The effect of the transition from elemental chlorine bleaching to chlorine dioxide bleaching in the pulp industry on the formation of PCDD/Fs.

The article reviews the transition from bleaching kraft pulp with elemental chlorine to bleaching with chlorine dioxide with respect to formation of chlorinated dioxins and furans (PCDD/Fs). New data is also presented for bleaching with 100% chlorine dioxide and the effect of elemental chlorine impurities. The typical fingerprint of PCDD/Fs in pulp bleached with elemental chlorine was unique compared to all other sources such as incineration and metallurgic processes. 2,3,7,8-TCDD and 2,3,7,8-TCDF were the dominating congeners formed during the period pulp was bleached with elemental chlorine. Elimination of unchlorinated precursors lowered, but did not eliminate, the formation of 2,3,7,8-TCDD and 2,3,7,8-TCDF. The formation of 2,3,7,8-TCDD and 2,3,7,8-TCDF increases exponentially with the amount of elemental chlorine used. Replacing elemental chlorine with chlorine dioxide (with levels of elemental chlorine contamination of <0.3% in the chlorine dioxide) in pulp bleaching eliminates the formation of 2,3,7,8-TCDD and 2,3,7,8-TCDF. PCDD/Fs can also be found in background levels in ecosystems, food, soil and air as well as in unbleached pulp, bleached pulp, and paper and fiber products. Thus, the only way to determine if PCDD/Fs are present from bleaching is to make a full congener analysis and compare to known sources and processes as well as to laboratory blanks and unbleached reference samples.