Mercury reactions in the human mouth with dental amalgams

This is a preliminary study of the reactions of mercury (Hg) in the human mouth with dental amalgams. It was conducted by analysing saliva samples from subjects with amalgam fillings and control subjects with no amalgams. Samples were collected both prior to and after cleaning the mouth. These samples were analyzed for elemental mercury (Hg⁰), inorganic mercury (Hg²⁺) and methylmercury (MeHg). We concluded that the concentrations after cleaning represented the systemic concentrations. Hg²⁺ and MeHg were found in all systemic samples from both subjects and controls, while Hg⁰ was found only in the samples from subjects with amalgams. In the control group, the concentrations found before and after cleaning the mouth were equivalent. In the amalgam group, concentrations of Hg²⁺ found before cleaning the mouth were 10 to 40 times higher than those found after cleaning, suggesting that the oxidation reaction of Hg° into Hg²⁺ takes place. For MeHg, a similar but less pronounced pattern as Hg²⁺ was found, supporting methylation in the mouth.     

Impact of the state-of-the-art of flue gas cleaning on mercury species emissions from coal-fired steam generators

When balancing the element mercury (Hg) two coal-fired power plant units — one with slag tap boilers (ST, 2 × 220 MW) and one with a dry bottom boiler (DB, 475 MW) were compared. Both systems are provided with electrostatic precipitators (ESP), nitrogen oxides removal (DeNO_x) and flue gas desulfurization (FGD) systems. The Hg in the flue gas is predominantly in gas phase. Only 15 % of the Hg introduced by the coal leaves the unit with the bottom or fly ash. Depending on the operating mode, 30 to 40 % of the Hg is separated in the FGD systems. The overall separation rate for the total system ranges between 45 to 55 %, the residue is emitted in the form of gaseous Hg species. At full load, the Hg concentration in the cleaned gas is less than 6 μg/m³. In the flue gas path of another dry bottom boiler (DB1, 480 MW) the concentrations of the gaseous species of bivalent mercury (Hg²⁺), elemental mercury (Hg⁰), and total mercury content (Σ Hg) were determined. The sum of the concentrations of Hg²⁺ and Hg⁰ is in agreement with the measurement of Σ Hg. Directly downstream of the boiler Hg²⁺ dominates with 77 %, while Hg⁰ amounts to 23 %. In the high-dust DeNO_x system Hg⁰ is oxidized almost completely to Hg²⁺ (96 %). Air heater and electrostatic precipitator do not influence the Hg species concentrations. The FGD system eliminates approximately 80 % of the Hg²⁺. At the same time the quantity of Hg⁰ increases by the factor 10. In the cleaned gas Hg⁰ dominates with 76 % as compared to Hg²⁺ with 24 %. At full load the concentration of Σ Hg in the cleaned gas is also below 6 μg/m³.     

Immobilization of Mercury Species under the Influence of Typical Organic Compounds in Waste Gases by the Circulating Fluidized Bed

Hearth furnace coke (HOK), a special type of lignite (brown-coal)coke produced in a manufacturing process called `hearth furnace process', and portlandite (Ca(OH)₂) particles were placed ina circulating fluidized bed reactor. Defined model waste gases containing HCl/SO₂/Hg⁰/Hg²⁺ and organic compounds were injected into the reactor to investigate the adsorption of different mercury species. Elemental mercuryreacted immediately with HCl to form HgCl₂, but for Hg²⁺ further investigations had to be made, because todaygas cleaning plants still have problems in observing national limits for the mercury output. The temperature, the mercury content of the gas, and its content of acid compounds as majorinfluences in cleaning exhaust gases were varied without relevantpositive effects on the adsorption rate which decreased from nearly 100% in the first five minutes to unsatisfactory20% some minutes later. The mercury load on the HOK particles onlyshowed a value of 60 μg Hg g^-1 HOK. Then organic compounds (guide pollutants such as 1-chlorobutane, monochlorobenzene, toluene, and naphthalene, which are alwayspresent in incineration plant exhaust gases) were added to thegas stream and the results improved significantly. The mercuryload on the HOK particles varied depending on the chemical nature of the organic compound and amounted to 300 μg Hg g^-1 HOK maximum. The measured values of mercury in the clean gas stream fell below 10 μg m^-3. The characterization of the dynamic behavior of mercury in hot, acid waste gases and the analytical identification of mercurysticking to HOK under the influence of organic compounds leadto new methods for improving the effectiveness and performanceof gas cleaning plants.     

