Total body burden of neurotoxicant Hg in Chinese mitten crab (Eriocheir sinensis) - Considerations of distribution and human risk assessment

The Chinese mitten crab (Eriocheir sinensis) is considered one of the 100 most invasive alien species in the world. Despite this, its role in ecosystems, among others, in the trophodynamics of pollutants including mercury, is still not fully understood. Becoming an increasingly important and widespread element of the trophic chain in new areas arouses interest from humans as consumers. Hence it is important to determine the level of contaminants (including Hg) in alien species. In the present study, great attention was paid separately to the soft tissues and hard tissues of the exoskeleton, which may play an important role in the detoxification of the crab's body from toxic Hg. The study was conducted on crabs collected in 2011-2021 in the Vistula Lagoon. Concentrations of total mercury and its forms were carried out using a Direct Mercury Analyzer, DMA-80 (Milestone, Italy). The present study showed that mercury accumulation of the crab's body largely occurred through the gills, followed by the oral route. The distribution of Hg in the crab's organs was related to the trophic origin of the mercury, while halide-bound mercury and semilabile forms from the respiration (filtration) process were redistributed into the crab's exoskeleton. Male crabs, compared to females, had a higher Hg burden on internal organs such as their hepatopancreas and gonads. Hg concentration in hard tissues was closely related to the type of mineralization of the carapace. The elimination of Hg from the muscles and from the hepatopancreas into the carapace was one of the important detoxification processes of the crab's body. Thus, moulting crabs effectively remove Hg protecting its body from the neurotoxin. As a result, a smaller Hg load is biomagnified, making the crab's muscle tissue fit for human consumption. The observed decrease in Hg concentrations from 2011 to 2021, as well as the spatial variability of Hg in the crab's muscles, testify that the crab can serve as a biomonitor for ecosystem changes.

Mercury fractionation - Problems in method application

Mercury (Hg) is a global pollutant with a negative effect on human and ecosystem health. Mercury is toxic in all forms. The toxicity, however, varies depending on the form of mercury, determining its physical and chemical properties. Therefore, knowledge on the chemical speciation of mercury is key for the understanding of its transport and transformations in the environment. Analysis of mercury speciation, however, is time-consuming and involves high risk of contamination. The mercury thermodesorption method offers many new possibilities. The main advantages of this method are identifying which groups of compounds are being transformed in the atmosphere, sediment and soil, suspended matter and plankton, and in organisms from different trophic levels. A great advantage of the method is also its application in mercury analyzers, where it is possible to control the heating and cooling temperatures of. The standardisation of fractionation nomenclature for all matrices (both biotic and abiotic) will be helpful in application of this mercury fractionation method too. It has also disadvantages, mostly in the technical preparation of the analyzer. The analyzer must be prepared for fractionation: setting the ventilator and adjusting the PID parameters so that the pre-set heating (t1) and combustion (t2) times reach the set value in the method program. Also, any modification of the heater forces a re-optimisation of the method with mercury standards, as certified reference materials for Hg fractionation in environmental matrices are not available. The HgF2 fraction cannot be used as the methylmercury concentration, which is undoubtedly the biggest drawback of this method.

Identification of mercury species in coal combustion by-products from power plants using thermal desorption-atomic fluorescence spectrometry on-line coupling system

Along with the environmental protection policies becoming strict in China, the air pollution control devices (especially selective catalytic reduction (SCR)) are widely equipped in coal-fired power plants. The installation and run of these devices will inevitably affect mercury (Hg) species distribution in coal fired by-products such like fly ash (FA) and gypsum. In this work, a new on-line coupling system based on atomic fluorescence spectrometry (AFS) with a home-made chromatographic workstation was successfully developed to identify Hg species through thermal programmed desorption (TPD). The influences of matrix, furnace temperature, and carrier gas flow on analytical performance were investigated and the parameters were optimized. The FA and gypsum samples from coal-fired power plants equipped with SCR were collected and the mercury species were analyzed by the developed coupling system. HgCl₂ and HgO were the main species in FA, while Hg₂Cl₂ and HgO were the main species in gypsum. All of Hg species in the studied FA and gypsum samples were released below 400 °C. A sequential extraction procedure was applied to further verify the operational Hg species including mobile and non-mobile fractions in FA and gypsum samples. This study demonstrated that AFS coupled with TPD procedure was an effective method to analyze Hg species in coal combustion by-products from power plants.

