Ethylbenzene is a colorless, aromatic hydrocarbon that exists as a flammable liquid at room temperature, possessing an odor often described as similar to gasoline. This organic compound is one of the most widely produced chemicals globally due to its extensive use in industrial processes. As a volatile organic compound (VOC), ethylbenzene readily evaporates into the air, contributing to its ubiquity in the environment and presence in various consumer products.
Chemical Identity and Primary Role
Ethylbenzene is chemically defined as a monocyclic aromatic hydrocarbon, meaning its structure includes a six-carbon benzene ring with a single ethyl group attached. This arrangement gives it the chemical formula \(C_8H_{10}\). The compound is a clear liquid with a density less than that of water, causing it to float if spilled. It is practically insoluble in water, though it is readily miscible with most organic solvents.
The overwhelming majority of ethylbenzene produced is dedicated to manufacturing styrene monomer. Styrene is the chemical building block used to create polystyrene, synthetic rubbers, and resins. The production process involves the catalytic dehydrogenation of ethylbenzene, where hydrogen is removed to form the styrene molecule. This establishes ethylbenzene as a foundational substance in the petrochemical industry, linking it directly to the global production of plastic consumer goods.
Common Sources of Exposure
Exposure to ethylbenzene for the general population occurs primarily through the air, both outdoors and indoors, as the chemical is highly volatile. Outdoors, a significant source comes from its use as a component of fuels, such as gasoline and aviation fuels, leading to releases in vehicle exhaust. The substance is also a natural component of crude oil and coal tar.
Indoor air concentrations are often detected at levels higher than in ambient outdoor air, due to off-gassing from common household materials. These consumer sources include products like paints, solvents, carpet glues, inks, and varnishes, which contain ethylbenzene as a solvent. Exposure is also possible through secondhand smoke and the direct handling of household products such as certain pesticides. Occupational exposure affects workers involved in the production of ethylbenzene and styrene, or those handling mixed xylene solvents.
Health Implications
Exposure to ethylbenzene can result in a range of effects on the human body, depending on the concentration and duration of contact. Acute, or short-term, exposure to high vapor concentrations causes immediate irritation to the eyes, nose, and throat. Higher levels can affect the central nervous system, leading to neurological symptoms like dizziness, light-headedness, and respiratory issues or chest constriction.
When the body takes in ethylbenzene, it is metabolized, primarily through the oxidation of the two-carbon ethyl side-chain. This process creates various metabolites, which are then excreted mostly in the urine. Long-term, chronic exposure in animal studies has indicated effects on the blood, liver, and kidneys. The International Agency for Research on Cancer (IARC) has classified ethylbenzene as a Group 2B agent, meaning it is possibly carcinogenic to humans, based on sufficient evidence of tumor increases in experimental animals.