Distribution Of Mercury Species Research Articles

Trophic distribution of mercury from an abandoned cinnabar mine within the Záskalská reservoir ecosystem (Czech Republic).

The distribution of mercury species was studied in all aquatic ecosystem components (i.e., water, sediment, emergent aquatic plants, invertebrates and omnivorous and piscivorous fish) of the Záskalská water reservoir (Central Bohemia, Czech Republic) which is in the vicinity of an abandoned cinnabar mine. The results indicate that the transport of mercury from the cinnabar mine is the major source of mercury in the Záskalská reservoir. The legal maximum limit (0.07μg/L) for total mercury concentration in water samples was exceeded only during rainy periods. The total mercury concentration in the surface sediments was in the range from 0.22 to 9.19mg/kg in dry matter (up to 0.2% CH3Hg+) and was sample site-specific. The dominant form of mercury in sediments was mercury sulphide (22.9-79.2%). The emergent macrophytes accumulated mercury primarily by the roots from sediments, and no significant translocation of mercury to leaves was observed. The legal maximum limit for mercury content in fish muscle (0.5mg/kg in the fresh matter) was exceeded up to 4.48 times for piscivorous fish. Hazard index values indicate a health risk concern for children and for people consuming more than 100g of fish muscle per day. Our results emphasise the need to implement legal restrictions on the consumption of piscivorous fish caught in ecosystems downstream of abandoned cinnabar mines.

Distribution of mercury species in different tissues and trophic levels of commonly consumed fish species from the south Bay of Biscay (France)

Mercury (Hg) is a contaminant of global concern in marine ecosystems, notably due to its ability to accumulate and concentrate in food webs. Concentrations of total mercury (THg), methylmercury (MeHg) and inorganic mercury (IHg) were assessed and compared in different tissues (liver, muscle, and gonads) of three common fish species (hake Merluccius merluccius, red mullet Mullus surmuletus, and sole Solea solea) from the continental shelf from the southern part of the Bay of Biscay. Several studies investigated Hg concentration in fish muscle, but few assessed concentrations in other organs, despite the importance of such data to understand contaminant organotropism and metabolization. Results showed that trophic position and feeding habitat are required to understand the variability of Hg concentration in muscle between fish species. In addition, high MeHg/THg ratio in muscle could be explained by the predatory behavior of the studied fish species and the biomagnification of this Hg species within the food web, MeHg. Despite differences between species, Hg concentration was always higher in muscle (from 118 ± 64 to 338 ± 101 ng g−1 w.w.) and liver (from 122 ± 108 to 271 ± 95 ng g−1 w.w.). These results can be related to physiological processes especially the MeHg detoxification strategies.

Determining seawater mercury methylation and demethylation rates by the seawater incubation approach: A critique

The discovery of a pervasive subsurface methylmercury maximum in the world's oceans highlights the importance of understanding the processes and rates that produce and destroy this potent neurotoxin in seawater. Two approaches have been published in the literature, one based on the spatial distribution of mercury species in seawater and, more recently, a second approach based on seawater incubation studies using additions of isotopically enriched mercury species. The reaction rates determined by these two approaches differ by several orders of magnitude. Using Arctic Ocean seawater and the incubation approach to determine mercury methylation and demethylation rates, we observed unexplainable methylation and demethylation at time zero and poor fitting of the data to first-order kinetics. A critical analysis of previous incubation studies reveals similar deficiencies, especially when the mercury was added at low concentrations to simulate ambient seawater conditions. These findings cast doubt on the validity of mercury methylation and demethylation rates determined by the seawater incubation approach, and call for the development of alternative methods to determine these crucially important rate constants in ambient seawater.

A Highly Selective and Ultrasensitive Fluorescent Probe for Monitoring Hg2+ and Its Applications in Real Water Samples.

