Mercury species

There are several environmentally significant mercury species. In the lithosphere, mercury is present primarily in the +II oxidation state as the very insoluble mineral cirmabar (HgS), as a minor constituent in other sulfide ores, bound to the surfaces of other minerals such as oxides, or bound to organic matter. In soil, biological reduction apparently is primarily responsible for the formation of mercury metal, which can then be volatilized. Metallic mercury is also thought to be the primary form emitted in high-temperature industrial processes. The insolubility of cinnabar probably limits the direct mobilization of mercury where this mineral occurs, but oxidation of the sulfide in oxygenated water can allow mercury to become available and participate in other reactions, including bacterial transformations. 

Laijava K, Laitinen T, Vahhnan T, Artmann S, Siemens V, Broekaert JAC, Klockow D. 1992. Measurements and control of mercury species in flue gases from liquid waste incineration. Int J Anal Chem 149 73-85. 

Bloom NS, Fitzgerald WF. 1988. Determination of volatile mercury species at the picogram level by low temperature gas chromatography with cold-vapor atomic fluorescence detection. Anal Chim Acta 208 151-161. 

Wildlife toxicologists should be attuned to developments in human health mercury, as assays that have been used successfully on humans may be suitable or adaptable for other vertebrate species. Echeverria and co-workers (Echeverria et al. 2005, 2006 Heyer et al. 2006) have characterized a gene encoding coproporphyrinogen oxidase, a gene in the heme biosynthetic pathway. Polymorphism in this gene predicts differential response to elemental mercury exposure in human subjects. Plans to modify this assay for other mercury species in matrices from wildlife are under way. 

Wagemann RE, Trebacz G, Boila G, Lockhhart WL. 2000. Mercury species in the liver of ringed seals. Sci Total Environ 261 21-32. 

Bettmer, J., Cammann, K., and Robecke, M., Determination of organic ionic lead and mercury species with high-performance liquid chromatography using sulphur reagents, /. Chromatogr., 654, 177, 1993. 

In order to gain information on the environments of certain atoms in dissolved species, in melts or in solids (crystalline or noncrystalline), which are not accessible to diffraction studies for one reason or another, X-ray absorption spectrometry (XAS) can be applied, with the analysis of the X-ray absorption near-edge structure (XANES) and/or the extended X-ray absorption fine structure (EXAFS). Surveys of these methods are available 39,40 a representative study of the solvation of some mercury species, ElgX2, in water and dimethylsulfoxide (DMSO) by EXAFS and XANES, combined with quantum-chemical calculations, has been published.41... 

Organolithium reagents have also been employed for the synthesis of novel bis(alkynyl)mercury derivatives. These include Hg(C=CCF3)263 and 46-48,64 which have been synthesized along with the bis(alkynyl)aurate analogs. Bis(alkynyl)mercury species such as 49 can also be obtained by reaction of monosubstituted alkynes with K2[Hgl4] in basic aqueous solutions.6 ... 

Mercury (Hg) can occur in a large number of physical and chemical forms with a variety of properties, thus determining complex distribution, bioavailability, and toxicity patterns [1]. The most important chemical forms are elemental Hg (Hg°), ionic Hg (Hg2+ and Hg22+), and alkylmercury compounds. Because of their capability to permeate through biological membranes and to bioaccumulate and to biomagnificate through the trophic chain, alkylmercury compounds are the most toxic mercury species found in the aquatic environment [2]. 

Techniques for analysis of different mercury species in biological samples and abiotic materials include atomic absorption, cold vapor atomic fluorescence spectrometry, gas-liquid chromatography with electron capture detection, and inductively coupled plasma mass spectrometry (Lansens etal. 1991 Schintu etal. 1992 Porcella etal. 1995). Methylmercury concentrations in marine biological tissues are detected at concentrations as low as 10 pg Hg/kg tissue using graphite furnace sample preparation techniques and atomic absorption spectrometry (Schintu et al. 1992). 

With respect to Cr a distinction should be made between Cr(III), which is the common oxidation state in the soils, being rather immobile and so toxic, and Cr(VI), which is very mobile and very toxic. With respect to Hg, the situation is even more complex, due to the occurrence of mercuric mercury (Hg2+), mercurous mercury (Hg2+), elemental mercury (Hg°) and organic mercury species, such as methyl mercury, (CH3)2Hg (see Section 18.5). Furthermore, volatilization of elemental mercury and organic mercury species is common. A description of these... 

