Pah

Polycyclic aromatic hydrocarbons (PAHs) are organic compounds composed of two or more fused aromatic rings of carbon and hydrogen. They are planar, hydrophobic, and poorly soluble in water. PAHs form during incomplete combustion of organic matter and are found in fossil fuels, smoke, and charred or grilled foods.

Common PAHs include naphthalene, phenanthrene, fluoranthene, pyrene, and benzo[a]pyrene. They are widespread in air, water, soil, and sediments, often attaching to particles in the atmosphere. In the environment they can persist for long periods unless acted upon by sunlight, microbial degradation, or other processes.

Health and ecological concerns arise because many PAHs are toxic and some are carcinogenic. Benzo[a]pyrene is a well-known example. Human exposure occurs mainly via inhalation of polluted air and ingestion of contaminated water or food; occupational exposure to coal tar, soot, or contaminated soils is also a risk. PAHs can affect aquatic life and tend to bioaccumulate in organisms.

Analytical monitoring uses gas chromatography–mass spectrometry or high-performance liquid chromatography with fluorescence detection. Regulatory frameworks, including the U.S. Environmental Protection Agency’s list of 16 priority PAHs and various international standards, assess risks and set limits for air, water, and soils.

Beyond environmental concerns, PAHs serve as precursors in the production of carbon materials and certain electronic components. Remediation of PAH-contaminated sites employs bioremediation, incineration, soil washing, or photodegradation, depending on concentration, matrix, and risk assessment.