Mercury ions as high toxic pollutants have received wide-spread attention because of their poisonousness, persistence and enrichment. To better understand the distribution of mercury species and supplement more detailed toxicological research, it is necessary to develop some methods for monitoring mercury ions with high sensitivity and selectivity. Therefore, a simple rhodol-based highly selective fluorescent probe, RH-Hg, has been developed for monitoring Hg2+ with thiocarbamate as the recognition receptor. The probe RH-Hg can quantificationally detect mercury ions in aqueous solution assisted by hydrogen peroxide (H2O2), and it can discriminate Hg2+ through "naked-eye" observation of the color changes from light orange to dark pink. Finally, the practical applications of the probe RH-Hg in the river water further demonstrated that it will be an effective and economical tool for monitoring the distribution of Hg2+ in the environment.

Effect of wet flue gas desulfurization facilities of coal-fired power plants on mercury emission

The speciation and content of mercury in flue gas were measured before and after WFGD of eight coal-fired units by Ontario Hydro method and the effect of WFGD on mercury species distribution and concentration was investigated. The results show that mercury is mainly composed of gaseous form and mercury emission concentration after WFGD in different units has very large difference. The effect of WFGD on mercury emission is embodied on synergistic removal of gaseous mercury with average mercury removal efficiency of 36.8%. Mercury is transferred from flue gas to desulfurization gypsum in WFGD. The mercury stability in desulfurization gypsum and the second mercury pollution are worthy of attention.

Selective recovery of mercury from high mercury-containing smelting wastes using an iodide solution system.

The mercury resources recovery and safe disposal of mercury-containing waste is an urgent problem. In this study, a new method using an iodide solution system was proposed to selectively recover mercury from high mercury-containing smelting wastes. The mercury leaching efficiency, yields, leaching kinetics and thermodynamics were researched. The major factors which affect mercury leaching efficiency including iodide concentration, oxidant, pH and temperature were evaluated. Over 97% and 93% of mercury can be efficiently leached from wastewater treatment sludge (W-S) and acid sludge (A-S). After leaching, the mercury concentration during leaching toxicity test is under the limits set for hazardous waste. Additionally, the electrolytic technology can efficiently recover mercury from leachate in the form of elemental mercury, and the leachate after electrolytic can be reused for mercury leaching. The mercury leaching kinetics follows the shrinking core diffusion model and is controlled by solid product diffusion. The mechanism research shows the leaching efficiency was strongly dependent on the distribution of mercury species in smelting waste. The consequence on mercury leaching and recovery could provide nonferrous smelters with a practical and yet easy-to-adopt perspective to reduce the risk of mercury contamination and selectively recover mercury resources from mercury-containing smelting wastes.

Distribution of mercury species and mercury isotope ratios in soils and river suspended matter of a mercury mining area.

Mercury (Hg) released by mining activities can be dispersed in the environment, where it is subject to species transformations. Hg isotope ratios have been used to track sources in Hg contaminated areas, although it is unclear to what extent variations in δ-values are attributed to distinct Hg species. Hg was mined as Hg sulphide (cinnabar) in Idrija, Slovenia for centuries. Sediments are loaded with mining-residues (cinnabar and calcine), whereas contaminated soils mainly contain Hg bound to natural organic matter (NOM-Hg) related to atmospheric Hg deposition. Hg released from soils and sediments is transported as suspended matter (SM) in the Idrijca river to the Gulf of Trieste (GT), Italy. We determine Hg isotope ratios in river SM, sediments and soils from the Idrijca-catchment to decipher the Hg isotope ratio variability related to Hg species distribution in different grain-size fractions. δ202Hg values of SM collected from tributaries corresponded to those found in soils ranging from -2.58 to 0.19‰ and from -2.27 to -0.88‰, respectively. Speciation measurements reveal that fine fractions (0.45-20 μm) are dominated by NOM-Hg, while larger fractions contain more cinnabar. More negative δ202Hg values were related to higher proportions of NOM-Hg, which are predominant in soils and SM. Rain events increase SM-loads in the river, mainly due to resuspension of coarse grain-size fractions of bottom sediments bearing larger proportions of cinnabar, which leads to more positive δ202Hg values. The large magnitude of variation in δ202Hg and the smaller magnitude of variation in Δ199Hg (-0.37 to 0.09‰) are likely related to fractionation during ore roasting. Soil samples with high NOM-Hg content show more negative δ202Hg values and larger variation of Δ199Hg. More negative δ202Hg values in GT sediments were rather linked to distant sedimentation of soil derived NOM-Hg than to sedimentation of autochthonous marine material. Heterogeneity in the Idrija ore and ore processing likely produce large variations in the Hg isotopic composition of cinnabar and released metallic Hg, which complicate the differentiation of Hg sources. Combining Hg isotope measurements with solid phase Hg speciation reveals that Hg isotope ratios rather indicate different Hg species and are not necessarily symptomatic for Hg pollution sources.

