A Comparison of Organochlorine Contaminant Levels in the Zebra Mussel, Dreissena polymorpha, versus its Unionid Attachment, Elliptio complanata, in the Rideau River, Ontario

Organochlorine contaminant levels were compared between the native unionid Elliptio complanata and the exotic zebra mussel, Dreissena polymorpha, at four sites along the Rideau River near Ottawa in 1995. Overall, the two taxa exhibited similar bioaccumulation patterns. PCB congeners, treated individually or as classes, showed strong positive and significant correlations between the two taxa. Additionally, the ratios DDD/ΣDDT, DDE/ΣDDT and DDT/ΣDDT were not significantly different between the two taxa. Mean concentrations of ΣPCB, ΣDDT, and Σchlordane were 65.8, 14.0, 1.2 and 227.9, 10.6, 1.8 ng/g soft tissue dry weight in E. complanata and D. polymorpha, respectively. These three organochlorine groupings accounted for 98.2 and 98.7% of the organochlorine soft tissue dry weight burden in E. complanata and D. polymorpha, respectively. However, while the bioaccumulation patterns were similar in E. complanata and D. polymorpha, the ΣPCB concentration was significantly higher in D. polymorpha. The organochlorine dry weight burden was 2.0 to 5.6 times greater in D. polymorpha compared to that in E. complanata and this was mostly attributable to differences in ΣPCB. This difference may be explained in part by the relative lipid content in D. polymorpha being 1.8 times greater on average than in E. complanata. We conclude that D. polymorpha is a good alternative freshwater biomonitor for E. complanata.