Main terms and chronology of marine oil spill in the last 20 years

Definitions and classifications will be easy to understand if readers have a basic level of knowledge of chemistry, physics, mathematics, and biology.

Hydrocarbons: Any type of organic chemical compound consisting solely of elements of carbon (C) and hydrogen (H). Carbon atoms join to form the framework of the compound, and hydrogen atoms join to them in different forms. Hydrocarbons are the main components of oil and natural gas (Aminzadeh & Dasgupta, 2013).

Classification of Hydrocarbons (according to API gravity): They are classified as light (greater than 31.1° API), medium (between 22.3° and 31.1° API), or heavy (less than 22.3° API).

Oil spill: Uncontrolled release of oil in violation of primary containment (Ndimele, 2017).

Oil Spill Contingency Plan: A guidance document that establishes response strategies through standard operating procedures and incident response protocols, understanding an incident as a natural or human-made event, requiring the intervention of emergency personnel to prevent or minimize loss of life or damage to property and/or natural resources (Fingas, 2011).

Sacrifice Zone: The area where the arrival of the hydrocarbon may cause less damage and where it may subsequently be removed as easily and quickly as possible by mechanical or human means. Appropriate areas may include coastal ramps, harbor areas, beaches, roads, etc. Areas that are difficult to clean and to access, or with a high ecological value (marsh areas, rocky areas, and pebble beaches) should be avoided (Casado, 2013Casado, P. 2013. Las Barreras Anticontaminacion Contra los Vertidos Hidrocarburos. Tesis de grado, Cantabria, España: Escuela Técnica Superior de Náutica, Available: <https://repositorio.unican.es/xmlui/bitstream/handle/10902/3935/Pablo%20Casado%20Ferreiro.pdf?sequence=1>, [Consulted: August 31, 2021].).

Refuge Zone: A location where a ship in distress may take measures to stabilize its condition, reduce the danger of navigation, protect human life, and the environment.

Emulsions: They are systems consisting of two or more immiscible liquid phases. They are generally made by homogenization of an oily phase and an aqueous phase in the presence of an active emulsifying surface. The emulsifier may decrease the interfacial tension between the oil and water phases and, thus, facilitate the formation of the emulsion and stabilization of the dispersed phase, after which the emulsion is formed (Pacwa-Płociniczak et al. 2011).

Lagrangian model (classification according to the method used): Mathematical model based on particles for which their magnitudes and position in time are known. It is very useful to evaluate the dispersion of a pollutant before a complex geography (Moroni et al., 2019Moroni, M.; Lupo, E. & La Marca, F. 2019. “Hydraulic separation of plastic wastes”. In: Use of Recycled Plastics in Eco-efficient Concrete, Cambridge, UK: Woodhead Publishing, pp. 39-68, ISBN: 978-0-08-102676-2, Available: <https://researchonline.jcu.edu.au/56477/1/56477_Tuladhar_et_al_2018_front%20matter.pdf>, [Consulted: August 15, 2020].).

Eulerian model (classification according to the method used): Mathematical model for which the properties of the field in which the fluid develops are known. The magnitudes of each variable will be determined by the point it occupies in space in a given time (Moroni et al., 2019Moroni, M.; Lupo, E. & La Marca, F. 2019. “Hydraulic separation of plastic wastes”. In: Use of Recycled Plastics in Eco-efficient Concrete, Cambridge, UK: Woodhead Publishing, pp. 39-68, ISBN: 978-0-08-102676-2, Available: <https://researchonline.jcu.edu.au/56477/1/56477_Tuladhar_et_al_2018_front%20matter.pdf>, [Consulted: August 15, 2020].).

Hybrid model (classification according to the method used): Mathematical model in which the oil concentration field is reconstructed by Eulerian approach from the Lagrangian approach advection-diffusion and transformation processes (De Dominicis et al., 2013De Dominicis, M.; Pinardi, N.; Zodiatis, G. & Lardner, R. 2013. “MEDSLIK-II, a Lagrangian marine surface oil spill model for short-term forecasting-Part 1: Theory”. Geoscientific Model Development, 6(6): 1851-1869, ISSN: 1991-9603.).