Water Column Distribution of Mercury Species in Permanently Stratified Aqueous Environments

Biogeochemical structures of three permanently stratified waterbodies were studied: a sea water basin (the Black Sea), an estuary (Hunnbunn fjord), and a freshwater lake (Nordbytjernet), with focus on the distributions of methylmercury (MeHg) and total mercury (THg). THg concentrations were similar in the sea water basin (0.2–1.8 ng/L) and the freshwater lake (0.8–1.2 ng/L), but significantly higher in the estuary (0.6–9.4 ng/L). An increase in the MeHg concentration and MeHg/THg ratio were found in the redox zone in all three basins, indicating bacterial production of MeHg in the aqueous phase. In the lake and estuary, the maximum MeHg concentration and MeHg/THg ratio were found in samples located closest to the bottom sediments, likely due to the formation of MeHg in surface sediments and subsequent diffusion to the overlying waters.

The Impact of the Major Baltic Inflow of December 2014 on the Mercury Species Distribution in the Baltic Sea.

The Baltic Sea is a marginal sea characterized by stagnation periods of several years. Oxygen consumption in its deep waters leads to the buildup of sulfide from sulfate reduction. Some of the microorganisms responsible for these processes also transform reactive ionic mercury to neurotoxic methylmercury. Episodic inflows of oxygenated saline water from the North Sea temporally re-establish oxic life in deep waters of the Baltic Sea. Thus, this sea is an especially important region to better understand mercury species distributions in connection with variable redox conditions. Mercury species were measured on three Baltic Sea campaigns, during the preinflow, ongoing inflow, and subsiding inflow of water, respectively, to the central basin. The inflowing water caused the removal of total mercury by 600 nmol m-2 and of methylmercury by 214 nmol m-2 in the Gotland Deep, probably via attachment of the mercury compounds to sinking particles. It appears likely that the consequences of the oxygenation of Baltic Sea deep waters, which are the coprecipitation of mercury species and the resettlement of the oxic deep waters, could lead to the enhanced transfer of accumulated mercury and methylmercury to the planktonic food chain and finally to fish.

Multi-model study of mercury dispersion in the atmosphere: vertical and interhemispheric distribution of mercury species

Abstract. Atmospheric chemistry and transport of mercury play a key role in the global mercury cycle. However, there are still considerable knowledge gaps concerning the fate of mercury in the atmosphere. This is the second part of a model intercomparison study investigating the impact of atmospheric chemistry and emissions on mercury in the atmosphere. While the first study focused on ground-based observations of mercury concentration and deposition, here we investigate the vertical and interhemispheric distribution and speciation of mercury from the planetary boundary layer to the lower stratosphere. So far, there have been few model studies investigating the vertical distribution of mercury, mostly focusing on single aircraft campaigns. Here, we present a first comprehensive analysis based on various aircraft observations in Europe, North America, and on intercontinental flights. The investigated models proved to be able to reproduce the distribution of total and elemental mercury concentrations in the troposphere including interhemispheric trends. One key aspect of the study is the investigation of mercury oxidation in the troposphere. We found that different chemistry schemes were better at reproducing observed oxidized mercury patterns depending on altitude. High concentrations of oxidized mercury in the upper troposphere could be reproduced with oxidation by bromine while elevated concentrations in the lower troposphere were better reproduced by OH and ozone chemistry. However, the results were not always conclusive as the physical and chemical parameterizations in the chemistry transport models also proved to have a substantial impact on model results.

