Diesel fuel is a petroleum product composed of a complex mixture of hydrocarbon molecules derived from crude oil. Contamination occurs when this fuel is released into the environment through accidental spills or structural failures. The resulting pollution impacts all major environmental compartments, including soil, surface water, groundwater, and the air through volatilization. Understanding the movement of these compounds through different media is necessary to address the widespread environmental and health consequences they cause.
Sources and Characteristics of Contamination
Diesel fuel is a blend of hydrocarbons, which are molecules containing only hydrogen and carbon atoms. These molecules are typically larger and heavier than those found in gasoline, with a boiling point range between 330 and 650 degrees Fahrenheit. Although primarily composed of heavier compounds, the fuel also contains smaller, highly volatile aromatic compounds that present environmental risk.
Among the smaller hydrocarbons are Benzene, Toluene, Ethylbenzene, and Xylenes. These compounds are highly mobile and toxic, allowing them to quickly vaporize into the air or dissolve and spread through water. Contamination frequently originates from failures in infrastructure, such as leaking underground storage tanks (USTs) or industrial facilities. Transportation incidents, including pipeline ruptures or tanker truck accidents, are also significant sources. Improper disposal practices, such as dumping waste oil or fuel residues, contribute to chronic, low-level contamination.
Environmental and Ecological Damage
The introduction of diesel fuel initiates physical and chemical damage, severely altering ecological systems. When the fuel infiltrates the ground, it quickly affects the structure and health of the soil. Toxic hydrocarbons directly poison the beneficial bacteria and fungi that drive nutrient cycles and maintain soil fertility.
Contamination physically coats soil particles, disrupting the natural exchange of air and water. This disruption impedes microbial activity and plant growth. The fuel’s components, especially the lighter aromatic fractions, can leach downward through the soil matrix until they reach the water table, resulting in extensive groundwater pollution. This pollution renders aquifers unusable for drinking or agriculture.
Aquatic ecosystems face severe impacts as surface spills spread rapidly or contaminated groundwater discharges into rivers and lakes. The fuel forms a surface film that impedes oxygen transfer and can fatally coat the feathers of birds and the gills of fish. Aquatic organisms absorb the toxic hydrocarbons, leading to bioaccumulation as the chemicals move up the food chain. This introduces concentrated toxins to fish-eating birds, mammals, and humans who rely on these water sources.
Health Effects from Exposure
Human exposure to diesel contaminants occurs through three primary pathways: inhalation, direct skin contact, and ingestion of polluted water or food. Inhalation is a major concern, as volatile compounds like Benzene and airborne particles from diesel exhaust penetrate deep into the lungs. Dermal contact typically occurs during cleanup or industrial handling, allowing the fuel’s organic solvents to pass through the skin and enter the bloodstream.
Acute exposure to high concentrations of diesel vapors can cause immediate, irritating effects, including burning eyes, headaches, dizziness, and respiratory tract irritation. The greatest concern, however, lies with chronic, long-term exposure to lower concentrations. Diesel exhaust, which shares many chemical components with the liquid fuel, is classified as a known cause of lung cancer and is associated with an increased risk of bladder cancer.
Aromatic hydrocarbons contribute to these long-term risks, acting as carcinogens and mutagens within the body. Prolonged exposure can also lead to chronic respiratory illnesses, decreased lung function, and adverse effects on the central nervous system. The microscopic particles in diesel exhaust are small enough to reach the deepest parts of the lungs, where they cause lasting cellular damage.
Methods for Cleanup and Restoration
Remediation efforts for diesel contamination are broadly categorized into methods that treat the material after removal (Ex Situ) and those that treat the contamination in place (In Situ). The choice of restoration method depends on factors such as the type of soil, the depth of the contamination, and the specific composition of the diesel fuel spill.
Ex Situ Techniques
Ex Situ techniques require excavating the contaminated soil and transporting it to a specialized treatment facility. One common method is thermal desorption, where the soil is heated to high temperatures to vaporize the hydrocarbons, which are then collected and destroyed. Landfarming is another approach, involving spreading the excavated soil in a lined area and periodically turning it to increase oxygenation. This aeration stimulates the natural microbial population, encouraging them to metabolize the hydrocarbons into harmless carbon dioxide and water.
In Situ Techniques
In Situ techniques treat the contamination without removing the soil, often by injecting materials directly into the subsurface. Bioremediation is frequently applied through biostimulation, where nutrients like nitrogen and phosphorus are added to accelerate the activity of existing soil microorganisms. Other methods involve injecting chemical oxidants to rapidly break down the contaminants.