Stochastic Model (classification according to the method used): It is the model in which the probable place of impact of a spill is estimated for defined periods of time. In order to do so, they use historical records of the flows involved. According to different conditions, this modeling produces a probable result of impact areas and time of arrival, which enables the implementation of contingency plans when estimating risk zones depending on changes in time (Hamed, 2000).

Deterministic model: It provides expected forecasts only for spills. The response time scale is much smaller, and the demands on the modeler to make accurate predictions are significant in order to plan the response in a timely manner. Access to high-resolution wind data and current forecasts are essential, and it should be possible to efficiently integrate these data with the oil spill model (Marzialetti, 2012Marzialetti, P. A. 2012. Monitoreo de Derrames de Hidrocarburos en Cuerpos de Agua Mediante Tecnicas de Sensado Remoto. Tesis de grado, Cordoba: Instituto de Altos Estudios Espaciales, 149 p., Available: <https://ishareslide.net/view-doc.html?utm_source=tesisaearte-pablo-marzialetti-pdf>.).

Receptor model: It is identified by estimating the origin of the spill analyzing the trajectory in the reverse direction (Marzialetti, 2012Marzialetti, P. A. 2012. Monitoreo de Derrames de Hidrocarburos en Cuerpos de Agua Mediante Tecnicas de Sensado Remoto. Tesis de grado, Cordoba: Instituto de Altos Estudios Espaciales, 149 p., Available: <https://ishareslide.net/view-doc.html?utm_source=tesisaearte-pablo-marzialetti-pdf>.).

Environmental Sensitivity Indexes (ESI): An index that sorts coastal classes on a 10-point scale following the fundamental principles that hydrocarbon sensitivity increases with increased coastal protection against wave action, hydrocarbon penetration into the substrate, natural coastal retention times, and biological production of coastal organisms (Momtaz & Kabir, 2013).

Environmental Sensitivity Maps: They are aimed at providing efficient and rapid advice to the Local Maritime Authority, On-scene Commander, or in charge of the Combat before an oil spill. They graphically represent the different types of coastline that we can find along the coast (sensitivity or type of coast) through lines, symbols, and polygons. The uses of these coasts and the natural resources that could exist in there, so that in the face of a disaster, this tool has a preponderant value in decision-making (Gonzalez, 2017).

When an oil spill occurs in a body of water, it splits into several slicks and disperses in the environment over time. This complex process is the sum of physical, chemical, and biological processes that interact with each other changing their extent, characteristics, and initial composition. The transformation of the slick may be divided into two parts: biodegradation, when referring to biological processes, and meteorization, considering physical and chemical processes.

Spreading (also referred to as runoff), evaporation, dissolution, and emulsification are very important processes in the early stages. Likewise, advection (the movement of the slick as a whole caused by the action of wind, currents, and waves) and diffusion (mainly the turbulence) determine the transport of the pollutant from its inception. Otherwise, oxidation-reduction, sedimentation, and degradation gain significance in later stages.

In many cases, the models incorporate only the most representative processes in the first spill stages although few include emulsification, which begins to be of interest after the first 8 or 15 hours because it is an extremely complicated process. The presence of this phenomenon results in the viscosity and density of the pollutant varying when mixed with seawater; therefore, defining the answers becomes extremely difficult; for this reason, the simplest programs avoid including this process.

In practice, the behavior of an oil slick is more difficult to predict than in theory. This is largely because the information is often incomplete in the early stages of the event. The model designer must therefore update the forecasts with new, highly reliable data in order to obtain results that are increasingly closer to reality, as well as the probability of the existence of alternative trajectories in a process called "trajectory analysis". The result of a trajectory analysis is often a map showing the forecast and the probable limits of uncertainty of the slick movement; these minimum estimates should be regarded as a reliable source of information to determine the minimum amount actually spilled (Barker & Galt, 2000).