Distribution of mercury species across a zonal section of the eastern tropical South Pacific Ocean (U.S. GEOTRACES GP16)

Monomethylmercury is a neurotoxin formed in the ocean that accumulates in fish. To better understand the chemical cycling of mercury (Hg) in the ocean, multiple Hg species were measured during the 2013 U.S. GEOTRACES section in the eastern tropical South Pacific Ocean (GP16) from Peru to Tahiti. Total Hg (HgT), elemental Hg (Hg0), monomethyl-Hg (MMHg), and dimethyl-Hg (DMHg) were measured in high resolution across the section, which included productive surface waters in the Peru upwelling region, a suboxic oxygen minimum zone (OMZ), and an expansive hydrothermal vent plume from the East Pacific Rise (EPR). Filtered HgT accumulated in upwelled waters near the coast of Peru where oxygen concentrations were the lowest, and MMHg represented 10–20% of the total Hg upwelling flux. The buoyant hydrothermal plume was not enriched with Hg; however, water below 2500m had anomalously high concentrations of filtered HgT beneath the plume and in warmer bottom waters in the eastern part of the section. Elemental Hg averaged <10% of HgT in the water column and concentrations were greatest near the Peru margin. Concentrations of MMHg and DMHg were greatest in low-oxygen thermocline waters, and in the upwelling region, vertical maxima of MMHg were found at the top, core, and bottom of the suboxic OMZ. The MMHg:DMHg molar ratio was variable throughout the upper water column, however, DMHg was the dominant form of methylated Hg in deep water masses. This section is the first examination of Hg speciation and distributions near the Peru coast, a region that supports a highly productive fishery and a potential source of MMHg to consumers of seafood.

Mercury methylation in paddy soil: source and distribution of mercury species at a Hg mining area, Guizhou Province, China

Abstract. Rice paddy plantation is the dominant agricultural land use throughout Asia. Rice paddy fields have been identified as important sites for methylmercury (MeHg) production in the terrestrial ecosystem and a primary pathway of MeHg exposure to humans in mercury (Hg) mining areas. We compared the source and distribution of Hg species in different compartments of the rice paddy during a complete rice-growing season at two different typical Hg-contaminated mining sites in Guizhou province, China: an abandoned site with a high Hg concentration in soil but a low concentration in the atmosphere and a current-day artisanal site with a low concentration in soil but a high concentration in the atmosphere. Our results showed that the flux of new Hg to the ecosystem from irrigation and atmospheric deposition was insignificant relative to the pool of old Hg in soil; the dominant source of MeHg to paddy soil is in situ methylation of inorganic Hg (IHg). Elevated MeHg concentrations and the high proportion of Hg as MeHg in paddy water and the surface soil layer at the artisanal site demonstrated active Hg methylation at this site only. We propose that the in situ production of MeHg in paddy water and surface soil is dependent on elevated Hg in the atmosphere and the consequential deposition of new Hg into a low-pH anoxic geochemical system. The absence of depth-dependent variability in the MeHg concentration in soil cores collected from the abandoned Hg mining site, consistent with the low concentration of Hg in the atmosphere and high pH of the paddy water and irrigation water, suggested that net production of MeHg at this site was limited. We propose that the concentration of Hg in ambient air is an indicator for the risk of MeHg accumulation in paddy rice.

