Mercury speciation and mercury stable isotope composition in sediments from the Canadian Arctic Archipelago.

Total mercury (THg) and monomethylmercury (MMHg) concentrations as well as mercury (Hg) isotope ratios were determined in sediment cores sampled from six locations from the Canadian Arctic Archipelago (CAA). At most sites, THg concentrations showed a decreasing trend with depth, ranging from 5 to 61 ng/g, implicating possible increased Hg deposition and/or riverine inputs in top sediment layers. MMHg values showed large oscillations within the top 10 cm of the cores. This variability decreased at the bottom of the cores with MMHg concentrations ranging from less than12 to up to 1073 pg/g. Average concentrations of THg and MMHg in the top 10 cm were linearly correlated, whereas no correlation was observed with organic matter (loss on ignition). Mercury isotope ratios showed negative values for both δ202Hg (-1.59 to -0.55‰) and Δ199Hg (-0.62 to -0.01‰). δ202Hg values became more negative with depth, while the opposite was observed for Δ199Hg. The former is consistent with predicted historical atmospheric Hg trends as a result of increased coal burning worldwide. Hg isotope ratio measurements in CAA sediments offer additional opportunities to trace Hg processes and sources in the Arctic.

Mercury mobility and effects in the salt-marsh plant Halimione portulacoides: Uptake, transport, and toxicity and tolerance mechanisms.

The plant Halimione portulacoides, an abundant species widely distributed in temperate salt-marshes, has been previously assessed as bioindicator and biomonitor of mercury contamination in these ecosystems. The present study aims to assess uptake and distribution of total mercury (THg) and methylmercury (MMHg) within H. portulacoides, potential mercury release by volatilization through leaves, and toxicity and tolerance mechanisms by investigating plant photochemical responses. Stem cuttings of H. portulacoides were collected from a salt-marsh within the Tagus estuary natural protected area, and grown under hydroponic conditions. After root development, plants were exposed to 199HgCl2 and CH3201HgCl, and sampled at specific times (0, 1, 2, 4, 24, 72, 120, 168 (7 days) and 432 h (18 days)). After exposure, roots, stems and leaves were analysed for total 199Hg (T199Hg) and MM201Hg content. Photobiology parameters, namely efficiency and photoprotection capacity, were measured in leaves. Both THg and MMHg were incorporated into the plant root system, stems and leaves, with roots showing much higher levels of both isotope enriched spikes than the other plant tissues. Presence of both mercury isotopes in the stems and leaves and high significant correlations found between roots and stems, and stems and leaves, for both THg and MMHg concentrations, indicate Hg translocation between the roots and above-ground organs. Long-term uptake in stems and leaves, leading to higher Hg content, was more influenced by temperature and radiation than short-term uptake. However, the relatively low levels of both THg and MMHg in the aerial parts of the plant, which were influenced by temperature and radiation, support the possibility of mercury release by stems and leaves, probably via stomata aperture, as a way to eliminate toxic mercury. Regarding photochemical responses, few differences between control and exposed plants were observed, indicating high tolerance of this salt marsh plant to THg and MMHg.

Evaluation of mercury methylation and methylmercury demethylation rates in vegetated and non-vegetated saltmarsh sediments from two Portuguese estuaries.

Neurotoxic methylmercury (MMHg) is formed from inorganic divalent mercury (Hg2+). However, it is poorly understood to what extent different mercury (Hg) pools contribute to existent MMHg levels. In this study, ambient concentrations of total Hg (THg) and MMHg as well as rates of methylation and demethylation were measured simultaneously in sediments with and without salt-marsh plant vegetation, which were collected in Guadiana and Tagus estuaries, Portugal. Concurrent processes of Hg methylation and MMHg demethylation were directly monitored and compared by spiking sediments cores with stable isotope tracers of 199Hg2+ and CH3201Hg+ followed by gas chromatographic separation and isotope-specific detection using inductively coupled plasma mass spectrometry. Compared to the Guadiana estuary, where concentrations were comparatively low, THg and MMHg levels varied between vegetated and non-vegetated sediments collected at the Rosário site (ROS) of the Tagus estuary. Methylation (KM) and demethylation rates (KD) were also different between estuaries being dependent on the presence of vegetation. In addition, the type of macrophyte species influenced KM and KD values. In fact, the highest KM value was found in Sarcocornia fruticosa vegetated sediments at the Castro Marim site in Guadiana (CM, 0.160 day-1) and the lowest KM was observed in non-vegetated sediments at the Alcochete site in Tagus (ALC, 0.009 day-1). KD varied by a factor of three among sites with highest rates of demethylation observed in non-vegetated sediments in Guadiana (12 ± 1.3 day-1, corresponding to a half-life of 1.4 ± 0.2 h). This study clearly shows that the presence of vegetation in sediments favors the formation of MMHg. Moreover, this effect might be site specific and further studies are needed to confirm the findings reported here.

