1e: Advances in analytical methods for environmental mercury speciation

Mercury (Hg) is a global pollutant due to its high toxicity, long-distance transport, persistence, and bioaccumulation in the environment, causing adverse effects in human body and animals. The global Hg emissions of anthropogenic sources from cement plants increased from 114 ton in 1990 to 189 ton in 2005 and reached 236 ton in 2010. Cement production has been targeted as the major anthropogenic source of atmospheric Hg, which covers 10% of global Hg emissions. The objective of this study was to understand the Hg mass flows and speciation in two cement plants in Taiwan using the precalciner process. The study results indicated that raw materials, added waste and fuel were the main Hg sources in the cement production process. Hg was mainly emitted in flue gases and present in clinker products. Hg emitted from flue gases was approximately 96.2% for plant 1 and 81.8% for plant 2. The Hg mass balance achieved 96.2% and 85.3% for plant 1 and plant 2, respectively. The Hg enrichment in the kiln and raw mill can be significantly affected by the proportion of Hg recirculated back to the kiln system and that caused high-concentration Hg gas flow emitted from cement plants. The raw mill stack was the main Hg emission source; the total Hg emission concentration was approximately 48.9 g/Nm3 for plant 1 and 23.9 g/Nm3 for plant 2, respectively. Elemental Hg was the major mercury species, followed by oxidized mercury and then particle-bound mercury in the cement process flue gas. The results of this study help gaining a better understanding on Hg emission intensity from the cement production process in Taiwan and provide useful information for developing Hg control strategies in the future.

Inorganic divalent mercury (HgII) has a very high affinity for reduced sulfur functional groups. Results from laboratory experiments suggest that HgII complexes with specific low molecular mass (LMM) thiol (RSH) ligands are central for controlling the rate of HgII transformation reactions, in particular the formation of neurotoxic methylmercury (MeHg). Because of methodological limitations for precise determination of the large stability constants of HgII complexes with LMM thiol ligands, constants reported in the literature remain inconsistent. This impedes accurate modelling of the chemical speciation of HgII in natural environments, and to elucidate the importance of HgII complexes with LMM thiols for MeHg formation in natural waters, soils and sediment. Here we report values on thermodynamic stability constants for 15 monodentate, two-coordinated HgII complexes with geochemically relevant LMM thiol ligands, determined by a 2-step ligand exchange procedure. The specific Hg(SR)2 complexes were quantified by liquid chromatography inductively coupled plasma mass spectrometry (LC-ICPMS) using the iodide ion (step 1) or mercaptoacetic acid and 2-mercaptopropionic acid as competing ligands. Determined thermodynamic constants (log 2) for the investigated Hg(SR)2 complexes ranged from 34.6, N-Cysteinylglycine, to 42.1, 3-mercaptopropionic acid, for the general reaction Hg2+ + 2RS- = Hg(SR)2, where RS- represents the thiolate group containing compound. Density functional theory calculations showed that HgIILMM thiol complexes are stabilized by electron-donating carboxyl and carbonyl groups, and destabilized by electron-withdrawing protonated primary amino groups. Experimental and modeling results demonstrated significant differences in the stability of Hg(SR)2 complexes, depending on the presence of the electron withdrawing or donating functional groups in the vicinity of the RSH group. These differences in stability are expected to largely effect the chemical speciation of HgII and its transformation reactions in environmental systems.

Methylmercury is the most toxic mercury species to humans. The main source of this species in our diets comes from seafood. It is therefore of high importance to monitor the concentration of MeHg in food of marine origin. Here, a simple extraction for MeHg in seafood is detailed. The method uses an extraction with 10mM APDC in 80% MeOH at 60oC, followed by ultrasonication. The mercury speciesare subsequently separated with RP-LC using 1.5mM APDC in 80% MeOH as a mobile phase. The eluting Hg species are then on-linechemicallyoxidisedand reduced with acidified Br-/BrO3- and SnCl2before AFS detection. This method of extraction has been tested using various marine CRMs with a moisture correction applied in each case. A higher concentration of APDC for extraction gave a yield much closer to the specified value,and also amuch smaller standard deviationcompared toan APDC concentration closer to that of the mobile phase. The results of all CRM measurements showed little to no loss of MeHg when compared to the specified concentrations.Recovery values rangedfrom 92.7% to 103.7%. The data also showed high precision, indicated by the low standard deviations obtained, which ranged from 0.3% to 5.1%.

