Inorganic mercury compounds determination

NIOSH determined a Recommended Exposure Limif (REL), time-weighted average, of 50 pg Hg m for mercury vapor, and 100 pg m for aryl and inorganic mercury compounds (NIOSFl 1983). ACGIFl established the same concentrations as 8-hour time-weighted averages as Threshold Limit Values" (TLVs). 

Langseth, W. (1986a) Determination of organic and inorganic mercury compounds by reverse-phase high-performance iiquid chromatography after extraction of the mercuries as aikyidithiocarbamate chelates. Fresenius Z. Anal. Chem., 325, 267-271. 

Mercury is uniquely determined by the reduction of inorganic mercury compounds (Hg and Hg ) to the elemental state (Hg°) using a reducing agent, followed by the transport of the elemental Hg vapor to the plasma in the Ar carrier stream. A unique physical property of elemental Hg is its high vapor pressure at room temperature. The chemical stability of elemental Hg in the vapor form provides for an operationally simple apparatus and vapor transport system. 

A number of analytical methods for the separation of organic mercury compounds use an initial extraction of the organic materials with an organic solvent. Klisenko and Shmigidina [83] then converted both the inorganic mercury held in the aqueous fraction and the organic mercury in the chloroform extract to dithizonate, separated the components on chromatographic columns, and determined the concentration of the various fractions by comparison with reference standards. This method is semi-quantitative at best. 

Kimura and Miller [29] have described a procedure for the determination of organomercury (methylmercury, ethylmercury and phenylmercury compounds) and inorganic mercury in soil. In this method the sample is digested in a steam bath with sulphuric acid (0.9M) containing hydroxy ammonium sulphate, sodium chloride and, if high concentrations of organic matter are present, potassium dichromate solution. Then, 50% hydrogen... 

Cappon and Crispin-Smith [59] have described a method for the extraction, clean-up and gas chromatographic determination of alkyl and aryl mercury compounds in sediments. The organomercury compounds are converted to their chloroderivatives and solvent extracted. Inorganic mercury is then isolated as methylmercury upon reaction with tetramethyltin. The initial extract is subjected to a thiosulphate clean-up and the organomercury species are isolated as their bromoderivatives. Total mercury recovery was in the range 75-90% and down to lpg kg-1 of specific compounds can be determined. 

A method [62] has been described for the determination of down to 2.5pg kg-1 alkylmercury compounds and inorganic mercury in river sediments. This method uses steam distillation to separate methylmercury in the distillate and inorganic mercury in the residue. The methylmercury is then determined by flameless atomic absorption spectrophotometry and the inorganic mercury by the same technique after wet digestion with nitric acid and potassium permanganate [63]. The well known adsorptive properties of clays for alkylmercury compounds does not cause a problem in the above method. The presence of humic acid in the sediment did not depress the recovery of alkylmercury compounds by more than 20%. In the presence of metallic sulphides in the sediment sample the recovery of alkylmercury compounds decreased when more than lmg of sulphur was present in the distillate. The addition of 4M hydrochloric acid, instead of 2M hydrochloric acid before distillation completely, eliminated this effect giving a recovery of 90-100%. 

Uncontrolled species transformations during analysis form another source of error. For methylmercury determinations in sediments it was demonstrated that errors of up to 80% resulted from the formation of the compound from inorganic mercury during separation and analysis [28, 29], For the study of possible species transformations during analysis multiple isotope dilution could be used as a diagnostic tool for identifying the error and bias inherent in specific methods of storage, sample preparation and measurement [30, 31]. 

Logar, M., M. Horvat, H. Akagi, and B. Pihlar. 2002. Simultaneous determination of inorganic mercury and methylmercury compounds in natural waters. Anal. Bioanal. Chem. 374 1015-1021. 

Lovenberg, Buchanan, and Rabinowitz (65) tested the response of ferredoxin to mercury compounds. Two mercurial reagents used, p-mer-curibenzoate (PCMB) and o-((3-hydroxymercuri-2-methoxypropyl)car-bamyl)phenoxyacetate (sodium mersalyl) reacted rapidly with ferredoxin and caused a bleaching of the visible spectrum and a concomitant loss of biological activity. C. pasteurianum ferredoxin was titrated with PCMB as described by Boyer (24) and the results showed that 20 moles of PCMB reacted with 1 mole of ferredoxin. In another determination, 2 moles of PCMB reacted with 1 mole of sodium sulfide. Since ferredoxin contained 7 moles of inorganic sulfide and 8 moles of half-cystine residues, 22 (7 x 2 = 14 14 + 8 = 22) moles of PCMB would be expected to react with 1 mole of ferredoxin. These data, summarized in Table 8, are consistent with the existence of two types of sulfur in ferredoxin. This conclusion was supported by the presence of half-cystine residues in ferredoxin after inorganic sulfide had been removed by acid hydrolysis, as well as results of sulfur analyses, which showed an amount of sulfur greater than could be attributed to half-cystine residues. 

Many other household products can be analysed in similar ways to those described above for chemicals. Household bleach is essentially an inorganic chemical. There has been concern expressed about mercury levels in hypochlorite bleach because of the way it is manufactured. The cold vapour reduction/aeration method referred to above is a good way of determining low mercury levels with minimal matrix problems [82]. In the past organo-mercurial compounds have been used (e.g. as bactericides) in some household products these may be selectively determined by extraction with an organic solvent (e.g. carbon tetrachloride or benzene), and then application of the cold-vapour method following the addition of cysteine acetate, or by coupled gas chromatography/atomic absorption [83],... 

In one tragic incident, an entire community on Minamata Bay in Japan was poisoned, with extremely serious birth defects, very painful reactions, mental disorders, and many deaths. Only after lengthy research was the cause determined to be mercury compounds discarded into a river by a plastics factory. Whether it was inorganic salts or methylmercury compounds seems uncertain, but the contamination was immense and methylmercury compounds were found in the silt and in animals and humans. The methylmercury was readily taken up by the organisms living in the bay and, because the people of the community depended on fish and other seafood from the bay for much of their diet, the entire community was poisoned. 

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. 

Reliable evaluation of the potential for human exposure to mercury and various mercury compounds depends in part on the reliability of supporting analytical data from environmental samples and biological specimens. Concentrations of mercury in unpolluted atmospheres and in pristine surface waters are often so low as to be near the limits of detection of current analytical methods even for determining total mercury. In reviewing data on mercury levels monitored or estimated in the environment, it should also be noted that the amount of chemical identified analytically is not necessarily equivalent to the amount that is bioavailable. The analytical methods available for monitoring mercury and various inorganic and organic mercury compounds in a variety of environmental media are discussed in Chapter 6. 

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