Concentrations and isotope ratios of mercury in sediments from shelf and continental slope at Campos Basin near Rio de Janeiro, Brazil.

Mercury (Hg) may originate from both anthropogenic and natural sources. The measurement of spatial and temporal variations of Hg isotope ratios in sediments may enable source identification and tracking of environmental processes. In this study we establish the distribution of mercury concentrations and mercury isotope ratios in surface sediments of three transects along the continental shelf and slope in Campos Basin-RJ-Brazil. The shelf showed on average lower total Hg concentrations (9.2 ± 5.3 ng g-1) than the slope (24.6 ± 8.8 ng g-1). MMHg average concentrations of shelf 0.15 ± 0.12 ng g-1 and slope 0.13 ± 0.06 ng g-1 were not significantly different. Distinct differences in Hg isotope ratio signatures were observed, suggesting that the two regions were impacted by different sources of Hg. The shelf showed more negative δ202Hg and Δ199Hg values ranging from -0.59 to -2.19‰ and from -0.76 to 0.08‰, respectively. In contrast, the slope exhibited δ202Hg values from -0.29 to -1.82‰ and Δ199Hg values from -0.23 to 0.09‰. Mercury found on the shelf, especially along the "D" and "I" transects, is depleted in heavy isotopes resulting in more negative δ202Hg compared to the slope. Isotope ratios observed in the "D" and "I" shelf region are similar to Hg ratios commonly associated with plants and vegetation and very comparable to those detected in the estuary and adjoining mangrove forest, which suggests that Hg exported from rivers may be the dominating source of Hg in near coastal regions along the northern part of the shelf.

Two Centuries of Coral Skeletons from the Northern South China Sea Record Mercury Emissions from Modern Chinese Wars.

The contemporary mercury (Hg) cycle in the world's oceans has been greatly affected by human activities. However, we are still lacking reliable, long-term, and continuous records of Hg in seawater. Here, we report for the first time on using annually banded Porites coral skeletons from the northern South China Sea (SCS) as an archive for recording changes of seawater dissolved Hg spanning the past two centuries. We developed a combustion-trapping method to preconcentrate ultratrace Hg concentrations from coral aragonitic skeletons for highly accurate total Hg measurements. Results show that Hg in the coral skeletons ranges from 0.3 to 5.1 pmol/g and is discriminated against Ca during coral skeletal calcification. Preindustrial (1798-1832) Hg levels in coral skeletons were found to be approximately 0.5 pmol/g. The highest Hg concentrations (3-5 pmol/g) were observed during the WWII period (1933-1942). Other distinct Hg maxima (∼3 pmol/g) are observed for the periods 1833-1847, 1858-1862, 1918-1927, 1978-1982, and 1988-1992, with the first four coinciding with contemporary Chinese wars. Our study suggests that the production and use of ammunitions in those wars likely account for the primary Hg emission sources in the northern SCS before 1950, and coral is potentially a robust indicator of historical, regional Hg contamination events.

Development of pre-concentration procedure for the determination of Hg isotope ratios in seawater samples.

Hg concentrations in seawater are usually too low to allow direct (without pre-concentration and removal of salt matrix) measurement of its isotope ratios with multicollector-inductively coupled plasma mass spectrometry (MC-ICP-MS). Therefore, a new method for the pre-concentration of Hg from large volumes of seawater was developed. The final method allows for relatively fast (about 2.5Lh(-1)) and quantitative pre-concentration of Hg from seawater samples with an average Hg recovery of 98±6%. Using this newly developed method we determined Hg isotope ratios in seawater. Reference seawater samples were compared to samples potentially impacted by anthropogenic activity. The results show negative mass dependent fractionation relative to the NIST 3133 Hg standard with δ(202)Hg values in the range from -0.50‰ to -1.50‰. In addition, positive mass independent fractionation of (200)Hg was observed for samples from reference sites, while impacted sites did not show significant Δ(200)Hg values. Although the influence of the impacted sediments is limited to the seawater and particulate matter in very close proximity to the sediment, this observation may raise the possibility of using Δ(200)Hg to distinguish between samples from impacted and reference sites.