Mercury speciation adsorption (MESA) method for combustion flue gas: Methodology,artifacts, intercomparison,and atmospheric implications

Chemical speciation of mercury (Hg) in a wide variety of combustion flue gas matrices has been determined using the mercury speciation adsorption (MESA) method. The MESA sampling system for gas phase Hg species employs a series of heated, solid phase adsorbent traps. Flue gas oxidized Hg species (Hg(II) and MMHg) are adsorbed by a potassium chloride (KCl) impregnated soda lime sorbent. Elemental Hg (Hg⁰) is collected by an iodated carbon sorbent after passing through the KCl/soda lime sorbent. Total Hg (Hg_t) is determined by summation of species. In the laboratory, cold vapor atomic fluorescence spectroscopy (CVAFS) is used for detection of Hg collected on the solid sorbents, after appropriate sample digestion and preparation. The MESA method has been evaluated for species stability, matrix effects, breakthrough, artifacts and precision. Based on eight duplicate samples a mean precision of 6.8% 11% and 4.5% (relative percent difference) has been calculated for Hg⁰, Hg(II) and Hgt respectively. Intercomparison of the MESA method with other methods shows very good agreement for Hgt. Mass balance calculations at 5 sites range from 75 to 140%, with a mean of 97±25%. Overall mean speciation results from 19 separate determinations suggest that Hg(II) has a 1 sigma range of 40 to 94% in coal combustion flue gas at, the inlet to pollution control devices.     

An experimental study of two potential methylation agents of mercury in the atmosphere: CH3I and DMS

Experimental results from a study of the gas and aqueous phase reactions of elemental mercury (Hg⁰) with methyl iodide (CH₃I) and dimethyl sulfide (DMS) are presented. In aqueous phase experiments with CH₃I we found no observable increase in methyl mercury (MeHg). A small formation of MeHg, however, was observed in some (but not all) gas phase experiments in sunlight. A loss of Hg⁰ and a simultaneous formation of oxidized mercury (Hg(II)) was also observed in these experiments. No reaction, neither methylation or oxidation, was found between Hg⁰ and DMS under any conditions investigated. These experiments suggest that a simple homogeneous gas or aqueous phase methylation of Hg⁰ by DMS or CH₃I in the atmosphere cannot account for the significant levels of MeHg observed in precipitation.     

Development of Highly Selective and Efficient Prototype Sensor for Potential Application in Environmental Mercury Pollution Monitoring

Mercury (Hg) is an environmental pollutant which is detrimental to the health of living beings due to the toxicity in its all oxidation states. To control mercury pollution development of low cost, efficient and highly sensitive prototype mercury sensor remains a challenge. In the present work, we have proposed a low-cost prototype device based on silver nanoparticle-impregnated poly(vinyle alcohol) (PVA-Ag-NPs) nanocomposite thin film for mercury detection. The thin film, fabricated through a facile protocol, is shown to be a fast, efficient, and selective sensor for Hg²⁺ in aqueous medium with a detection limit of 10 ppb. We have utilized the aggregation and amalgamation of Ag-NPs with Hg²⁺ to develop the low-cost, highly efficient and feasible prototype mercury sensor. In the presence of Hg²⁺, the yellowish thin film turned into colourless due to the loss of intense surface plasmon resonance (SPR) absorption band of the silver nanoparticles (Ag-NPs) through aggregation and amalgamation with mercury. The developed sensor has high selectivity for Hg²⁺ ions over a wide range of other competing heavy metal ions, generally present in water of natural sources. The sensor response is found to be linear over the Hg²⁺ ion concentration regime from 10 ppb to 5 ppm. The developed sensor has shown to determine a trace Hg²⁺ ions in real water samples. Finally, using the proposed technique, we have developed a simple and inexpensive prototype device for monitoring in field environmental mercury pollution.

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Graphical Abstract ?

