The Stability of Pentachlorophenol and Chlorinated Dioxins to Sunlight, Heat, and Combustion

Pentachlorophenol in field-use conditions is subjected to environmental factors leading to its degradation, resulting theoretically in chlorinated dibenzo-p-dioxin formation. Analysis of combustion products of wood and paper treated with pentachlorophenol indicated no increase and possibly a decrease in octachlorodibenzo-p-dioxin concentration while paper treated with sodium pentachlorophenate increased slightly in octachlorodibenzo-p-dioxin concentration after combustion. Photolysis of sodium pentachlorophenate under different sources of artificial sunlight and natural daylight resulted in severe degradation of the pentachlorophenate with only trace amounts of octachlorodibenzo-p-dioxin formed. 2,7-Dichloro- and 2,3,7,8-tetrachlorodibenzo-p-dioxins are subject to rapid photolytic decomposition under artificial sunlight while octachlorodibenzo-p-dioxin shows considerably more stability. 2,3,7,8-Tetrachlorodibenzo-p-dioxin is somewhat stable to 700°C while decomposition is complete at 800°C.