Mercury methylation in cyanide influenced river sediments: A comparative study in Southwestern Ghana

Studies on the influence of CN on Hg methylation rates in aquatic systems draining gold mining (artisanal and small-scale) communities in Africa are rare. The study assessed the influence of CN on Hg methylation in aquatic sediments of two major river systems draining artisanal and small-scale gold mining (ASGM) communities of the Prestea-Huni Valley district, Southwestern Ghana. The miners extract gold (Au) through exclusive amalgam [Hg-Au] formation or cyanidation of Au-rich Hg-contaminated tailings, or a combination of both techniques. Hg water solubility and probable mercuric compounds in sediments of Hg-contaminated CN-loaded (River Aprepre) and Hg-contaminated non-CN (River Ankobra) aquatic systems within the district were investigated. THg was determined by CV-AAS after HF/HNO₃/HCl digestion. MeHg in sediments were extracted with H₂SO₄/KBr/CuSO₄-CH₂Cl₂; followed by aqueous-phase propylation, preconcentration-on-Tenax, and GC-CV-AFS. River Aprepre showed 4.58-14.83 ngMeHg/g as Hg (1.4-3.7% THg as MeHg), with 241-415 ngTHg/g, and 0.05-0.21 mgCN/kg. For River Ankobra, MeHg ranged 0.24-1.21 ngMeHg/g (0.08-0.35% THg as MeHg) with 162-490 ngTHg/g dw and CN < 0.001 mg/kg. There was positive correlation (r² = 0.5974; p < 0.01) between MeHg and CN in River Aprepre. The water-soluble fraction of Hg in sediment from both rivers was < 1% of THg. Hg in sediments from River Aprepre were generally more soluble than that from River Ankobra, indicating that Hg in sediments from River Aprepre were potentially more bioavailable for methylation. Accordingly, the presence of CN in Hg-dominated river sediments potentially influences and enhances the solubility and mobility of Hg, resulting in increased Hg methylation rates.

Meteorological phenomenon as a key factor controlling variability of labile particulate mercury in rivers and its inflow into coastal zone of the sea

Mercury (Hg) is recognized as a global pollutant, which can be transported to the sea by suspended particulate matter (SPM) via rivers constituting the main source of mercury in the southern Baltic sea. The aim of the present study was to characterize the mercury fractions in suspended particulate matter, as well as the transformations of Hg during its riverine transportation into the sea. The thermo-desorption method was used to determine the labile and stable mercury fractions in SPM of rivers (Reda, Zagórska Struga, Gizdepka, Płutnica) within the Baltic Sea basin. In this paper six "periods" were designated (heating, non-heating, drought, rains, downpour/flood and thaws), during which the river suspended particulate matter was enriched with various fractions of mercury. Meteorological and hydrological phenomena such as downpours and thaws intensified surface runoff, causing an increase in the share of Hg_abs and Hg_ads1 mercury fractions in suspended particulate matter. Whereas, droughts contributed to the formation of HgS in a large river and to an inflow of adsorbed Hg in smaller rivers decrease of air temperature leads to increase of fossil fuel combustion and then increases the share of adsorbed Hg (mainly bound with halides) in riverine particulate matter. In the non-heating season, the main fraction was the mercury absorbed inside organic matter.

Temporal changes in the content of labile and stabile mercury forms in soil and their inflow to the southern Baltic Sea

Rivers represent the main source of mercury (Hg) in the Southern Baltic. Nevertheless, the concentration and proportion of individual Hg forms in rivers depend on the management of the river basin, as well as on the intensity of meteorological phenomena. Hence the aim of the present study was to determine the influence of drought and rains/intense rains on the content of labile and stable Hg forms in the soil of river catchments with various types of land management, and on the inflow of bioavailable mercury to the coastal zone of the sea. Soil and sediment samples were taken from two rivers flowing into Puck Bay (Southern Baltic): the Reda and Gizdepka. In order to determine Hg concentration and the proportions of its particular forms in the collected material, the thermo-desorption method was used. Five periods were identified during which the soil was enriched with various Hg forms. The obtained results showed that in periods of intensive development of vegetation, the soil becomes enriched with absorbed mercury (Hg_abs). On the other hand, as a result of Hg emissions during the heating of buildings, mercury associated with halides (Hg_ads1) is deposited on land, as was primarily recorded in catchments where individual household furnaces were found. Both mild and intense rainfalls intensified the surface run-off, which contributed to soil erosion, causing the transport of both Hg_abs and Hg_ads1 to the river bed. However, the soil was more enriched with labile mercury in anthropogenic catchments, as they are only slightly overgrown with vegetation, the presence of which limits soil erosion. During periods of snow melting, there was intensive leaching and transportation of Hg_ads1, which had been deposited on the land surface during the intensive combustion of fossil fuels. In each of the designated periods, stable mercury sulphide was formed in the soil. However, the highest proportion of HgS was found during a period of drought, when organic matter decomposed and there was inflow of sulphur compounds from farms. Taking into consideration the anomalous study periods, the largest load of mercury introduced along with the bed sediment of the Gizdepka into the sea was recorded during downpour/flood. Nevertheless, the most bioavailable Hg-enriched load was introduced during snow melting period.

