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Atmospheric mercury measurements carried out in the recent decades have been a subject of bias largely due to insufficient consideration of metrological traceability and associated measurement uncertainty, which are ultimately needed for the demonstration of comparability of the measurement results. This is particularly challenging for gaseous HgII species, which are reactive and their ambient concentrations are very low, causing difficulties in proper sampling and calibration. Calibration for atmospheric HgII exists, but barriers to reliable calibration are most evident at ambient HgII concentration levels. We present a calibration of HgII species based on nonthermal plasma oxidation of Hg0 to HgII. Hg0 was produced by quantitative reduction of HgII in aqueous solution by SnCl2 and aeration. The generated Hg0 in a stream of He and traces of reaction gas (O2, Cl2, or Br2) was then oxidized to different HgII species by nonthermal plasma. A highly sensitive 197Hg radiotracer was used to evaluate the oxidation efficiency. Nonthermal plasma oxidation efficiencies with corresponding expanded standard uncertainty values were 100.5 ± 4.7% (k = 2) for 100 pg of HgO, 96.8 ± 7.3% (k = 2) for 250 pg of HgCl2, and 77.3 ± 9.4% (k = 2) for 250 pg of HgBr2. The presence of HgO, HgCl2, and HgBr2 was confirmed by temperature-programmed desorption quadrupole mass spectrometry (TPD-QMS). This work demonstrates the potential for nonthermal plasma oxidation to generate reliable and repeatable amounts of HgII compounds for routine calibration of ambient air measurement instrumentation.

Natural microbial processes in seawater and sediments can convert inorganic mercury into its toxic form, methylmercury (MeHg). Our research tries to identify relationship between mercury species and microbial abundance in seawater. We performed series of samplings during oceanographic cruises aboard the research vessel Bios Dva from March 2014 to December 2015 in the Central Adriatic Sea. Research was constrained in transect from the Bay of Kastela to the island of Vis. We collected non-filtered water samples for determination of total mercury (THg), dissolved gaseous mercury (DGM), methylmercury (MeHg) and microbial species in Adriatic coastal and open waters. Plankton samples for the determination of THg and MeHg were collected using vertical towing nets (53 and 200 μm). THg concentrations are the lowest in the pristine environment of the island of Vis (0.14-1.10 ng/L). The highest THg values (0.92-5.58 ng/L) are found in the Bay of Kastela which had been affected by previous contamination from chlor-alkali industrial waste waters. DGM always shows slightly higher values in contaminated areas (31.8-351 pg/L) than in the pristine environment (22.1-245 pg/L). MeHg concentrations vary, but range from 1.07-34.3 pg/L for all stations, with the highest values found in the Bay of Kastela. Percentage of THg present as MeHg is low (1.2% and 3.1% in coastal and open sea, respectively) indicating deficiency of conditions for mercury methylation or high MeHg demethylation. MeHg concentration in seawater is correlated with abundance of picoeukaryotes, indicating possible microbial methylation in the water column. Number of picoeukaryotes is the highest in the Bay of Kastela (0.44-31.8 millions/L) which has been affected by industrial effluents from surrounding cities. The lowest number (0.63-19.9 millions/L) is found near the island of Vis. The highest THg concentrations in plankton are found in the Bay of Kastela (49.8-1115 ng/g and 103-249 ng/g d.w. for 53 and 200 μm fraction, respectively), while the lowest values are found at the Split Channel station (39.5-96.5 ng/g and 5.27-96.8 ng/g d.w. for 53 and 200 μm fraction, respectively). MeHg concentrations are more variable (0.29-14.2 ng/g and 2.00-24.3 ng/g d.w. for 53 and 200 μm fraction, respectively). THg concentrations in plankton show biodilution effect which is best seen in the Bay of Kastela. On the contrary, MeHg bioaccumulation along trophic levels is observed through higher MeHg concentrations and MeHg percentage in 200 μm fraction, compared to 53 μm fraction.

