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.