Polycyclic aromatic hydrocarbons and for short, PAHs. Do you want the technical description of carbon chains and bonds or perhaps something more relevant? Let’s go with relevant and why they are even something that environmental consultants look for. For starters, PAHs comprise a group of compounds that are probably most commonly associated with the use of creosote as a wood preservative, which is most often seen with treated railroad ties and power poles. However, they are also created through incomplete combustion of petroleum hydrocarbon products (i.e. fires).
So why is this a problem? PAHs are highly toxic to aquatic life as they tend to stick to sediment/soil and persist in the environment. A handful of PAHs are also considered carcinogens (cancer causing). So the next time someone offers you a pile of old rail ties that you want to line your garden with, maybe reconsider, or at least put a plastic liner between those ties and your soil!