Long-term polychlorinated biphenyl elimination by three size classes of yellow perch (Perca flavescens)

Three size classes of yellow perch (Perca flavescens) were dosed with a polychlorinated biphenyl (PCB) mixture and allowed to depurate the chemicals over 1 year while reared in 5000 L experimental tanks maintained under ambient environmental conditions. During the summer, PCB elimination rate constants for small perch (mean = 10.1 g) averaged approximately three times those calculated for medium-sized individuals (mean = 45.9 g) and four times those determined for the largest fish (mean = 86.7 g). Significant differences in PCB congener depuration were observed among the three size classes with negligible elimination of congeners of the octanol-water partition coefficient (log K-ow) > 6.5 occurring for the two larger size classes. Over the winter months, medium and large perch eliminated PCB 19 only, the least hydrophobic congener, with no elimination of PCBs of log K-ow > 5.8 observed for the smallest individuals. An increase in lipid-normalized PCB concentrations was observed during the overwinter period because of the depletion of lipids as an energetic reserve. For medium and large perch, this increase was sufficient to overwhelm any elimination achieved during the spring and summer seasons. These results demonstrate that the allometry of species bioenergetics and seasonal temperature fluctuations are responsible for the degree of chemical biomagnification observed in aquatic food webs.