Proficiency testing for dioxin laboratories determination of polychlorinated dibenzo-p-dioxins and dibenzofurans in sewage sludge

Commissioned by the Ministry for the Environment Baden-Württemberg a proficiency testing on the analysis of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) was carried out. With sixty participating laboratories from eight countries, mainly from the Federal Republic of Germany, this study is the largest proficiency testing in the field of dioxin analysis ever organised. In the study involved were the determination of the seventeen 2,3,7,8-substituted PCDD/PCDF congeners, the toxicity equivalent according to NATO/CCMS (I-TEQ) and of the homologue groups of the tetra- to heptaCDD/CDF. The laboratories were instructed to use their preferred method of clean-up and quantitative determination of PCDD/PCDF. No significant influence of the type of mass spectrometric equipment (high or low resolution GC/MS) or of the type of capillary column (polar and/or non-polar) or any combination of capillary columns upon the quality of the analysis measured by the z-score of the I-TEQ values is apparent. According to a proposal of the IUPAC and derived from the Ordinance on Sewage Sludge (AbfKlärV), the fulfilment of the Q-score and the ‘z-score 75 %’ was defined as the decisive quality criterion for successful participation in the proficiency test. 41 participants (according to 68 %) met this quality criterion for both sewage sludge samples.