Novel silica sol-gel passive sampler for mercury monitoring in aqueous systems.

A novel passive sampler for mercury monitoring was prepared using organosilica sol-gel materials. It comprises a binding layer with thiol groups for mercury complexation and a porous diffusive layer through which mercury can diffuse and arrive at the binding layer. Our study demonstrated that this new sampler follows the principle of passive sampling. The mass of mercury accumulated in the binding layer depends linearly on the mercury concentration in solution, the sampling rate and the exposure time. A typical sol-gel sampler is characterized by a diffusive layer of 1.2 µm, in which mercury ions diffuse with a coefficient of D=0.09×10(-6) cm(2) s(-1), resulting in an uptake R(s) of 8.8 mL h(-1). The capacity for mercury uptake is approximately 0.64 µg cm(-2). Mercury diffusion and binding in the passive sampler are independent of the type of mercury-chloride complex, which potentially opens the door to use this device for mercury monitoring in a wide range of natural waters.

A novel approach for determining total titanium from titanium dioxide nanoparticles suspended in water and biosolids by digestion with ammonium persulfate.

Titanium dioxide (i.e. TiO(2)) in nano-form is a constituent of many nanomaterials that are used in sunscreens, cosmetics, industrial products and in biomedical applications. Quantification of TiO(2) nanoparticles in various matrixes is a topic of great interest for researchers studying the potential health and environmental impacts of nanoparticles. However, analysis of TiO(2) as Ti(4+) is difficult because current digestion techniques require use of strong acids that may be a health and safety risk in the laboratory. To overcome this problem, we developed a new method to digest TiO(2) nanoparticles using ammonium persulfate as a fusing reagent. The digestion technique requires short times to completion and optimally requires only 1 g of fusing reagent. The fusion method showed >95% recovery of Ti(4+) from 6 µg mL(-1) aqueous suspensions prepared from 10 µg mL(-1) suspension of different forms of TiO(2,) including anatase, rutile and mixed nanosized crystals, and amorphous particles. These recoveries were greater than open hot-plate digestion with a tri-acid solution and comparable to microwave digestion with a tri-acid solution. Cations and anions commonly found in natural waters showed no significant interferences when added to samples in amounts of 10 ng to 110 mg, which is a much broader range of these ions than expected in environmental samples. Using ICP-MS for analysis, the method detection limit (MDL) was determined to be 0.06 ng mL(-1), and the limit of quantification (LOQ) was 0.20 ng mL(-1). Analysis of samples of untreated and treated wastewater and biosolids collected from wastewater treatment plants yielded concentrations of TiO(2) of 1.8 and 1.6 ng mL(-1) for the wastewater samples, respectively, and 317.4 ng mg(-1) dry weights for the biosolids. The reactions between persulfate ions and TiO(2) were evaluated using stoichiometric methods and FTIR and XRD analysis. A formula for the fusing reaction is proposed that involves the formation of sulfate radicals.

Predicting net mercury methylation in sediments using diffusive gradient in thin films measurements.

Diffusive gradient in thin film (DGT) sediment probes for methylmercury (MMHg) were successfully deployed for up to 30 h in three mudflat sediments in San Francisco Bay for measuring labile fractions of dissolved MMHg in pore water. Our calculations show that the local DGT-induced depletion of MMHg in sediment pore waters should be fully compensated by the natural in situ MMHg production and its subsequent remobilization from the solid phase. DGT results were interpreted in terms of labile pore water concentration and provide MMHg concentration depth profiles with a centimeter resolution. Average concentrations of DGT-labile MMHg were 2.10 ± 0.29 and 1.64 ± 0.30 ng L(-1) at China Camp and Hamilton Army Airfield sediment pore waters, respectively, while the riverine location at Petaluma showed a distinct peak of 7.1 ng L(-1) near the sediment surface. Using isotope-enriched mercury species, high resolution depth profiles of MMHg net production rates ranging from 0.2 to 9.8 ng g(-1) d(-1) were obtained in parallel sediment cores sampled closely to DGT deployment sites. A positive, linear relationship between MMHg net production rates and labile MMHg concentrations acquired through DGT measurements was found and explained 79% of the variability in the data set. The latter illustrates that mercury methylation, a biogeochemical process, strongly affected the quantity of MMHg accumulated by the DGT device in the sediment and suggests that DGT measurements have the potential to predict net methylation rates.

