The Japan Society for Analytical Chemistry carried out a sixth proficiency testing for the determination of dioxins (polychlorodibenzo-p-dioxins, polychlorodibenzofurans and dioxin-like polychlorobiphenyls) in wastewater. This proficiency testing of analytical laboratories was based on ISO/IEC Guide 43-1, "Proficiency testing by interlaboratory comparisons". The testing was carried out from February '05 to May '05, with the participation of 105 laboratories. As a result, 93 laboratories (88.5%) were estimated as "satisfactory", 5 laboratories (4.8%) as "questionable" and 7 laboratories (6.7%) as "unsatisfactory". Dioxins in wastewater were classified in two groups: existing in SS particulates, and dissolved in water. It was shown from the results that those compounds with a high dissolved state %, such as many CoPCBs, gave a high CV% in their analytical results.