The chemical speciation and bioavailability of mercury (Hg) is markedly influenced by its complexation with naturally dissolved organic matter (DOM) in aquatic environments. To date, however, analytical methodologies capable of identifying such complexes are scarce. Here we utilize ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) coupled with electrospray ionization to identify individual Hg-DOM complexes. The measurements were performed by direct infusion of DOM in 1:1 methanol:water solution at a Hg to dissolved organic carbon (DOC) molar ratio of 3×10-4. Heteroatomic molecules, especially those containing multiple S and N atoms, were found to be among the most important in forming strong complexes with Hg. Major Hg-DOM complexes of C10H21N2S4Hg+ and C8H17N2S4Hg+ were identified based on both the exact molecular mass and patterns of Hg stable isotope distributions detected by FTICR-MS. Density functional theory was used to predict the solution-phase structures of candidate molecules. These findings represent the first step to unambiguously identify specific DOM molecules in Hg binding, although future studies are warranted to further optimize and validate the methodology so as to explore detailed molecular compositions and structures of Hg-DOM complexes that affect biological uptake and transformation of Hg in the environment.

In this study, we used the diffusive gradients in thin films (DGT) to understand how soil properties (i.e., organic matter content) affect partitioning behaviors of Hg between soil particles and pore water. The accumulated mass of Hg in DGT gel and soil pore water was monitored for 10 days, while Hg concentration changed from 1 to 50 ppm and soil peat moss content from 5% to 20%. Using these experimental data, we were able to estimate Tc (response time) and Kd (distribution coefficient between soil and pore water) as a kinetic and equilibrium parameter, respectively, of Hg using the DGT induced fluxes in sediments and soils (DIFS) model, and k1 (DGT uptake rate constant) and k2 (DGT elimination rate constant) using the one compartment model (OCM). When Hg concentration in soil increased from 1 to 50 ppm, Tc decreased from 146 to 1 (s) and Kd increased from 18 to 107 cm3 g-1. Using the same data, the OCM predicted that k1 decreased from 2.6 x 10-6 to 5.8 x 10-7 kg soil cm-2 d-1 and k2 increased from 3.1 x 10-2 to 2.0 x 10-1 d-1 along with increases in Hg concentration. When the soil peat moss content increased from 5 to 20%, Tc increased from 338 to 1000 (s), and Kd decreased from 82 to 1.5 cm3 g-1. Using the same experimental data, the OCM predicted that k1 decreased from 1.2 x 10-5 to 4.0 x 10-6 kg soil cm-2 d-1, and k2 increased from 0.21 to 1.1 d-1 while peat moss content increased. These results indicate that the mobilization rate of Hg from soil to DGT, indicated by Kd and k1, tends to decrease with increasing organic matter content, which could be a result of the strong binding of Hg to the soil organic matter. In addition, pore water depletion of Hg was quantified as a function of distance from the DGT interface and deployment time. These results also showed that high organic content in soil increase the depletion of Hg in pore water. The combined approaches of DGT, DIFS and OCM allow us to obtain better understanding on the partitioning of Hg involved in soil retention and mobilization, suggesting that these are suitable tools to predict metal bioavailability in soils.

The Tekran Atmospheric Mercury Speciation system is the only commercially available instrumentation capable of measuring mercury species semi-real time producing high resolution data required to identify local point sources. Recently problems with Gaseous Oxidized Mercury capture efficiency and retention have been identified and several groups are working on improving these measurements.

In September, 2015, the National Oceanic and Atmospheric Administration and the National Atmospheric Deposition Program (NADP) organized a Tekran User Group Meeting in Washington DC. The group discussed these speciation collection problems and improvements to measurement methodology. Experimental tasks were assigned to groups to test ideas for improving the speciation measurements. This poster will examine these experimental results and identify potential modifications to the NADP Atmospheric Mercury Network (AMNet) Standard Operating Procedures. Additionally, this poster will give Tekran users the opportunity to discuss these changes with the AMNet Site Liaison.

