Effect of cooking temperature on metal concentrations and speciation in fish muscle and seal liver

Fish and marine mammals constitute a significant part of the country food diet of many Indigenous communities in Canada. These animals sometimes accumulate essential elements as well as elevated levels of toxic metals. We experimentally assessed how changes in cooking temperature (23-99 °C by boiling) modified elemental concentrations in whitefish muscle and grey seal liver (two organs commonly consumed in some northern communities). Wet and dry elemental concentrations changed linearly as a function of temperature, and two patterns were observed: methylmercury, selenium, and rare earth elements tended to remain associated with the food during cooking, whereas alkali, alkaline-earth metals, and arsenic were significantly transferred to cooking juices. Mass balances indicated that speciation of mercury was stable during cooking. Because elements generally behaved similarly as those of their periodic table group or their ecotoxicological classes (A, B, intermediate), we propose that elemental behavior during cooking is partly a function of chemical affinity, and this relationship can be used to predict the behavior of data-poor elements of emerging concern, such as technology-critical elements. Furthermore, the marked increases and decreases in elemental concentrations during cooking (e.g., -14% As and +39% Se in whitefish; -22% Cd and +55% Hg in seal liver, on a wet weight basis) should be considered when assessing risk because current exposure models usually only consider elemental concentrations in raw food.

Preliminary exploration of direct mercury speciation in solid samples by using thermal release coupled to electrothermal atomic absorption spectrometry

It is known that monitoring of mercury and notably its species is very important to assess their impact and distribution in the environment. In this regard, the development of a methodology for mercury speciation in natural and man-made media is of particular importance. There are a variety of studies in this area associated with the application of thermal release in combination with electrothermal atomic absorption detection for direct mercury speciation in solid samples without preliminary extraction of analytes. Nevertheless, a number of issues remain that hinder its practical application as a reliable analytical method. However, in order to achieve progress in this field, it is necessary to understand the features of the evaporation process itself. The goal of this work is to study the thermal behavior of the most common mercury species in order to eliminate the gaps in this approach. At this stage, studies were carried out using pure substances and their mixtures as a starting point for a subsequent transition to real natural samples. For this the installation scheme was modernized by introducing a module that provides programmable heating of the sample and variation of the heating rate. As a result of the experiments it was shown that the transformation of studied compounds with the examples of mercury chloride, methylmercury chloride, mercury sulfide and mercury sulfate occurs under thermal exposure, which leads to a change in their physicochemical characteristics, but, nevertheless, does not prevent their baseline separation for 30 min using programmable heating mode, which includes a continuous increase in temperature with a subsequent stop until the thermal peak is formed.

Behavior of mercury release from iron ores during temperature-programmed heat treatment in air

The behavior of Hg release from iron ores during temperature-programmed heat treatment (TPHT) in air is studied, primarily using an online monitoring method. The Hg release behavior during TPHT depends significantly on the type of ore being processed, involving the evolved forms, Hg⁰ and Hg²⁺, and those that remain thermally stable up to 950 °C. Furthermore, TPHT experiments for model Hg compounds suggest the presence of several types of Hg forms (HgCl₂, Hg₂Cl₂, HgS, HgO, HgSO₄, and associated mineral Hg) in the considered iron ores. The findings of this study provide insights for designing an efficient method for the removal of Hg from iron ore and gaseous Hg.

Can Sediments Contaminated by Mining be a Source of Mercury in the Coastal Environment Due to Dredging? Evidence from Thermo-Desorption and Chemical Speciation

The sediments in the Gulf of Trieste (northern Adriatic Sea, Italy) are contaminated by mercury (Hg) due to historic mining which took place in Idrija (Slovenia). Despite many studies having been done regarding Hg, no information is available on the potential impact of dredging required along the main channel approaching the Port of Monfalcone. Sixteen surface sediment samples were collected along the channel to determine both total Hg concentration and chemical species using the thermo-desorption (TD) technique. Six samples were also chosen to apply a selective sequential extraction (SSE). The TD technique showed the maximum Hg release approximately at 260 and 335°C, corresponding to metacinnabar (β-HgS) and cinnabar (α-HgS), respectively. The SSE demonstrated that Hg was mainly associated with poorly soluble or insoluble compounds (98.7%). A resuspension event over a limited period of time can be considered of negligible impact to the water column due to the scarce Hg mobility from sediments.