Methylated mercury species in Canadian high Arctic marine surface waters and snowpacks.

We sampled seawater and snowpacks in the Canadian high Arctic for methylated species of mercury (Hg). We discovered that, although seawater sampled under the sea ice had very low concentrations of total Hg (THg, all forms of Hg in a sample; on average 0.14-0.24 ng L(-1)), 30-45% of the THg was in the monomethyl Hg (MMHg) form (on average 0.057-0.095 ng L(-1)), making seawater itself a direct source of MMHg for biomagnification through marine food webs. Seawater under the ice also contained high concentrations of gaseous elemental Hg (GEM; 129 +/- 36 pg L(-1)), suggesting that open water regions such as polynyas and ice leads were a net source of approximately 130 +/- 30 ng Hg m(-2) day(-1) to the atmosphere. We also found 11.1 +/- 4.1 pg L(-1) of dimethyl Hg (DMHg) in seawater and calculated that there could be a significant flux of DMHg to the atmosphere from open water regions. This flux could then resultin MMHg deposition into nearby snowpacks via oxidation of DMHg to MMHg in the atmosphere. In fact, we found high concentrations of MMHg in a few snowpacks near regions of open water. Interestingly, we discovered a significant log-log relationship between Cl- concentrations in snowpacks and concentrations of THg. We hypothesize that as Cl- concentrations in snowpacks increase, inorganic Hg(II) occurs principally as less reducible chloro complexes and, hence, remains in an oxidized state. As a result, snowpacks that receive both marine aerosol deposition of Cl- and deposition of Hg(II) via springtime atmospheric Hg depletion events, for example, may contain significant loads of Hg(II). Overall, though, the median wet/dry loads of Hg in the snowpacks we sampled in the high Arctic (5.2 mg THg ha(-1) and 0.03 mg MMHg ha(-1)) were far below wet-only annual THg loadings throughout southern Canada and most of the U.S. (22-200 mg ha(-1)). Therefore, most Arctic snowpacks contribute

Speciation of arsenic in water, sediment, and plants of the Moira watershed, Canada, using HPLC coupled to high resolution ICP-MS.

High-performance liquid chromatography (HPLC) coupled with high-resolution sector field ICP-MS was applied to the speciation of arsenic in environmental samples collected from the Moira watershed, Ontario, Canada. Arsenic contamination in Moira River and Moira Lake from historic gold mine operations is of increasing environmental concern to the local community. In this study, the current arsenic contamination status in water, sediment, and plants was investigated. Elevated levels of arsenic in the surface water of up to 75 ng mL(-1) in Moira River and 50 ng mL(-1) in Moira Lake were detected, 98% of which was present as arsenate. High concentrations of arsenic (>300 ng mL(-1)), mainly present as arsenite, were detected in sediment porewaters. A sediment profile of As from the West basin of Moira Lake showed lower As concentrations compared with data from the 1990s. An optimized extraction procedure using a phosphoric acid-ascorbic acid mixture demonstrated that an unknown "As-complex" which may consist of As, sulfide and organic matter is potentially responsible for the release of arsenite from the sediment to the overlying water column. Arsenic concentrations in plant samples ranged from 2.6 to 117 mg kg(-1), dry weight. Accumulation of arsenic was observed in submerged plants collected from Moira River and Moira Lake. Only a small part of the arsenic (6.3-16.1%) in the plants was extractable with methanol-water (9:1), and most of this arsenic (70-93%) was inorganic arsenic. A variety of organic arsenic compounds, including simple methylated compounds (methylarsonic acid and dimethylarsinic acid), trimethylarsine oxide, and tetramethylarsonium cation were detected at trace levels. No arsenobetaine and arsenocholine was found in any plant sample. An unknown compound, most probably an arsenosugar was detected in the two submerged plants, coontail ( Ceratophyllum demersum) and long-stemmed waterwort ( Elatine triandra). These submerged plants are constantly exposed to high arsenic concentrations in the surrounding water. Apparently, they are able to grow in this environment without invoking the same biochemical defence known from marine algae to detoxify inorganic arsenic. The detoxification mechanism of these plants remains unknown.