PCDDs/PCDFs in unbleached pulp

Contamination of unbleached pulp by tetra, penta and hexa chlorinated dibenzo-p-dioxins (PCDDs) was observed at one of the five pulp mills examined during the years 1987 and 1988. Unbleached pulp did not contain 2378-TCDD or 2378-TCDF, which were found in bleached pulp only. The amount of the toxic PCDD congeners varied in a wide range (0.5 to 20 ppt of Nordic 2378-TCDD equivalents) during the sampling period. Contamination in pulps (unbleached and bleached) and paper boards was found occasionally, with 123678- and 123789-HxCDD as the major toxic PCDD congeners. The samples taken from batch cooking process used at the mill (unbleached pulp, black liquor and the incrusts inside the black liquor heat exchanger) showed slight, but clear PCDD contamination at the sampling time. The isomer distribution of PCDDs homologues was constant but the total amounts and the degree of chlorination differed between samples.