User:AlgalBloom34/Environmental impact of the Deepwater Horizon oil spill

The 2010 Deepwater Horizon oil spill in the Gulf of Mexico has been described as the worst environmental disaster in the United States, releasing about 4.9 million barrels (210 million US gal; 780,000 m3) of crude oil into the open ocean for 87 consecutive days. White House energy adviser Carol Browner called the spill "the worst environmental disaster the US has faced. Deepwater Horizon as well as the subsequent cleanup efforts adversely impacted various aspects of the marine environment. Factors such as petroleum toxicity, oxygen depletion and the use of Corexit are expected to be the main causes of damage. The spill was by far the largest in US history, almost 20 times greater than the usual estimate of the Exxon Valdez oil spill.

Ecotoxicology of the Spill (Daddona)
The ecotoxicological impacts of the Deepwater Horizon spill conveys a narrative in which the effects of released contaminants span both time and multiple trophic levels of which humans are only a small part. Oil Spills release toxins such as Polycyclic Aromatic Hydrocarbons (PAHs) and volatile organic compounds into surrounding marine and terrestrial ecosystems.(newly cited) Both classes of compounds have complex routes of exposure to organisms that characterize the extent of their stress on ecosystems: the Gulf of Mexico, surrounding coastal zones, and salt marshes.

Methane (Zampetti)
Oceanographer John Kessler estimated that the crude oil gushing from the well contained approximately 40% methane by weight, compared to about 5% found in typical oil deposits. Methane can potentially suffocate marine life and create dead zones where oxygen is depleted. Oceanographer Dr. Ian MacDonald believes that the natural gas dissolving below the surface has the potential to reduce the Gulf oxygen levels and emit benzene and other toxic compounds.

In years after the spill, research has developed exposing a major and sudden depletion of the crude oil methane. Subsequent research has shown reductions in crude oil methane. Because of the sheer size of the spill, studies concluded that methanotrophs were able to grow and consume the methane. It was also discovered that immediately following the spill, the released methane formed a large column concentrated at around 4,000 feet (1,200 m) below the surface instead of traveling to the surface because of the water's low temperature and high pressure. This rapid abundance of methane supported a population of methanotrophs for about seven months before the methane and methanotroph levels sharply decreased.

Additional Volatile Organic Compounds (Daddona)
In response to the spill, US EPA (newly cited) staff monitored the Gulf's Coastal Air Quality by comparing average volatile contaminant levels from atmospheric samples with average human blood screening levels. Benzene, ethyl-benzene, toluene, xylene, and other volatile organic compounds (VOCs) created acutely harmful health impacts on humans and other organisms, causing caused eye and lung irritations and as well as cancer. Whereas the volatile compounds rise into the atmosphere, other PAHs can persist in the environment causing chronic health issues. Wildlife experience similar respiratory and ocular distress, especially in marine mammals that respire at the surface.  

Toxicity from polycyclic aromatic hydrocarbons (Zampetti)
Terry Wade of Texas A&M University, Steven Lohrenz of the University of Southern Mississippi and Stennis Space Center found evidence of the polycyclic aromatic hydrocarbons (PAH) as deep as 3,300 feet (1.0 km) and as far away as 8 miles (13 km) in May 2010 and claim it likely worsened as more oil spilled. PAHs are enriched in oil and include carcinogenic compounds and chemicals making them the most toxic component of crude oil to marine life After the spill, many seafood species frequently caught in the Gulf of Mexico exhibited physical and reproductive deformities, such as shrimp without eyes. Dr. Jim Cowan proposes that PAHs weathered from leaked oil on the seabed are likely the cause of the mutations. "From the time that these observations were made, there was an extensive release of additional oil and dispersants at the site. Therefore, the effects on the deep sea ecosystem may be considerably more severe than supported by the observations reported here," the Wade and Lohrenz wrote in the journal Geophysical Research Letters. PAH's, they said, include a group of compounds, with different types at different depths. "It is possible they dissipate quickly, but no one has yet showed this".

In September 2010, researchers found sharply heightened levels of chemicals in the waters off the coast of Louisiana in August 2010, the last sampling date, even after the well was capped one month prior. Near Grand Isle, Louisiana, the team discovered that PAH remained at levels 40 times higher than before the spill. The PAH's were most concentrated in the area near the Louisiana Coast, but levels also jumped 2–3 fold in other spill-affected areas off Alabama, Mississippi and Florida. As of August 2010, PAH levels remained near those discovered while the spill was still flowing heavily.

