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Surface techniques for rapid analysis of organic particles in the seawater

Surface techniques for rapid analysis of organic particles in the seawater Nadica Ivošević DeNardis1, Vesna Svetličić1, Suzana Šegota1, Galja Pletikapić1, and Zoran Kljajić2 1Ruđer Bošković Institute, Division for Marine and Environmental Research, Zagreb, Croatia 2 Institute of Marine Biology, Kotor, Montenegro 1ivosevic@irb.hr, svetlicic@irb.hr, ssegota@irb.hr, gpletik@irb.hr, 2biokotor@gmail.com detection, atomic force microscopy 1. Introduction Naturally occurring organic surface-active particles in seawater are mostly formed from excreted and decomposed products of phytoplankton. Beside of their role as food source, transport of gas, microconstituents and pollutants, they are also considered as precursor particles of giant gels occurring in the Nothern Adriatic know as mucilage phenomenon [1], [2]. Understanding dynamics of highly reactive organic particles in the seawater is facing difficulties with sampling, sample handling and insufficient sensitivity and selectivity of analytical methods [2]. The aim of this paper is to present the application of two complementary surface methods, electrochemical and atomic force microscopy, for characterization of marine organic micro- and nanoparticles based on two field-oriented studies undertaken in the northern Adriatic Sea and Boka Kotorska Bay (south Adriatic sea). 2. Methods Electrochemical method of amperometry at mercury electrode meets requirements for non-invasive, simple and rapid analysis of aquatic samples suitable for monitoring needs. The mercury electrode is immersed directly into fresh seawater sample. Electrochemical approach enables simultaneous and direct detection of different organic constituents in seawater based on their different electrochemical response at the interface. This method is applicable for detection of oil droplets, living cells, lipid vesicles, gel microparticles, while inorganic particles stay undetected in aqueous media [3], [4], [5], [6]. Electrochemical measurement takes about 2 minutes per sample to detect soft particles in the size range from 1-500 µm and concentration range 105- 108 particles/L. Atomic force microscopy has been recently introduced as a tool in marine ecology [7], [8], allowing direct visualization of biotic and abiotic particles in seawater at micro- and nanometer scale. The advantages over conventional light or electron microscopy include high resolution imaging under physiologically relevant conditions without the need for vacuum, complex sample preparation methods. Samples can be non- destructively imaged in air or in liquids. 3. Results The first field-oriented study is refereed to monitoring of microparticles distribution in the Northern Adriatic Sea in relation to mucilage formation (Figure 1). This study was carried out in the framework of the long term National Monitoring Programme (Systematic Study of the Adriatic Sea as a Base for Sustainable Development of the Republic of Croatia, 1998-2012). We recorded the pronounced spatial and temporal variability of organic microparticles, depending on the season, depth and trophic gradient. In the years without mucilage phenomenon microparticles concentration follows seasonal dynamics of organic matter and submicron particles correlated well to DOC values. However, before the onset of mucilage formation, it was found that microparticles accumulate at the halocline reaching one order of magnitude higher concentrations. . Fig. 1 Northern Adriatic gel aggregates: remote sensing by satellite showing gel phase in red colour and at 10 m depth captured by a scuba-diver (adopted from [8]) The second field study was undertaken due to the recent accidental sinking of the ship and spilling of diesel fuel in the bay of Boka Kotorska (Montenegro). The mechanical removal of the oil spill was performed at the polluted region of about 1000 m2 using the floating fence and oil spill adsorbent pads. We postulate the presence of remaining fuel in the form of dispersed droplets. Indeed, we have detected dispersed oil droplets in the whole water column one month after the event. The characterized oil droplets were in the size range from hundreds of micrometers down to tens of nanometers. Using light microscopy and DAPI staining revealed bacterial colonization of micrometer sized fuel droplets. The smaller oil droplets tend to accumulate at the halocline, while larger ones rise to the surface and undergo coalescence [6]. Revealed presence of dispersed diesel fuel poses a serious threat to plankton community dynamics and could enter the food web in this semiclosed bay. The persistence time of three years was required for recovery of phytoplankton variability and abundance after heavy fuel oil spill in the Marmara sea, Turkey [9]. Consequently, monitoring of dispersed fuel micro- and nanodroplets is recommended due to the intensive boat trafficking and shipyard activity in the Boka Kotorska bay. This study was carried out in the framework of the Croatia-Montenegro bilateral project (Impact assessment and determination of organic pollutants in the waters) and partially through international project of TEN ECOPORT. 3. Conclusions The combination of complementary surface methods (electrochemical and atomic force microscopy) allowed to extend the characterization of organic constituents down to nanometric scale providing important insight into their fate in aquatic systems. The possible applications of these methods are towards: prediction of mucilage events and monitoring of organic pollution arising from boat trafficking and anchoring, shipyard activity, fish farming and oil spill accidents. References [1] Giani M, Degobbis D, Rinaldi A (2005) Mucilages in the Adriatic and Tyrrhenian seas. Sci Total Environ 353:1-380 [2] Žutić V, Svetličić V (2000) Interfacial Processes. In: Wangersky P (ed.) The Handbook of Environmental Chemistry. Marine Chemistry, vol 5. Part D, Springer-Verlag, Berlin-Heidelberg, pp 150–165 [3] Baldi F, Ivošević N, Minacci A, Pepi M, Fani R, Svetličić V, Žutić V (1999) Adhesion of Acinetobacter venetianus to diesel fuel droplets studied by in situ electrochemical and molecular probes. Appl Environ Microbiol 65:2041-2048 [4] Žutić V, Svetličić V, Ivošević N, Hozić A, Pečar O (2004) Northern Adriatic mesocosm experiment Rovinj 2003: Dynamics of organic microparticles studied by the electrochemical technique. Period Biolog 106:67-74, references therein [5] Ivošević DeNardis N, Šegota S, Svetličić V, Castelli A, Kljajić Z (2013) Characterization of marine organic matter in the bay of the Boka Kotorska by electrochemical and atomic force microscopy imaging. Studia Marina 26:5-22 [6] Ivošević DeNardis N, Šegota S, Svetličić V, Pletikapić G, Kljajić Z (2014) Presence of dispersed diesel fuel in water column in the Boka Kotorska bay: A case study (submitted) [7] Mišić Radić T, Svetličić V, Žutić V, Boulgaropoulos B (2011) Seawater at the nanoscale: marine gels imaged by atomic force microscopy. J Mol Recognit 243:397-405 [8] Svetličić V, Žutić V, Pletikapić G, Mišić Radić T (2013) Marine polysaccharide networks and diatoms at the nanometric scale. Int J Mol Sci 14:20064-20078. [9] Tas S, Erdogan O (2007) Effects of oil pollution on the phytoplankton community in the kucukcekmece bay (northt-east sea of Marmara, Turkey). Rapp Comm Int Mer Medit 38:320-320

marine organic particles; fuel oil droplets; monitoring study; electrochemical particle detection; atomic force microscopy

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