PARENT SESSION
PW7 - Biotransformation / Metabolisms / Degradation
Wednesday, 20 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P791) PCB Elimination and Metabolite Formation in Captive and Field Leopard Frog (Rana pipiens) Populations.
Balkwill, Karen1, Hauschild, Karl1, Drouillard, Ken*,1, Gilbertson, Mary1, Dixon, Brian2, Bennett, Erin1, Haffner, Doug1, Letcher, Robert, 1 Great Lakes Institute, University of Windsor, Windsor, Ontario, Canada2 Department of Biology, University of Waterloo, Waterloo, Ontario, Canada
ABSTRACT- Amphibian declines around the globe has been attributed to several factors including exposure to contaminants such as PCBs and DDTs. The induction of enzyme-mediated metabolism is a major factor in determining the bioaccumulation, fate and potential toxicity of environmental contaminants. In the present study, congener-dependent elimination kinetics and the formation of retained hydroxylated (OH) PCB and persistent methyl sulfone (MeSO2) PCB metabolites were investigated in captive and field populations of leopard frog (Rana pipiens). In captive studies, leopard frogs were i.p. dosed with an Aroclor mixture (1242:1254:1260, 1:1:1 by wt.) and sacrificed after 0, 60, 120 and 150 d. Elimination rate constants and half lives were determined for 63 individual PCB congeners. Half-lives ranged from 17 to 282 d and increased with increasing degree of chlorination on the PCB, and were partially dependent on the molecular chlorine substitution pattern. PCBs containing vicinal hydrogen substituents at meta-para carbon sites on at least one of the phenyl rings were more readily eliminated. These congeners are precursors to MeSO2-PCB metabolites. In field studies, PCBs and PCB metabolites were determined in leopard frogs from 4 populations in southwestern Ontario, and control populations from the Ottawa and Collingwood (Ontario) areas. Individuals from Point Pelee contained the highest sum PCB concentrations (whole body homogenates), as well as high levels of other organochlorines (OCs). Regardless, MeSO2-PCB were below detection (i.e., < 2.0 pg/g, wet wt.). Two pentachloro- and one heptachloro-OH-PCB metabolites were tentatively detected in plasma at apparent levels ranging from 0.9 to 19.3 pg/g (wet wt.), although concentrations approached the method detection limit (0.8 pg/g, wet wt.) These results indicate that leopard frogs slowly eliminate PCBs, although meta-para-PCBs are eliminated more quickly. Metabolic pathways leading to OH-PCBs, and to a lesser extent to MeSO2-PCB appear to be relatively unimportant. Our findings suggest that leopard frogs are efficient accumulators of PCBs.
Key words: leopard frogs, PCB elimination, metabolite formation, captive/field populations