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Raziskave so bile opravljene na več raziskovalnih postajah v Tržaškem zalivu in v lagunah Marano in Grado. Gre za okolja, v katerih vladajo različne fizikalne, kemijske in biološke razmere. Cilj doktorskega dela je bil preučiti povezave med organsko snovjo (OM) in živim srebrom (Hg) v omenjenih okoljih ter ugotoviti, kako različni okoljski dejavniki in različen izvor OM ter Hg vplivajo na morebitne povezave in njihov obseg. Tržaški zaliv je onesnažen s Hg iz rudnika Hg Idrija, laguni pa sta podvrženi vplivu dveh oblikHg iz dveh ločenih virov. En je prav tako idrijski rudnik, medtem ko je drugi nedolgo nazaj delujoča kloralkalna tovarna, locirana v zgornjem delu toka reke Aussa, ki se izliva v maranski sektor lagune. Delo se je osredotočalo na povezave med OM in Hg v vodnem stolpcu in sedimentih obeh sistemov. Izkazalo se je, da je organska snov v vodnem stolpcu Tržaškega zaliva pomemben vezalec Hg in tudi drugih kovin, povezav med njimi pa v sedimentih ni bilo mogoče zaznati. Podobno se je izkazalo tudi pri analizi vzorcev iz lagun. Razlike v povezavah med OM v vodnem stolpcu in sedimentih sopovezane z različno sestavo in strukturo OM, saj je v sedimentih večinoma mogoče najti močno rekalcitrantno OM, medtem ko je OM v vodnem stolpcu bolj biodostopna in vsebuje več funkcionalnih skupin, ki omogočajo vezavo kovin. V Tržaškem zalivu oz. celotnem severnem Jadranu občasno prihaja tudi do tvorbe makroagregatov, velikih skupkov OM. Raziskovanje mehanizmov njihove tvorbe in razgradnje ter sestave in strukture je izjemnega pomena, saj je s tem omogočentudi vpogled v dinamiko naravne OM v Tržaškem zalivu. Ob analizi netopne frakcije makroagregatov so bile zaznane visoke koncentracije nekaterihkovin, kar je kazalec vključitve mineralnih delcev v strukturo. Analiza topnega dela makroagregatov je pokazala, da ima raztopljena OM makroagregatov enake lastnosti in sposobnosti vezave Hg kot naravna OM v tem okolju. Združitev metode ultrafiltracije in uporabe radioaktivnih ali stabilnih izotopov bi v prihodnje pomembno pripomogla k še natančnejšemu poznavanju mehanizmov, ki vodijo do povezav med OM in kovinami v okolju. OM ima velik vpliv na biogeokemijsko kroženje Hg, saj je pomembna z vidika napajanja mikrobnega metabolizma, s tem pa tudi tistih mikrobov, ki vodijo pretvorbe Hg. Z izvedbo eksperimentov v okoljih, v katerih ima OM različen izvor, različen izvor ima pa tudi Hg, je bila potrjena hipoteza o pomembnosti biološke dostopnosti tako OM kot Hg pri tvorbi MeHg. Research was conducted in various experimental stations throughout Gulf of Trieste and Grado and Marano Lagoon. Ecosystems observed are governed by different physical, chemical and biological conditions. The main aim of this research was to investigate the existence and extent of interactions between organic matter (OM) and mercury (Hg). The influences of various environmental conditions were also studied. The most important factor in our study was the effect that the origin, thus structure and composition, of OM as well as Hg has on the existence and extent of interactions. Gulf of Trieste is contaminated with Hg from Idrija mercury mine whereas Hg found in Lagoon has two origins. One is Idrija mercury mine, while the other is chloralkali plant operating until recently and situated upstream of Aussa River. Aussa River is as an Aussa-Corno river system discharged into the Lagoon. During the researchdissolved and sedimentary OM and its interactions with Hg were investigated. It turned out that dissolved OM present in water column plays animportant role as Hg and other metal complexation agent, however no conclusive evidence was found that interactions between sedimentary OM and Hg exist. Similar results were obtained also on samples from the lagoon environment. It was concluded that the absence of interactions in sediments was a consequence of OM quality, meaning that its recalcitrance does not support Hg binding in the extents as water column OM does. Water column OM is apparently more bioavailable and contains functional groups more suitable for metal binding. Macroaggregates, large aggregates of OM, are relatively regularly formed in the waters of northern Adriatic, also in waters of Gulf ofTrieste. Knowledge on mechanisms of macroaggregate formation and degradationis necessary, since it offers an invaluable insight into dynamics of natural OM as well. Analyses on macroaggregate matrix showed high metal concentrations which suggested an incorporation of inorganic particles, while the results on interstitial soluble portion of macroaggregates revealed similar to identical properties in terms of structure and metal binding capacity as natural OM. In future the combined usage of ultrafiltration and radioactive or stable isotopes could prove to be invaluable tool for identifying the mechanisms behind interactions between OM and Hg. OM is one ofthe most important actors in the biogeochemical cycle of Hg, since it servesas a fuel for microbial metabolism. It supports also the microbes responsible for transformations of Hg. The experiments performed in different environments where OM and Hg have different origins allowed us to confirm the hypothesis on importance of bioavailability of OM and Hg in the formation of MeHg.