This review focuses on mercury speciation in the Adriatic Sea, a marginal sea of the Mediterranean, which represents its distinct biogeochemical subunit due to anthropogenic mercury loadings. The current knowledge about mercury cycling in the Adriatic is presented through an overview of the state of the art of research in this area: temporal and spatial distributions and occurrence of mercury species in seawater and sediment, and chemical transformations. We summarised research results of mercury speciation in order to describe its presence and fate in the Adriatic Sea. The Adriatic Sea represents a net source of mercury to the Mediterranean Sea due to the highest total mercury concentrations observed in the North Adriatic Sea and the highest methylmercury concentrations in the South Adriatic Pit. However, the biogeochemical cycle of mercury is not completely known and our understanding of mercury transport between compartments and its (bio)transformations is limited. Future research needs to focus on microbial and chemical processes of mercury transformations to improve our understanding of the impacts of mercury contamination on the environment and human health in the Adriatic Sea., Ovaj pregledni članak usredotočuje se na specijaciju žive u Jadranskom moru, rubnom moru Mediterana, koje predstavlja njegovu posebnu biogeokemijsku podjedinicu zbog antropoloških izvora žive. Trenutno znanje o kruženju žive u Jadranu je predstavljeno kroz pregled vrhunskih istraživanja na ovom području o vremenskim i prostornim raspodjelama i pojavnostima živinih specija u vodi i sedimentu te kemijskim transformacijama. Sumirani su rezultati istraživanja o specijaciji žive kako bi se opisala njena prisutnost i sudbina u Jadranskom moru. Jadransko more predstavlja neto izvor žive u Sredozemlju zbog najviših koncentracija ukupne žive uočenih u sjevernom Jadranu te najviših koncentracija metilžive u južnojadranskom ponoru. Međutim, biogeokemijski ciklus žive nije u potpunosti poznat te je ograničeno naše razumijevanje živinog transporta između odjeljaka i njenih (bio)transformacija. Buduće istraživanje se treba usredotočiti na mikrobne i kemijske procese živinih transformacija kako bi se bolje razumio utjecaj kontaminacije živom na okoliš i zdravlje ljudi u Jadranskom moru.

This article presents an overview of available research on mercury speciation in the most studied biota of the Adriatic Sea as a specific biogeochemical subunit of the Mediterranean. We present current knowledge about mercury concentration, speciation, spatial distribution and temporal changes in plankton, bivalves and fish from the Adriatic Sea. Results from mercury speciation studies in marine organisms are used to describe the extent of mercury bioaccumulation in the Adriatic Sea. Mercury biogeochemical cycle in the Adriatic is characterised by increased mercury concentrations from the water column, through plankton, bivalves and smaller fish to predator fish species. Although the Adriatic Sea has the highest mercury concentration in the whole Mediterranean Sea, fish species at the higher trophic levels have similar mercury concentrations everywhere in the Mediterranean, indicating incomplete understanding of the transfer mechanisms of mercury from seawater to upper trophic levels. As consumption of (contaminated) food is the main route of human exposure to mercury, it is of great importance to understand the influence of mercury contamination in the Adriatic Sea., Ovaj članak predstavlja pregled dostupnih istraživanja o specijaciji žive u najproučavanijoj bioti Jadranskog mora kao posebne biogeokemijske podjedinice Mediterana. Predstavljamo postojeće znanje o koncentraciji žive, specijaciji, prostornoj raspodjeli i vremenskim promjenama u planktonu, školjkašima i ribi Jadranskog mora. Rezultati studija o specijaciji žive u morskim organizmima su korišteni za opis razdiobe bioakumulacije žive u Jadranskom moru. Biogeokemijski ciklus žive u Jadranu karakterizira povećanje koncentracije žive od vodenog stupca, preko planktona, školjkaša i manjih riba do predatorskih ribljih vrsta. Iako Jadransko more sadrži najviše koncentracije žive u cijelom Mediteranu, riblje vrste na višim trofičkim razinama imaju slične koncentracije žive posvuda u Mediteranu, ukazujući na nepotpuno razumijevanje prijenosnih mehanizama žive iz morske vode na više trofičke razine. Budući da je konzumiranje (kontaminirane) hrane glavni put ljudske izloženosti živi, od iznimne je važnosti razumijevanje utjecaja kontaminacije živom u Jadranskom moru.

Mercury (Hg) natural biogeochemical cycle is complex and a significant portion of biological and chemical transformation occurs in the marine environment. To better understand the presence and abundance of Hg species in the remote ocean regions, waters of South Atlantic Ocean along 40°S parallel were investigated during UK-GEOTRACES cruise GA10. Total mercury (THg), methylated mercury (MeHg), and dissolved gaseous mercury (DGM) concentrations were determined. The concentrations were very low in the range of pg/L (femtomolar). All Hg species had higher concentration in western than in eastern basin. THg did not appear to be a useful geotracer. Elevated methylated Hg species were commonly associated with low-oxygen water masses and occasionally with peaks of chlorophyll a, both involved with carbon (re)cycling. The overall highest MeHg concentrations were observed in themixed layer (500m) and in the vicinity of the Gough Island. Conversely, DGM concentrations showed distinct layering and differed between thewater masses in a nutrient-like manner. DGM was lowest at surface, indicating degassing to the atmosphere, and was highest in the Upper Circumpolar Deep Water, where the oxygen concentration was lowest. DGM increased also in Antarctic Bottom Water. At one station, dimethylmercury was determined and showed increase in region with lowest oxygen saturation. Altogether, our data indicate that the South Atlantic Ocean could be a source of Hg to the atmosphere and that its biogeochemical transformations depend primarily upon carbon cycling and are thereby additionally prone to global ocean change.