Mercury criteria

WHO (World Health Organization). 1976. Environmental Health Criteria Mercury. World Health Organization, Geneva, Switzerland, 121. 

From the viewpoint of chemical and physical requirements the permissible indicators involve a number of criteria mercury, selenium, cadmium, vanadium, chromium, arsenic, silver, lead, barium, cyanides, hydrogen sulphide, fluorides, phenols, oil and oil substances, COD(Mn), colour, odour, taste and turbidity. The most stringent criterion concerns the content of mercury, followed by selenium, cadmium, vanadium, cyanides, oil and oil substances. Another important indicator is the content of organic matters characterized by COD(Mn). 

Moore DR, Teed RS, Richardson GM. 2003. Derivation of an ambient water quality criterion for mercury taking account of site-specific conditions. Environ Toxicol Chem 22 3069-3080. 

Table 5.11 Proposed Mercury Criteria for Protection of Various Resources and Human Health Resource and Criterion (units in parentheses) Mercury Concentration Reference11...

Resource and Criterion (units in parentheses) Mercury Concentration Reference11... 

Similar criterion has been obtained by Taylor. 2051 Hinze[270] estimated Wecri, to be 22 for a free-fall droplet, and 13 for a low-viscosity liquid droplet exposed suddenly to a high-velocity air stream. The latter value is comparable to those for water, methyl alcohol, mercury, and a low-viscosity silicone oil obtained by other investigators. 1275H277]... 

In the Rayleigh scattering just outlined the relative size parameter was small. Table 1 indicates that a rough criterion of this is that the major dimension of the scattering particle should not exceed ca. X/20. For example, for a dilute aqueous solution of the particles irradiated with green mercury light the upper limit of the dimension would be given as... 

Precedent had been established for mercury (II) mediated cycloetherification reactions (24,25) but not in such a highly functionalized molecule and to give a strained system. Since it was also known that oxidative removal of the mercury transformed the alkylmercurial into an alcohol (26), this method would not only allow access to the tetrahydropyran portion of the molecule, but the criterion of a functionalized terminus (C-8 ) would also be met. 

It has been a major point of interest in the study of small metal particles to determine the precise point (if indeed there is a precise point) at which metallic character is lost. The broader context of this problem as it relates to other metals such as mercury and sodium has been discussed in a series of important papers by Peter Edwards and his associates.135,136 The difficulty seems to be that there is no agreed criterion by which membership of the metallic state can be judged, and various physical techniques give somewhat different answers because they sense slightly different aspects of electron behaviour. The question has been earnestly addressed in the case of gold, partly because of the familiar sensitivity of catalytic activity to particle size as noted above (Section 2.1) the way in which electrons are used to form metallic bonds determines the character of the free valences at the surface, and hence the kind of chemisorption bond that is formed with the reactants. 

The contaminant chosen for this application is a trace compound, such as mercury (Hg). The U.S. Environmental Protection Agency (1999) sets the Criteria Maximum Concentration (CMC) for mercury in fresh water at 1.4 pg/l and the Criterion Continuous Concentration (CCC) at 0.77 pg/l. Given the three types of contaminant sources available in three-dimensional MRTM, this application seeks... 

The electronic bands of an infinite crystal can cross as a function of some parameter (pressure, concentration etc.). If one treats the e /r,2 term of the electron repulsion correctly, one sees that the crossing transition of the two bands is a first-order phase transition, between the metallic and insulating states. This transition was predicted by Mott in 1946 and has carried his name ever since. In fact, the original Mott criterion does not predict such a transition for Hg, but the criterion was derived for monovalent atoms. For divalent mercury it should not be applicable. Also the semiempirical Herzfeld criterion, which was very successful in predicting the insulator to metal transition in compressed xenon, predicts bulk Hg to be non-metallic. All this seems to imply that Hg is a rather special case. 

In accordance with the authority of the Safe Drinking Water Act (SDWA), EPA has established a safe drinking water standard for mercury at 2 g/L (FSTRAC 1995). Under the Clean Water Act (CWA) EPA provides criterion concentrations for mercury as a priority toxic pollutant (EPA 1992). 

In the dl region, comparison of the i E) and C E) curves can be used as a first test [one should be able to deduce one from the other, the current being only capacitive, (i = CdE/dt)]. The shape of the minimum (corresponding to the capacity of the diffuse part of the electrochemical dl) on the C(E) and i(E) curves (Fig. 15) for the case of no adsorption in dilute solution, is another criterion it should not be too different than that observed for mercury, but its position in the range of potential can be completely different. The shape of the adsorption peak is another criterion (in the case of adsorption) it should be sharp and reproducible. Of course, the stability and reproducibility of the curves are important and should be observed not only in the dl region but over all the range of potential explored. 

In a similar study, 14 MHz gold crystal were used for the measurement of mercury in air (48). Linear relationship were established between the frequency change and the action period of mercury vapor. The calculated detection limit based on 3a criterion is 3 X 10 g/m with a measurement period of 10 min. 

The dangers of mercury (Hg) and its derivatives, especially organomercury compounds, have been well documented for almost half a century. Significant concerns remain regarding mercury contamination in aqueous ecosystems. The US EPA has advanced water quality criteria [1] for the protection of organisms native to water environments. The criterion for mercury in fi esh water ecosystems is 12 nanogram/liter (ng/1), and the mercury chronic criterion for salt water is 25 ng/1. These extremely low criteria present significant demands for the analyst, and atomic fluorescence spectroscopy provides a viable option for the measurements. 

Varying the height of the mercury column h) above the orifice of the capillary provides a useful criterion for distinguishing among the various possible current-limiting processes. Diffusion currents are linearly proportional to A kinetic currents are independent of A and adsorption currents are linearly proportional to h (Fig. 3,7). The dependence of adsorption currents (I a) on h should be measured at... 

Selenium may be a problem in the freshwater environment 5 pg/1 is the criterion for protection of aquatic life at chronic exposure and modifications of this criterion have been proposed recently [90]. A similar situation apparently does not exist in the marine environment. Selenium is a relatively abundant trace element in the marine environment and seems to counteract the toxic effects of mercury. 

Resource and Other Variables Criterion or Effective Mercury Concentration... 

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