Methyl mercury compounds water

The solubility of organomercury compounds depends primarily on the nature of the X group nitrates and sulfates tend to be salt-like and relatively water-soluble, whereas chlorides are covalent, nonpolar compounds of low water solubility. Methyl mercury compounds tend to be more volatile than other organomercury compounds. 

Horvat, M., Bloom, N.S., and Liang, L., Comparison of distillation with other current isolation methods for determination of methyl mercury compounds in low level environmental samples, Part II, Water Analytica Chimica Acta, 282, 153-168, 1993. 

Mercury contaminated foodstuffs and water supplies are a concern because of the extreme toxicity of the element and its compounds. Elemental mercury is used in the production of chlorine gas, and organomercury compounds formerly found use as pesticides and fungicides. Alkyl mercury compounds are of greatest concern since they do not degrade readily, and methyl mercury compounds concentrate in fish lipid tissue [9]. Pregnant women are at greatest risk since methyl mercury readily crosses the placenta, affecting the fetus [6]. 

R. Pongratz, K. G. Heumann, Determination of concentration profiles of methyl mercury compounds in surface waters of polar and other remote oceans by GC-AFD, Int. J. Environ. Anal. Chem., 71 (1998), 41-56. 

It has been known since 1970 that inorganic mercury contained in sediments could be converted into methyl mercury compounds by biological processes (Wood et al. 1968, Jensen and Jernelov 1969). The significance of this process is still unclear however, it seems from recent reports (Billen 1974, Lindberg et al. 1975) that the rates of methylation are very low and are likely to be balanced by demethylation reactions. Thus, the amount of methyl mercury compounds present in natural waters is likely to be very small and of minor importance in terms of toxic effects to aquatic organisms. This is borne out by the fact that methyl mercury has never been detected in natural waters. 

To help prevent this, the U. S. Public Health Service has recommended a maximum limit of 0.5 ppm mercury in any food. If the fish are to have less than this level of methyl mercury and the concentration factor is 3,000, then the surrounding water in which the fish live should have less than 0.16 ppb (parts per billion). Currently the oceans have about 0.1 ppb, but it is not known whether this is in the form of organic or inorganic compounds.8 It is also not known whether fish can convert inorganic mercury into methyl mercury.8 However, a large number of microorganisms can do this, so possibly its usual form is unimportant. 

There are several different types of organic mercury, but by far the most important in terms of health effects is methyl mercury. When atmospheric mercury is deposited on the ground or in the water, it is converted to methyl mercury by bacteria. Mercury compounds are very toxic and this is the bacteria s way to detoxify mercury. Small animals then consume the bacteria, along with the methyl mercury and bigger animals in turn consume the smaller animals, thus increasing the concentrations of methyl mercury. Methyl mercury accumulates in the larger carnivorous animals, most important of which are fish such as tuna, pike, and shark. 

The rate of methylation of mercury in anaerobically incubated estuarine sediments proved to be inversely related to salinity (267) this is consistent with results reported in Section II,A. Methylmercuric ion forms in sediments upon addition of HgCl2, with a lag phase of 1 month (268). Biomethylation by lake water columns and by sediments coincided, apparently being related to overall microbial activity, and showed periodic fluctuations (269). Topping and Davies have demonstrated that mercury can be methylated in the water column of a sea loch (270). As has previously been noted, tin compounds can be methylated by sediments (121-124), and this is also true for lead (134-136, 271). The relative proportions of biotic and abiotic methylation processes for such systems still remain to be determined. 

The photophysics and photochemistry of gaseous PuFe have been ex-amined. Studies involving zinc porphyrins have been reported and include photo-oxidations in aqueous solution, photoreductions of Zn-TPP with hydrazines, and the role of Zn-TPPSa/ethyl viologen in photoredox processes. The mechanism of the photo-oxidation of water to oxygen with silver chloride has been discussed, and the synthesis of bis(chlorosilyl)-mercury compounds described. Colloidal CdSe has been shown to sensitize the photoreduction of O2 and of methyl viologen by cysteine. ... 

Species such as CHsHg"" and (CHj)2Hg are hydrophobic and can penetrate cell membranes. Cobalamins are very active methyl-transfer reagents that can methylate anything in the cell, which is bad news for the human body. Unlike many other mercury compounds, methylmercury is soluble in water. Methylation of Hg thus increases concentration of this cation in body fluids. 

Metal-carbon bonds that are stable under environmental conditions are known from elements ranging from Hg to Sn, Pb, and As the simple alkylated compounds are nonpolar with low solubilities in water and are strongly lipophilic. On account of the extreme toxicity of methyl mercury, considerable... 

Mercury used to get into the environment in large amounts from the production of chlorine, from slimicides and fungicides used in the paper industry, and from fumigants. Mercury is one of the electrodes for the electrolysis of salt water to produce chlorine and sodium hydroxide. The contaminated mercury used to be dumped into lakes and rivers (0.45 Ib/ton of CE produced) because it was believed to be so heavy that it would just settle to the bottom. However, it was found that certain microorganisms could convert the mercury to organic mercury compounds, almost exclusively methyl mercury, which can be quite toxic. 

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