Development of electroanalytical methods for detection and characterization of metal sulfide and sulphur nanoparticles in aquatic environment

Fizikalno-kemijska svojstva nanočestica (NČ), prvenstveno visoka reaktivnost, utječe na biodostupnost i sudbinu NČ u vodenom okolišu. Ovaj rad opisuje primjenu elektroanalitičkih metoda u određivanju i karakterizaciji NČ. Kronoamperometrijskim (CA) i voltametrijskim mjerenjima su detektirane NČ metalnih sulfida (MeS) i elementarnog sumpora (So) u modelnim sustavima. Na osnovu primijenjenog potencijala živine elektrode (Hg) određena je vrsta NČ MeS. Naboj detektiranih šiljastih signala u CA ovisi o dijametru NČ, dok frekvencija udara ovisi o udjelu NČ s dijametrom manjim od 200 nm. S CA je praćen proces aglomeriranja u ovisnosti o primijenjenim eksperimentalnim uvjetima. Kako bi se potvrdila elektroanalitička mjerenja na Hg elektrodi, provedena su mjerenja pri istim eksperimentalnim uvjetima metodama koje se standardno koriste u karakterizaciji NČ (DLS, NTA, AFM i EC-STM). Razvijena CA metoda je primijenjena za detekciju NČ u prirodnim euksiničnim vodenim sustavima.Physico-chemical properties of nanoparticles (NPs), mainly high reactivity, affect their bioavailability and fate in aquatic environment. This work shows development of electroanalytical methods in detection and characterization of NPs. Chronoamperometry (CA) and voltammetry were used for detection of the metal sulphide (MeS) and sulphur (So) NPs in modal solutions. Based on the applied potential of the working mercury electrode (Hg) it is possible to differentiate between MeS NPs. The charge of recorded spike like signals is related to NPs size, while signal frequency depends on the presence of the NPs smaller than 200 nm. With use of CA agglomeration processes under different experimental conditions were monitored. In order to confirm electrochemical measurements in parallel intercomparison measurements with methods used in the characterization of NPs (STM, AFM, DLS, NTA) were done under same experimental conditions. CA was applied in detection of the NPs in natural aquatic euxinic systems

Electroanalytical methods in characterization of sulfur species in aqueous environment

Electroanalytical (voltammetric, polarographic, chronoamperometric) methods on an Hg electrode were applied for studying of different sulfur compounds in model and natural water systems (anoxic lakes, waste water, rain precipitation, sea-aerosols). In all investigated samples typical HgS reduction voltammetric peak, characteristic for many different reduced sulfur species (RSS: sulfide, elemental sulfur, polysulfide, labile metal sulfide and organosulfur species) was recorded at about -0.6 V vs. Ag/AgCl reference electrode. In addition, in anoxic waters which are enriched with sulfide and iron species, voltammetric peaks characteristic for the presence of free Fe(II) and FeS nanoparticles (NPs) were recorded at -1.4 V and around -0.45 V, respectively. Depending on the used electroanalytical method and experimental conditions (varying deposition potential, varying time of oxidative and/or reductive accumulation, sample pretreatment i.e. acidification followed by purging) it is possible to distinguish between different sulfur species. This work clearly shows a large potential of the electrochemistry as a powerful analytical technique for screening water quality regarding presence of different reduced sulfur species and their speciation between dissolved and colloidal/nanoparticle phases

Voltammetric Study of Organic Matter Components in the Upper Reach of the Krka River, Croatia

The increased amount of organic matter (OM) accompanied with the development of hypoxia/anoxia and appearance of the sulphur species are indicators of eutrophication in natural waters. To predict biogeochemical and ecological changes, specific OM components in the Lake Brljan (the karst Krka River, Croatia; station B and station B2 downstream) were studied during 2011 and in January 2012 using voltam¬metry. Surface‒active substances (eq. 0.018 to 0.150 mg dm–3 Triton‒X‒100) and Cu complexing capacity (54‒680 nmol dm–3) showed the highest values in surface water layer in May 2011 (B) and in November 2011 (B2), associated with the highest dissolved (0.505‒1.530 mg C dm–3) and particulate (0.051‒0.725 mg C dm–3) organic carbon and phytoplankton biomass. Autochthonously produced OM did not cause hypoxia/anoxia during the investigated period. Brljan\u27s lake water could be characterised as oligotrophic with occasionally elevated OM concentration depending on season and Krka River water regime. This work is licensed under a Creative Commons Attribution 4.0 International License

Zmajevo oko – a unique example of anchialine system on the Adriatic coast (Croatia) during spring-summer stratification and autumn mixing period

