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A series of relatively simple incubation experiments to assess and evaluate microbial mercury (Hg) transformations in water column and sediments were performed monthly or bimonthly in a period from March 2011 to December 2011. Sampling campaigns were performed at station F in the southeastern part of Gulf of Trieste, northern Adriatic Sea. Gulf of Trieste has been for the last 500 year continuously impacted with inflow of Hg, originating from the Idrija Hg mine. The microbial mercury transformations were assessed using a short-lived (t1/2=64.12 h) radioisotope 197Hg. Calculated activities of microbial Hg reduction and methylation were correlated with other environmental factors, such as temperature, nutrient availability, oxygenation, organic matter, substrate (Hg in bioavailable chemical form) availability, structure of microbial community and presence of mer operon. Preliminary results show that in water column a substantial Hg reduction occurs, whereas methylation was not observed. On the other hand, long-term incubation experiments with sediments show that methylation process is active however preliminary results also suggest a significant MeHg degradation.

The determination of low concentration of iron in natural waters can be difficult due to the complexity of natural water, but primarily because it requires preconcentration of the sample with solvent extraction. In this work we report on results of thermal lens spectrometry (TLS) coupled to flow injection analysis (FIA) as a highly sensitive FIA-TLS method of iron detection. The concentration of iron redox species was determined using 1,10-phenanthroline (PHN), that forms stable complexes with Fe(II) ions which are characterized by an absorption maximum at 508 nm. The TLS system using a 633 nm probe laser and 530 nm pump laser beam was exploited for on-line detection in flow injection analysis, where a PHN solution was used as the carrier solution for FIA. The concentration of the complexing agent affects the quality of the TLS signal, and the optimal concentration was found at 1 mM PHN. The achieved limits of detection (LODs) for Fe(II) and total iron were 33 nM for Fe(II) and 21 nM for total iron concentration. The method was further validated by determining the linear concentration range, specificity in terms of analytical yield and by determining concentration of iron in a water sample from a local water stream.

In this work we have developed a novel method for determination of iron redox species by the use of diffusive gradients in thin-film (DGT) technique coupled to photothermal beam deflection spectroscopy (BDS). The combination of both methods achieved low limit of detection (LOD) of 0.14 μM for Fe (II) ions. The total Fe concentration determined in the Vrtojbica river sediment (Slovenia, Rožna Dolina, 5000 Nova Gorica) was 49.3 µgL-1. The Fe (II) and Fe (III) concentration amounted to 12.8 µgL-1 and 39.9 µgL-1, respectively. Such an approach opens new opportunities for monitoring the content of iron species in natural waters and sediments and provides highly sensitive chemical analysis and an accurate qualitative and quantitative characteristic of the materials under study.

The variability in the stable isotope signature of carbon and nitrogen in particulate organic matter and dissolved species in the water column of the mesotrophic subalpine Lake Bled in NW Slovenia has been determined. After the algae bloom from August to December in 2008, samples were taken from the deepest part of the lake which develops an anoxic hypolimnion for most of the year. C/N molar ratios and δ13CPOC and δ15NPN values suggest an autochthonous source for particulate organic matter (POM). According to the isotope model, autochthonous carbon accounted for a major part of the particulate organic carbon (POC), ranging from 86% to 96% in September and October, while in December the proportion of allochthonous carbon was more pronounced, ranging from 57% to 59%. Low δ13CPOC and δ15NPN values (from −36 to −33‰ and from 0.8 to 1.8‰), observed below 24 m in August and September, indicate the bacterial origin of POM, mainly from methanotrophic bacteria. δ15NNO3 and δ15NPN values decreased with depth. The relations between δ15NPN and NO3- and NH4+ concentrations suggest that NH4+ is the main assimilation species for nitrogen in POM. Nitrification was active between 12 and 18 m deep in September and October, indicated by increased NO3- concentrations and decreased δ15NNO3 values. The correlation between nitrate concentrations and δ15NNO3 values suggests active water column denitrification in October 2008. The decrease in δ15NNO3 values observed in December could be explained by degradation of organic matter, followed by nitrification of the degradation products. During our sampling period, there was no evident influence of sewage, agriculture, or atmospheric deposition on the nitrogen balance in the lake.

Abstract: A highly sensitive laboratory methodology for simultaneous determination of methylation and reduction of spiked inorganic mercury (Hg2+) in marine water labelled with high specific activity radiotracer (197Hg prepared from enriched 196Hg stable isotope) was developed. A conventional extraction protocol for methylmercury (CH3Hg+) was modified in order to significantly reduce the partitioning of interfering labelled Hg2+ into the final extract, thus allowing the detection of as little as 0.1% of the Hg2+ spike transformed to labelled CH3Hg+. The efficiency of the modified CH3Hg+ extraction procedure was assessed by radiolabelled CH3Hg+ spikes corresponding to concentrations of methylmercury between 0.05 and 4ngL−1. The recoveries were 73.0±6.0% and 77.5±3.9% for marine and MilliQ water, respectively. The reduction potential was assessed by purging and trapping the radiolabelled elemental Hg in a permanganate solution. The method allows detection of the reduction of as little as 0.001% of labelled Hg2+ spiked to natural waters. To our knowledge, the optimised methodology is among the most sensitive available to study the Hg methylation and reduction potential, therefore allowing experiments to be done at spikes close to natural levels (1–10ngL−1). [Copyright &y& Elsevier]

The determination of low concentration of iron in natural waters can be difficult due to the complexity of natural water, but primarily because it requires preconcentration of the sample with solvent extraction. In this work we report on results of thermal lens spectrometry (TLS) coupled to flow injection analysis (FIA) as a highly sensitive FIA-TLS method of iron detection. The concentration of iron redox species was determined using 1,10-phenanthroline (PHN), that forms stable complexes with Fe(II) ions which are characterized by an absorption maximum at 508 nm. The TLS system using a 633 nm probe laser and 530 nm pump laser beam was exploited for on-line detection in flow injection analysis, where a PHN solution was used as the carrier solution for FIA. The concentration of the complexing agent affects the quality of the TLS signal, and the optimal concentration was found at 1 mM PHN. The achieved limits of detection (LODs) for Fe(II) and total iron were 33 nM for Fe(II) and 21 nM for total iron concentration. The method was further validated by determining the linear concentration range, specificity in terms of analytical yield and by determining concentration of iron in a water sample from a local water stream. [ABSTRACT FROM AUTHOR]