Chlorophenols (CPs) are organic chemicals formed from phenol (1-hydroxybenzene) by substitution in the phenol ring with one or more atoms of chlorine. Nineteen congeners are possible, ranging from monochlorophenols to the fully chlorinated pentachlorophenol (PCB). Chlorophenols, particularly trichlorophenols (T3CP), tetrachloro-phenols (T4CP), and PCP, are also available as sodium or potassium salts.