Zmajevo oko is a naturally eutrophicated saline lake situated on the Gradina Peninsula, close to the village of Rogoznica on the central Dalmatian coast. Since 1992 the Lake has been intensively studied and in 2011 hydrographic and water column stratification in relation with reduced sulfur species and microbial activity was investigated during two different seasons: the spring-summer stratification and autumn mixing period

Coupled Mo-U abundances and isotopes in a small marine euxinic basin: constraints on processes in euxinic basins

Sedimentary molybdenum (Mo) and uranium (U) abundances, as well as their isotope systematics, are used to reconstruct the evolution of the oxygenation state of the surface Earth from the geological record. Their utility in this endeavour must be underpinned by a thorough understanding of their behaviour in modern settings. In this study, Mo-U concentrations and their isotope compositions were measured in the water column, sinking particles, sediments and pore waters of the marine euxinic Lake Rogoznica (Adriatic Sea, Croatia) over a two year period, with the aim of shedding light on the specific processes that control Mo-U accumulation and isotope fractionations in anoxic sediment. Lake Rogoznica is a 15 m deep stratified sea-lake that is anoxic and euxinic at depth. The deep euxinic part of the lake generally shows Mo depletions consistent with near-quantitative Mo removal and uptake into sediments, with Mo isotope compositions close to the oceanic composition. The data also, however, show evidence for periodic additions of isotopically light Mo to the lake waters, possibly released from authigenic precipitates formed in the upper oxic layer and subsequently processed through the euxinic layer. The data also show evidence for a small isotopic offset (~0.3‰ on 98Mo/95Mo) between particulate and dissolved Mo, even at highest sulfide concentrations, suggesting minor Mo isotope fractionation during uptake into euxinic sediments. Uranium concentrations decrease towards the bottom of the lake, where it also becomes isotopically lighter. The U systematics in the lake show clear evidence for a dominant U removal mechanism via diffusion into, and precipitation in, euxinic sediments, though the diffusion profile is mixed away under conditions of increased density stratification between an upper oxic and lower anoxic layer. The U diffusion-driven precipitation is best described with an effective 238U/235U fractionation of +0.6‰, in line with other studied euxinic basins. Combining the Mo and U systematics in Lake Rogoznica and other euxinic basins, it is apparent that the two different uptake mechanisms of U and Mo can lead to spatially and temporally variable Mo/U and Mo-U isotope systematics that depend on the rate of water renewal versus removal to sediment, the sulfide concentration, and the geometry of the basin. This study further emphasises the potential of combining multiple observations, from Mo-U enrichment and isotope systematics, for disentangling the various processes via which redox conditions control the chemistry of modern and ancient sediments

REPRODUCTION CYCLE OF THE Chlamys varia L. AND LARVAE MONITORING OF THE Pectinidae IN PLANKTON OF THE MOUTH OF THE RIVER KRKA

Razvoj akvakulturne djelatnosti i bogata populacija male kapice (Chlamys varia L. Š Pectinidae) u ušću rijeke Krke potaknuli su provedena istraživanja indeksa kondicije te pojave i raspodjele ličinaka u planktonu ušća kako bi se upoznao njezin reproduktivni ciklus i utvrdila mogućnost sakupljanja mlađa za potrebe kontrolirana uzgoja. Rezultati istraživanja (slike 1-4) pokazali su da je mriješćenje male kapice dualnoga tipa, s primarnim maksimumom u proljeće i sekundarnim u jesen. Najintenzivnija pojava ličinaka češljaša u planktonu zabilježena je pri temperaturi od 18 do 20 ºC i slanosti većoj od 30 x 10-3 . Optimalno vrijeme za sakupljanje mlađa male kapice u ušću rijeke Krke, za potrebe kontrolirana uzgoja, jest razdoblje od lipnja do rujna, a najpovoljnija dubina za postavljanje kolektora jest između 10 i 15 m.The development of aquaculture and the rich population of Chlamys varia L. Š Pectinidae in the mouth of the river Krka prompted investigations carried out on the condition indexes and the occurrence and distribution of larvae in the plankton of the rivers mouth, to find out more about its reproductive cycle and to determine the possibility to collect young for use in controlled culture. Results of the investigations showed that spawing of the Chlamys varia L. is of a dual type, with a primary maximum in spring and a secondary maximum in autumn. The most intensive occurrence of the larvae Pectinidae in plankton was recorded in temperatures of from 18 to 20 ºC and at a salinity of above 30 x 10-3. The optimal time for collecting young Chlamys varia L. in the mouth of the river Krka, for use in controlled culture, is the period between June and September, and the most satisfactory depth for placing the collectors is at a depth beetwen 10 and 15 m