Mercury (Hg) is one of the primary health concerns in natural and urbanised environments due to past and present natural and anthropogenic emissions. Its environmental cycle is driven by redox ...reactions, microbial metabolism and organic matter (OM) interactions, which may all lead to formation of bioaccumulative organic Hg species; methylmercury (MeHg), with damaging consequences for human and ecosystem health. Hence, Hg lability and bioavailability has been the focus of many investigations and assessed with a variety of chemical proxies in order to improve understanding of the conditions that lead to enhanced bioavailability of Hg and its species. We investigated Hg labile species with Diffusive Gradient in Thin-film technique (DGT) in the water column and sediment of Zenne River (Brussels, Belgium) and Gulf of Trieste (North Adriatic). They represent two contemporary important Hg-impacted areas; the former by anthropogenic urban pollution, and the latter by historic pollution from Hg mining. Hg speciation of labile inorganic and methylmercury in these two environments was not yet investigated using DGT technique. The results show labile Hg species changing with season in the water column of Zenne River, while the sediments are the source of bioavailable MeHg to the water column that is transported further creating a halo effect in the region. Values of labile Hg species for water column and sediments in Gulf of Trieste differ from previous research, highlighting the need for more investigation into Hg bioavailability. MeHg/THg ratios were compared to other sampling methods for labile Hg species.
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•Labile Hg species were measured using a Diffusive Gradient in Thin-film technique.•DGTs were used in the Zenne River Brussels and Gulf of Trieste (North Adriatic).•Winter-time THg in Zenne is highly labile and mobilized far from its source.•MeHg/THg% in Gulf showed higher labile Hg bioavailability than previously thought.•Labile MeHg in the sediment of the Gulf represents up to 75% of total labile Hg.
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 study, seasonal changes of mercury (Hg) species in the highly variable estuary of Soča/Isonzo River (northern Adriatic Sea) were investigated. Samplings were performed on a seasonal basis ...(September 2009, May, August and October 2010) and Hg species (total Hg, methylmercury (MeHg), dissolved gaseous Hg (DGM)) in waters, sediments and pore waters were determined. In addition, a range of ancillary parameters were measured (salinity, nutrients, organic carbon (OC), nitrogen species). Hg values were interpreted using these parameters and hydrological conditions (river flow, wave height) around the time of sampling. There were no significant changes in Hg load from river to the gulf, compared to previous studies. The load was temporarily higher in May 2010 due to higher river flow. Wave height, through changing hydrostatic pressure, was most likely to cause resuspension of already deposited Hg from the bottom (August 2010). The estuary is a net source of DGM to the atmosphere as suggested by DGM profiles, with salinity, redox potential and organic matter as the most probable controls over its production. MeHg is produced in situ in sediment or in water column, rather than transported by river, as indicated by its correlation with OC of the marine origin. Calculated fluxes for THg and MeHg showed sediment as a source for both the water column. In pore waters, OC in part affects partitioning of both THg and MeHg; however other factors (e.g. sulphide and/or oxyhydroxides precipitation and dissolution) are also probably important.
► Water, sediment and pore water mercury species in front of Soča River estuary were measured. ► Seasonally variable hydrological conditions were shown to influence water column Hg speciation. ► Fluxes for total Hg and MeHg from sediment to water were calculated. ► Sediment is a source of total Hg and MeHg to the water column. ► Correlation of MeHg with organic carbon of marine origin suggests in situ formation.
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 mechanisms of mercury (Hg) microbial transformations in coastal marine water column are poorly understood. In an effort to study seasonal Hg transformation mechanisms and underlying processes in ...the coastal marine ecosystem of the Gulf of Trieste (northern Adriatic Sea), we have successfully applied the 197Hg radiotracer technique in series of incubation experiments. This area is characterized by continuous Hg input from the Soča/Isonzo River as a consequence of nearly 500years of activity at the Idrija Mine (W Slovenia). The method proved to be valuable, since it allowed us to follow Hg transformations at concentrations similar to those found in the study site. During our study, Hg methylation in the marine water column could not be detected, suggesting that sediments are the principal methylation site and the source of MeHg to the water column. Conversely, the water column showed a pronounced Hg reduction potential, mostly of photochemical origin, suggesting that the Gulf of Trieste is a source of Hg0 to the atmosphere. However, the high Hg reduction potential observed in autumn was most likely related to a phytoplankton (diatom) autumn bloom, indicated by high Chl a concentrations measured during that period. We hypothesize that the microbial reduction was either linked to the expression of mer genes or, a consequence of non-specific redox reactions. Variations in bacterioplankton community fingerprints (as determined by Denaturing Gradient Gel Electrophoresis) suggested that community structure had little influence on microbial Hg reduction potential. Nevertheless, our results indicate that in the absence of photochemistry, interactions between microbes and organic matter may enhance biogeochemical Hg2+ reduction potential in some coastal marine environments.