Actual mercury speciation and mercury discharges from coal-fired power plants in Inner Mongolia, Northern China

Mercury species distribution in the flue gas from three typical coal-fired power plants have been investigated using a C-5000 sampler for Ontario Hydro Method (OHM) to evaluate specified Hg emission inventories in the largest coal-production province of China, Inner Mongolia. The feed coal, bottom ash, fly ash and gypsum have also been sampled in the field. Mercury emissions are in the dominant form of Hg0 (>85%). The Hg2+ (<15%) and the Hgp (<2%) emissions are minor fractions of Hgt in the flue gas. The wet limestone flue gas desulfurization device (WLFGD) showed much higher removal efficiency for Hg2+ (87–95%) than for the other two Hg species. The input Hg/output Hg varied from 92% to 115% for the tested 3 coal-fried utility boilers during sampling time. We obtained comprehensive Hg discharge factors, including direct atmospheric Hg emission factors and indirect discharge factors of Hg associated with bottom ash, fly ash and gypsum, to the environment, designating the fates of Hg in coal. We estimated the Hg discharges from coal-fired power plants in Inner Mongolia in 2008–2014 and expanded to China. The maximum of direct Hg emissions from coal-fired power plants of Inner Mongolia was 24Mg in 2012. The Chinese coal-fired power plants emitted directly 100Mg Hg to the atmosphere every year at the nationwide air control actions. The maximum discharges of Hg associated with fly ash and gypsum of Inner Mongolia was 81Mg and 11Mg in 2012, respectively. The national Hg discharges with fly ash and gypsum every year are respectively about 300Mg and 82Mg, majority of which may be reemitted to the atmosphere by the utilization industry. Therefore, mercury emissions from coal-fired power plants are not the largest single source of Hg to the atmosphere in normal operation of the current efficient denitrification, particles control and desulfurization devices. Instead, the utilization industry of fly ash and gypsum would be emitting more Hg to the atmosphere.

Some aspects of speciation and reactivity of mercury in various matrices

Speciation of mercury compounds in environmental and biological samples requires different techniques and different approaches. This speciation is mandatory to explain the toxicity, the reactivity and the bioavailability of mercury. It is dominated by inorganic mercury species Hg(II) and Hg(0), and the organic mercury species CH3Hg and (CH3)2Hg. In this paper, some aspects of mercury speciation are presented in terms of: - mercury reactivity (Hg(II) complexation and reduction), - mercury species distribution in the main compartments of the environment La spéciation du mercure dans les échantillons environnementaux et biologiques nécessite différentes techniques et différentes approches. Cette spéciation permet d’expliquer la toxicité, la réactivité et la biodisponibilité du mercure. Elle est dominée par les espèces de mercure inorganique Hg(II) et Hg(0) et les espèces organiques CH3Hg et (CH3)2Hg. Dans cet article, quelques aspects de la spéciation du mercure sont présentés en termes de : - réactivité du mercure (complexation et réduction de Hg(II)), - distribution des espèces du mercure dans les principaux compartiments de l’environnement.

Emission and Species Distribution of Mercury during Thermal Treatment of Coal Fly Ash

The thermal treatment of coal fly ash (FA) utilized by industries will inevitably lead to the emission of mercury, potentially causing atmospheric pollution. The present study is aimed at understanding the emission amount and species distribution of mercury during FA thermal treatment, and attempts were made to further provide basic data of mercury emission for environmental utilization of the FA by industries as raw materials. The physio-chemical properties of FA were analyzed and FA samples were heated at 200–1200°C in a tubular furnace in an oxidizing atmosphere. Thermogravimetric analysis (TGA) was carried out to determine the content of residual carbon in FA. The mercury species distribution was determined using United States EPA method 3200. The results indicated that semi-mobile mercury was the main mercury species in FA. Owing to the adsorption of residual carbon on Hg0, more residual carbon which lead to higher proportion of semi-mobile obtained in coarser size grades. 20% of total mercury emitted at 206°C, followed by a rapid growth of the emission rate of mercury at above 206°C, and the emission of total mercury achieved to be 50% and 90% corresponding to 291°C and 515°C, respectively. A distinct transformation from semi-mobile mercury to extractable mercury occurred at 200°C due to catalytic oxidation of Hg0 and enhance the mobility and potential toxicity of mercury. Both extractable and semi-mobile mercury decreased sharply at 300–400°C. Finally, the non-mobile mercury was emitted with combustion of residual carbon in FA at 600–800°C. It was thus concluded that measures would be taken to control emission of mercury for environmentally friendly utilization of coal FA by industries when the FA was heated higher than 300°C.

