Dioxins and the Paper Industry, 1993 China Paper Conference Proceedings

Thomas J. McDonough

Polychlorinated dibenzodioxins and dibenzofurans ("dioxins") include compounds that are environmentally objectionable because of their toxicity, lipophilicity, and persistence. Consequently, their discovery in effluents, sludges, and pulps led to a massive research effort by the pulp and paper industry. This research, which required sophisticated analytical methodology, has been successful. It has resulted in the identification of the chlorination stage as the source of the dioxins, their unchlorinated analogs as important precursors, and direct substitution of chlorine as an important mechanism of formation. A variety of control strategies have been developed. Some of these decrease the amount of precursors entering the chlorination stage, while others decrease the amount of chlorine used. Their implementation has resulted in a reduction of more than 90% in the amount of dioxins released by North American bleached pulp mills. This paper reviews the subject of dioxins as it relates to the paper industry, with reference to their nature, analysis, toxicity, risk assessment, mechanism of formation, control strategies, and current discharge levels.