What happens after an oil spill?

Marine oil spills have plagued the fossil fuels industry since the introduction of offshore extraction and transport. The current spill in Southern California is just the latest episode.

Before touching upon the actions of spilled oil on impacted ecosystems, it is important to review its fate. First, oil is a mixture of both large and small carbon compounds; larger ones form relatively inert tar while the smaller ones tend to be more mobile. We also know that while oil and water do not mix, they do interact — immediately upon release oil begins to spread, disperse and evaporate; it also simultaneously degrades via the actions of both sunlight and bacteria. Thus, an oil spill breaks into smaller and smaller patches until it completely disperses.

Toxic impacts to marine organisms may be most apparent near the point of release as the oil is most concentrated, and over time impacted ecosystems recover as it dissipates. This process, known as “weathering,” can be assisted by response techniques such as the use of booms, skimmers and detergent-based dispersants. However, ultimately it is the environment that “cleans up” a spill.

Upon release, oil coats the organisms it comes in contact with. With birds and mammals, it can mat fur and feathers such that they no longer efficiently trap air. This results in a loss of both insulation and buoyancy, and often results in death due to hypothermia. Both birds and mammals may attempt to remove the oil through preening. However, the ingested oil can cause both vomiting and neurological effects in the short term, and tumor formation over time. Again, death is often the end result.

Other marine organisms can also be significantly impacted by spilled oil. Plankton and algae, at the base of the marine food web, are often heavily impacted due to coating. Most invertebrates, such as clams and mussels, as well as fishes rely on external fertilization for reproduction. Thus, their reproductive cells and larvae are also directly subject to the toxicity of oil. In fact, they tend to be much more sensitive than adults and can be heavily impacted (thus they are referred to as “sensitive life stages”). This can result in reproductive failure and ultimately population declines that may last for years.

Both invertebrates and fishes also take up the smaller carbon compounds by way of both ingestion and respiration (via their gills). Similar to birds and mammals this can lead to neurological effects and tumor formation over time. However, they are also capable of excreting residues. Thus, once an oil spill dissipates their tissue concentrations also tend to decline. This is important when considering seafood species and human consumption, and tissue levels are usually monitored over time to determine when they are again safe to eat.

Humans are primarily affected by spilled oil in two ways: inhalation and skin contact. As mentioned above, the smaller carbon compounds which tend to be most toxic usually evaporate quickly. If inhaled, they can cause lung irritation, nausea and vomiting; if exposure persists over time, cancer risk may be elevated. Skin contact, usually from tar that washes ashore, can cause irritation and rash.

Over time ecosystems can recover, as spilled oil dissipates and decimated populations recover. Bear in mind that petroleum has been present in our environment for millions of years via seeps and pools, a good example being the La Brea Tar Pits near Los Angeles, Calif.. The discovery of seeps likely led to the first use of oil by humans. It is possible that in areas rich in oil from natural seeps, such as the Gulf of Mexico and the Santa Barbara Channel, bacteria have evolved the capability of not only degrading oil but using it as an energy source. Otherwise, it would likely have accumulated over time. Thus, the good news is the environment is resilient and capable of recovering after a spill, though it may take time.

Moving into the future, the use of fossil fuels has not only contributed to the frequency of oil spills, but also our changing climate. The carbon that is released via energy production and transportation has potentially not been mobile in the environment for millions of years. We pump oil to the surface, extract its energy content, then dispose of it as carbon dioxide into the atmosphere — the ultimate throw-away commodity. It is suspected that it is this “new carbon” that is causing the elevation in atmospheric carbon concentrations, and thus global warming. Therefore, the current shift toward the use of green energy sources holds the promise of not only reducing the frequency of oil spills but also the release of additional carbon to the atmosphere.

The challenge facing us now is more political than technological. How can all the nations of the world coordinate to make it happen? Hopefully, we will find a way.

Ronald Tjeerdema, Ph.D., is a distinguished professor of environmental toxicology and Crosby endowed chair in environmental chemistry at the University of California, Davis. For nearly 35 years he has focused his research on oil spills and has published extensively on the environmental fate and toxic actions of petroleum hydrocarbons and dispersants in the marine environment. He also served on the National Oceanic and Atmospheric Administration (NOAA) committee providing response guidance during the Deepwater Horizon oil spill, and more recently on the National Academy of Sciences Committee on the Evaluation and Use of Chemical Dispersants in Oil Spill Response.