Mercury species and potential leaching in sludge from coal-fired power plants

Wet flue gas desulfurization (WFGD) sludge, generated from the WFGD effluent treatment process, is suitable for multiple uses in various industries. However, risk assessments of its utilization are limited. Systematic study of Hg species occurrences, partitioning and risks of leaching is required, and these concerns were addressed in the present study. Hg temperature-programmed decomposition (Hg-TPD) and an improved European Community Bureau of Reference (BCR) method indicated residual Hg in WFGD sludge was related to HgS, and the content of this fraction was from 2 to 3%. HgCl₂, HgO and HgSO₄ were assigned to the water/acid-soluble fractions, and reducible Hg was related to Fe species in the sludge. Leachate evaluation of the WFGD sludge indicated potentially high Hg leaching risk. WFGD sludge with higher Hg concentrations and smaller particulate diameters exhibited greater leaching potential. Leaching of Hg from WFGD sludge in China into the environment was estimated at 7.46 t/yr.

Highly Efficient and Selective Hg(II) Removal from Water Using Multilayered Ti3C2Ox MXene via Adsorption Coupled with Catalytic Reduction Mechanism

Mercury (Hg) removal is crucial to the safety of water resources, yet it lacks an effective removal technology, especially for emergency on-site remediation. Herein, multilayered oxygen-functionalized Ti₃C₂ (Ti₃C₂O_x) (abbreviated as M-Ti₃C₂) nanosheets were prepared to remove Hg(II) from water. The M-Ti₃C₂ has demonstrated ultrafast adsorption kinetics (the concentration decreased from 10 400 to 33 μg L^-1 in 10 s), impressively high capacity (4806 mg g^-1), high selectivity, and broad working pH range (3-12). The density functional theory (DFT) calculations and experimental characterizations unveil that this exceptional Hg(II) removal is owing to the distinct interaction (e.g., adsorption coupled with catalytic reduction). Specifically, Ti atoms on the {001} facets of M-Ti₃C₂ prefer to adsorb Hg(II) in the form of HgClOH, which subsequently undergoes homolytic cleavage to form radical species (e.g., ^•OH and ^•HgCl). Immediately, the ^•HgCl radicals dimerize and form crystalline Hg₂Cl₂ on the edges of M-Ti₃C₂. Up to ∼95% of dimeric Hg₂Cl₂ can be efficiently recovered via facile thermal treatment. Notably, owing to the adsorbed ^•OH and energy released during the distinct interaction, M-Ti₃C₂ has been oxidized to TiO₂/C nanocomposites. And the TiO₂/C nanocomposites have shown to have better performance on the photocatalytic degradation of organic pollutants than Degussa P25. These exceptional features coupled with mercuric recyclable nature make M-Ti₃C₂ an outstanding candidate for rapid/urgent Hg(II) removal and recovery.

Traceable Determination of Atmospheric Mercury Using Iodinated Activated Carbon Traps

Traceable determination of atmospheric mercury (Hg) represents a major analytical problem due to low environmental concentrations. Although Hg pre-concentration on activated carbon (AC) traps is a simple method for sample collection, Hg determination is difficult due to a complex matrix that cannot be easily digested using wet chemistry. Two approaches for Hg loading on iodinated AC, the purging of elemental mercury (Hg0) and the spiking a solution of standard reference material (SRM), were used to test whether spiking SRM solution on AC can be used for the traceable determination of atmospheric mercury collected as Hg0. Mercury on AC was determined using atomic absorption spectrometry after sample combustion. The detector’s response for both loading methods was identical in a wide concentration range, indicating that the spiking of SRM on AC can, indeed, be used for the calibration of analytical systems used for the determination of atmospheric mercury. This was confirmed by the determination of Hg in a real atmospheric sample collected on an iodinated AC trap and using an SRM spiking calibration. Different ACs were compared regarding their ability to quantitatively capture Hg while having the lowest breakthrough. Use of a specific impregnating solution probably converted Hg on AC to Millon’s iodide, as estimated from the fractionation thermogram.

