Polychlorinated biphenyls in the Eurasian otter (Lutra lutra).
Several authors have suggested that contamination by polychlorinated biphenyls (PCBs) constitutes one of the major causes of the decline of the Eurasian otter (Lutra lutra) in large parts of Europe. This chapter provides an overview of available information regarding PCBs in European otters. Data on PCB concentrations in European otter tissues differ qualitatively among authors. Variations may be found in the organs used for analysis, the analytical method, and format of reported data (lipid weight vs. fresh weight, total PCB vs. congener-specific), which complicates a comparison of all data. Further, concentrations may be highly variable within an otter population, or even among individuals inhabiting the same area. Generally, average PCB levels in otters appear to be highest in areas where the species is in decline (mean levels ranging from 50 to 180 mg/kg fat) and thriving otter populations are correlated with low mean PCB tissue concentrations (mean levels less than 30 mg/kg fat). However, high levels have recently been found in thriving otter populations in Scotland, especially Shetland, leading some researchers to the conclusion that the alleged role of PCBs in the decline of the otter is likely to have been exaggerated. However, it is neither possible to dismiss the role of PCBs in the otter's decline as exaggerated nor to assume their important role as proven. The data presented in this review include information in support of both views. Most studies on PCBs in otters report total PCBs only, congener-specific data being quite rare. Information on levels of non-ortho congeners, the most toxic PCBs, is even more limited. Because congener patterns may vary between different otters, the total PCB concentration may not always be an accurate estimator of toxicity. To make a proper assessment of the impact of environmental PCB levels on the performance of otter populations and to establish "safe PCB levels" in sediment and fish, a number of toxicokinetic processes have to be elucidated. In general, the following chain of effects should be studied: concentrations in sediment-->concentrations in prey organisms-->concentrations in otter-->physiological effects-->population effects. Recommendations are made regarding possible areas of research.