Chemical dispersants are substances designed to break down oil spills. They transform large oil slicks into smaller droplets, accelerating the natural breakdown of oil. This helps mitigate the immediate impact of spills on surface ecosystems.
Understanding Chemical Dispersants and Their Action
Chemical dispersants are composed of surfactants and solvents. Surfactants are the active ingredients, possessing a dual molecular structure with parts attracted to oil (oleophilic) and parts attracted to water (hydrophilic). The solvent helps deliver and distribute these surfactants throughout the oil slick.
When applied, surfactants migrate to the interface between oil and water, reducing surface tension. This allows the oil slick to break apart into tiny droplets, often smaller than a human hair. This process, known as emulsification, creates an oil-in-water emulsion where small oil droplets remain suspended in the water column rather than coalescing back into a slick. These dispersed droplets are then more readily diluted by currents and biodegraded by microorganisms.
When and How Dispersants Are Applied
Chemical dispersants are primarily used for oil spills in open water, away from sensitive coastal areas. They are considered when other oil removal methods, such as mechanical containment and recovery, are limited by factors like weather or resource availability. The goal is to prevent oil from reaching shorelines and protect surface-dwelling marine life.
Application methods include aerial spraying from airplanes or helicopters, and deployment from vessels. Responders aim to optimize dispersant droplet size, concentration, and application rate for maximum effectiveness. Conditions influencing their use include water salinity, temperature, sea state, and the type of oil spilled; lighter oils disperse more effectively than heavy crude oils. Dispersants are most effective when applied swiftly after a spill, before the oil has undergone significant weathering.
Environmental and Health Impacts
The use of chemical dispersants carries potential environmental and human health implications. While they move oil from the surface into the water column, this increases marine organisms’ exposure to both dispersed oil and dispersant chemicals. Studies indicate that dispersed oil, a mixture of oil and dispersant, can be more toxic to marine life than untreated oil alone.
Aquatic organisms, including invertebrates, fish, and corals, can experience adverse effects from exposure to dispersed oil and dispersants, with observed impacts such as irritation. Some dispersant formulations, like Corexit 9500, have raised concerns due to documented toxicity to aquatic life and potential effects on exposed workers. While concentrations in open water can decline rapidly due to dilution, long-term ecological effects are a subject of ongoing research.
Human health concerns primarily involve responders and nearby communities. Workers involved in dispersant operations face the highest risk of direct exposure through inhalation and skin contact, with reported symptoms including respiratory irritation, skin rashes, eye irritation, headaches, dizziness, and gastrointestinal issues. For the general public, brief contact with small amounts of dispersants is not expected to cause harm, as ingredients in most modern dispersants are designed to biodegrade, limiting their persistence. The decision to use dispersants often involves a trade-off between immediate cleanup needs and potential long-term ecological and health consequences, leading to ongoing discussion and careful regulation.