Enhancing the catalytic oxidation of elemental mercury and suppressing sulfur-toxic adsorption sites from SO2-containing gas in Mn-SnS2

It is difficult to stabilize gaseous elemental mercury (Hg°) on a sorbent from SO₂-containing industrial flue gas. Enhancing Hg° oxidation and activating surface-active sulfur (S*) can benefit the chemical mercury adsorption process. A Mn-SnS₂ composite was prepared using the Mn modification of SnS₂ nanosheets to expose more Mn oxidation and sulfur adsorption sites. The results indicate that Mn-Sn₂ exhibits better Hg° removal performances at a wide temperature range of 100-250 °C. A sufficient amount of surface Mn with a valance state of Mn⁴⁺ is favorable for Hg° oxidation, while the electron transfer properties of Sn can accelerate this oxidation process. Oxidized mercury primary exists as HgS with surface S*. A larger surface area, stable crystal structure, and active valance state of each element are favorable for Hg° oxidation and adsorption. The Mn-SnS₂ exhibits an excellent SO₂ resistance when the SO₂ concentration is lower than 1500 ppm. The effects of H₂O and O₂ were also evaluated. The results show that O₂ has no influence, while H₂O and SO₂ coexisting in the flue gas have a toxic effect on the Hg° removal performance. The Mn-SnS₂ has a great potential for the Hg° removal from SO₂-containing flue gas such as non-ferrous smelting gas.

Catalytic removal of mercury from waste carbonaceous catalyst by microwave heating

Waste carbonaceous catalyst (WCC) from vinyl chloride monomer (VCM) production is a potential environmental threat due to the mercury toxicity. Microwave heating (MWH) was used to decontaminate WCC. Treatment temperature had a stronger influence on mercury removal than that of treatment time while mercury removal was highly depended on treatment time at lower temperature. When WCC was treated at 350 °C for 60 min, 400 °C for 30 min and 450 °C or more for 10 min, leaching toxicity of mercury conformed to the US EPA standard. 99.98% of total mercury was removed and residual mercury concentration was only 4.5 mg kg^-1 when treated at 500 °C for 30 min. Soluble and exchangeable Hg and Hg combined with labile organics were more easily to be removed than that of Hg bound to crystalline Fe/Al oxides, Hg combined with non-labile organics and HgS. The removal limit for different mercury species may be achieved at 500 °C. Evaporation removal of mercury followed exponential decay model. Activation energy for mercury removal was reduced due to the catalytic effect of MWH. Removal mechanisms of mercury included thermal evaporation, breakdown of molecular bonds, selective stripping of carbonaceous impurities.

Mercury fractionation in gypsum using temperature desorption and mass spectrometric detection

A quadrupole mass spectrometer was used to study the thermal release of mercury from wet flue gas desulphurization (WFGD) gypsum using temperature-programmed desorption/decomposition (TPD). The inability in direct detection of low concentrations of mercury halogenides in gypsum by mass spectrometry is discussed in detail. The hydrolysis of HgCl2 vapours under specific experimental conditions in the mass spectrometer was considered theoretically and proved experimentally. The mercury concentration in different gypsum fractions varies from 0.22 mg kg-1 (3.27-148 μm, coarse particles) to 20.6 mg kg-1 (0.41-88.0 μm, fine particles). All samples had a similar, symmetrical, single-peak (peak maximum 253–266°C) in the TPD spectra. In the present study, the use of ‘wet’ methods for preparing mercury compounds is introduced in addition to the mercury standards prepared using the ‘dry’ method, as commonly found in TPD. The study showed that selected metals, such as Fe enriched in gypsum samples, significantly influence the shape and the maximum temperature of the Hg TPD curves and that during the mercury compound preparation and the TPD process, Hg species undergo transformations that prevent the identification of their original identity.

Study on non-isothermal kinetics of the thermal desorption of mercury from spent mercuric chloride catalyst

Kinetics of the thermal desorption of mercury from spent mercury chloride catalysts were investigated using non-isothermal thermal analysis technique. Complex mercury species absorbed on waste catalysts were revealed by sequential extraction procedure. A scheme of six reactions was applied to elucidate mercury desorption kinetics. Activation energy estimated by model-free isoconversional methods is a slightly increasing function of conversion, implying a variation in the mechanism controlling mercury desorption. Average value of apparent activation energy (116.32kJ/mol) calculated by isoconversional Starink method was used to determine reaction mechanism using model-fitting and z(α) master method. One dimensional diffusion appears to govern mercury desorption process in the conversion range of 10%-40%, and then the reaction kinetic is controlled by two and three dimensional diffusion at greater conversion.