PAHs

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds composed of two or more fused aromatic rings of carbon and hydrogen. They are nonpolar, hydrophobic molecules with low water solubility and high affinity for organic matter. PAHs include naphthalene, anthracene, pyrene, and benzo[a]pyrene, ranging from two to several rings.

PAHs form mainly during incomplete combustion of organic material. Major sources include vehicle exhaust, power generation, industrial processing, residential wood burning, and tobacco smoke. They are widespread in the environment, detected in air particulates, soils, sediments, and water, and can be present in charred foods.

Environmental fate is governed by hydrophobicity: PAHs sorb to soils and sediments and can bioaccumulate in fatty tissues. They are relatively persistent, though some undergo photochemical degradation or microbial metabolism.

Health and environmental concerns: many PAHs are mutagenic or carcinogenic; benzo[a]pyrene is a well-studied example. Metabolic activation by enzymes such as cytochrome P450 yields reactive intermediates that can form DNA adducts, contributing to cancer risk. Exposure routes include inhalation, ingestion of contaminated water or food, and dermal contact with contaminated soils.

Detection and regulation: PAHs are typically analyzed by GC-MS or HPLC after extraction and cleanup. Regulators monitor PAHs in air, soil, water, and food, and set limits for certain individual PAHs or for the total PAH burden.

Remediation and control: strategies include reducing emissions, preventing exposure, and treating contaminated media (activated carbon adsorption, bioremediation, or thermal treatment).