In the environment, metals are common as a chemical species, and as usual the metal-organic species are more toxic. For example, the inorganic lead and mercury species are less toxic for living organisms than the organic ones (methyl mercury, tetraethyl lead). However inorganic arsenic compounds are more toxic than organic... 

Driscoll et al. (1994) have studied the mercury species relationships among water, sediments, and fish (yellow perch) in a series of Adirondack lakes in New York state, USA. In most lakes, approximately 10% of the total mercury loading was in the form of C2HsHg+. Mercury concentrations increased as pH fell, but the best correlation was found between [dissolved Al] and [dissolved Hg] suggesting that the same factors are responsible for mobilizing both these metals. Methylmercury concentrations correlated strongly with the dissolved organic carbon content in the water. Fish muscle tissue was analyzed for mercury and showed an increase with age. However, the study was unable to resolve the question of whether the principal source of mercury to these lakes was atmospheric deposition or dissolution from bedrock due to acid rains. 

In order to identify the mercury species in the C3 and C4 cuts, experiments were carried out on propylene and on a raw steam-cracked C3 cut, containing methylacetylene (MA) and propadiene (PD). TTie steam-cracker C3 cut was found to be able to take up to 10 times more mercury than pure propylene. So MAPD has an effect on the mercury concentration in the C3 fraction. 

Once a representative sample of the matrix is available, the second most difficult problem is to provide adequate chemical procedures to convert all of the mercury species into inorganic mercury. The chemistry required to complete this will be dictated primarily by the nature of the sample. The three different procedures outlined in Fig. 7. 19 (a-c) are designed to cope with a range of chemical situations. 

In spite of these limitations it is possible to obtain valuable data provided specific questions are posed. For example, it has been suggested that the level of methyl-mercury in a sample is a good indicator of the level of mercury toxicity Therefore it will be most useful to detect and quantify this species rather than to use the available resources to detect a wide range of mercury species, whose biological behaviour are yet to be established. It is essential to clearly define the purpose and use to which the information will be put before any speciation experiments are performed. This helps not only in the choice of the appropriate techniques and methods, but also helps to focus attention on the parameters that are useful for the interpretation of the results. 

The certification procedure for seven trace metals (Ba, Ca, Li, Mg, Mn, Na and Sr) in the certified reference material FEBS-1 (National Research Council Canada, Institute for National Measurement Standards, Ottawa, Canada) based on fish otolith matrix by isotope dilution - ICP-MS in comparison to ICP optical emission spectrometry and X-ray fluorescence analysis, is described by Sturgeon et al4X The isotope dilution technique is also employed for species analysis in biological systems,46 e.g., for the determination of mercury species in tuna material,54 or in aquatic systems using cold vapour ICP-MS.55... 

Figure 7.1 Isotope ratios on transient signals with capillary CC-MC-ICP-MS. Chromatogram of mercury species obtained with CC coupled to Axiom MC-ICP-MS. Open squares 198Hg trace, filled circles 202Hg trace, black line 205TI trace continuously introduced as liquid solution. (E. Krupp and O. Donard, Int. j. Mass Spectrom. 242, 233 (2005). Reproduced by permission of Elsevier.)...

T. Stoichev, R. C. Rodriguez-Martin-Doimeadios, D. Amouroux, N. Molenat and O. F. X. Donard, Application of cryofocusing hydride generation and atomic fluorescence detection for dissolved mercury species determination in natural water samples, J. Environ. Monit., 4, 2002, 517-521. 

C. Schickling and J. A. C. Broekaert, Determination of mercury species in gas condensates by online coupled high-performance liquid chromatography and cold-vapor atomic absorption spectrometry, Appl. Organo-met. Chem., 9(1), 1995, 29-36. 

The mercury absorption of HgN03 in 0.1 M NaN03 solutions exhibited a typical Langmuir isotherm curve, as shown in Figure 4a. The maximum loading is 635 mg/g (or 3.2 mmol Hg/g). Similar adsorbing behavior is observed for other mercury species, such as... 

That the mercurial species released during the ring-closure step can, at least with some mercury(ll) salts, recycle and act catalytically is shown by the finding that mercury (II) trifluoroacetate, used in 0.1 M proportions (and even lower), in aqueous acetone at room temperature catalyzes the reaction of alkene 43 (R1 = Me, R2 = R3 = Bn, R4 = Ac a-isomer), and gives the cyclized products in 96% yield as a mixture of the alcohol 46 (R2 = R3 = Bn, R4 = Ac) and its epimer at the alcohol center, in the ratio 8 1 [24]. 

---