Kim Anderson, a professor of environmental and molecular toxicology, said that based on the findings of other researchers, she suspected that the abundant use of dispersants by BP increased the bio-availability of the PAHs. "There was a huge increase of PAHs that are bio-available to the organisms – and that means they can essentially be uptaken by organisms throughout the food chain." The use of dispersants can increase the bioavailability of PAHs, which are typically hydrophobic, by making them more soluble in water and therefore easier to uptake. PAHs primarily enter marine species via ingestion, ventilation (through gills), and dermal exposure. Therefore, organisms with more frequent exposure to PAHs through more of these pathways will accumulate a higher concentrations of PAHs. A 2015 study of PAH concentrations in three demersal fish species: golden tilefish, red snapper, and king snake eel, revealed that golden tilefish had six times more naphthalene, a type of PAH, than red snappers and nine times as much as king snake eels. Golden tilefish are known to permanently burrow in the sediment, and bioturbate to build burrows, while the two other species are less exposed to the sediment. Their high concentrations can be explained by the additional exposures and frequency only common to the golden tilefish.

Dispersal Throughout Water Column (Daddona)
Petroleum from the Deep Water Horizon Spill was released 1.5 kilometers deep, from the Macondo Well in the Gulf of Mexico, resulting in more extensive fate than that of a solely surface spill. The chemical properties of petroleum components, Gulf water, and various physical/geographical phenomena altered the fate of Deep Water Horizon’s deep-water spilt oil components, dispersing from the seafloor, to the surface, eventually beaches and wetland marshes, and even suspended in plumes.

Due to the deep water nature of the spill, volatile organic compounds including a majority of methane and a minority of propane, ethane, and other VOCs were not as quickly released into the atmosphere, and many more hydrocarbons were dissolved into the water column. Aqueous compounds do not include insoluble petroleum and other components which settled onto the sea floor or rose to the surface depending on density.

A 2010 analysis of aqueous compositions of oil/Gulf water samples determined that due to increased residence time in the water column, methane was the gas most readily metabolized by microbial respirators, resulting in nearly 75% of oxygen depletion in fresh plumes. Remaining loss of oxygen may be due to degradation of propane and ethane. (newly cited) Hypoxic conditions create loss of marine species in addition to acute poisoning, which is exacerbated by microbial retention of PAHs and suspected bioaccumulation in species. It is not thought that PAHs increase in concentration toxicity (biomagnify) up trophic levels.

Impact to Shoreline (Zampetti)
A 2016 study to quantify the scope of shoreline destruction from the oil disaster concluded that 2,113 km of the 9,545 km of shoreline studied were impacted by shoreline oiling, with 52% of impacted shoreline being coastal wetlands and 46% being beaches. Of the coastlines bordering the Gulf of Mexico, the majority of shoreline oiling affected Louisiana, then Mississippi, Alabama, and Florida, and less significantly, Texas. The overall shoreline impact depends on a wide variety of factors, including: the type of oil, how weathered the oil was when it reached the shore, the season the oil exposure occurs in, etc. Oil weathering is the process by which oil transforms into various different forms as it goes through various natural processes. Typically, oil is the most toxic to wildlife before it is weathered.

Coastal Wetlands
The oil acutely catalyzed the erosion of land by killing much of the marsh vegetation. 95% of the heavy oiling damage to salt marshes occurred along the coast of Louisiana, primarily among marshes dominated by Spartina alterniflora and Juncus roemerianus. A 3.5 year study investigated the long term impacts to salt marshes along the Gulf Coast, specifically Barataria Bay. Acute toxicity immediately following the spill was evident with total vegetation mortality due to suffocation. Though a few more resilient systems recovered, many entered a regime of longer term impacts. The areas of the highest concern were those where large amounts of oil infiltrated marsh soil, continuously coming into contact with roots, and weakened the marsh edge and thus accelerating shoreline erosion. Studies of vegetation death and accelerated marsh erosion have shown that “injuries” can be related to the percent of oiling on the stems of marsh vegetation. It was found that where stems were 90-100% oiled the mean erosion rate was 1.4 meters per year higher than expected.

