Mercury speciation studies

In mercury speciation studies, pressurized liquid extraction (PLE), microwave-assisted extraction (MAE), and supercritical fluid extraction (SEE) are employed [33]. In particular, methyl-mercury is extracted by the Westoo method [33,34], which consists in a leaching process with hydrochloric acid, the extraction of the metal chloride into benzene or toluene, the addition of ammonium hydroxide that converts the metal species to hydroxide and the saturation with sodium sulfate. Most of the HPLC methods reported in literature for the determination of organomercury compounds (mainly monomethyhnercury, monoethyhnercury, and monophenylmercury) are based on reversed... 

Bloxam et al. [482] used liquid chromatography with an inductively coupled plasma mass spectrometric detector in speciation studies on ppt levels of mercury in seawater. 

Advantages High analysis rate 3-4 elements per hour Applicable to many more metals than voltammetric methods Superior to voltammetry for mercury and arsenic particularly in ultratrace range Disadvantages Nonspecific absorption Spectral interferences Element losses by molecular distillation before atomisation Limited dynamic range Contamination sensitivity Element specific (or one element per run) Not suitable for speciation studies in seawater Prior separation of sea salts from metals required Suspended particulates need prior digestion About three times as expensive as voltammetric equipment Inferior to voltammetry for cobalt and nickel... 

Batley [28] examined the techniques available for the in situ electrodeposition of lead and cadmium in estuary water. These included anodic stripping voltammetry at a glass carbon thin film electrode and the hanging drop mercury electrode in the presence of oxygen and in situ electrodeposition on mercury coated graphite tubes. Batley [28] found that in situ deposition of lead and cadmium on a mercury coated tube was the more versatile technique. The mercury film, deposited in the laboratory, is stable on the dried tubes which are used later for field electrodeposition. The deposited metals were then determined by electrothermal atomic absorption spectrometry, Hasle and Abdullah [29] used differential pulse anodic stripping voltammetry in speciation studies on dissolved copper, lead, and cadmium in coastal sea water. 

Schintu, M., F. Jean-Caurant, and J.C. Amiard. 1992. Qrganomercury determination in biological reference materials application to a study on mercury speciation in marine mammals off the Faroe Islands. Ecotoxicol. Environ. Safety 24 95-101. 

Lu, D.Y., Granatstein, D.L. and Rose, D.J. (2004) Study of mercury speciation from simulated coal gasification. Industrial and Engineering Chemistry Research, 43(17), 5400-404. 

A study by Rasemann et al. demonstrated to what extent mercury concentrations depend on the method of handling soil samples between sampling and chemical analysis for samples from a nonuniformly contaminated site [152], Sample pretreatment contributed substantially to the variance in results and was of the same order as the contribution from sample inhomogeneity. Welz et al. [153] and Baxter [154] have conducted speciation studies on mercury in soils. Lexa and Stulik [155] employed a gold film electrode modified by a film of tri-n-octylphosphinc oxide in a PVC matrix to determine mercury in soils. Concentrations of mercury as low as 0.02 ppm were determined. 

Ribo, J.M., Yang, J.E. and Huang, P.M. (1989) Luminescent bacteria toxicity assay in the study of mercury speciation, in M. Munawar, G. Dixon, C.I. Mayfield, T. Reynoldson and M.H. Sadar (eds), Environmental Bioassay Techniques and their Application Proceedings of the 1st International Conference held in Lancaster, England, 11-14 July 1988, Kluwer Academic Publishers, Dordrecht, Netherlands, pp. 155-162. 

Speciation studies have been focused on relatively few elements, mainly aluminum, antimony, arsenic, chromium, lead, mercury, selenium, and tin. The primary species of these elements studied with ICP-MS detection are presented in Table 3 and they include different oxidation states, alkylated metal and/or metalloid compounds, selenoaminoacids, and selenopeptides. In addition, applications in studies of the pharmacokinetics of metal-based drugs (Pt, V, Au), metalloporphyrins (Ni, V, Fe, etc.), heavy metals in phytochelatins (Cd, Cu, Zn, Hg, etc.) and in humic substances should be mentioned. 

