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Under the sponsorship of the World Health Organization (WHO), an interlaboratory calibration on the analysis of PCDD/PCDFs in human milk and blood was carried out which included 19 laboratories from 14 countries. The study design involved the analysis of three samples of each matrix in triplicate. Selected samples were spiked with native standards of certain 2,3,7,8-substituted congeners at concentrations known only to WHO staff. The study design resulted in approximately 4000 individual pieces of PCDD/PCDF data generated by a variety of analytical methods, at various concentrations, and by laboratories of widely different experience. This was, by considerable margin, the largest study which allowed for the direct comparison of laboratory and method performance. The results of statistical analysis of this data base addresses the effect on data quality of clean up methods, instrumental methods, analyte concentration, laboratory QA programs, and laboratory experience. The study has shown that the laboratory is the single most important determinant of data precision and accuracy. The method of analyte enrichment (sample clean up), analyte measurement [gas chromatography/mass spectrometry (GC/MS) protocol], and analyte concentration have weaker correlations with data quality.

The activities of three plasma lysosomal hydrolases, beta-galactosidase, beta-glucuronidase and beta-N-acetylglucosaminidase, were studied in 20 workers exposed to metallic mercury vapor in a chlorine alkali plant and in 10 nonexposed referents. The urinary excretion and blood levels of mercury were determined on the day of study, and the history of mercury exposure was reviewed from the records of mercury concentrations in urine and blood over periods of up to 133 months. The average levels of beta-N-acetylglucosaminidase and beta-glucuronidase were higher in the plasma of exposed workers, but the difference was not significant. No significant positive correlation was seen between lyosomal enzyme activities and cumulative long-term exposure to mercury. It is concluded that measurement of plasma lysosomal hydrolase-activities is not of great value in the biological monitoring of workers exposed to low concentrations of metallic mercury vapor. In line with published data, the concentration of mercury showed a clear-cut diurnal variation in nonexposed persons, persons currently exposed and persons with a history of past exposure. The excretion rate of mercury remained constant throughout the day.

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