Beaches
In the months following the spill (June-July) sandy beaches were inundated with oil. Some of this oil washed up on shores in the form of tarballs that were regularly located by BP contractors as well as local residents. More oil washed up on shores as sunken oil mats (SOMs). Through natural beach processes, much of the oil that arrived at the beaches was mixed into the sand and became remnant oil. A 2012 study of the sands of the contaminated beaches showed that the species diversity had dropped dramatically since the spill. The remaining species are believed to be those that consume hydrocarbons and favor polluted conditions. This could result in long-lasting effects to the ecosystem. The study expressed concerns that trace minerals and metals such as mercury and arsenic deposited by the oil may cause harm to both wildlife and humans.

The use of dispersant made oil sink faster and more deeply into the beaches and possibly groundwater supplies, according to a November 2012 a study released by Florida State University and Utrecht University in the Netherlands. The researchers found that Corexit 9500A allowed the PAHs to permeate sand where, due to a lack of sunlight, degradation is slowed.

Aquatic Vegetation (Zampetti & Daddona)
(Zampetti) Submerged aquatic vegetation serve multiple ecological purposes across a wide variety of ecosystems. Multiple studies have been conducted since the spill to analyze the impact of oiling on the chemical composition of aquatic vegetation. A 2015 study used manipulative experimentation with various oil concentrations (0; 0.26; 0.53; and 1.05 mL oil/L tank volume) to understand the impact that oiling has on the chemical composition of Ruppia maritima. This plant was chosen for this and many other studies because it is one of the most abundant seagrass species in the areas surrounding the Deepwater Horizon wellhead. The study found that regardless of oil concentration, the samples all grew an average of 0.78g from an initial mass of 0.31 g. However, with increasing oil concentration the results demonstrated decreasing fruit production, flower production, root length, and force needed to uproot plants. In the field, a comprehensive 2017 study of five different species of seagrass abundant near the coasts of Chandeleur Islands estimated a total loss of 104.22 acres of seagrass due to oiling.

(Daddona) A related geomorphic phenomenon was also discovered by Silliman et al. (2016) in which the oiling and consequent death of vegetation increased erosion rates along Gulf Coastlines. Although high classes of shore oiling are necessary to pass the threshold for coastal vegetative resilience, the consequences include loss of coastal regions’ primary defense against sea level rise and land loss: critical salt marsh habitat. (newly cited)

Aquatic Animals (Zampetti)
Eight U.S. national parks were threatened and more than 400 species that live in the Gulf islands and marshlands were put at risk, including the endangered Kemp's ridley turtle, the green turtle, the loggerhead turtle, the hawksbill turtle, and the leatherback turtle. In the national refuges most at risk, about 34,000 birds were counted, including gulls, pelicans, roseate spoonbills, egrets, terns, and blue herons. A comprehensive 2009 inventory of offshore Gulf species counted 15,700. The area of the spill includes 8,332 species, including more than 1,200 fish, 200 birds, 1,400 molluscs, 1,500 crustaceans, 4 sea turtles, and 29 marine mammals. The spill threatened 39 marine species in addition to the 14 currently under federal protection. Threatened species, the report found, ranged from 'whale sharks to seagrass".

Harry Roberts has stated that 4 million barrels (640,000 m3) of oil would be enough to "wipe out marine life deep at sea near the leak and elsewhere in the Gulf" as well as "along hundreds of miles of coastline." Mak Saito indicated that such an amount of oil "may alter the chemistry of the sea, with unforeseeable results." Samantha Joye indicated that the oil could harm fish directly, and microbes used to consume the oil would reduce oxygen levels in the water. The ecosystem could require years or decades to recover, as with previous spills. Damage to the ocean floor would endanger the Louisiana pancake batfish in particular, whose range is entirely contained within the area affected by the spill.

Contamination of the Food Web (Zampetti)
Signs of an oil-and-dispersant mix were found under the shells of blue crab larvae in the Gulf by researchers at Tulane University in 2010. This finding indicated that the use of dispersants had broken the oil into droplets small enough to easily enter the food chain. Marine biologists found "orange blobs" under the shells of crab larvae in "almost all" of the larvae collected from over 300 miles (480 km) of coastline stretching from Grand Isle, Louisiana, to Pensacola, Florida. According to a March 2012 study, spilled oil entered the ocean's food chain through zooplankton. Dr. Michael Roman stated "traces of oil in the zooplankton prove that they had contact with the oil and the likelihood that oil compounds may be working their way up the food chain". Alabama researchers in July 2012 found that dispersants may have killed microscopic plankton and disrupted the food chain. Scientists commenting on the study, published in PLOS ONE, said the findings pointed toward "major future effects of the spill". Carbon isotopic evidence has revealed that oil from the disaster has entered the bodies of land animals and birds (terrestrial fauna) leading to a reduction in the reproductive success of some species.