The fate of mercury in fluidized beds under oxy-fuel combustion conditions

Among the different pollutant gases released from oxy-coal combustion, mercury is the responsible for important operational issues in the CO2 processing unit, being able to cause material corrosion. Some studies concerning the fate of mercury during oxy-coal combustion are referred to pulverized coal (PC) boilers. However, the fate of mercury emissions in fluidized bed (FB) combustors has yet to be elucidated.In this work, mercury emissions from a 3kWth bubbling FB combustor operating under oxy-fuel combustion conditions have been evaluated. For this purpose, two Spanish Ca-based sorbents and two Spanish coals were used. The effects of type of Ca-based sorbent, the Ca/S molar ratio, temperature and recycled gases (NO, SO2 and H2O) typical in oxy-fuel combustion process on the distribution of mercury species have been analyzed.It was observed that the presence of Ca-based sorbents in the combustor favored mercury fixation as particle-bound mercury which exhibited a maximum at a temperature about 925°C corresponding to the highest degree of limestone sulfation. SO2 recirculation inhibited the Hg0 oxidation and thus the mercury fixation as particle-bound mercury decreased. However, neither NO nor steam recirculation affected mercury speciation.

Studying mercury partition in monoethylene glycol (MEG) used in gas facilities

Mercury partitioning from monoethylene glycol (MEG) during natural gas production is a highly complicated process. Understanding this process will help determine the distribution of mercury species within a given industrial process so that appropriate mercury removal control systems can be effectively managed. In this study, the partitioning of elemental mercury (Hg0) from the gaseous phase into MEG solutions is investigated under standard laboratory conditions. Additionally, the partitioning of dissolved ionic mercury (Hg2+) from MEG solutions into the gaseous phase is also investigated under atmospheric pressure and room temperature conditions. It was found that the solubility of Hg0 in MEG ranged from 0 to 60ppb (ng/mL) with slight increase to ∼80ppb when the pH was reduced from ∼9 to ∼6 at room temperature. On the other hand oxidized mercury (Hg2+) was found to be retained in the laboratory grade MEG and industrial samples of MEG (industrial-MEG). However, in the case of the industrial-MEG, the dissolved mercury (HgCl2 salt) was found to be unstable with approximately 3.6% and 10% converting within the solution and leaving in the gas phase as Hg0 and Hg2+, respectively, while the balance was retained in the MEG solution. The distribution was found to be highly pH dependent and was not observed when the experiments were repeated using laboratory grade MEG solutions. These findings help in better understanding the type and ratio of mercury species that are partitioned in and out of MEG in the gas processing facilities.

Mercury species accumulation and trophic transfer in biological systems using the Almadén mining district (Ciudad Real, Spain) as a case of study

