Experiments have been conducted to help establish the source of polychlorinated dibenzo-pdioxins and polychlorinated dibenzofurans (PCDD/F) that are produced during bleaching of pulp with high levels of chlorine. Conditions have been established for observing the progressive development of ring chlorination of dibenzo-p-dioxin (DBD) and dibenzofuran (DBF) which were adsorbed onto cotton linters. The distribution and types of mono-, di-, tri-, and tetrachlorinated dibenzofurans produced as a function of time for the chlorination of DBF-spiked cotton linters were similar to that obtained from chlorination of an extracted pulp; this result indicates that DBF is probably the principal PCDF precursor in pulp. Because of the greater reactivity of DBD upon chlorination, few lower chlorinated PCDD were observed and the mechanism of PCDD formation is less clear.

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