Benzene and polynuclear hydrocarbons containing more than two benzene rings fused together are toxic and said to possess cancer producing property. Such polynuclear hydrocarbons are formed on incomplete combustion of organic material like tobacco, coal and petroleum. They damage DNA and cause cancer. Some of the carcinogenic polynuclear hydrocarbons are 1,2-Benzanthracene, 3-methylcholanthracene, 1, 2 Benzpyrene, 1, 2, 5, 6 - Dibenzanthracene and 9, 10 - Dimethyl 1, 2, -Benzanthracene.