During trajectory analyses, spill data is generally inaccurate and observations and forecasts of environmental data are not always available. Therefore, analysts should keep in mind the above services and ultimately appeal to their experience.

If the initial forecast is inaccurate, what may happen due to some misinformation about the spill (e.g. location, type of oil, or amount of oil spilled) and/or the environmental data are inaccurate or outdated, the process would lead to miscalculations. Thus, it would be necessary for the modeling team to review the new information and update the run. In general, as the spill progresses, the forecast of its movement and evolution becomes more precise since the quality and quantity of the observed data also improves while the data on the initial spill becomes relatively less important (IPIECA, 2020IPIECA. 2020. Ipieca. The global oil and gas association for enviromental and social issues, Available: <http://www.ipieca.org>, [Consulted: May 28, 2020].).

The core aspects that are contributed by the trajectory models and that are taken for the elaboration of the Contingency Plan are shown below:

If all or, at least, most of these aspects are known at the time of decision-making, the impact of the pollutant might be optimally reduced (if resources are available), and thought might be given to reviving affected ecosystems. For this reason, the exchange between the modelling group, maritime safety experts, environmental specialists, and decision-makers must be effective and direct in order to accomplish this purpose.

Oil spills may be classified according to their initial volume into three groups: small, when the volume spilled is less than 100 Bbls (14.2 t); medium, when it is between 100 and 5 000 Bbls (14.2 - 714.2 t); and big, when it is greater than 5 000 Bbls (714.2 t) (Fingas, 2011).

According to experiments carried out by the American Petroleum Institute (API), one may have an idea of the existing relationship between the thickness of the hydrocarbon in the slick and its color, according to Table 1 (Rodríguez, 2008Rodríguez, J. M. S. 2008. Manual de lucha contra la contaminación por hidrocarburos. Servicio Publicaciones UCA, 356 p., ISBN: 978-84-9828-156-9.).

Depending on the spill magnitude, the characteristics of the affected area, meteorological and oceanographic conditions, and the means available for assuming a timely response to the disaster, priorities are designed for this purpose. Response objectives, in general, are considered in the following order: protect the safety and health of responders and the general public; reduce the impact on the environment, and protect property.

It is worth noting that the main priorities are people's health and safety and the following factors should be considered: Potential fire and explosion due to vapors at or near the spill location; potential oil adverse effects; safe handling of chemicals used as countermeasures; proper use of industrial safety equipment; sunstroke/heat exhaustion or hypothermia; safety of small vessels; helicopter and aircraft safety and handling of volunteer personnel.

After having the results of the numerical models and equipment to face the slick action in the sensitive and economically important locations, the anti-spill group must focus its efforts, so that the response time is minimal. Rapid removal of hydrocarbons may prevent them from reaching the coasts, where it is difficult to clean up and the greatest environmental damage occurs, as mentioned earlier.

The techniques for responding to the spill, also known as strategy options (figure 1), according to specialists in the field, are as follows (COCATRAM, 2015COCATRAM. 2015. Plan Regional De Preparación, Respuesta Y Cooperación Contra Derrames De Hidrocarburos Y Sustancias Nocivas Y Potencialmente Peligrosas Para América Central (PRC-CA). Technical Note, Ciudad de Panamá, Panamá: MARINE POLLUTION PREVENTION AND PREPARATION, S.A., 108 p., Available: <http://prcca.cocatram.org.ni/PRC_CA_Contra%20Derrames%20de%20Hidrocarburos%20y%20Sustancias%20Nocivas_Final_2015.pdf>, [Consulted: September 23, 2018].): monitoring and surveillance, dispersant application, containment and recovery, coastal cleaning, and in-situ burning.

When a ship is in distress, the main option for the owners is to try to take it to sheltered waters, where distress may be remedied or minimized before continuing the voyage. However, coastal states denied aid to ships carrying oil. In the other hand, main difficulty posed by the above spills was the proximity to coastal areas or shallow waters. This condition is a hazardous threat for ecosystems and other locations with high economic significance.