     

Rapid Determination of Mercury in Plant and Soil Samples Using Inductively Coupled Plasma Atomic Emission Spectroscopy, a Comparative Study

The objectives of this study were to simplify sample preparation and validate mercury detection in soil and plant samples using inductively coupled plasma atomic emission spectroscopy (ICP-AES). A set of mercury contaminated and mercury free soil and plant samples were digested and analyzed by ICP-AES, inductively coupled plasma mass spectrometry (ICP-MS), and cold vapor atomic absorption spectroscopy (CVAAS). Results show that mercury measurements in soil and plant samples using ICP-AES were in agreement with those analyzed using ICP-MS and CVAAS. The concentrations of mercury in soils and plant tissues determined by ICP-AES were 92.2% and 90.5% of those determined by CVAAS and ICP-MS, respectively. Digestion of soil samples with 4 M HNO₃ and direct measurement by ICP-AES without reduction of Hg²⁺ to Hg⁰ gave a reasonable and acceptable recovery (92%) for determining Hg in soils. We conclude that ICP-AES with optimized conditions (addition of gold chloride, extension of washing time, linear working range, and selection of wavelength – 194 nm) resulted in reliable detection of mercury in environmental samples.     

Solubility of cinnabar (red HgS) and implications for mercury speciation in sulfidic waters

New experiments have been conducted to determine the speciation of dissolved mercury (Hg) over wide pH (1–12) and sulfide concentration ranges (0.5–30 mM) and in the presence of elemental sulfur (S⁰) or Hg⁰, conditions that encompass those of near-bottom and pore waters of sediments. Samples containing synthetic red mercuric sulfide (HgS, cinnabar), buffer solution, aliquots of bisulfide (HS^?1) solution, and, in special cases, S⁰ or Hg⁰ were prepared anaerobically and allowed to equilibrate for several months. Filtered samples were analyzed for pH, total sulfide (ΣS^2?), and total mercury [Hg]_tot. Plots of [Hg]_tot values vs. pH at varying ΣS^2? verified the formation of three previously known mercury-sulfide complexes (HgS₂H_n ^n?2) and revealed that a new Hg₂SOH⁺ complex is important at low pH and low ΣS^2?. Our constants for ionic strength (I) 0.7 and 25⁰ C are as follows: K₁=10^{?5.76(+0.71, ?1.02)} for HgS_cinn+H₂S ? HgS₂H₂ ⁰; K₂=10^{?4.82(+0.72, ?1.10)} for HgS_cinn+HS^? ? HgS₂H^?; K₃=10^{?13.41(+0.76, ?0.93)} for HgS_cinn+HS^? ? HgS₂ ^2?+H⁺; K₄=10^{?8.36(+0.71, ?0.93)} for 2HgS_cinn+H⁺+H₂O ? Hg₂SOH⁺+H₂S. With decreasing pH, below 1, Hg solubility decreased sharply, indicating the formation of a new solid phase, inferred to be corderoite (Hg₃S₂Cl₂). From our solubility data, we calculated the free energy of formation (ΔG_f ^o) of Hg₃S₂Cl₂ to be ?396 (+3, ?11) kJ/mol. In experiments where excess S⁰(s) was present, a new mercury-polysulfide dimer was identified; its formation constant is K₅=10^{?1.99(+0.69, ?1.27)} for 2HgS_cinn+2HS^? + nS⁰ ? Hg₃S₄ ^IIS_n ^oH₂ ^2?. Data from experiments where Hg⁰(aq) was added confirmed the reversibility of HgS dissolution. An application of our mercury-sulfide speciation model to a natural anoxic basin, Saanich Inlet, British Columbia, is discussed.     

Evidence of microbial control of Hg0emissions from uncontaminated terrestrial soils

It is known that in wetland soils and soils contaminated with mercury (Hg), direct biotic reduction of Hg²⁺ to Hg⁰ leads to Hg⁰ emissions to the atmosphere. In terrestrial soils, numerous factors have been reported that control Hg⁰ emissions, but it is still unclear if biotic processes are also important. In this study, microbiological activity of Cambisol monoliths from a subalpine grassland with Hg concentrations of approx. 100 ng g^–1 were manipulated in laboratory incubation experiments. Elemental Hg emissions were recorded together with CO₂ emission rates as proxy for microbiological respiration. Emissions of Hg⁰ increased from approx. 5 ng m^–2 h^–1 up to 130 ng m^–2 h^–1 with stimulated biological activity (glucose addition, increase in temperature) and decreased with inhibited activity (chloroform fumigation, autoclaving, drying). Similar patterns with evasion rates of >90 ng m^–2 h^–1 were observed after dried soils were remoistened again. Our results indicated that processes leading to Hg⁰ emissions from uncontaminated terrestrial soils are at least partly controlled by biotic processes. However, it is still uncertain if Hg⁰ emission is caused directly by biotic reduction of Hg²⁺ or indirectly by abiotic reduction, induced by products of microbiological degradation, e.g., humic acids.     

