How Deepwater Horizon's Petroleum Met Its Fate
On April 20, 2010, an explosion on the Deepwater Horizon oil rig killed 11 workers and unleashed one of the worst environmental disasters in history. For 87 agonizing days, oil gushed uncontrollably from the Macondo well deep beneath the Gulf of Mexico, releasing approximately 4.9 million barrels of crude oil into the ocean 2 .
The petroleum released wasn't a single substance but thousands of different chemical compounds, each with its own personality and propensity to change, move, and interact with the environment 1 .
To understand what happened to the Deepwater Horizon oil, we must first understand what it was. Crude oil is far from a simple substance; it's a complex mixture of thousands of chemical compounds, primarily consisting of hydrocarbons (molecules containing only carbon and hydrogen) along with smaller amounts of heteroatom-bearing compounds containing nitrogen, oxygen, sulfur, or metals 1 .
| Hydrocarbon Class | Chemical Characteristics | Environmental Behavior | Toxicological Concerns |
|---|---|---|---|
| Light Alkanes (C1-C10) | Low molecular weight, volatile | Rapid evaporation/dissolution, highly biodegradable | Narcotic effects to marine life, explosion risk |
| PAHs (Polycyclic Aromatic Hydrocarbons) | Multiple fused benzene rings | Persistent, accumulate in sediments and tissues | Carcinogenic, mutagenic, toxic to aquatic life |
| Biomarkers | Complex molecular structures (e.g., hopanes) | Extremely persistent, resistant to degradation | Used for forensic fingerprinting of spill sources |
| Oxy-hydrocarbons | Oxygenated hydrocarbons | Formed through photo-oxidation, more polar and soluble | Increased toxicity to some marine organisms |
As petroleum surged from the damaged wellhead nearly a mile beneath the surface, it immediately began undergoing a series of physical and chemical changes collectively known as weathering processes 1 .
Within hours of reaching the sea surface, approximately 30-40% of the liquid oil by weight transformed into gaseous form and entered the atmosphere 1 .
Soluble components dissolved directly into the water column, creating subsurface plumes of dissolved hydrocarbons that stretched more than 32 kilometers from the wellhead 4 .
Naturally occurring hydrocarbon-degrading bacteria began multiplying exponentially, breaking down hydrocarbon molecules for energy and carbon 5 .
Chemical reactions driven by solar energy produced entirely new compounds called oxy-hydrocarbons, changing the oil's properties and toxicity 1 .
Faced with an unprecedented spill, responders turned to a controversial tool: chemical dispersants. Nearly 3 million liters of Corexit dispersants were injected directly at the leaking wellhead, with another 3.8 million liters sprayed on surface slicks 4 .
| Component | Chemical Category | Function in Dispersant | Environmental Behavior |
|---|---|---|---|
| Sorbitan monooleate | Surfactant | Lowers oil-water interfacial tension | Biodegradable, breaks down over weeks |
| Ethoxylated sorbitan monooleates | Surfactant | Enhances droplet formation and stability | Moderate persistence in marine environment |
| Dioctyl sodium sulfosuccinate | Detergent | Improves oil penetration and dispersion | Also used in pharmaceutical laxatives |
| Hydrocarbon solvents | Petroleum distillates | Carrier for active ingredients | Volatile, evaporates from application site |
One of the most fascinating chapters in the Deepwater Horizon story belongs to the Gulf's native population of oil-eating microbes. The spill triggered a massive feeding frenzy among hydrocarbon-degrading bacteria, which multiplied exponentially as they consumed the petroleum invasion 5 .
Different bacterial species dominated at different depths and locations, each adapted to specific hydrocarbon types 5 .
Some newly discovered bacteria could degrade multiple hydrocarbon classes, while others specialized in particular compounds 5 .
Some research suggested that chemical dispersants might actually harm these natural microbial communities 5 .
A decade after the disaster, scientists have accounted for the ultimate destinations of most of the spilled oil. The final distribution reveals much about the persistent environmental impacts.
| Environmental Compartment | Major Hydrocarbon Types Present | Persistence Timeline | Ecosystem Impacts |
|---|---|---|---|
| Surface waters | Dissolved light aromatics, transformation products | Months to few years | Exposure to plankton and water column species |
| Coastal sediments | Heavy alkanes, asphaltenes, weathered residues | Years to decades | Contamination of burrowing organisms, slow leaching |
| Deep-sea sediments | Weathered PAHs, biomarker compounds | Decades or longer | Deep-sea coral impact, benthic community changes |
| Marine biota | Bioaccumulative PAHs, metabolic products | Variable (depends on organism lifespan) | Physiological stress, reproductive impacts |
A comprehensive study examining 91 fish species in the Gulf of Mexico found evidence of oil exposure in all 2,500 individual fish sampled between 2011 and 2018—nearly a decade after the spill 5 . The researchers discovered that polycyclic aromatic hydrocarbons (PAHs) were accumulating in fish livers, potentially making them less healthy and more susceptible to disease 5 .
The spill revealed unexpected weathering pathways, particularly the significance of photo-oxidation and marine snow formation 1 .
While microbial communities demonstrated remarkable capacity, certain ecosystems showed extreme vulnerability and slow recovery 1 5 .
The disaster drove developments in oil spill tracking and chemical fingerprinting techniques 5 .