Mercury fractionation in marine macrofauna using thermodesorption technique: Method and its application

Mercury (Hg) is one of the most dangerous elements, and its toxicity and ability to accumulate in organisms depend on its chemical form. There are numerous methods of Hg speciation analysis, out of which the least expensive and the least time-consuming one is thermodesorption. The method has been successfully used for the analysis of abiotic samples - soils and sediments. The aim of this study was to verify whether the simplified thermodesorption method can be used in the analysis of the tissues of animal organisms from different trophic levels. Hg fractionation analyses were performed on a DMA-80 analyser (Milestone, Italy). The results presented in this paper are the first published data on Hg fractionation by thermodesorption method in animal tissues. The study showed that the 5-step thermodesorption method can be applied to various types of environmental matrices, which makes it universal. This method is of great importance in terms of estimating the Hg uptake and transfer in the trophic chain, and also enables the assessment of global Hg circulation in the environment. The presented method does not require previous digestion of samples or the use of expensive reagents. It can also be used for the preliminary selection of samples for MeHg analysis. The results obtained by this 5-step fractionation could be comparable with different research, conducted using other Hg analysers.

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.

Simple screening technique for determination of adsorbed and absorbed mercury in particulate matter in atmospheric and aquatic environment

The threat connected to mercury results from its capacity to be transported over long distances and its ability to bioaccumulate and biomagnify in the trophic chain, making it a global problem. Humans are situated at the top of the trophic ladder, and excess mercury manifests itself mainly in the onset of neurological conditions. The toxicity of mercury, as well as its residence time, depends on the form in which it occurs. However, analysis of mercury speciation is time-consuming and poses a high risk of additional or negative contamination. Hence, the mercury thermodesorption method, and particularly its use for fractionating Hg, offers many new possibilities. Here, the thermodesorption technique was applied to the determination of mercury fraction in particulate matter using a DMA-80 direct mercury analyser (Milestone, Italy). The presented method allows direct (without prior mineralisation) determination of labile and stabile mercury fractions within a relatively short time. Heating sample in subsequent temperatures enables determination the share of mercury adsorbed on the surface (mainly associated with halogenides (Hg_ads1) and HgSO₄/HgO/HgF₂ (Hg_ads2), as well as absorbed within the suspended particulate organic matter (Hg_abs), in a relatively short time. This fractionation is of great importance in terms of estimating the transfer of mercury to and along the trophic chain. This method determines the contribution of two stable mercury fractions:: HgS and residual Hg, strongly bound to particulate matter matrix (Hg_res). The novelty of this technique is also its joint ability to determine gaseous mercury bound to airboirne particulate matter, which will enable better understand Hg cycling in the atmosphere as well as mercury fraction in dry deposition flux. This method enables assessment of global mercury circulation in environment.

Mercury fractionation in soil and sediment samples using thermo-desorption method

Mercury is one of the most hazardous elements. Its transformation and transport in the environment strongly depend on its chemical form. The 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. Therefore the aim of this research was to develop a simple thermo-desorption method for mercury fractionation in soil and sediment samples using a direct mercury analyser. The DMA-80 direct mercury analyser (Milestone, Italy) was chosen for this purpose and Hg species were characterised by the temperature range at which they were released. Thirteen synthetic standard materials as well as "natural" standards for a humus-like substance and methyl mercury were used in this work. The method was tested on a certified reference material as well as on natural samples: soil, beach sand and marine sediment. The obtained results show that the temperature fractionation, in spite of some limitations, could be considered as a screening method for the evaluation of the percentage contribution of certain groups of Hg compounds with similar properties in solid samples. This method could be applied for solid samples with low, environmental Hg concentration. The result obtained by this four-step fractionation could be comparable with different research, conducted using other mercury analysers.