Ionic mercury

Atmospheric deposition is an important source of mercury for surface waters and terrestrial environments that can be categorized into two different types, wet and dry depositions. Wet deposition during rainfall is the primary mechanism by which mercury is transported from the atmosphere to surface waters and land. Whereas the predominant form of Hg in the atmosphere is Hg° (>95%), is oxidized in the upper atmosphere to water-soluble ionic mercury, which is returned to the earth s surface in rainwater. In addition to wet deposition of Hg in precipitation, there can also be dry deposition of Hg°, particulate (HgP), and reactive gaseous mercury (RGM) to watersheds [9-11]. In fact, about 90% of the total Hg input to the aquatic environment is recycled to the atmosphere and less than 10% reaches the sediments [12]. By current consensus, it is generally accepted that sulfate-reducing bacteria (SRB)... 

Kimura and Miller [30] also described the following methods for the determination in soil samples of extractable organic mercury, total mercury and extractable ionic mercury. 

Ionic mercury is extracted from about lg soil by shaking for 2h with each of two 25mL portions of 2M sodium chloride. The combined centrifuged and filtered (using 1M sodium chloride for washing) extract is analysed by the procedure of Polley and Miller [31]. 

Complexation of metals with organic compounds can also increase the toxicity of metals. This is the case with mercury, in which the organo-Hg species, methyl- and dimethylmercury, are fer more toxic than elemental or ionic mercury (Hg (aq)). The enhanced toxicity is caused by the increased tendency of the organo species to be retained, and therefore concentrated within, organisms. As discussed in Chapter 28.6.8, mercury is naturally biomethylated by bacteria under conditions of low pH and low... 

Methyl mercury is of much greater concern when health effects are considered, as it is much more toxic than ionic mercury or free mercury. Methyl mercury is also much more likely to be bioaccumulated, leading to serious contaminations, especially of fish. The speciation for mercury can be accomplished by derivatizing the methyl mercury and Hg2+ with sodium tetraethylborate, NaBEt4. The volatile MeHgEt, from methyl mercury, and HgEt2, from Hg2+, species formed are purged from the sample solution and separated in a GC column. An atomic emission spectrometer is used as a detector. 

It was quickly realized that the mercury species to be found in greatest abundance in precipitation was ionic mercury (e.g., Fogg and Fitzgerald, 1979). Some typical values of total mercury in precipitation are shown in Table 10. Extensive databases of precipitation mercury concentrations are available from monitoring networks in the US, Canada, and Nordic countries (e.g., US Mercury Deposition Network http //nadp.sws.uiuc.edu/ mdn). The discrepancy between the dominant gas and precipitation phase species implied a process of oxidation of elemental mercury in the atmosphere and its subsequent scavenging as being a major component of the mercury cycle. Since the initial work, and partially in response to... 

RaholaT, HattulaT, Korolainen A, Miettinen JK. Elimination of free and protein-bound ionic mercury in man. Ann Clin Res 1973 5 214-19. 

The method is based on the reduction-aeration technique by Hatch and Ott [2]. Ionic mercury in the sample is reduced to the elementary state by means of Sn ". Instead of a direct measurement, the mercury is captured on an absorber while aerating the sample with nitrogen-gas [3]. This absorber consists of gold-coated sea-sand (about 1 g) packed in a quartz tube. By electrothermally heating ( 800°C), the mercury is released and transferred to a second absorber, which is continuously connected to the inlet of the optical cell (the permanent absorber). 

A number of chemicals are used as reducing agents. The most common chemicals used for reduction of chromium are sulfur dioxide, sodium metabisulfite, sodium bisulfite, and ferrous salts. Other reducing agents used or which can be potentially used for water and wastewater treatment include sodium borohydride to reduce ionic mercury to metallic mercury and alkali metal hydride to alter the chemical form of lead so that it can be precipitated and also to recover silver. The common chemicals used as reducing agents are discussed on the following sections. 

Many chemicals can also exist as various species or states of ionization. For example, nitrogen can exist as nitrate, nitrite, or ammonia, arsenic can exist as arsenate or arsenite, and lead can exist as lead nitrate or lead chloride. The species or ionization state may depend upon abiotic variables such as soil or water pH, amount of dissolved oxygen in the water, and presence of other chemicals. Alternatively, bacteria and fungi may change the species or ionization state of a chemical. For example, bacteria can convert arsenite to arsenate, and add methyl groups to ionic mercury to produce methylmercury. 

Sorption colloid flotation has shown to be capable of quantitatively separating ionic mercury from sea water at levels down to 0.02 gg/1 using a cadmium sulfide collector and octadecyltrimethylammonium chloride as a surfactant. The sea water samples need only to be acidified with hydrochloric acid. For flotation an adjustment to pH 1.0 is crucial. Mercury concentrations generally seemed to decrease with the depth of sea water 99). 

This ionic mercury (Hgll) adheres to aerosols and thus has a short (days to weeks) residence time in the atmosphere rainfall delivers it to the local soils and rivers. Ionic mercury is readily methylated (eqn. 5.24) by both abiotic and biotic pathways. However, most scientists now agree that methylation by anaerobic sulphate reducing bacteria (SRB) is most important. 

Mercury vapour is also rapidly converted into ionic form in the lungs and absorbed into the bloodstream. Ionic mercury, irrespective of whether it is absorbed from the lungs or from the gastrointestinal tract. 

Mercury entering a landfill will be subjected to a number of reactions. Firstly, part of the mercury would evaporate due to the high volatility of the element coupled with the working face that is the compaction of the wastes. The remaining mercury would be oxidised to ionic mercury (monovalent or divalent), that would either precipitate reacting with sulphate ions, or percolate in the leachates, or undergo the methylation process and be liberated through the form of methyl mercury in the landfill gas. 

Mercury contents were determined by flameless atomic absorption spectrophotometer M.A.S. 50 (Mercury Analyzer System, Bacharach, USA). Ionic mercury was reduced with SnCl2 (5 g/Liter) to metallic mercury which was volatilized by a vector gas (air) and detected at 253.7 nm by the atomic absorption spectrophotometer. 

The surface sediments are considered as the most probable place in which one part of the inorganic ionic mercury (Hg2+) is converted to monomethylmercury (MeHg+) subsequently bioaccumulated in the aquatic... 

Elemental mercury vapor can enter the body through inhalation and be carried by the bloodstream to the brain, where it penetrates the blood-brain barrier. It disrupts metabolic processes in the brain causing tremor and psychopathological symptoms such as insomnia, shyness, depression, and irritability. Divalent ionic mercury, Hg +, damages the kidney. Organometallic mercury compounds such as dimethylmercury, Hg(CH3)2, are also very toxic. 

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