Appendix D: Analytical Methods 



PCB sum represents the sum of concentrations of the congeners, accurately quantified 

 individually. PCB sum , therefore, approximates the sum of all congeners present in the sample 

 (defined as total PCB) and it can serve as the basis for quantitative comparisons of total PCB 

 concentrations in different samples. Therefore, in addition to concentrations of individual 

 congeners, the reporting format requires their sum (PCB sum ) and their percentage contributions to 



PCB sum . 



The principles of this method are illustrated by a simple example, involving two samples 

 and four congeners only. 



PCB sum 10ngg-l 20ng g- 1 



PCB sum is an underestimation of total PCB concentration. The difference may depend on 



sample matrix and geographic region, and may typically be in the 10-30% range. It should also be 

 appreciated that the same value of PCB sum (and of course of total PCB) can represent widely 



different PCB compositions. This is the inherent difficulty of representing the content of PCB 



with one number. 



Therefore, PCB sum or total PCB values can only be compared reliably between samples if 



the corresponding mixtures are the same. This may be the case for mussels in different regions, or 

 for different tissues of the same organisms, etc., but it may not apply for water and mussel tissue 

 even in the same region. 



Other congeners may be considered for evaluation as well. For this purpose, the PCB 

 CBL 1 standards can be used. 



6. Quality Assurance 



During the Initial Implementation Phase, field-collected samples will be analyzed by two 

 central laboratories. These laboratories will participate in Quality Assurance/Quality Control 

 (QA/QC) exercises which are organized by the Project. 



105 