Mercury Methylation Capacity and Removal of Hg Species from Aqueous Medium by Cyanobacteria

Most technologies used for decontamination presents good results for high concentrations, but limitations for lower ones. The desirable Hg concentration in the water is extremely low because of its toxicity. The aims of this study were to evaluate inorganic mercury (Hg²⁺) and methylmercury (CH₃Hg⁺) toxicity in Nostoc paludosum, to assess the potential of this cyanobacteria strain to remove these Hg species from aqueous medium and also to investigate Hg methylation by the cyanobacteria. CH₃Hg⁺ determination was performed by gas chromatography-pyrolysis-atomic fluorescence spectrometry in cultures exposed to a concentration of 20 μg L^?1 for 30 days. Both Hg species were removed from the supernatant, ranging from 73 to 96% of Hg²⁺ and from 73 to 95% of CH₃Hg⁺. Ultrastructural Hg²⁺ effects in the cyanobacteria cells investigated by transmission electron microscopy revealed higher production of glycogen, cyanophycin, and intrathylacoidal spaces than the control group. When Hg was added to the culture in the form of CH₃Hg⁺, a decrease corresponding to approximately 60% of the initial concentration due to Hg volatilization was observed. The production of CH₃Hg⁺ by the cyanobacteria was detected in concentrations near the limit of detection (0.0025%) of the bioaccumulated THg. This is an advantage for biotechnological decontamination applications, as CH₃Hg⁺ is a very toxic specie and can be bioaccumulated and biomagnified. The results demonstrated that cyanobacteria cells are an efficient alternative to retain and/or remove Hg at low concentrations and they constitute a potential tool for a “final cleaning” of contaminated waste water.     

The aqueous reduction of divalent mercury by sulfite

Divalent Hg is reduced by sulfite in aqueous solutions. The proposed mechanism involves the formation of an instable intermediate, HgSO₃, which decomposes to produce Hg⁺ which in turn is rapidly reduced to Hg⁰. The overall rate of the reaction is inversely dependent on the concentration of sulfite. This reaction may influence the concentration of Hg in cloud- and rain-water by reducing water soluble Hg²⁺ to volatile Hg⁰. At low concentrations of SO₂(g) (5 μg m⁻³, 25 °C), the rate of the conversion of Hg(SO₃)₂ ²⁻ to Hg⁰ becomes significant (> 1 % h⁻¹) at pH < 5.5. At higher S02 concentrations (500 pg m⁻³), the same rate is expected at pH < 4.5.     

The gas phase oxidation of elemental mercury by ozone

The gas phase reaction between elemental mercury (Hg⁰) and ozone (0₃) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s/v) ratios. At 0₃ concentrations above 20 ppm, a loss of Hg⁰ and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of 3±2×10^?20 cm³ molec.^?1 s^?1 at 20 °C. This corresponds to an atmospheric Hg half-life of about one year at a mean global 0₃ concentration of 30 ppb.     

Enhanced Tolerance to Mercury in a Streptomycin-Resistant Strain of Euglena gracilis

Toxicity of Hg²⁺ was determined in two strains of Euglena gracilis var. bacillaris: the wild-type (B) and a streptomycin-resistant strain (Sm^r). Cells were cultured under 12-h dark/12-h light regime or under continuous darkness. In the dark/light cultures, cellular growth was severely diminished in the B strain by Hg²⁺, whereas only a slight decrease was attained in the Sm^r strain; Hg²⁺ also affected the photosynthetic and respiratory activities of the B strain, but not those of Sm^r strain. Under continuous darkness, cellular growth of both strains was lower than under dark/light cycles, but it was inhibited by Hg²⁺ to a much lesser extent. Cell culture by 5 days under continuous dark or by 8 days of dark/light cycles resulted in a higher intracellular content of mercury in B strain than in Sm^r strain. In contrast, in both culture conditions, the fraction of mercury removed from medium by B strain was lower than that attained by Sm^r strain, whereas the ability to bio-transform (reduce) Hg²⁺ was two times higher in the mutant strain. The results suggested that Sm^r strain cells acquired an ability to remove Hg²⁺ from the medium, which was not associated to accumulation and which conferred protection against mercury.     

