A model of PCB s bioaccumulation in the blue mussel ( Mytilus edulis ) from the Bay of Seine

1. Véronique Loizeau and Philippe Cugier DEL/EC, Ifremer Centre de Brest, BP 70, 29280 Plouzané, France vloizeau@ifremer.fr - pcugier@ifremer.fr Introduction • The purpose of this poster is to present a generic framework for modelling bioaccumulation of PCBs in blue mussel from the Bay of Seine. This bay and its estuary are heavily polluted by various contaminants from terrestrial origin. The National Monitoring Network (RNO: Réseau National d’Observation), the « French mussel watch », has revealed high PCB contamination at proximity of the Seine estuary including the bay of Seine. The present work is part of an interdisciplinary program including studies on the phytoplanktonic production, the hydrodynamic and the sediment dynamic in the Bay of Seine. The development and the validation of the present model for the bioaccumulation of PCBs in the blue mussel was carried out following a step by step approach: • A deterministic model, based on ecophysiological data from the litterature on Mytilus edulis was developed. It can estimate the mussel trophic needs and its growth. • This ecophysiological model was coupled with a bioaccumulation model. • Validation of the coupled model was done using RNO’s data (concentration of CB153 in mussel) Water PCB Simulation (1997) ; Dewarumez (1984) data (eastern channel) Simulation (1997) ; A model of PCBs bioaccumulation in the blue mussel (Mytilus edulis) from the Bay of Seine • Objectives • Evaluate the fate of PCBs in blue mussels from the Bay of Seine. • Develop a simple model of PCBs bioaccumulation in blue mussels based on models developed previously for fish. • Parameterize and validate the model with existing data (« French mussel watch »: RNO) PCB contamination in estuaries and coastal areas in Europe The study site : The Bay of Seine * * Winter in white and summer in yellow Model concept and structure Ecophysiological model : Blue mussels feed by actively pumping water across their mantle and capturing food particles from total particulate matter (TPM). Filtration rate varies with organism weight, ambient temperature (TEMP) and TPM. The rate of consumption depends upon filtration rate. The rate of ingestion depends on consumption rate and on efficiency of particles capture (SEFF). The fraction of particulate matter that is not ingested is egested by blue mussel as pseudofeces. Absorption rate depends on characteristics of the particulate matter, such as concentration, size and food quality (AEPHY, AEDET) and controls the increment of state variables x(1) and x(2). Bioaccumulation model The formulation of the blue mussel bioaccumulation model follows the developments of Thomann and Connolly (1984) and Loizeau and Ménesguen (1994). The bioaccumulation model is based on a single-compartment chemical mass balance for the organism, which controls the time evolution of state variable x(3). Forcing variables TOTAL PARTICULATE MATTER Most of the physiological processes depend on environmental conditions that vary during the year, such as temperature, phytoplankton biomass and suspended particulate matter concentration. Cugier (1999) has developed and validated a three dimensional ecological model that can reproduce the main physical and biological characteristics of the Bay of Seine. It has provided time series for temperature, chlorophyll concentration, particulate organic and inorganic matter that were used as forcing variables in the bioaccumulation model. PCB PCB Detritic matter Phytoplankton PIM TEMP FILTRATION TPM CONSUMPTION SEFF Pseudofeces PCB INGESTION Feces PCB AEPHY AEDET ABSORPTION Respiration PCB flesh x(3) Shell weight x(2) Flesh Dry Weight x(1) Environmental forcing parameters in the blue mussel model (results provided by the 3D ecological model, Cugier 1999), at 4 locations: Villerville – Antifer – Port en Bessin – Le Moulard Schematic structure of the blue mussel model Ecophysiological model Bioaccumulation model RESULTS 4 1 1 4 Antifer 4 Le Moulard 1 2 3 2 3 Villerville Port en Bessin 3 2 RNO measurements (1995 – 1999) RNO measurements (1997) The results of the ecophysiological model were compared with the size/age relationship developed by Dewarumez in 1984. Simulations obtained show a good agreement with this size/age relation, particularly for Villerville and Port en Bessin locations. However the results of the model will have to be validated by measurements which are currently under way in each zone. Good agreement has been obtained between calculated and measured concentrations of one of the most persistent PCB congeners (CB153) in mussels from the Bay of Seine (RNO). The blue mussel bioaccumulation model could reproduce variation of PCB contamination level between different areas (factor of ten). Morever, seasonal variations are well simulated by the model. • Conclusions and perspectives • The good agreement between simulations and measurements validates the processes taken into account in the model. • The model represents the variations of contamination according to the geographical distribution of the mussels : mussels near the estuary have the strongest contamination levels. This confirms that the Seine is the main source of PCBs in the area. • In a given zone, the model reproduces the seasonal variations reasonably well. Future development • Taking the spawning into account • Validation of the biological model (growth), by measurements of condition index (size and weight of shell, flesh weight, etc…) • Validation for other PCB congeners. C:/gemco/textes/meeting/setac/poster.ppt