Bioconcentration of polychlorinated biphenyls (PCBs) in rainbow trout caged in the River Po.

Two groups of rainbow trout were caged in the River Po upstream and downstream of the confluence with the River Lambro, a relatively small tributary which drains the most industrialized and urbanized area of the entire basin. Fish were analyzed for PCB concentration at the start of the experiment and after 7, 15, and 30 days of exposure. The results demonstrate that the emission of the River Lambro represents an important point source of PCBs to the River Po and that part of the transported load is readily bioavailable, since caging virtually excluded trophic transfers. On the basis of PCB levels measured in downstream trout, the steady-state concentration and the congener pattern were predicted by means of a computer program. These projections were compared with published data obtained with native fish caught downstream from the River Lambro.