POLYCHLORINATED DIBENZODIOXINS AND DIBENZOFURANS IN PVC PYROLYSIS

The tars produced by PVC pyrolysis under different conditions of tempe rature and oxygen concentration were analysed for PCDDs and PCDFs cont ent. The tar collected after low temperature pyrolysis (500 degrees C) and in reduced oxygen atmosphere (11.6% O-2) had the highest PCDDs/PC DFs content. The toxicity of the tars is mainly due to the high PCDFs concentration. The most toxic compound, 2,3,7,8-T4CDD, had a contribut ion of only 0.5-4.4% of the total toxicity of the tar. Several hypothe ses for PCDDs/PCDFs formation during PVC pyrolysis, based on the analy sis of the tar composition, temperature interval in which is formed an d the mechanism of PVC breakdown are proposed. (C) 1998 Elsevier Scien ce Limited. All rights reserved.