Toxic species mercury

Literally hundreds of complex equilibria like this can be combined to model what happens to metals in aqueous systems. Numerous speciation models exist for this application that include all of the necessary equilibrium constants. Several of these models include surface complexation reactions that take place at the particle-water interface. Unlike the partitioning of hydrophobic organic contaminants into organic carbon, metals actually form ionic and covalent bonds with surface ligands such as sulfhydryl groups on metal sulfides and oxide groups on the hydrous oxides of manganese and iron. Metals also can be biotransformed to more toxic species (e.g., conversion of elemental mercury to methyl-mercury by anaerobic bacteria), less toxic species (oxidation of tributyl tin to elemental tin), or temporarily immobilized (e.g., via microbial reduction of sulfate to sulfide, which then precipitates as an insoluble metal sulfide mineral). 

The nature and severity of the toxicity that may result from mercury exposure are functions of the magnitude and duration of exposure, the route of exposure, and the form of the mercury or mercury compound to which exposure occurs. Since the ultimate toxic species for all mercury compounds is thought to be the mercuric ion, the kinetics of the parent compound are the primary determinant of the severity of parent compound toxicity. It is differences in the delivery to target sites that result in the spectrum of effects. Thus, mercury, in both inorganic and organic forms, can be toxic to humans and other animals. 

Mercury is essentially nontoxic in its elemental form (Hg ). In the absence of any chemical or biological system that chemically alters Hg , it can be consumed orally without any significant side effects. However, once Hg is chemically modified to the ionized, inorganic species, Hg T it becomes toxic. Further bioconversion to an alkyl Hg, such as methyl Hg (CHaHg ), yields a very toxic species of Hg that is highly selective for lipid-rich tissue, such as the neuron. The relative order of toxicity is as follows ... 

We end this chapter with a brief discussion of two sample preparation methods. The first is to determine mercury (Hg) and the second method determines cyanide (CN ). Both parameters are important with respect to the evaluation of a sample as a hazardous waste. The presence of either Hg or cyanide renders a sample hazardous due to the acute toxicity of both species. Mercury exists either in elemental form, as the dimer ion Hg2 in which the oxidation state of the element is +1, or as the divalent ion Hg. The elemental form is the familiar liquid silver metal obtained by roasting cinnabar, HgS (106). The cyanide ion is a moderately strong base derived from the weak acid hydrocyanic acid, HCN. HCN is a gas at room tem-... 

A number of fatalities occurred at Minamata and Niigata, Japan between 1955 and 1962, caused by the consumption of fish and shellfish, which had been contaminated by the direct release of methyl mercury species to the waterways (33). It was discovered in Sweden in 1966 that even in remote areas, methyl mercury species form the major part of the mercury in the fish muscle tissue (38), and that the less toxic inorganic mercury species can be converted in sediments to the more toxic methyl mercury species (22). Since then, many studies have been carried out on mercury in the aquatic environment (29). 

What we may be seeing here is mercury as an indicator of how fast acid precipitation is affecting the fishery of the lake. Toxicity of mercury is probably not a factor, but it s a time-averaged indicator when you find mercury in comparable species at higher levels in one lake than the other. 

Table III). The log-probit LC values usually were in reasonable agreement with MATCs determined in or estimated from such investigations. The static renewal LCi was an underestimate of the toxicity of mercury to embryos and larvae of the rainbow trout, but the value was in close agreement with MATCs reported for other sensitive species. Differences between LCj values and MATCs generally were no greater than variations among MATCs reported for specific metals. This was particularly evident for zinc and lead. 

The system was quite efficient and was probably an inspiration for Jong Hwa Jung et al. [143] who, more recently, have proposed a similarly engineered system for the sensing and separation of toxic species like lead and mercury in different matrices. They have synthesized nickel nanoparticles coated with a silica shell (30 0 nm in diameter), then grafted with a di-silanized 4,4-difluoro-4-bora-3a,-4a-diaza-s-indacene (BODIPY) derivative (Fig. 29). This dye, buffered at pH 7, is... 

Mercury is, without doubt, the most important element nowadays in analytical chemistry, as it has been declared a global pollutant because of the extreme toxicity of mercury vapor and many of the mercury compounds, particularly its methylated species. 

According to Torres [2], mercury is a well-known heavy metal pollutant of the aquatic environment, which is transformed to other more toxic species as methylmercury [3]. Many technologies were developed to avoid the throughput of mercury to the environment, however this element and its toxic species still cause many ecological problems due to wrong waste management by mining, electronic, chloro-alkali, etc. industries [4]. 

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