Oil spills at sea are among the most spectacular and dramatic polluting events which threaten wildlife, livelihoods and regional economies. The April 20, 2010 Deepwater Horizon oil well blow out and massive amounts of oil and gas which are spewing out into the Gulf of Mexico is one of the more recent disasters that is drastically affecting the marine and coastline ecosystems. This has happened once before in 1979 with the Ixtoc I disaster when 1 500 000 tons of oil spilled into the sea and washed to shore along the Gulf Northwest coast. The best predictor of the future is sometimes the past, and the experience with the 1979 disaster can provide lessons as to what is and will continue to occur in the Gulf of Mexico and US coastlines following the April 20 oil spill, where, as of June 10, 2010, oil continues to flow into the gulf in amounts of around 40,000 barrels a day. These lessons already learned could help minimize the impact of the pollution.

The first and most spectacular effects of massive oil spills are most evident when oil arrives on the coastlines, covering the beaches, plants, sea birds, aquatic mammals and dead fish washing to shore covered with oil. How much death might the April 10 blowout cause? In 1999 the Erika oil tanker sank off the coast of France, causing one of the worst environmental disasters in the history of Europe. Over 20,000 tones of fuel oil spilled into the ocean, killing more than 150 000 birds representing 65 species along 400 Km of coastlines (Laubier, 2007). Unfortunately, the deadly impact is not limited to birds and fish, but to the environment.

Crude oils and petroleum are mixtures containing thousand of different molecules among which hydrocarbon compounds are dominant. Once in the water the fate of the oil dependis on its own properties (e.g., light vs heavy crude) and on physical-chemical parameters. As oil spreads along the water surface it undergoes a weathering due to wind, ocean waves and swell and heat and sun-induced evaporation. In consequence, the oil is transformed and undergoes physical-chemical modification, dispersion, emulsification, dissolution and sedimentation. For example, hydrocarbons are transformed by both biological reactions and photooxidation, leading respectively to their mineralization or to compounds resistant to degradation.

These modified petroleum and the hydrocarbon molecules are transported to coastal ecosystems which also react differently, due to their own unique characteristics, e.g. beaches, estuaries, mudflats, marshlands, mangroves. They are also dispersed in a variety of ways: the water column, the sea bed and the sediments, thereby affecting organisms all along the food chain.

When oil seeps beneath the surface it sedimentation such that oil is trapped in anoxic layers which prevent it from undergoing biotic or abiotic degradation (Garcia de Oteyza & Grimalt, 2006). This creates pollutant reservoirs that will for years menace and damage the ecosystem when released in the water column due to biotic and abiotic reworking of the sediments.

Residual contamination was detected in the Prince William Sound ecosystem (Alaska) seventeen years after the Exxon Valdez oil spill (Harwell & Gentile, 2006) and thus the potential toxic effect of this residues is under debate (Deepthike et al. 2009). During the accident in 1989, there were anecdotal reports of respiratory, nervous system, liver, kidney, heart and blood disorders, including the killing of fish eggs.

The toxicity of hydrocarbons and petroleum derived compounds depends on the nature of the hydrocarbons, the poly-aromatic hydrocarbons (PAH) are the most toxic and persistent components in coastal sediments (Menzie et al. 1992). It has been demonstrated that below 10 mg/L of hydrocarbons the food chain is polluted resulting in fecundity decreases and apparition of genetic anomalies while over 10 mg/L plankton, mollusks, crustaceans, gastropods, worms, larva and fishes will be destroyed(Hyland & Schneider, 1976). These impacts have been observed during the previous Erika and Sea Empress oil spills (Law & Kelly, 2004; Bocquené et al. 2004).

At sub-lethal levels these hydrocarbons can be bio-accumulated through the food chain as has been demonstrated for the Erika oil spill. These hydrocarbons were transferred from mussels to mammals by ingestion and resulted in genotoxic damages to liver cells (Lemière et al. 2004). Human health was also directly impacted. Cytogenetic damages and alterations in hormonal status was directly attributed to the 2002 Prestige oil spill (Pérez-Cadahía et al. 2007), after the Prestige oil tanker sank off the Galician coast.

The oil toxicity is increased by the application of dispersant, during cleanup operations. These oil dispersants have high toxicity and can dissolve hydrocarbons resulting in enhancing its bioavailability (Ramachandran et al. 2004).

Oil spills change the structure of microbial communities, such that microorganisms able to digest hydrocarbons become dominant (Bordenave et al. 2007), and deplete ocean waters of oxygen thereby killing oxygen dependent life forms. For example, oil dispersants destroyed microbial mats which structure guarantees fundamental functions in the ecosystem including oxygen production by photosynthetic cyanobacteria and sulfur recycling by Sulfur-Oxidizing bacteria (Duran & Goñi, 2010).In mangroves, microbial communities play a key role in dinitrogen fixation maintaining the balance of C:N:P ratio necessary for organic matter mineralization including oil biodegradation (Taketani et al. 2009), these microbes are also impacted by the oil and the toxic dispersants. Oil perturbation of microbial communities could break the fragile balance in the ecosystem resulting on important damages similar to dystrophic crisis.

Considering the current estimation, as of June 1, 2010, of more than 240 000 tons of oil having so far flowed from the broken oil well at the bottom of the gulf, this oil spill is now among the top10 of the worst oil spills in the history of this planet, with the Ixtoc I and the 1991 Arabian Gulf spills being considered as the largest and worst of them all. However, whereas the Ixtoc I oil spill blow out in the Bay of Campeche of the Gulf of Mexico, occurred at depths of 50 m (160 ft) deep and was eventually contained, the oil blow out off the coast of Louisiana has taken place at a depth of 5,000 ft and as of June 15, 2010, is still pouring around 40,000 barrels of oil a day into the gulf. The 1991 Arabian Gulf took place on land, was purposeful, but was also eventually brought under control. Thus, the April 10 gulf disaster has the potential to become the worst oil spill in the history of this planet.