•Water column in Gulf of Trieste has great potential for Hg2+ reduction.•Reduction potential depends on physico-chemical and biological process, including interaction with DOM.•Radiotracer methodology is sensitive to follow Hg reduction at environmental concentrations.
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 the mixed layer (500 m) and in the vicinity of the Gough Island. Conversely, DGM concentrations showed distinct layering and differed between the water 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.
Key Points
Hg speciation was determined along the 40°S parallel
Hg(0) concentration differed in water masses and evaded from surface to atmosphere
Organomercury compounds were associated with regions of lower oxygen or chlorophyll a peak
Mercury (Hg) in seawater is subject to interconversions via (photo)chemical and (micro)biological processes that determine the extent of dissolved gaseous mercury (DGM) (re)emission and the ...production of monomethylmercury. We investigated Hg speciation in the South Atlantic Ocean on a GEOTRACES cruise along a 40°S section between December 2011 and January 2012 (354 samples collected at 24 stations from surface to 5250 m maximum depth). Using statistical analysis, concentrations of methylated mercury (MeHg, geometric mean 35.4 fmol L−1) were related to seawater temperature, salinity, and fluorescence. DGM concentrations (geometric mean 0.17 pmol L−1) were related to water column depth, concentrations of macronutrients and dissolved inorganic carbon (DIC). The first-ever observed linear correlation between DGM and DIC obtained from high-resolution data indicates possible DGM production by organic matter remineralization via biological or dark abiotic reactions. DGM concentrations projected from literature DIC data using the newly discovered DGM–DIC relationship agreed with published DGM observations.
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•Dissolved gaseous mercury can be calculated from modeled dissolved inorganic carbon.•Modeled dissolved gaseous mercury agrees well with worldwide observations.•Dissolved gaseous mercury is related to depth and macronutrients concentrations.
The Gulf of Trieste (northern Adriatic Sea) is considered as an important "natural bioreactor" that can be stimulated to increase sedimentary methylmercury (MeHg) production by mobilizing its ...extensive mercury (Hg) pool. Sediment samples, collected in the southern pristine, less contaminated, part of the gulf, were amended with radioactive
197
Hg in incubation experiments to determine the seasonal variation of Hg methylation potential at two depth layers (surface 0-2 cm and subsurface 2-4 cm). In parallel, Hg and MeHg were determined in the sediment solid phase and pore water. Total Hg and MeHg in the sediment solid phase ranged between 151 and 223 ng g
−1
and between 0.17 and 0.68 ng g
−1
, and in pore water between 3.1 and 25.6 ng L
−1
and between 0.03 and 6.16 ng L
−1
. Distribution coefficients (K
d
) suggested that Hg species are strongly bound to the sediment (log K
d
3.86-4.87 and 1.67-3.39 for Hg and MeHg, respectively). Hg methylation potentials showed that MeHg is continuously produced, albeit not at a constant rate. The methylation potential in the sediment surface layer was higher and more variable in autumn, in parallel to higher bottom water temperature and O
2
content and sediment sulfate reduction, than in late spring and summer except in July in the presence of higher labile sedimentary organic matter (OM) level. Surface sediment showed rapid methylation of added traced Hg (0-0.66% day
−1
Hg methylated). However, a significant fraction of the radiolabeled Hg remained available. In the subsurface sediment, methylation was lower (0-0.22% day
−1
Hg methylated). Hg methylation potentials suggest that MeHg is continuously produced, albeit not at a constant rate, in the studied sediment of the Gulf of Trieste.
A highly sensitive laboratory methodology for simultaneous determination of methylation and reduction of spiked inorganic mercury (Hg
2+) in marine water labelled with high specific activity ...radiotracer (
197Hg prepared from enriched
196Hg stable isotope) was developed. A conventional extraction protocol for methylmercury (CH
3Hg
+) was modified in order to significantly reduce the partitioning of interfering labelled Hg
2+ into the final extract, thus allowing the detection of as little as 0.1% of the Hg
2+ spike transformed to labelled CH
3Hg
+. The efficiency of the modified CH
3Hg
+ extraction procedure was assessed by radiolabelled CH
3Hg
+ spikes corresponding to concentrations of methylmercury between 0.05 and 4
ng
L
−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 Hg
2+ 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 (1–10
ng
L
−1).
► Inorganic mercury methylation and reduction in marine water were studied. ► High specific activity
197Hg was used to label Hg
2+ spikes at natural levels. ► Methylmercury extraction had 73% efficiency for 0.05–4
ng
L
−1 levels. ► High sensibility to assess methylation potentials, below 0.1% of the spike. ► High sensibility also for reduction potentials, as low as 0.001% of the spike.
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