Polycyclic aromatic hydrocarbons (PAHs) are not microplastics; they are separate chemical compounds that can bind to plastic particles.
What are PAHs?
PAHs are organic molecules made of two or more fused benzene rings. They consist only of carbon and hydrogen and have well‑defined molecular formulas, such as naphthalene (C10H8) or benzo[a]pyrene (C20H12). Because they are discrete molecules, they do not form long chains or networks.
What defines a microplastic?
Microplastics are solid fragments of synthetic polymers that measure between 1 µm and 5 mm. Common polymers include polyethylene, polypropylene, polystyrene and PET. These particles are composed of thousands of repeating monomer units linked together, giving them a macromolecular structure that persists for decades.
How PAHs are produced
PAHs form when organic material burns incompletely. Sources include vehicle exhaust, coal‑fired power plants, forest fires and volcanic eruptions. The process breaks down larger hydrocarbons into smaller aromatic rings rather than building polymer chains.
Why the confusion arises
Both PAHs and microplastics are hydrophobic, so PAHs readily adsorb onto the surface of plastic particles in water or sediment. This sorption can make contaminated plastics appear to carry the PAHs, leading some to think the two are the same thing.
Environmental interaction
When organisms ingest microplastics that have PAHs attached, the plastics act as a "Trojan horse," delivering concentrated PAHs directly to the gut. The chemicals can then desorb in the lipid‑rich environment, increasing exposure risk. The interaction amplifies toxicity but does not change the classification of PAHs.
Key distinction
In short, PAHs are small, soluble organic pollutants; microplastics are solid polymer debris. Their overlap lies in surface sorption, not in chemical identity.