Previous research on mercury (Hg) showed strong contamination of the Piallassa Baiona (P.B.) lagoon, near Ravenna. The lagoon received between 100 and 200 tons of Hg generated by an acetaldehyde factory in 1957-1977. In this study, the Hg cycling at the sediment-water interface in the P.B. lagoon was investigated by means of an in situ benthic chamber. The 8-h integrated flux of the methylated form was extremely low and estimated to be only 7% of the result obtained for a summer experiment performed in a similar Hg-contaminated environment (Grado lagoon). Conversely, the in situ flux of Hg accounted for a comparable amount to that observed in the Grado lagoon, although Hg contents in its sediments are almost 50% lower than in P.B. lagoon. Hg mobilization and sequestration in the system, limiting its bioavailability despite the high contents of metal buried in the bottom sediments, seem related to extremely anoxic conditions., Des recherches précédentes sur le mercure (Hg) ont mis en évidence un taux de contamination élevé de la lagune de Piallassa Baiona (P.B.), près de Ravenne. Entre 1957 et 1977, la lagune a accumulé 100 à 200 tonnes de mercure issues d'une usine d'acétaldéhyde. Cette étude reconstitue la remobilisation du Hg à l'interface eau-sédiments à l'aide d’une chambre benthique in situ. Le flux quotidien (8 heures) de la forme méthylée obtenue est extrêmement bas, soit 7% de la valeur mesurée expérimentalement dans la lagune de Grado (Italie), aussi contaminée au Hg. Le flux total in situ de Hg est en revanche comparable, bien que son contenu dans les sédiments de Grado soit inférieur de pratiquement 50% à celui de P.B. Malgré des concentrations élevées en Hg, les conditions extrêmement anoxiques du milieu semblent liées à la mobilisation et à la séquestration du Hg dans le système, ce qui en limite la biodisponibilité., Precedenti ricerche sul mercurio (Hg) hanno evidenziato un elevato stato di contaminazione della Pialassa Baiona (P.B.) presso Ravenna. La laguna è stata interessata da un apporto di Hg (100-200 tonn) prodotto da una fabbrica di acetaldeide nel periodo 1957-1977. In questo studio, è stata indagata la rimobilizzazione del Hg all’interfaccia acqua-sedimento per mezzo di una camera bentica in situ. Il flusso giornaliero (8 ore) per la forma metilata si è rivelato estremamente basso, pari al 7% di quanto osservato sperimentalmente in un ambiente simile contaminato da Hg, la laguna di Grado. Viceversa, il flusso di Hg totale è risultato comparabile a quanto osservato in laguna di Grado sebbene il contenuto di Hg nei sedimenti fosse inferiore di ca. 50% rispetto alla Pialassa. Mobilizzazione ed accumulo del Hg nel sistema, che limitano la biodisponibilità a dispetto delle elevate concentrazioni di Hg nei sedimenti, appaiono relazionati dalle condizioni anossiche del sedimento., EQA - International Journal of Environmental Quality; Vol 3 (2010); 33-40

Date du colloque: 06/2012; International audience

Mercury in the aquatic environment is present at very low levels and its determination can be a subject to losses and/or contamination during sampling, sample preparation and analysis. Speciation of chemical forms of mercury in natural waters is even more demanding. The monomethyl mercury form (MeHg) is persistent, it accumulates and biomagnifies in the food webs. MeHg is formed in the nature, particularly in the aquatic environment. Therefore, the accurate determination is of great importance. The aim of this study was to optimize a simple and efficient separation technique for MeHg determination in natural waters using aqueous phase distillation followed by derivatisation using ethylation, purging and room temperature adsorption on Tenax, gas chromatography, pyrolysis and detection by cold vapour atomic fluorescence spectrometry (CV AFS). Optimisation steps included temperature of distillation unit, duration of distillation, purging with nitrogen (N2) and addition of reagents prior distillation. Due to the absence of Certified reference Materials (CRM), the accuracy of the results was compared with an independent separation technique based on solvent extraction. Optimal conditions were found and the Limit of Detection (LOD) achieved was 0.42 pg/L based on 50 mL of natural water sample taken for distillation. The method was used for the samples taken from the Mediterranean Sea, where values from 1.4 to 72.5 pg/L were determined.

Date du colloque: 07/2012; International audience