Marine currents will carry the petroleum from the April 20 blowout ashore and will impact several thousand Km of US coasts from Louisiana to Florida. The proximity of the loop current and its connection with the Gulf Stream and given that oil continues to gush into the gulf, leads to the possibility of a worst scenario with oil carried into the Atlantic Ocean affecting the East coast of Florida and reaching the North Atlantic Ocean (Vanvleet et al. 1983).

Although the current oil spill still limited to the US coasts of the Gulf, this accident is already entering in history because it is injuring an unprecedented large variety of ecosystems characterized by their unique biodiversity and richness.

The Deepwater Horizon blow out in the Mexico Gulf will have unprecedented ecological impact and will damage more than 12 hectares of highly productive and sensitive coastal ecosystems such as mangroves and marshes in preserved areas as diverse as Louisiana’s Bayous in fresh water, black and white mangroves along the Louisiana and Florida coasts. These ecosystems, impossible to cleanup with the classic mechanical procedures, will suffer from the oil spill, and it may be hundreds of year before these ecosystems recover.

Oil will persist for long periods due to the vegetation density and slow degradation in anaerobic sediments. The oil will also asphyxiate mangrove trees, perturb microbial communities and disrupt the ecological stability affecting animals and microbes throughout the food chain for decades into the future. If oil continues to flow into the Gulf into late August as predicted, it will become the worst and possibly the most far reaching of any previous oil disaster in the history of this planet.

Bocquené, G., Chantereau, S., Clérendeau, C., Beausir, E., Ménard, D., Raffin, B., Minier, C., Burgeot, T., Pfohl Leszkowicz, A., Narbonne, J.F. (2004) Biological effects of the "Erika" oil spill on the common mussel (Mytilus edulis). Aquatic Living Resources 17: 309-316.

Bordenave, S., Goñi-Urriza, M.S., Caumette, P., Duran, R. (2007) Effects of heavy fuel oil on the bacterial community structure of a pristine microbial mat. Appl. Environ. Microbiol. 73: 6089-6097.

Pérez-Cadahía, B., Lafuente, A., Cabaleiro, T., Pásaro, E., Méndez, J., Laffon, B. (2007). Initial study on the effects of Prestige oil on human health. Environment International 33: 176–185.

Deepthike, H.U., Tecon, R. Vankooten, G., Van der Meer, J.R., Harms, H., Wells, M., Short, J. (2009) Unlike PAHs from Exxon Valdez crude oil, PAHs from Gulf of Alaska coals are not readily bioavailable. Environmental Science and Technology. 43, 5864–5870

Duran, R., Goñi Urriza, M.S. (2010) Impact of Pollution on Microbial Mats. Microbes and Communities Utilizing Hydrocarbons, Oils and Lipids - Chapter 53 in K. N. Timmis (ed.), Handbook of Hydrocarbon and Lipid Microbiology, Springer-Verlag Berlin Heidelberg, 2010. pp 2339-2348.

Garcia de Oteyza, T., Grimalt, J. (2006) GC and GC-MS characterization of crude oil transformation in sediments and microbial mat samples after the 1991 oil spill in the Saudi Arabian Gulf coast. Environmental Pollution. 139: 523-531.

Harwell, M.A., Gentile, J.H. (2006) Ecological significance of residual exposures and effects from the Exxon Valdez oil spill. Integrated environmental assessment and management 2 (3), pp. 204-246.

Hyland, J.L., Schneider, E.D. (1976) Petroleum hydrocarbons and their effects on marine organisms, populations, communities, and ecosystems. In: Sources, effects and sinks of hydrocarbons in the aquatic environment. American Institute of Biological Sciences, Washington, D.C., 463.

Laubier, L. (2007) La marée noire de l’Erika. Quelles conséquences écologiques? Institut océanographique éditeur, Paris-Monaco. pp 118.

Law, R.J. and Kelly, C. (2004) The impact of the "Sea Empress" oil spill. Aquatic Living Resources 17: 389-394.

Lemière, S., Cossu-Leguille, C., Chaty, S., Rodius, F., Bispo, A., Jourdain, M.J., Lanhers, M.C., Burnel, D., Vasseur, P. (2004) Genotoxic and CYP 1A enzyme effects consecutive to the food transfer of oil spill contaminants from mussels to mammals. Aquatic Living Resources 17: 303-308.

Menzie, C.A., Potocki, B.B., Santodonato, J. (1992) Exposure to carcinogenic PAHs in the environment. Environmental Science and Technology. 26: 1278-1284. Ramachandran, S.D., Hodson, P.V., Khan, C.W., Leeb, K. (2004) Oil dispersant increases PAH uptake by fish exposed to crude oil. Ecotoxicology and Environmental Safety 59 : 300- 308.

Taketani, R.G., dos Santos, H.F, van Elsas, J.D., Rosado, A.S. (2009) Characterisation of the effect of a simulated hydrocarbon spill on diazotrophs in mangrove sediment mesocosm. Antonie van Leeuwenhoek. 96:343–354

Vanvleet, E.S., Sackett, W.M., Weber, F.F., Reinhardt, S.B. (1983) Input of pelagic tar into the NorthWest Atlantic from the gulf loop current – chemical characterization and its relationship to weathered Ixtoc-i oil. Canadian Journal of Fisheries and Aquatic Sciences. 40: 12-22.