<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>A major group of unsaturated cyclic hydrocarbons containing two or more rings. The vast number of compounds of this important group, derived chiefly from petroleum and coal tar, are rather highly reactive and chemically versatile. The name is due to the strong and not unpleasant odor characteristic of most substances of this nature. (From Hawley's Condensed Chemical Dictionary, 12th ed, p96)</n0:def-definition><n0:def-source>MSH2002_06_01</n0:def-source></n0:ComplexDefinition>
<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>Polycyclic aromatic hydrocarbons (PAH) are a large class of organic compounds containing two or more fused aromatic rings made up of carbon and hydrogen atoms. They have high melting and boiling-points, low vapour pressure, water solubility, and are highly lipophilic. PAH are produced during incomplete combustion or pyrolysis of organic matter, are found in cigarette smoke, motor vehicle exhaust, used motor lubricating oil, broiled meat, coal tar, crude oil, creosote, roofing tar, dyes, plastics, and pesticides. Some members of PAH class were shown to have carcinogenic, genotoxic, and immunotoxic properties, developmental toxicity and affect reproductive health. (NCI)</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>