Mercury (Hg) toxicity is known to be strongly dependent on its speciation, being monomethylmercury (MeHg) the most dangerous species since it is bioaccumulative in food webs. Seabirds are considered as effective sentinels of environmental marine contamination and their feathers are extensively used as non-lethal samples for contaminant biomonitoring. This tissue represents the main route for Hg elimination in seabirds and contains predominantly MeHg. However, measuring both MeHg and inorganic Hg (iHg) in feather samples is necessary to better evaluate the impact of Hg in seabirds and understand their metabolic response. In addition, it has been documented that historical feather collections could experience a contamination with iHg associated to museum preservatives, consequently Hg speciation analyses are required in these cases. In this work, we developed a robust analytical technique for precise and accurate simultaneous quantification of MeHg and iHg in feathers by gas-chromatography (GC)-ICPMS analyses using double species-specific isotope dilution technique (D-IDA). An optimisation of the extraction method was carried out by testing different extraction systems, reagents and spiking procedures in an internal reference feather sample (composed of a pool of feathers of king penguins). The procedure was validated with a human hair certified reference material (NIES-13). Microwave nitric acid extraction with spike addition before the extraction provided the best recoveries relative to certified NIES-13 values (96.0±1.2% for MeHg and 95.9±0.2% for THg) and was then chosen as the most appropiate extraction method. Our developed method was applied to feather samples from a large number of seabird species from the Southern Ocean (Antarctic prions, petrels, albatrosses, penguins and skuas) to investigate the variability of Hg speciation across a large range of diet, areas and therefore of Hg exposure conditions and concentrations.

Mercury transformation and transport in the environment strongly depend on its chemical form. Information about Hg form is also important for understanding the bioavailability as well as toxicity of this element. There are many methods for Hg speciation but most of them are expensive and time consuming. Therefor none of them is used in routine analysis. The aim of this research was to develop and validate a simple thermo-desorption technique for mercury fractionation in soil and sediment samples using commercially available mercury analyzer.

The direct mercury analyzer DMA-80 (Milestone, Italy) was used for the detection of Hg. For temperature fractionation the same instrument was used, only the temperature of catalytic tube heating was changed. In this case the temperature at which Hg was released from the samples was controlled. Each sample was heated from 50 to 750 degrees Celsius and result was presented as a thermo-desorption curve. The Hg species were characterized by the temperature range at which they were release. Fourteen synthetic standard material were used in this work. Additionally, the natural standards: humus-like substance and MeHg standard were used. The method was tested on a certified reference material (INCT-TL-1; NCS DC 87103; BCR-414) as well as on natural samples: soil, beach sand and marine sediment.

The obtained results show that the four-step thermo-desorption method can be considered as a fast and reliable screening technique for the evaluation of the percentage contribution of certain groups of Hg compounds with similar properties in solid samples with low, environmental Hg concentration. The developed method allows for separation of Hg fraction associated with labile compounds such as: mercury halides, mercury perchlorate, mercury nitrate, mercury cyanide, mercury thiocyanate,mercury fulminate,mercury acetate,methyl mercury and humus-like substance (labile-1); mercury sulfate, mercury oxide (red) andmercury fluoride (labile-2) as well as with mercury sulphide (stabile-1) and mineral matrix (stabile-2). The method was tested in the range of Hg concentrationfrom 2.4 to 262.5 ng/g d.w. Good repeatability and accuracy of the results were obtained. The developed method is less expensive than alternative methods for Hg fractionation, because it does not require the use of reagents. It also limits the possibility of contamination of the sample. The method was introduced on commercially available mercury analyzer without additional software modifications. This will allow for standardization of operational conditions. This makes the method can be widely used in laboratories engaged in biogeochemical transformations of mercury in the environment.

