Hydrocarbons là các hợp chất bao gồm carbon và hydro một mình. Họ có thể được phân loại thành hai nhóm chính: 1. Thơm hydrocarbon có chứa hệ thống vòng tròn với các điện tử delocalized, ví dụ, benzen. 2. Nonaromatic hydrocarbon không chứa một hệ thống vòng. Bao gồm ở đây là alkan, hoàn toàn bão hòa hydrocacbon alkene, có chứa một hoặc nhiều liên kết đôi và alkynes, có chứa một hay nhiều liên kết ba. Một số ví dụ về các loại khác nhau của hydrocarbon được đưa ra trong hình . | 9 Polycyclic Aromatic Hydrocarbons BACKGROUND Hydrocarbons are compounds composed of carbon and hydrogen alone. They may be classified into two main groups 1. Aromatic hydrocarbons that contain ring systems with delocalized electrons for example benzene. 2. Nonaromatic hydrocarbons that do not contain such a ring system. Included here are alkanes which are fully saturated hydrocarbons alkenes which contain one or more double bonds and alkynes which contain one or more triple bonds. Some examples of different types of hydrocarbons are given in Figure . Nonaromatic compounds without ring structure are termed aliphatic whereas those with a ring structure . cyclohexane are termed alicyclic. Aromatic hydrocarbons often consist of several fused rings as in the case of benzo a pyrene. Both classes of hydrocarbon occur naturally notably in oil and coal deposits. Aromatic compounds are also products of incomplete combustion of organic compounds and are released into the environment both by human activities and by certain natural events for example forest fires and volcanic activity. Aromatic hydrocarbons the subject of this chapter are of particular concern because of their mutagenic and carcinogenic properties. In the first place this raises issues about human health risks. However there are also questions about possible harmful effects on ecosystems that are exposed to high levels of aromatic hydrocarbons. Nonaromatic hydrocarbons are usually of low toxicity have not received much attention in ecotoxicology and will not be discussed further in the present text. It should however be remembered that crude oil consists mainly of alkanes and large releases into the sea due to the wreckage of oil tankers have caused the death of many seabirds and other marine organisms because of their physical effects of oiling or smothering see Clark 1992 . Also released crude oil may act as a vehicle for other lipophilic pollutants that dissolve in it for example organotin .
