000103735 001__ 103735
000103735 005__ 20181007231013.0
000103735 0247_ $$2doi$$a10.5075/epfl-thesis-3796
000103735 02470 $$2urn$$aurn:nbn:ch:bel-epfl-thesis3796-5
000103735 02471 $$2nebis$$a5339378
000103735 037__ $$aTHESIS_LIB
000103735 041__ $$aeng
000103735 088__ $$a3796
000103735 245__ $$aLinking chemical speciation to metal bioavailability$$brole of dissolved organic matter on cadmium and lead bioavailability by green microalgae
000103735 269__ $$a2007
000103735 260__ $$aLausanne$$bEPFL$$c2007
000103735 300__ $$a164
000103735 336__ $$aTheses
000103735 502__ $$aKevin Wilkinson, Marc Benedetti, Tamar Kohn
000103735 520__ $$aIt is recognized that dissolved organic matter (DOM) plays an utmost role in aquatic ecosystems by binding trace metals and influencing their speciation, bioavailability and detrimental effects. DOM is considered to protect the aquatic microorganisms from heavy metal stress by decreasing free metal ion concentration and thus decrease their bioavailability. Nonetheless, a fundamental understanding of the relationship between trace metal speciation, bioavailability and effects is still lacking for many environmental systems, although progresses have been made in recent years. The main objective of the present thesis was to link Pb(II) and Cd(II) speciation to its bioavailability to green micro algae in presence of DOM. In particular, (i) to characterize metal binding properties of different DOM components (e.g. EPS), (ii) to determine their effect on metal bioavailability and (iii) to quantify as rigorously as possible the relationship between chemical speciation and bioavailability in presence of different DOM components. The proton, Pb2+ and Cd2+ binding capacities of extracellular polymeric substances (EPS), in particular alginate and Rhizobium meliloti exopolysaccharides were quantified by determination of complex stability constants and the concentration of binding sites using ion selective electrodes in static or dynamic titration. The influence of ionic strength, pH and metal to EPS ratio was determined over large concentration ranges. Metal binding and conditional stability constants increased with increasing pH due to a decrease of competition with the proton. In contrast, an increase in the metal to EPS ratio or ionic strength resulted in a decrease in the average conditional stability constants as could be expected by the polyelectrolytic and polyfunctional character of the EPS. A non ideal competitive adsorption isotherm (NICA) combined with a Donnan electrostatics approach previously developed for humic substances, takes into account the intrinsic polyfunctionality and polyelectrolytic properties and can reasonably account for electrostatic and competition effects. It was successfully applied to describe Pb(II) and Cd(II) complexation by EPS. Results demonstrated that EPS played a non neglected role in Pb and Cd speciation. The influence (both direct and indirect) of different DOM components on Pb bioavailability by green algae Chlorella kesslerii was studied. Results demonstrated that some of the studied EPS (e.g. alginate) may exhibit similar influences on Pb bioavailability as humic substances. DOM components had several simultaneous effects on Pb bioavailability including complexation in the medium, adsorption to algal surfaces, and modification of membrane permeability. An important discrepancy between Pb bioavailability in the presence of HS and alginates (as individual components or mixtures) and that predicted for similar free Pb ion concentrations in the presence of synthetic ligands (NTA, citrate) was obtained. In contrast, the experimental results of Cd and Cu uptake were in good agreement with that predicted from free metal concentration. An improved fit between experimental observations and Pb speciation was obtained by extending the free ion activity model (FIAM) when the formation of a ternary complex between metal, DOM and the algal surface is taken into account. The contribution of ternary complexes on metal biouptake was thus dependent on (i) the metal affinity to microorganisms, (ii) the concentration of different components that constituted DOM, (iii) their capacity to adsorb onto the surface of the microorganisms and (iv) their affinity to bind the metal. By simultaneously examining metal speciation and biological availability in the presence of different DOM components and their mixtures, this work provided new information with respect to the applicability and limitation of existing equation models. An extension of existing models will further improve a site specific predictive capacity by avoiding underestimation of metal biouptake in presence of high DOM concentration.
000103735 6531_ $$aSpeciation
000103735 6531_ $$adissolved organic matter
000103735 6531_ $$aextracellular polymeric substances
000103735 6531_ $$aexopolysaccharides
000103735 6531_ $$ahumic substances
000103735 6531_ $$acadmium
000103735 6531_ $$alead
000103735 6531_ $$aNICA-Donnan
000103735 6531_ $$abioavailability
000103735 6531_ $$amicroalgae
000103735 6531_ $$aFIAM
000103735 6531_ $$aBLM
000103735 6531_ $$aternary complexes
000103735 6531_ $$aSpéciation
000103735 6531_ $$amatière organique dissoute
000103735 6531_ $$asubstances polymériques extracellulaires
000103735 6531_ $$aexopolysaccharides
000103735 6531_ $$asubstances humiques
000103735 6531_ $$acadmium
000103735 6531_ $$aplomb
000103735 6531_ $$aNICA-Donnan
000103735 6531_ $$abiodisponibilité
000103735 6531_ $$amicro algues
000103735 6531_ $$aFIAM
000103735 6531_ $$aBLM
000103735 6531_ $$acomplexes ternaires
000103735 700__ $$0240065$$aLamelas, Cristina$$g166424
000103735 720_2 $$aSlaveykova-Startcheva, Vera$$edir.
000103735 8564_ $$s1472457$$uhttps://infoscience.epfl.ch/record/103735/files/EPFL_TH3796.pdf$$yTexte intégral / Full text$$zTexte intégral / Full text
000103735 909CO $$ooai:infoscience.tind.io:103735$$pthesis$$pDOI$$qDOI2$$qthesis-bn2018
000103735 918__ $$aENAC$$bENAC-SSIE$$cISTE
000103735 920__ $$a2007-5-11$$b2007
000103735 970__ $$a3796/THESES
000103735 973__ $$aEPFL$$sPUBLISHED
000103735 980__ $$aTHESIS