[Origin, structure and distribution of dioxins].

Polychlorinated dibenzo-para-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) are generated as unintentional by-products in a number of thermal and chemical-industrial processes. Biogenic formation through dimerization of chlorinated precursors, such as chlorophenols, is know but does not play a major role in national dioxin release inventories and in most cases is not quantified. PCDD/PCDF are semi-volatile substances and undergo long-range transport; they are persistent and accumulate in the environment and organismus; and they are toxic. They have become a global environmetnal problem. At the international level this issue is addressed by the Stockholm Convention on Persistent Organic Pollutants, a legally binding instrument to eliminate PCDD/PCDF through step-wise implementation of reduction measures. Within the Stockholm Convention, Parties have to develop national or regional dioxin inventories. First results show that in most industrialized countries, incineration of municipal solid waste does no longer represent the largest dioxin source; instead, certain processes in the metallurgical industry have become largest emitters. In developing countries, the situation is very different: open burning processes such as forest and grassland fires, burning of agricultural residues either before or after harvest as well as fires in waste dumps or the private fires to dispose of municipal waste represent the largest dioxin sources. First steps for a global environmental monitoring program under the Stockholm Convention have been initiated.