Translocation of 203Hg labelled HgCl2 and CH3HgCl in an iron-humus podzol studied by radio-analytical techniques

Since increased Hg-concentrations in fish in lakes and rivers in northern Europe, northern parts of the U.S.A. and Canada were found, environmental Hg research has focused intensively on the factors determining leaching of mercury from soil into water systems. This article presents the results of a leaching experiment with undisturbed soil columns treated with HgCI₂ and CH₃HgCl using radio-analytical techniques. The columns were irrigated with rain of different acidity, rain volumes and irrigation intensities. The leaching of mercury was traced by detecting the vertical distribution of ²⁰³Hg in the soil profiles. Advantages and disadvantages of radioanalytical scanning techniques are discussed. The results of Hg leaching in the soil columns indicate a considerably stronger leaching of monomethyl mercury compared to inorganic mercury. Leaching of the two Hg-species is ruled by competition of H⁺ induced soil-Hg desorption with DOM-Hg complex formation; both being affected by rain acidity. Rain intensity had no visible effect on leaching of Hg²⁺ and CH₃Hg⁺. An extended rain duration increased the leaching of CH₃Hg⁺.     

Kinetic and Product Studies of the Reactions of NO2, with Hg0 in the Gas Phase in the Presence of Titania Micro-Particle Surfaces

As global mercury emissions from coal fire power plants increase with the continuing rise of coal consumption, mercury capture methods are being developed to prevent mercury??s escape into the atmosphere. Titanium dioxide (TiO₂) in the presence of ultra violet light (UV-A; ?? _max ??360?nm) and oxygen will capture mercury as the solid product HgO_(s). Testing the effects of TiO₂ in the presence of other pollutants has so far been limited. We have performed kinetic and product studies of mercury adsorption in the presence of the gaseous flue co-pollutant NO_2(g). We extensively studied the gas-phase reaction of NO₂(g) with Hg _(g) ⁰ . We compared the gas-phase reaction to the same reaction performed in the presence of thin TiO₂ particle surfaces from 0 to 100?% relative humidity. The second-order rate constant was measured to be k?=?(3.5?±?0.5)?×?10^?35?cm⁶ molecules^?2?s^?1, independent of the presence of titania or the total surface area available for adsorption. Exposure of NO_2(g) to titania surfaces that were already saturated in captured mercury (HgO_(s)) increased total mercury uptake onto the surface. We discuss the implications of this study to the capture of mercury emissions prior to release to the atmosphere.     

Mercury Content of Illinois Soils

For a survey of Illinois soils, 101 cores had been collected and analyzed to determine the current and background elemental compositions of Illinois soils. Mercury and other elements were determined in six samples per core, including a surface sample from each core. The mean mercury content in the surface samples was 33 ± 20 g/kg soil, and the background content was 20 ± 9 g/kg. The most probable sources of mercury in these soils were the parent material, and wet and dry deposition of Hg⁰ and Hg²⁺ derived from coal-burning power plants, other industrial plants, and medical and municipal waste incinerators. Mercury-bearing sewage sludge or other fertilizers applied to agricultural fields could have been the local sources of mercury. Although the mercury content correlated with organic carbon content or clay content in individual cores, when all the data were considered, there was no strong correlation between mercury and either the organic carbon or the clay-size content.     

Catalytic effect of various metal ions on the methylation of mercury in the presence of humic substances

Methylation of Hg²⁺ (Hg(NO₃)₂) in the presence of fulvic acid (FA) and various metal ions has been studied. The concentrations of Hg²⁺ and FA ranged from 5 to 20 mg L^?1 and 171 to 285 mg L^?1 DOC, respectively. The pH range was 3 to 6.5. FA was isolated from an acid brown-water lake by XAD-8 polymeric adsorbent. Methylmercury production in the dark during 2 to 4 days incubation at 30 °C increased with increasing concentrations of Hg²⁺ ion and FA as well as with additions of metal ions (5 to 10 × 10^?5 mole L^?1 The observed catalytic activity of metal ions followed the order Fe³⁺ (Fe²⁺) > Cu²⁺ ≈ Mn²⁺, > Al³⁺. The production of methylmercury had a pH-optimum around 4 to 4.5 at the conditions tested.     

