Dot gov

Official websites use .gov
A .gov website belongs to an official government organization in the United States.


Secure .gov websites use HTTPS
A lock () or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Aromatic Concentrates

Learn what you need to know about aromatic concentrates.

Also known as: C5+, Pyrolysis Gasoline, Pentenes Plus

What are aromatic concentrates?

Aromatic concentrates are purified mixtures of chemicals found in crude oil. These mixtures are used to make gasoline and other fuels. They are strong-smelling liquids that range in color from yellow to black.

Aromatic concentrates are made up of other chemicals: benzene (45%), dicyclopentadiene (13%), cyclopentadiene (7%), and toluene (6%). The remaining 29% of the formula is a blend of other chemicals found in crude oil.

Where are aromatic concentrates found?

If spilled, aromatic concentrates evaporate quickly. However, part of the spill can go into the air, the soil, and sink down into the groundwater. When spilled in lakes or streams, they evaporate more slowly.

Aromatic concentrate exposure

Aromatic concentrates evaporate quickly and could contaminate the air near industries where they are used or in places where they are disposed. If home water supplies are contaminated, people could inhale the chemical's vapors while bathing, washing, or cooking.

People may be exposed by drinking contaminated groundwater or handling the chemical or contaminated soil. People may also be exposed if they bathe or wash with contaminated water.

What regulations and guidelines are available to protect people from aromatic concentrates?

There are no standards for regulating aromatic concentrates. However, there are standards for some of the chemicals that make up the mixture. We will focus on the major ingredient, benzene, in this section.

No standards exist for the amount of benzene allowed in the air of homes. We use a formula to convert workplace limits for benzene to home limits. Based on the formula, we recommend levels of benzene be no higher than 0.2 parts per million (ppm). You can smell benzene when levels reach 0.2 ppm.

The Wisconsin Department of Natural Resources regulates the amount of the individual chemicals found in aromatic concentrates that can be released by industries.

The federal and state standards for benzene are both set at 5 parts per billion (ppb). We suggest you stop drinking water containing more than 5 ppb benzene. If the level of aromatic concentrates is very high in your water, you may need to avoid using it for washing, bathing or for other purposes. Contact your local public health agency for more information specific to your situation.

Health effects

Everyone's reaction is different

A person's reaction to chemicals depends on several things, including individual health, heredity, previous exposure to chemicals including medicines, and personal habits such as smoking or drinking. It’s also important to consider the length of exposure to the chemical, the amount of chemical exposure, and whether the chemical was inhaled, touched, or eaten.

The following symptoms may occur immediately or shortly after exposure to levels over 100 ppm in air of aromatic concentrates:

  • Breathing problems and irritation of the throat and lungs
  • A feeling of light-headedness followed by headache, confusion, dizziness, drowsiness, and loss of balance
  • Temporary changes in liver or kidney functions
  • Development of an irregular heart beat and blood pressure changes
  • Convulsions, coma, blurred vision, and tremors at very high levels

Benzene can be measured in blood and breath. In the body, it changes to a chemical called "phenol," which can be measured in urine. Other tests can be done by a doctor to determine the effects on the liver, kidneys, and blood.

The following health effects can occur after several years of exposure to some of the chemicals in aromatic concentrates:

Leukemia can develop after repeated exposure to benzene. 1,3-butadiene, which makes up less than 2% of the mixture, is suspected of causing cancer in humans.

The nervous system, blood-forming tissues, liver, kidneys, and lungs can all be affected by exposure to aromatic concentrates. Anemia is a common response to work place exposure. Allergic skin rashes may occur as a result of direct contact.

Questions? Can't find what you're looking for? Email:

Last revised February 9, 2023