IMW Initial Phase Report 



The NOAA-NIST sample is a working reference material that has been analyzed by'a larger 

 set of laboratories but the analytical data can be assessed within the context of the results of this 

 project (Table 9 and Figures 6 and 7). These preliminary comparisons taken with permission 

 from a draft NOAA report show that GERG and MEL were generally within +/- one standard 

 deviation from the consensus mean for analytes with the following exceptions : MEL's 

 concentrations for 4,4' DDE, CB18, CB44, CB66/95, 101/90 were between one and two standard 

 deviations below the consensus mean, and MEL's concentration for CB 195 was greater than the 

 consensus mean by more than one standard deviation; GERG's concentration for CB 180 was 

 higher than the consensus mean by more than two standard deviations. During final data 

 interpretation, NOAA coordinators may revise the consensus means and standard deviations as a 

 result of checks for data transcription errors and elimination of outliers by statistical treatment of 

 the data set. 



Participation of the IMW Analytical Centers within the larger group of NOAA-NIST 

 laboratories provides a valuable QA/QC check on IMW results and provides a framework for cross 

 comparison of IMW data with other bivalve tissue chlorinated pesticide and chlorobiphenyl data. 

 Participation in the NOAA-NIST intercomparison activities or similar exercise should be a 

 continuing requirement for the IMW Analytical Centers in future phases. 



D) IMW Field Samples. 



Representative results for analyses of splits of the replicate field samples are presented in 

 Tables 10 and 11, and Figures 8 and 9. Much of the field sample data are near, at, or below the 

 limits of detection and we would not expect close agreement between the two laboratories. 

 Overall, given the low concentrations of the analytes in several of the field-collected samples, the 

 results of the QA/QC are encouraging. 



There is excellent agreement for the dry weight determination (Figure 10) which eliminates 

 this factor as a cause of any significant discrepancies between laboratories for the pesticide and CB 

 analytes. For those samples where analyte concentrations are significantly above the detection 

 limits, the agreement between laboratories is usually very good, and generally within a factor of 

 two or better. IMW samples of particular concern with apparent significant differences between 

 laboratories are sample nos. 1 153-54 for 4,4' DDE, 2,4' DDD; sample nos. 1 175-76 for 2,4' DDD 

 and 4,4' DDD; and sample nos. 1279-80 2,4' DDD ; and for gamma chlordane concentrations, 

 sample nos. 1 153-54 and 1 193-94. 



There may be a slight systematic difference between GERG and MEL for dry weight to wet 

 weight ratio and for lipid concentrations (Table 10 and Figures 10 and 1 1). This may account for 

 some of the variability between these two laboratories for some samples. It might be that one 

 laboratory has an extraction method which yields more lipid or is more efficient for lipids and 

 associated chlorinated- lipophilic compounds such as chlorobiphenyls and chlorinated pesticides. 



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