Faunal effects on the distribution of gamma emitting radionuclides in four forested soils

Brown trouts, Salmo trutta, were exposed via aquarial water to ²⁰³Hg²⁺ or to CH₃ ⁻²⁰³Hg⁺ alone or together with one of the following S-containing substances: sodium dimethyldithiocarbamate (SMC), sodium diethyldithiocarbamate (SEC), potassium ethylxanthate (PEX), sodium isopropylxanthate (SIX), sodium diethyldithiophospbate (SEP), sodium diisopropyldithiophosphate (SIP) or sodium pyridinethione (SPyr). The distribution of the ²⁰³Hg²⁺ and the CH₃−²⁰³Hg⁺ in the fishes were then studied by whole-body autoradiography and gamma spectrometry. The results showed that the examined complexing substances can induce increased uptake of both ²⁰³Hg²⁺ and CH₃−²⁰³Hg⁺ by the fishes: for ²⁰³Hg²⁺ most of the complexing substances induced a similar increase in various tissues; for CH₃−²⁰³Hg⁺ marked variations were seen for different substances. Determinations of chloroform/water partition coefficients showed that the examined substances are able to form lipophilic complexes both with Hg²⁺ and CH₃−Hg⁺. A facilitated penetration of the lipophilic complexes over the membranes of the gills and other tissues may underly the increments of the tissue-levels of the Hg. It is possible that increased uptake of Hg²⁺ and CH₃−Hg⁺ induced by complexing substances of this type may have toxicological implications for fishes and for other aquatic organisms.     

Infiltration and Distribution of Elemental Mercury DNAPL in Water-Saturated Porous Media: Experimental and Numerical Investigation

Liquid elemental mercury occurrence in the subsurface as dense non-aqueous phase liquid (DNAPL) is reported worldwide in proximity of several industrial facilities, such as chlor-alkali plants. Insight into Hg⁰ DNAPL infiltration behavior is lacking and, to date, there are no experimental observations of its infiltration and distribution in water-saturated porous media, except for capillary pressure-saturation column experiments. To better understand the processes governing elemental mercury DNAPL flow behavior, a series of flow container experiments were performed using mercury DNAPL (in sands and glass beads) and tetrachloroethylene (PCE) (in sands). While liquid Hg⁰ was not able to infiltrate in the sand-filled container due to an overall lower permeability of the sample and a defect of the setup, in the glass beads experiment mercury DNAPL infiltration occurred. Dual gamma ray measurements showed that, in glass beads, liquid Hg⁰ preferentially migrated towards higher porosity zones. As for PCE, infiltration and distribution of Hg⁰ DNAPL are strongly affected by the heterogeneities within the porous formation. However, compared to other DNAPLs, liquid Hg⁰ shows a strong attenuation potential of gamma rays. Finally, numerical simulations of the glass beads experiment showed an overall good agreement with the experimental results, highlighting that, among the factors influencing the prediction of liquid Hg⁰ migration in water-saturated porous media, the most critical are (i) the knowledge of the inflow rate, (ii) the reliable estimation of the porous formation permeability, and (iii) the accurate representation of the correlation between retention properties and intrinsic permeability.     

Soil Remediation – Mercury Speciation in Soil and Vapor Phase During Thermal Treatment

Spectroscopic (XRD, XPS, ICP-MS and AAS) and microscopic (ESEM) techniques have been used in order to study the chemical effects with emphasis on mercury speciation, during thermal treatment of a mercury contaminated soil. In the untreated soil, mercury was found concentrated in spherical particles, which were successively broken down upon thermal treatment. Hg⁰ and inorganic mercury compounds (presumably HgO(s) and HgSO₄(s)) could be detected. No (CH₃)₂Hg and only traces of CH₃Hg⁺ could be found. The dependence on temperature and heating time indicated that the evaporation of mercury from the soil was partly controlled by diffusion mechanisms. Mercury volatilized in two separate stages during heating; initial elemental vaporization, and subsequent volatilization of the oxide or sulfate phase at higher temperatures (>230°C). By thermal treatment at 470°C and 20 min, a removal of >99% of the mercury could be achieved.