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Figure 25.7. Calculated concentrations of tri- and penta-CB for a 1987 striped bass cohort.

slow rates (of several months or more) for the accumulation andloss of more chlorinated homologues by perch.

Calculated PCB homologue concentrations in white perch further downstream in the mid estuary at Km 94 (RM 58.5) (not shown) also compared well to observed data. At this location, PCB responses in perch exhibit a slow decline, largely in response to the slow decline in exposure concentrations (as previously shown in Fig. 25.5 for dissolved PCBs). The resulting concentrations of PCBs in perch at Km 94 (RM 58.5) decreased from a high of 5 |g g-1 (wet weight) in 1987 to approximately 1 |gg-1 (wet weight) at the end of our simulationperiod in 2002. Perchin this portion of the river are particularly important as a food source for striped bass.

PCB accumulation in striped bass, however, is further complicated by fish migration behavior. This is best illustrated by examining the accumulation of tri- and penta-CB in a striped bass cohort born in 1987. As shown in Figure 25.7, the 1987 cohort quickly accumulates PCBs during the first two years of life in the mid estuary (solid lines in Fig. 25.7). As the cohort ages, fish begin to migrate from the mid estuary into the New York Bight (open triangles), and for older fish, the Atlantic Ocean (open circles). During their time out of the estuary, striped bass feed on less contaminated prey and their stored PCB concentrations are reduced by depuration and growth dilution. Each year, as striped bass migrate back into the estuary, their PCB concentrations increase as fish again feed on more contaminated prey.

Differences in homologue behavior are shown in Figure 25.7. As shown, there is a significant loss of tri-CB from striped bass during their migration to less contaminated waters. This is accompanied by a slow decline in tri-CB concentrations over many years. In contrast, penta-CB shows only moderate reductions in concentration during migration. Since the reduction in penta-CB is less than the accumulation of penta-CB by striped bass during their return to the mid estuary, a long-term buildup in penta-CB concentrations occurs over the years. Differences in homologue responses are related to their hydrophobicity (as measured by the log Kow). In this case, penta-CB has a greater affinity to remain in fish lipids and its loss by depuration occurs at very slow rates. Reduction in penta-CB concentrations in striped bass is therefore slow and is largely controlled by growth dilution. This results in a slow decline of penta-CB during migration and ultimately leads to a long-term buildup of penta-CB over time. A shift in PCB homologue distributions to high chlorinated homologues is therefore expected for older striped bass.

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