A class of stable organic molecules made up of only carbon and hydrogen. These molecules are highly carcinogenic, but also very common in the enviropnment. Pahs are formed during the incomplete burning of coal, oil and gas, garbage, and other organic substances, such as tobacco or even charcoal broiled meat. Pahs enter water through discharges from industrial and wastewater treatment plants or through the release of boat engine exhausts. Ultraviolet light (UV) transforms the pahs into toxic forms that kill crustaceans, polychaetes, and coral larvae.