The bioaccumulation behaviour of single PCB congeners in three trophic
levels of a food chain in an aquatic ecosystem was studied. Congener-
specific biotransfer factors were calculated comparing PCB concentrati
ons in tissues of 4 water bird species with the contents measured in t
heir food source. The coplanar PCBs were of particular interest. The m
aximum concentrations of individual PCB congeners detected in mussels,
fish and birds were 0.5, 4, and 26 mu g/g extractable lipids, respect
ively. In general, the mussel-feeding tufted ducks showed lower PCB le
vels than the fish-feeding bird species. The biotransfer factors were
highest for the non-ortho chloro-substituted coplanar PCB congeners fr
om lake trout to grey herons (3 to 15, depending on the congener). If
the TCDD toxic equivalency (TEq) concept based on mammalian toxicity d
ata is used for the toxicological assessment the detected PCB levels a
re in the range where effects on the reproductive impairment of theses
bird species could result. However, no indication for such effects co
uld be observed. This suggests that species-specific TEF values are re
quired. (C) 1997 Elsevier Science Ltd.