Aquatic Mammals (Zampetti) (New section with reordered info from other sections)
The actual number of mammal deaths due to the spill may be as much as 50 times higher than the number of recovered carcasses, according to a study published in the Journal Conservation Letters. "The Deepwater oil spill was the largest in US history, however, the recorded impact on wildlife was relatively low, leading to suggestions that the environmental damage of the disaster was actually modest. This is because reports have implied that the number of carcasses recovered... equals the number of animals killed by the spill" stated Rob Williams from University of British Columbia.

From mid-January to late March 2011, scientists counted almost 200 dead dolphins in the Gulf, with another 90 in 2010. After investigating the deaths, NOAA put a gag order on the results, saying that the research is part of a criminal investigation of the spill. Numerous independent scientists said they have been "personally rebuked by federal officials for speaking out of turn to the media about efforts to determine the cause" of the deaths.

In April 2011, one year from the onset of the spill, scientists confirmed that they had discovered oil on dead dolphins found along the Gulf Coast. Fifteen of the 406 dolphins that had washed ashore in the last 14 months had oil on their bodies; the oil found on eight of them was linked to the spill. A NOAA spokesperson said it was "significant that even a year after the oil spill we are finding oil on the dolphins, the latest just two weeks ago." A NOAA study in the summer of 2011 showed dolphins that came in contact with the petroleum were "seriously ill" with drastically low weight, low blood sugar and for some, cancer of the liver and lungs.

In December 2013, the journal Environmental Science & Technology published a study finding that of 32 dolphins briefly captured from 24-km stretch near southeastern Louisiana, half were seriously ill or dying from liver disease, pneumonia, loss of teeth, and one pregnant female was carrying a dead fetus. The animals compared unfavorably with dolphins from an area of the gulf unaffected by the spill. BP said the report, which was the first study of the spill's impact on dolphins, was “inconclusive as to any causation associated with the spill”.

On 12 April 2016, a research team reported that 88 percent of about 360 baby or stillborn dolphins within the spill area "had abnormal or under-developed lungs", compared to 15 percent in other areas. The study was published in the April 2016 Diseases of Aquatic Organisms.

Fish (Zampetti)
" Disturbing numbers" of mutated fish were seen in the Gulf. Scientists and fishermen are pointing to the the dispersants and chemicals used in the spill cleanup as the cause of these deformities which include shrimp born without eyes, fish with lesions, fish with oozing sores and, according to a local fisherwoman, "eyeless crabs, crabs with their shells soft instead of hard, full grown crabs that are one-fifth their normal size, clawless crabs, and crabs with shells that don't have their usual spikes ... they look like they've been burned off by chemicals". The dispersants are known to be mutagenic. Another lifelong fisher-woman reported seeing "fish without covers over their gills and others with large pink masses hanging off their eyes and gills". A 2014 study of the effects of the oil spill on bluefin tuna, published in the journal Science, found that oil already broken down by wave action and chemical dispersants was more toxic than fresh oil.

Prior to the spill, approximately 0.1% of Gulf fish had lesions or sores. A report from the University of South Florida said that many locations showed 20% of fish with lesions, and later expeditions some as high as 50%.

A 2014 paper in the journal Science found that toxins released by the oil spill killed fish by causing cardiac arrest. The study found that even very low concentrations of crude oil can slow the pace of fish heartbeats. The study was conducted by researchers at Stanford University and the National Oceanic and Atmospheric Administration as part of the federal Natural Resource Damage Assessment process required by the Oil Pollution Act. It focused on tuna partly because the spill occurred in an area where Atlantic bluefin tuna were spawning. The effects were considered especially problematic for fish embryos and early developing fish, because the heartbeat changes could affect the development of other organs, including the lungs and liver. BP disputed the study, raising questions about the study and the use of its findings in the damage assessment process. Another peer-reviewed study, released in March 2014 and conducted by 17 scientists from the United States and Australia and published in the Proceedings of the National Academy of Sciences, found that tuna and amberjack that were exposed to oil from the spill developed deformities of the heart and other organs. BP responded that the concentrations of oil in the study were a level rarely seen in the Gulf, but The New York Times reported that the BP statement was contradicted by the study.

