Interlaboratory QA/QC is an essential component for any regional program involving 

 multiple analysts and it's importance cannot be overstated. If the QA/QC effort is not initiated prior 

 to the analysis of field samples, data interpretation delays and other difficulties are likely and may 

 even compromise the program. 



E) Summary of QA/QC Data 



There was general agreement between the two Analytical Centers within factors of two to 

 four for analy te concentrations which are above the limits of detection by at least a factor of four 

 (i.e. for concentrations 1 ng/g dry weight or higher). These QA/QC results provide a framework 

 for interpretation of the entire field data set . For example, differences of factors two to three 

 between stations cannot be accepted as significant if the data were not produced by the same 

 laboratory. 



Results and Discussion of Combined IMW Dataset 



The combined set of IMW data as produced from the analysis of field-collected samples by 

 the two IMW Analytical Centers is appended (Appendix A). Some of the results are discussed in 

 this section. 



COMPARISON OF CONCENTRATIONS BETWEEN DIFFERENT SPECIES 



One of the main objectives of the International Mussel Watch Project is to compare the 

 occurrence and concentrations of selected trace organic contaminants among sampling locations. 

 Although bivalves have been targeted as the sentinel organism for the study, it was not possible to 

 collect the same species at every location because of the large extent of the area under study. This 

 issue must be faced by any monitoring program which involves organisms and covers a broad 

 tropical-subtropical-temperate range. There are only a few coastal areas in the IMW South and 

 Central America and Caribbean combined data set where the same species was present in more than 

 four to five stations in sequence. Figure 12 illustrates the distribution of the different species of 

 bivalves sampling during this study. 



The IMW Project has collected a larger number of species throughout the region than have 

 been collected by other national programs, for example, in the U.S. NOAA Status and Trends 

 Program (primarily three species). Most other national programs are limited to one to three 

 species. Understanding how species differences might influence comparisons of chemical 

 concentration data between and among stations is essential to the interpretation of this data set. 

 Fortunately, the sampling strategy made 



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