MODELING OF PCB TROPHIC TRANSFER IN THE GULF OF LIONS; MARS3D/ECO3M COUPLED MODEL APPLICATION E. Alekseenko 1,3 , B. Thouvenin 1* , C. Tixier 2 , J. Tronczyński 2 , M. Baklouti 3 , V. Loizeau 4 , P. Garreau 1 , R. Verney 1 , F. Carlotti 3 , B. Espinasse 3 and B. Queguiner 3 1 IFREMER, DYNECO/PHYSED, B.P. 70, 29280, Plouzané, France; 2 IFREMER, RBE/BE/LBCO, B.P. 21105, 44311 Nantes, France; 3 University of Aix-Marseille, University of South Toulon-Var, CNRS/INSU, IRD, MIO, UMR 110 4 IFREMER, RBE/BE/LBCO, B.P. 70, 29280, Plouzané, France This work aims at assessing the role of plankton in the transfer of PCBs to higher trophic levels in the Gulf of Lions by coupling biogeochemical and hydrodynamical processes and taking into account the physico-chemical properties of PCBs (PCB153 and PCB28). Plankton plays a key role in biogeochemical cycles of PCBs in aquatic environments. Since phytoplankton and bacteria are only exposed to the contaminants via water, it seems probable that the bioaccumulation is governed by sorption between the cells and the surrounding water 1,2 . On the other hand, for zooplankton feeding on them, two contamination pathways must be considered: diffusive exchanges and ingestion of contaminated food [1]. There is little information on the transfer of PCBs to zooplankton actually occurring in the field. However such information is crucial to make reliable predictions about PCB transfer to the higher trophic levels. In the coastal area as Gulf of Lions, the process of PCBs bioaccumulation along the trophic web is ruled by interactions between compounds physico-chemical properties, organism biological properties and also by hydrodynamical and biogeochemical processes. We have developed a coupled three-dimensional model for the assessment of PCB dispersion in space and time and of its transfer to zooplankton via biogeochemical processes. Specifically, the MARS3D hydrodynamical model 3 taking into account the PCB transport was coupled with a biogeochemical model Eco3M 4,5,6 . The case of two PCBs congeners was studied: PCB153 and PCB28. Transport of various PCB species were simulated during one year: total dissolved, freely dissolved, particulate, biosorbed on plankton, assimilated by zooplankton. PCB budgets and fluxes into the Gulf of Lions between various species were governed by different processes, such as: adsorption/desorption, bacteria and plankton mortality, zooplankton excretion, grazing, mineralization, volatilization and biodegradation. In the first step, the simulated PCBs distributions within particulate matter and plankton were compared with several in-situ measurements performed in the Gulf of Lions (COSTAS and Merlumed campaigns) for two size classes of plankton X (60μ m<X<200μ m and 200μ m<X<500μ m). The model reproduces quite well the orders of magnitudes. Although the model cannot be fully validated for PCBs in terms of transfers in the trophic chain, its application on an annual period can highlight the impact of dominating forcing and the importance of processes necessary to explore in future research. Processes influencing PCB transfer were thereby analyzed: (i) physical and chemical processes, such as riverine and atmospheric inflow, volatilization, sorption and resuspension and (ii) biogeochemical processes, namely grazing, mortality, mineralization and excretion. The Rhone River input appears to play a major role in the PCB contamination of the planktonic trophic chain of the Gulf of Lions. The contamination propagation from east to west, from the coast to the sea, from the surface to the bottom and its transfer from water and particles to bacteria and plankton is displayed according to seasonal events. The riverine PCB adsorbed to particulate matter desorbs into the water phase and, then contaminate the lower trophic levels (phytoplankton and bacteria) by sorption process. The higher trophic levels (zooplankton) are contaminated by PCBs mostly by grazing (feeding on the contaminated lower trophic levels) and slightly by sorption. Acknowledgements This study is part of COSTAS project (Contaminants dans le système trophique: phytoplancton, zooplancton, anchois, sardine) supported by ANR-CES-007. References 1. Magnusson K. and Tiselius P., (2010). Aquatic Toxicology, 98: 374-380. 2. Del Vento S. and Dachs J., (2002). Environmental Toxicology and Chemistry, 21, 10: 2099-2107. 3. Lazure, P., Dumas, F., (2008). Advances In Water Resources, 31, 2: 233-250. 4. Baklouti, M., Diaz, F., Pinazo, C., Faure, V., Quequiner, B., (2006a). Progress in Oceanography 71: 1- 33. 5. Baklouti, M., Faure, V., Pawlowski, L., Sciandra, A., (2006b). Progress in Oceanography 71: 34-58. 6. Alekseenko E., Raybaud V., Espinasse B., Carlotti F., Queguiner B., Thouvenin B., Garreau P., Baklouti M. (2014). Ocean Dynamics 64: 179-207.