Seasonal dynamics of PCBs in the plankton of Lake Erie

Plankton net samples, containing both phytoplankton and zooplankton populat ions, were collected from April to October 1996, and analyzed for PCB conge ner concentrations and other organochlorines; in order to quantify seasonal dynamics of contaminants in the base of the pelagic food web of Lake Erie. Seasonal variations in plankton concentrations of Aroclor 1254/1260 were o bserved to range from 3.25 to 35.2 mu g/kg (wet wgt.). In order to compare the relative differences of chemical activity (fugacity), at the base of th e pelagic food web with that of the benthic food web, fugacity ratios were determined for chemicals in the plankton and the sediment. If the two phase s are in chemical equilibrium, the fugacity of chemicals in the two phases should be equal, or fp/fs = 1. Congener specific plankton:sediment fugacity ratios (fp/fs), however, ranged from 0.05 to 0.63, and revealed a signific ant gradient of chemical activity between the plankton and the sediment. Tr ophic dilution in the pelagic food web, where algal growth rates exceed che mical kinetic rates, is concluded to be an important process in regulating contaminant exposure dynamics in the pelagic food web of the western basin of Lake Erie. It is hypothesized that higher fugacities at the base of the benthic food web can influence chemical concentrations in the upper trophic levels as a result of coupling between the benthic and pelagic food webs.