Mercury is one of a number of toxic heavy metals that occur in trace amounts in fossil fuels, particularly coal, and are also present in waste materials. During the combustion of fuels or wastes in power plants and utility boilers, these metals can be released to the atmosphere unless remedial action is taken. Emissions from municipal waste incinerators can substantially add to the environmental audit of heavy metals, since domestic and industrial waste often contains many sources of heavy metals. Mercury vapor is particularly difficult to capture from combustion gas streams due to its volatility. Some processes under study for the removal of mercury from flue gas streams are based upon the injection of finely ground activated carbon. The efficiency of mercury sorption depends upon the mercury speciation and the gas temperature. The capture of elemental mercury can be enhanced by impregnating the activated carbon with sulfur, with the formation of less volatile mercuric sulfide [37] this technique has been applied to the removal of mercury from natural gas streams. One of the principal difficulties in removing Hg from flue gas streams is that the extent of adsorption is very low at the temperatures typically encountered, and it is often impractical to consider cooling these large volumes of gas. 

Speciation studies have been carried out for methylated species of As, Sb, Ge, and Sn and on different redox states of these elements—As(III-V), Sb(III-V), or Cr(III-VI)— (Andreae and Froehlich, 1984), as shown in Fig. 13.2. In oxic Baltic waters the pentavalent species of As and Sb predominate, while in the anoxic basins the distribution shifts to the trivalent species and possibly also to polysulfide complexes. The methylated species of As, Sb, and Ge are detectable throughout the water column. Since the mid-1980s, an improvement in the understanding of the behavior of trace elements in the Baltic Sea has been achieved. First investigations into the speciation of mercury have been realized by Brugmann (1979) and Brugmann et al. (1991). A special emphasis has been made on the different physicochemical forms, such as dissolved Hg, weakly associated Hg with particles, and total Hg. 

Suzuki, K. T., Ogra, Y. Metabohsm of selenium audits interaction with mercury mechanisms by a speciation study. Phosphorus, Sulfur Silicon Relat Elem 2001, 171-172, 135-169. 

The programme to improve the quality of MeHg determinations started in 1987 with a consultation of European experts. From the beginning it was clear that it was essential to examine critically each step of the methods used in mercury speciation analysis. As described below, a series of exercises of increasing difficulty were designed and interlaboratory studies were conducted in 1987-88 (first round-robin with simple solutions), 1988-89 (cleaned and raw extracts) and 1989-90 (extracts and real samples). The certification of... 

The significance of mercury concentrations in amphibian tissues is not Imown with certainty and requires additional research for satisfactory risk assessment. The following areas are recommended for study acclimatization and adaptation to mercury mercury remobilization during periods of metamorphosis, hibernation, estivation, and reproduction critical organ concentrations and biomarkers of adverse mercury effects. These studies should also consider the influence of exposure duration and dose, mercury speciation, and mercury interaction with other metals. 

DeVito MS, Rosenhoover WA. Flue gas mercury and speciation studies at coal-fired utilities equipped with wet scrubbers, in 15 International Pittsburgh Coal Conference, Pittsburgh, PA, September 15-17, 1998. 

In the environment one may be interested in some single components like NOs , Cl, NH/, Cu, etc. but nowadays there is an increasing need to know the form in which elements like copper are present, i.e. not only free metal ion concentrations but also the concentrations of the complexes and other compounds in which the metal is present and the inertness or the lability of these compounds. The reason for this need for more detailed information is the difference in toxicity of the various forms in which copper and other elements are present. For instance, the organo-mercury compounds are much more toxic than the inorganic mercury compounds whereas for arsenic the opposite is true. The detailed analysis of the forms in which elements are present is often denoted as speciation and asks, in general, for combinations of sophisticated techniques. For the moment it is difficult to see the role pTAS can play in such speciation studies but for... 

Various analytical strategies based on the use of chemically modified electrodes are presented. We describe the use of conventionally sized as well as microelectrodes in the determination of mercury and copper ions in solution and point to the potential utility of modMed electrodes in carrying out speciation studies. Also discussed is the use of carbon fiber microelectrodes modified with alkaline phosphatase as amperometric biosensors. Finally, we present some preliminary findings on the development of a mo fied platinum electrode for the determination of nitric oxide. 

Thus, this study demonstrates not only the feasibility of performing mercury determinations at veiy low levels, but in addition points to the possibility of employing this analytical approach to speciation studies. 

Garcia-Monco Carra et al. [296] have described a hybrid mercury film electrode for the voltammetric analysis of copper (and lead) in acidified seawater. Mercury plating conditions for preparing a consistently reproducible mercury film electrode on a glassy carbon substrate in acid media are evaluated. It is found that a hybrid electrode , i.e., one preplated with mercury and then replated with mercury in situ with the sample, gives very reproducible results in the analysis of copper in seawater. Consistently reproducible electrode performance allows for the calculation of a cell constant and prediction of the slopes of standard addition plots, useful parameters in the study of copper speciation in seawater. 

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