Bioaccumulation of persistent organic pollutants from floodplain lake sediments: linking models to measurement

The main research questions of this research were (1) what is the extent and nature of bioavailability of sediment-bound polychlorobiphenyls (PCBs) and polyaromatic hydrocarbons (PAHs) and (2) what are the effects of lake ecosystem structure on fate and bioaccumulation of PCBs and PAHs. Fast-desorbing fractions in the sediment of floodplain lakes were estimated by the 6-h Tenax-extractable fractions with a correction factor. These fractions varied between 1 and 40% and did not show a clear trend with log KOW. This means that contaminants in these sediments were available, but to a smaller extent than total concentrations would suggest. The 6-h Tenax extractable concentration often correlated better with bioaccumulation than the total extractable concentration in sediment. Despite the reduced availability, benthivorous fish and invertebrates in floodplain lakes still rapidly accumulated substantial amounts of PCBs. PAHs were accumulated relatively less because PAHs were relatively less available than PCBs due to their stronger sorption to carbonaceous materials, also referred to as soot or black carbon. For fish, metabolic transformation caused even lower PAH concentrations. Contaminants that have been present in the sediment for longer periods of time (years to decades), were less available for Tenax extractions as well as for uptake by biota in different parts of the food web than contaminants that were recently added. Thus, aging may translate directly into reduced uptake at higher trophic levels. Nutrient additions in enclosures with benthivorous fish had a positive effect on PCB accumulation by these fish. Measured bioaccumulated concentrations of PCBs and PAHs in invertebrates in flood plain lakes were not influenced greatly by seasonal effects or ecological structure. Although effects were statistically significant, their magnitude in terms of accumulation factors was small, which may have been caused by the similar sediment composition and bioavailability of contaminants in our systems. Differences between compounds were much larger than differences due to ecosystem structure, seasons, or species composition. As for total masses of PCBs and PAHs in certain compartments however, lake ecosystem structure appeared to have a large influence on the biomass of biota and therefore also on the mass distribution of PCBs and PAHs in biotic compartments. Thus, changes in ecosystem structure strongly influenced PCB and PAH dynamics, although concentrations within the biotic compartments were not significantly influenced by biotic biomass. As for bioaccumulation modelling, when aquatic exposure concentrations were quantified accounting for sorption to carbonaceous materials, model results improved substantially. Including metabolic transformation and sediment uptake in the model accounted for a further improvement of the model fit. Implications are discussed for food chain bioaccumulation modeling, bioavailability assessment, sediment policy making and floodplain lake management.