Technical Bulletin No. 0591: An Intensive Study of the Formation and Distribution of 2,3,7,8-TCDD and 2,3,7,8-TCDF During the Bleaching of Kraft Pulps

Kraft bleaching operations encompassing a wide range of bleaching technologies were studied at 23 bleach plants to learn about 2,3,7,8-tetrachlorodibenzodioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) formation sites in the bleach plant, factors influencing the amount formed, and partitioning between pulps and filtrates. Analysis of samples of interstage pulp and filtrates provided information from which to calculate mass movement of 2,3,7,8-TCDD and 2,3,7,8-TCDF within and out of the bleach plants. Production of TCDD occurred mostly in the chlorination stage and ranged from <0.6 to 78 ng TCDD/kg oven-dried brownstock (odbs) at the mills studied. Production of TCDF, also produced mainly in the chlorination stage, ranged between <1.1 and 668 ng/kg odbs.