The impact of mercury (Hg) pollution in the terrestrial environments and the terrestrial food chains including the impact on human food consumption is still greatly under-investigated. In particular, studies including Hg speciation and detoxification strategies in terrestrial animals are almost non-existing, but these are key information with important implications for human beings. Therefore, in this work, we report on Hg species (inorganic mercury, iHg, and monomethylmercury, MeHg) distribution among terrestrial animal tissues obtained from a real-world Hg exposure scenario (Almadén mining district, Spain). Thus, we studied Hg species (iHg and MeHg) and total selenium (Se) content in liver and kidney of red deer (Cervus elaphus; n = 41) and wild boar (Sus scrofa; n = 16). Similar mercury species distribution was found for both red deer and wild boar. Major differences were found between tissues; thus, in kidney, iHg was clearly the predominant species (more than 81%), while in liver, the species distribution was less homogeneous with a percentage of MeHg up to 46% in some cases. Therefore, Hg accumulation and MeHg transfer were evident in terrestrial ecosystems. The interaction between total Se and Hg species has been evaluated by tissue and by animal species. Similar relationships were found in kidney for both Hg species in red deer and wild boar. However, in liver, there were differences between animals. The possible underlying mechanisms are discussed.

Mercury and methylmercury distribution in tissues of sculpins from the Bering Sea.

Fish skeletal muscle is often used to monitor mercury concentrations and is used by regulatory agencies to develop fish consumption advisories. However, the distribution of mercury species (MeHg+ and THg) in muscle tissue and other organs is not well understood in a number of fish species. Here we evaluate the spatial distribution of THg and MeHg+ in skeletal muscle and internal organs (heart, liver, and kidney) of 19 sculpin representing three species: Myoxocephalus scorpius (shorthorn sculpin n = 13), Myoxocephalus jaok (plain sculpin, n = 4), and Megalocottus platycephalus (belligerent sculpin, n = 2). Four subsamples of muscle were taken along the lateral aspect of each fish, from muscle A (cranial) to muscle D (caudal). Using Games-Howell post hoc procedure to compare mean concentrations of all tissues, muscle samples were significantly different from internal organs, although there was no difference between muscle-sampling locations. THg concentrations (ww) were higher in muscle (muscle A through D mean ± SD, 0.30 ± 0.19 mg/kg) than that in heart (0.06 ± 0.05 mg/kg), kidney (0.08 ± 0.06 mg/kg), and liver (0.09 ± 0.08 mg/kg). Percent MeHg+ decreased with age in both skeletal muscle and organs (p < 0.05). In contrast to some previous reports for other fish species, this study found significantly higher THg concentrations in muscle than in the liver. This study highlights the importance of using muscle samples when evaluating potential Hg exposure in risk assessments for piscivorous wildlife and human populations, and assumptions related to organ mercury concentrations should be examined with care.

Partitioning effect of mercury content and speciation in gypsum slurry as a function of time

For gypsum slurry samples taken from wet flue gas desulfurization (WFGD) systems, a mercury partitioning effect was observed between the solid and liquid components. This partitioning effect, which appears to be pseudo-second-order, is a function of time which results in an increase in mercury content for the solid portion of the gypsum slurry as time increases. Moreover, the mercury content for the solid portion of the slurry reaches a plateau after 24 h. Thus, the sampling method for the gypsum slurry is an important factor in determining an accurate mercury mass balance in the WFGD systems. Temperature-controlled decomposition techniques were employed to acquire an understanding of the mercury species in WFGD gypsum. It was determined that the primary mercury species in WFGD gypsum was mercuric sulfide (HgS). Moreover, the content of HgS as well as mercuric oxide (HgO) in the solid portion of the slurry was susceptible to the partitioning effect and steadily increased with separation time. Other mercury compounds present were mercury sulfate and mercury chloride; however, these mercury species exhibited less change with separation time. Additionally, a comparison of the mercury present in WFGD gypsum from five different coal-fired power plants using thermal decomposition techniques showed that the distribution of mercury species was not the same; however, HgS was primary and mercury chloride compounds or HgO secondary. HgO varied between 15 and 25 % of the total mercury in gypsum. No clear correlation between mercury speciation and sulfur and chlorine content in the coal was determined. Thermogravimetric analysis was employed to compare the effects of settling time with gypsum quality. Data show that longer settling times results in lower quality gypsum.