Toluene

How Tersus Can Help with Toluene

Tersus Environmental provides several technologies that can be used to address toluenein soil and groundwater. Treatment selection depends on site geochemistry, contaminant distribution, source conditions, and remediation objectives.

Commonly utilized products include:

Chemical Properties

Toluene is lighter than water and is classified as a Light Non-Aqueous Phase Liquid (LNAPL). When released as part of gasoline or other petroleum products, toluene may remain within free-phase product, dissolve into groundwater, sorb to soil, or partition into soil gas.

Common Sources of Toluene

Toluene may be present due to:

• Petroleum releases from underground storage tanks (USTs)
• Gasoline spills and leaks
• Petroleum pipelines
• Fuel terminals and bulk storage facilities
• Refineries and petrochemical facilities
• Paints, coatings, and paint thinners
• Adhesives and industrial solvents
• Chemical manufacturing operations

Toluene is commonly found alongside other petroleum hydrocarbons, particularly benzene, ethylbenzene, and xylenes (BTEX compounds).

Environmental Concerns

Toluene is a mobile and volatile petroleum hydrocarbon that can migrate from contaminated soil into groundwater and soil gas.

Unlike chlorinated solvents, toluene does not undergo reductive dechlorination. Instead, biodegradation may occur through aerobic or anaerobic processes. Aerobic biodegradation is generally rapid when sufficient dissolved oxygen is available.

Toluene can also biodegrade under anaerobic conditions using electron acceptors such as nitrate, iron, or sulfate, as well as under methanogenic conditions. Because microorganisms can utilize toluene relatively efficiently under a variety of redox conditions, it is generally more biodegradable and less persistent in groundwater than benzene.

However, elevated concentrations may persist where contaminant mass is continuously released from residual or free-phase petroleum, or where the availability of suitable electron acceptors and nutrients limits microbial activity.

Behavior in Soil and Groundwater

Toluene contamination may exist as:

• Free-phase petroleum product (LNAPL)
• Dissolved contamination in groundwater
• Sorbed contamination attached to soil particles
• Vapor-phase contamination within the vadose zone

Toluene is less soluble in water than benzene but can still migrate with groundwater away from a petroleum source area.

Because toluene is volatile, it readily partitions from contaminated soil and groundwater into soil gas and may contribute to vapor intrusion concerns where contamination is located beneath or near occupied buildings.

Natural attenuation may significantly reduce toluene concentrations where an active microbial population and suitable geochemical conditions are present. As a result, evaluating dissolved oxygen, nitrate, sulfate, iron, methane, and other geochemical indicators can help determine whether biodegradation is occurring within a groundwater plume.

Human Health Effects

Exposure to elevated concentrations of toluene may affect the:

• Central nervous system
• Kidneys
• Liver
• Respiratory system
• Coordination and cognitive function

Short-term exposure to high concentrations may cause headaches, dizziness, fatigue, confusion, nausea, and impaired coordination.

Long-term or repeated exposure to elevated concentrations may affect the nervous system, kidneys, and liver.

Because of these potential health effects, toluene concentrations in groundwater, drinking water, soil gas, and indoor air may be evaluated as part of environmental investigations and risk assessments.

Regulatory Standards

Regulatory criteria vary by jurisdiction; however, the United States Environmental Protection Agency has established a Maximum Contaminant Level (MCL) for toluene in drinking water of 1 mg/L (1,000 µg/L).

Many states have additional groundwater, soil, soil gas, vapor intrusion, and risk-based screening criteria for toluene.

Frequently Asked Questions

What is toluene commonly used for?
Toluene is widely used as an industrial solvent and as a raw material in the manufacture of paints, coatings, adhesives, inks, rubber, pharmaceuticals, and other chemical products. It is also a naturally occurring component of crude oil and gasoline.

Is toluene an LNAPL?
Pure toluene has a density less than water and is classified as a Light Non-Aqueous Phase Liquid (LNAPL). At petroleum-release sites, however, toluene is more commonly encountered as a dissolved constituent of gasoline or other petroleum products rather than as a separate pure-phase liquid.

Can toluene biodegrade naturally?
Yes. Toluene can biodegrade under both aerobic and anaerobic conditions. Aerobic biodegradation is often rapid when sufficient dissolved oxygen is present, while anaerobic degradation may occur under nitrate-reducing, iron-reducing, sulfate-reducing, or methanogenic conditions.

Is toluene more biodegradable than benzene?
Generally, yes. Toluene is often more readily biodegraded than benzene under both aerobic and anaerobic conditions. As a result, toluene may attenuate more quickly within petroleum groundwater plumes when favorable microbial and geochemical conditions are present.

How is toluene removed from groundwater?
Tersus supports several approaches for toluene remediation, including enhanced aerobic bioremediation, sulfate-enhanced anaerobic biodegradation, source-area treatment, and in-situ chemical oxidation. Treatment selection depends on contaminant concentrations, groundwater geochemistry, source conditions, geology, and remediation objectives.

Can toluene contribute to vapor intrusion?
Yes. Toluene is volatile and can partition from contaminated soil and groundwater into soil gas. Vapor intrusion may therefore be a concern where impacted soil or groundwater is located beneath or near occupied buildings.

Related Contaminants

• Benzene
• Ethylbenzene
• Xylenes
• Naphthalene
• Methyl tert-Butyl Ether (MTBE)
• Tertiary Butyl Alcohol (TBA)
• Ethylene Dibromide (EDB)
• 1,2-Dichloroethane (1,2-DCA)