymes (Wise 2011).

Significance and Limitations of Research

From the different research that has been conducted or is ongoing with the dispersants and various different species of animals, the research itself is providing useful information which helps in knowing exactly how safe these dispersants are when they are deployed on a wide scale. Since about 757 million liters of crude oil were released into the Gulf of Mexico over a period of 88 days, these dispersants were used in very large amounts for the first time ever as almost 7.57 million liters of these dispersants were used. Prior to the Deep Water Horizon oil spill, in the Exxon-Valdez oil spill of 1989 these dispersants were also used but in very limited amounts and the effects of these dispersants had not been examined. The chemical components were also not widely known. As there are a lot of unanswered questions and questionable outcomes from the application of dispersants in the cleanup of oil spills the research is highly significant. From evaluating these dispersants and knowing their toxic effects, better dispersants can be manufactured in the future and the toxic effects can be minimized. Less harmful chemical components can be used in the manufacture of these dispersants in the future and safer methods in the cleanup of future oil spills can be employed.

Since research is ongoing and as the Deep Water Horizon oil spill of 2010 was the first large scale application in which dispersants were used there are limitations to research that is currently being conducted. One of the major limitations to the research is that the oil spill itself occurred in a large scale with dispersants also being administered in a large scale. With much of the research that is being conducted, the effects and applications are measured and conducted on a much smaller scale. Many of the toxicity tests are confined to a select group of species of animals at a time where as in real life large groups or organisms of varying species are exposed at the same time. Also, it is difficult to simulate the environmental conditions present during the cleanup of the actual oil spill. Factors such as temperature, wind, sea conditions, pH all would have an effect on the cleaning up of the oil spill as certain conditions may be more favorable over others. From this, the toxicological effects can also be affected as with the proper combination of these conditions put together may create conditions in which the toxicity of the dispersant and oil are increased and may have more severe affects versus if the conditions were not as favorable. The results being obtained from these studies could vary slightly as the conditions within the studies conducted may not always be uniform. In addition, as seen in many of the studies different groups of organisms react differently to the oil and the dispersant and the environmental conditions in which these organisms are exposed could play a role. Multiple studies would have to be conducted using the same species with both similar and different environmental conditions over a long period of time in order to get more accurate results.

Another limitation to the research is the amount of time that is required in conducting the studies. In the actual Deep Water Horizon oil spill that occurred in 2010 the immediate effects of the spill were observed however it is uncertain as to what will happen in the future and whether populations of organisms that were most affected will be able to recover. It is also questionable as to how the overall ecosystem was impacted and it will take quite a long time to see and better understand the large scale use of dispersants within the oil spill. As of right now, much of the research is ongoing and ample time has not been put into the studies. Most of the studies conducted are done in really short periods of time with the majority of the studies being conducted recently after the Deep Water Horizon oil spill occurred in 2010 which is one of the key limitations for this research right now.

Future Direction Research Can Take

With the limitations that are currently seen with the research right now there are different directions in which research done in the future could take. As the majority of the research being conducted is ongoing, improvements and modifications to the research can occur. One approach to future research would be incorporating various different environmental factors similar to that of actual oil spills which occur. With much of the research that has been conducted so far, different species of animals are usually directly exposed to the dispersants and the amounts and their toxicological effects are evaluated. Environmental factors and conditions are not simulated and are not usually taken into consideration when the bulk of this research is conducted. Also most of the research is confined in a small scale laboratory setting with few species of animals at a time. With research done in the future these environmental factors could be incorporated and simulated within studies conducted in the future. The incorporation of these environmental factors could help not only in evaluating how dispersants coupled with these factors affect animal species but also in the development of newer and safer methods in cleaning up oil spills.

When oil spills occur, depending on the conditions present, the use of dispersants or implementing many of the other cleanup methods may not do as well of a job in cleaning up or may not be as effective. With the dispersants that were used within the Deep Water Horizon oil spill, very large amounts had to be used in order to clean up the oil and with the use of these large amounts, negative effects on the environment were seen. Both Corexit 9500 and 9527, being that they were used for the first time on a large scale with Corexit 9527 being more toxic compared to Corexit 9500, could be modified or be remanufactured in a way in which their level of toxicity is drastically reduced. From the studies that were conducted it was seen that the dispersants were harmful to every species of animals in which studies were conducted in one way or another. It was also seen that often times the dispersant itself was more toxic to many of the animal species than the oil itself which shows that dispersants in the end can have damaging effects to the environments in which they are used. In the future, with research that may be conducted, the use in the amounts of the dispersants could be minimized leading to less damaging effects on the environment. Also the more harsh components used in the manufacture of the dispersants could be substituted for other less harsh components which could be safer and would allow for faster and efficient cleanup of future oil spills from the future research that could be conducted.