ABSTRACT
Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), also known under the generic, cumulative name “dioxins,” are environmental pollutants particularly relevant because of their toxic effects. Their structure formulas are shown in Figure 27.1. Each of the carbon atoms at the 1,2,3,4and 6,7,8,9-positions can bond either with chlorine or with hydrogen atoms, thus yielding 210 possible congeners (75 PCDDs and 135 PCDFs), different in the number and/or position of chlorine atoms. The PCDDs and PCDFs are chemically and thermally stable and very persistent in the environment. More importantly, the 17 congeners (7 PCDDs and 10 PCDFs) bearing chlorine atoms at the 2,3,7,8-position are considered to be carcinogenic (the 2,3,7,8-T4CDD has been classied as carcinogenic to humans by the International Agency for Research on Cancer-IARC) (IARC 1997) and endocrine disrupting agents (USEPA 1997); consequently, only these 17 congeners, thereinafter briey dened as “toxic,” are generally determined.