Coral (Edited and Added to, Daddona)
In February 26th, federally funded scientists found damage to deep sea coral several miles from the well. Expedition leader and biologist with Penn State University Charles Fisher said there was "an abundance of circumstantial data" suggesting coral damage is related to the spill. This discovery indicated that the spill's ecological consequences may be greater than was previously officially claimed. Key circumstantial evidence found included NOAA modeling of the deep-water plume's trajectory and depth that corroborated coral site impacts. "The research site is at the right depth and direction to have been impacted by a deep-water plume, based on NOAA models and empirical data; and the impact was detected only a few months after the spill was contained." (newly edited)

In March 2012, definitive link was found between the death of a Gulf coral community the size of half a football field and the spill. The scientists wrote: "The presence of recently damaged and deceased corals beneath the path of a previously documented plume emanating from the Macondo well provides compelling evidence that the oil impacted deep-water ecosystems." A 2011 study by White et al. (2011) located a coral colony 11 kilometers from the Macondo Well in which over half of the corals displayed signs of fibrosis, abnormal color, and/or attachment posture.

Birds (Daddona)
Birds were one of the most devastated species in terms of suffered among the highest mortalities, with close to 100,000 conservatively estimated deaths across 93 species according to US Fish and Wildlife estimates. A majority of the deaths and injuries were related to flying impairment from oiled feathers, resulting in loss of fitness, as well as hypothermia from degraded feather insulation.

Chemical Dispersant (Zampetti)
In response to the spill, BP sprayed about 2.1 million gallons of chemical dispersant, mostly Corexit EC9500A, on the surface and floor of the Gulf of Mexico. Chemical dispersants are commonly used in oil spill remediation because they are composed of a mix of surfactants, solvents and other chemicals that disperse thick deposits of oil into smaller droplets. These smaller oil deposits then enter the water column where they are absorbed by microbes or swept away by current. When used correctly and with the correct temperature and salinity conditions, spraying chemical dispersant can be an effective method to reduce the impact of oil spills on beaches and salt marshes because the oil is broken down in the open ocean before it travels. However, studies have shown that the dispersed oil in the water column may be even more toxic. A 2011 study on beached oil samples from Elmer's Island Wildlife Refuge provided evidence that while Corexit 9500A does in fact work to disperse oil, it can have highly toxic effects on microbial communities that are involved with hydrocarbon degradation. The harm done to the microbes can therefore negatively impact their ability to metabolize the oil and remediate spills.

In terms of aquatic species, studies show that Corexit 9500A was not significantly more or less toxic that its Corexit predecessors, however there was still strong evidence that the dispersant was acutely toxic to embryonic membranes of marine organisms, specifically the red abalone and the kelp forest mysid. The resulting deformities were a direct result of the dispersant's ability to increase membrane permeability and hinder barrier function and osmotic function. The literature review titled, "The current state of knowledge for toxicity of Corexit EC9500A dispersant" offers a very comprehensive list of the impacts of the dispersant used for mitigation of the Deepwater Horizon spill on a myriad of marine and freshwater species.

Human exposure to the Corexit 9500A primarily impacted workers responsible for spraying the dispersant. Though little is known of the acute and chronic affects of exposure to humans, experiments were conducted using rats and mice to mirror potential impacts on humans. Experiments showed acute dermal irritations and ear swelling of mice and rats exposed to the dispersant via aerosol, and a reduction of olfactory response in brain scans 7 days after exposure.

Remaining Oil in the Water (Edited by Daddona)
Remaining Oil in the water exists on the seafloor, in a suspended and dissolved state, as well as on the surface.   The quantity and location of remaining oil in the Gulf of Mexico was predicted by a number of scientific projections and continual discoveries of oil and oil substances on shoreline.   At the 2013 "Gulf of Mexico Oil Spill and Ecosystem Science Conference", oceanographer David Hollander presented data that showed as much as one-third of the oil released during the spill may still be in the gulf. By November 2010, joint US and BP efforts were predicted to contain, eliminate, and disperse an estimated 41% of the oil released from the deep-sea well, corroborating the large quantity of remaining oil. Hurricane Isaac in September 2012 challenged claims of passing damage when oiled material traced to the spill was brought to land once again.

A Coast Guard report released on 17 December 2010, stated that little oil remained on the sea floor except within a mile and a half (2.5 km) of the well. By November 2010, joint US and BP efforts were predicted to contain, eliminate, and disperse an estimated 41% of the oil released from the deep-sea well, corroborating the large quantity of remaining oil. Remaining oil could extend acute harms to both terrestrial and aquatic wildlife, as well as contribute to chronic harms and environmental degradation, however more research is needed to confirm and qualify these impacts..