In this work several approaches for the preparation of nanogold-modified accumulation chips (dipsticks) are presented. Due to its chemical inertness and its thermal stability quartz glass slides were used as a substrate. In a first step, the surface of the substrate was coated with a thin gold film by vapor plating. By use of an annealing process, the smooth gold film was nano-structured. Investigation by atomic force microscopy confirmed successful formation of gold islands or rods in the nano-scale and a significant increase in the surface roughness of the carrier. Furthermore, AFM images show that the size of the nanogold particles could easily be regulated by variation of temperature and heating time. In order to prove the feasibility of the prepared dipsticks for mercury accumulation, several experiments in Hg(II) aqueous solutions were performed. After accumulation, Hg was released from the dipstick by thermal desorption and measured by atomic fluorescence spectrometry. A successful calibration experiment in the ng L-1 range evidences a linear increase in the fluorescence intensity with higher Hg concentrations. The limit of detection (LOD) was found to be as low as 0.18 ng Hg L-1 and a high reproducibility with a relative method standard deviation of 7.3 % (n=12) is given. Time-dependent accumulation experiments show a linear correlation between the mercury accumulation rate and the exposure time of the dipstick in the aqueous Hg(II) solution. However, in order to enhance the accumulation rate, in a second approach dipsticks with higher load of small gold nanoparticles should be prepared. Therefore, the glass surface was first functionalized using 3-aminopropyltrimethoxysilane (APTMS). Then, silica nanoparticles with a diameter of approx. 300 nm were immobilized on the surface to enlarge the surface area. After a second APTMS coating a thin gold film (10 nm thickness) was deposited on the surface by vapor plating. By use of an annealing process, the smooth gold film was transformed into nanoparticles. The successful formation of gold nanoparticles and their homogeneous distribution on the surface was proved by scanning electrode microscopy images, revealing an average particle diameter of 31.4 15.3 nm (N=364) after thermal treatment. Here again, mercury accumulation was tested in several exposition experiments in aqueous model solutions.

A novel Automated Gaseous Mercury Analyzer (AGMA) was custom-made to fully investigate the gaseous elemental mercury (GEM) in the overlying air of Taipei, Taiwan. The design principle is based on hyphenation technique by flow injection-Au amalgamation analysis with cold vapor atomic fluorescence detector. This analyzer gained several advantages in terms of simplicity, efficiency, precision, accuracy and versatility. The characteristic feature of the AGMA is firstly a computer-assisted dual-channel detection device so that continuous measurements can be simultaneously performed in two separate channel lines for Hg sampling and analysis. The automated system effectively increases the sample throughput and analytical performance of the GEM in environmental ultra-trace levels. The AGMA is also well suitably employed in the general laboratory or other field stations (e.g., shipboard use) with any risk of ambient contamination to obtain the high-quality Hg data in different environmental airs. In a field test in Taipei, we observed the diurnal GEM variation with higher levels in the noon and lower in the mid-night, similar to those in the ozone, PM10, PM2.5, solar irradiance. The observed diel pattern was closely related to local human activities, solar irradiance and surface air temperature in metropolitan Taipei.A novel Automated Gaseous Mercury Analyzer (AGMA) was custom-made to fully investigate the gaseous elemental mercury (GEM) in the overlying air of Taipei, Taiwan. The design principle is based on hyphenation technique by flow injection-Au amalgamation analysis with cold vapor atomic fluorescence detector. This analyzer gained several advantages in terms of simplicity, efficiency, precision, accuracy and versatility. The characteristic feature of the AGMA is firstly a computer-assisted dual-channel detection device so that continuous measurements can be simultaneously performed in two separate channel lines for Hg sampling and analysis. The automated system effectively increases the sample throughput and analytical performance of the GEM in environmental ultra-trace levels. The AGMA is also well suitably employed in the general laboratory or other field stations (e.g., shipboard use) with any risk of ambient contamination to obtain the high-quality Hg data in different environmental airs. In a field test in Taipei, we observed the diurnal GEM variation with higher levels in the noon and lower in the mid-night, similar to those in the ozone, PM10, PM2.5, solar irradiance. The observed diel pattern was closely related to local human activities, solar irradiance and surface air temperature in metropolitan Taipei.