“…12 These authors have reported that the dominant congeners -1,2,3,7,8-pentachlorodibenzo-p-dioxins (PnCDD), 1,2,3,6,7,8-HxCDD, 2,3,7,8-TCDD, 2,3,7,8-TCDF, 1,2,3,7,8,9-HxCDD, 2,3,4,7,8 pentachlorodibenzofurans (PnCDF) -fell markedly during the early 1990s after the pulp mills changed from molecular chlorine bleaching to alternative bleaching technologies and restricted usage of chlorophenolic wood preservatives and antisapstains. 13 Nevertheless, most published data of surveys and tests in the pulp and paper research had been limited to determining only 2,3,7,8-TCDD and 2,3,7,8-TCDF, where the minimum detection level was usually 10 pg/l, for example, in the minimum level of the U.S. Environmental Protection Agency (EPA) method 1613. 7 Thus, with setting the environmental standard at 1 pg TEQ WHO1998 /l in Japan, it becomes necessary to perform new surveys and investigations of whether the addition of excessive chlorine dioxide might cause chlorine molecule formation and subsequent dioxin generation.…”