DISTRIBUTION OF PCB CONGENERS IN 7 LAKE SYSTEMS - INTERACTIONS BETWEEN SEDIMENT AND FOOD-WEB TRANSPORT

A study was conducted to examine the role of two processes, partitioning of PCBs between sediment and biota and food-web transport, in determining the concentration of PCB congeners in the biota of seven lakes. Biota PCB concentration (lipid)-to-sediment PCB concentration (organic carbon), or BSF, ratios were calculated as markers of the partitioning of PCBs between biota and sediment, and biota PCB concentration (lipid)-to-zooplankton PCB concentration (lipid), or BAF, ratios were calculated as markers of the transport of PCBs through food webs. The lakes ranged from a shallow, well-mixed lake with a historic input of Aroclor technical mixtures to deeper, oligotrophic systems in which atmospheric deposition was the only known source. BSF ratios ranged from approximately one in cyprinids and zooplankton in all lakes to 30 in yellow perch in one lake. A significant correlation between lake maximum depth and the combined BSF ratios for all biota indicated that PCBs were generally more available for accumulation in the shallower lakes, regardless of the PCB source. Principal component analysis (PCA) showed that the biota in the shallower lakes had higher ratios of higher chlorinated congeners, suggesting that predictions of equal concentrations of hydrophobic contaminants on a lipid basis in sediment and lower trophic levels may significantly underestimate the accumulation of very hydrophobic compounds in the organisms of some lake systems. BAF ratios ranged from approximately one in the lower trophic levels to approximately 10 in lake trout. A significant relationship between the BAF ratio and lake maximum depth for combined data for all biota, and particularly for smallmouth bass (Micropterus dolomieui Lace-pede), probably indicated the increasing role of food-web transport of PCBs in deeper lakes. PC analysis of BAF ratios for individual congeners characterized lake trout (Salvelinus namaycush Walbaum) and yellow perch (Perca flavescens) on the basis of higher ratios for the majority of congeners but also split the two species on the basis of higher ratios of lower chlorinated congeners in perch and highly chlorinated congeneTS in lake trout. The separation of the two species collected from the same lakes was attributed to their position in the food web.