Ludovic Lesven, Gabriel Billon and Jean-Claude Fischer Lille, 28 March 2008 S patial and T emporal A ssessment of high R esolution D epth profiles U sing novel S ampling T echnologies Vlaams Institute Voor de Zee Université des Sciences et Technologies de Lille Vrije Universiteit Brussel Programme INTERREG III : STARDUST Bilan Stardust 2 Main results for Stardust 2 FEDER

INTRODUCTION Lille, 28 March 2008  Stardust Project has allowed to carry out different studies at water-sediment interface.  More particularly, behaviour of trace metals in relationship with sulphides have been followed in 3 sites: Spierre, Helkjin and Wervik.  In addition, the measurement of metallic fluxes (natural) at water-sediment interface have been realized.  Finally, new analytical tools have been developed:  Solid microelectrodes for trace metals analysis in natural media  DGT – AgI for in situ measurements of sulphides

DIAGENETIC PROCESSES Lille, 28 March 2008 BOAT Oxygen reduction: O 2  H 2 O Denitrification: NO 3 -  N 2 Reduction of manganese hydroxides: Mn(III, IV)  Mn 2+ Reduction of iron hydroxides: Fe(III)  Fe 2+ Sulfate reduction: SO 4 2-  S 2- …  MS with M= Fe, Pb, Zn, Cu, Cd… Organic matter Water Sediment ?

CORE SAMPLING Lille, 28 March 2008 Sed. Wat. Sed. Pore Wat.Susp. Mat. Wat. Sequential extraction Filtration in a glove-box ANALYSIS - ICP-MS - ICP-AES - Ionic chromatography - Potentiometry Core 1 pH, Eh (by potentiometry) O 2 (by amperometry) Core 2 Centrifugation Cutting in a glove-box with N2 A lot of steps Real concentration of element? Sample conservation (oxygen)

NEW ANALYTICAL TOOLS Lille, 28 March 2008 Analytical development Solid microelectrodes: Au and Ag-CuDGT – AgI In situ measurements Labile fraction Good detection limits Cheap method In situ sampling Good detection limits High resolution profiles Quick screening for site rich in sulphides Trace metalsDissolved sulphides

NEW ANALYTICAL TOOLS: solid microelectrodes Lille, 28 March 2008 Analytical development Solid microelectrodes: Au and Ag-Cu In situ measurements Labile fraction Good detection limits Cheap method Trace metals

NEW ANALYTICAL TOOLS: solid microelectrodes Lille, 28 March 2008 ElectrodeDiameter (µm) MethodsDeposition time (s) Analytical window (V) Metals (ppb) MnZnCdPbCuHg Ag-Cu80DPASV to Au25DPASV SWASV to Applications:  Monitoring of trace metals in the water compartment  Metal profiles in the porewater sediments Skogvold O., Mikkelsen O., Billon G., Garnier C., Lesven L., Barthe J.F. (2006). Electrochemical propertiesof silver-copper alloy microelectrodes for use in voltammetric field apparatus, Anal. Bioanal. Chem. ; 384(7-8): Garnier C., Lesven L., Billon G., Magnier A., Mikkelsen O., Pizeta I. (2006). Voltammetric procedure for trace metal analysis in polluted natural waters using homemade bare gold-disk microelectrodes, Anal. Bioanal. Chem. ; 386(2):

NEW ANALYTICAL TOOLS: DGT - AgI Lille, 28 March 2008 Analytical development DGT – AgI In situ sampling Good detection limits High resolution profiles Quick screening for site rich in sulphides Dissolved sulphides

NEW ANALYTICAL TOOLS: DGT - AgI Lille, 28 March 2008 Deployment Calibration Scanning and treatment Microprofiles of S -2

BEHAVIOUR OF METALS IN SEDIMENT: Sites Lille, 28 March 2008 Wervik Spierre Helkjin

BEHAVIOUR OF METALS IN SEDIMENT: definitions Lille, 28 March 2008 Sulphides cycle

BEHAVIOUR OF METALS IN SEDIMENT: definitions Lille, 28 March 2008 AVS: A cid V olatile S ulphide Predominantly FeS (troillite), not stable, easily oxidized CRS: C hromium R educible S ulphide Predominantly FeS 2 (pyrite), to a lesser extend S 0 Toxicity index (TI): ratio of SEM (simultaneously extracted metals) in ppm/AVS With SEM: Cd + (Co) + (Hg) + Ni + Pb + Zn Log TI <0: metals only bound to sulphides with low bioavailability Log TI >0: metals partly bound to labile forms such as carbonates

BEHAVIOUR OF METALS IN SEDIMENT: results Lille, 28 March 2008  Very negative potential values: diagenetic processes  Active mineralization of the labile organic matter

BEHAVIOUR OF METALS IN SEDIMENT: results Lille, 28 March 2008  Fe(II) and Mn(II) concentrations are weak in the first centimetres in comparison to the Wervick site.  Sulphate reducing bacteria seem to be less active in the Wervick sediment, especially in the first centimetres.

BEHAVIOUR OF METALS IN SEDIMENT: results Lille, 28 March 2008  High values of AVS and CRS in Spierre site can explain the low values of iron and manganese at the same depth.  In Spierre sediment the toxicity index is always negative due to the high sulphide amounts.  AVS play an efficient role of trap for trace metals in Spierre sediment (in the first cm).

BEHAVIOUR OF METALS IN SEDIMENT: conclusions Lille, 28 March 2008 Biogeochemical conditions in the Spierre river different from the 2 other sites:  Very high levels of AVS and CRS  Very low values of log SEM/AVS  Low concentrations of total (DET) and labile (DGT) metals in porewater, especially in upper layer  Remobilisation of trace metals from Spierre sediment to the water column is limited L. Lesven, Y. Gao, G. Billon, M. Leermakers, J-C. Fischer and W. Baeyens, Influence of sulphides on trace metals mobility in river sediments (in preparation)

CONCLUSION AND PERSPECTIVES Lille, 28 March 2008  New analytical tools:  DGT – AgI for sulphides  Solid microelectrodes (Au and Ag-Cu) for trace metals in water column and sediment  Common sampling in the cross-border rivers (Lys and Escaut) between France and Belgium  Biogeochemistry in the sediments and characterization of the water-sediment interface  Metallic fluxes study in the same sites  In perspective:  Continue the metallic fluxes determination (comparison incubation chambers and DGT)  Evaluate the metallic bioaccumulation for aquatic organisms during anthropogenic remobilisation in polluted rivers  Continue the analytical development (monitoring station, DGT…)