Chronic Effects of Mercury on Organisms:

General survey of mercury and its distribution in the environment


NOTE: These are notes are incomplete.
Please refer to the original for scientific research.

GENERAL SURVEY OF MERCURY AND ITS DISTRIBUTION IN THE ENVIRONMENT Physical and Chemical Properties of Mercury and its Compounds Metallic mercury, appearing at room temperature conditions as a liquid metal, has the highest (for liquids) specific gravity and the highest (for metals) melting and vaporizing temperature, relatively high electro-and heat conductivity, significant chemical stability and density. Thanks to these properties it is used in the production of thermometers, barometers, areometers, electric contacts and a multiple of other physical and chemical devices. The arc spectrum of mercury is especially rich in ultraviolet rays. Therefore it is used in the production of quartz and fluorescent bulbs, and also for luminescent lighting. Mercury has the property of entering into combinations with most metals, forming amalgams. This property of mercury use to be widely used for the extraction of useful metals from ores and alloys, with silver and gold in various uses, and for coating mirrors. This property of mercury generated its use for the amalgamation of silver and gold for the preparation of dental fillings. The catalytic properties of mercury are significant in their use in the production of acetaldehyde from acetylene, and also in the analysis of organic substances for the determination of nitrogen. The specific gravity of mercury is: at 0°C - 13.59546, at 20°C - 13.59546, at 20°C - 13.54616, at 100°C - 13.35166. Under ordinary conditions mercury appears as a bright silvery white heavy metal. It freezes at a temperature of -38.89°C. Its boiling point is 357.25°C. However, at ordinary atmospheric and industrial environmental temperature conditions it has a noticeable partial vapor pressure (at 0°C - 0.00019mm Hg standard, at 20°C -0.0012 mm Hg. standard, etc.) The above described properties of mercury distinguish it from all other metals. Upon vaporizing its behavior in the air under standard temperatures is that of a colorless vapor having no odor. Its presence in the air is detected only by chemical analysis. Thus in cases where an organoleptic amount of mercury in the air has not been discovered, there is often created among mercury workers the illusion that it is absent from the air and harmless to the environment. Besides this, mercury is easily disseminated in the air of buildings and afterwards is found not only near its place of constant use, but quite far removed from it. Mercury vapor penetrates the pores of the body comparatively easily, and this property of mercury vapor called itself to the attention of hygienists as often "there appear to be cases of poisoning through the walls." (B. B. Koyranskiy, 1923.) The considerable hygienic significance of data on the vaporization rate of mercury and pressure of its vapors should be noted. these observations therefore should be used first of all in the determination of zones of the greatest accumulation of mercury vapors in the air of industrial sites and shops by calculation and the establishment of necessary volumes of pure air. The vaporization rate of mercury, as with other high boiling point volatile compounds, is connected with its vapor pressure, which when saturated at a given temperature; an increase in the temperature can significantly increase the vapor pressure. change in the vapor pressure is dependent on temperature as expressed in a logarithmic equation. The degree of this increase in case of a further increase in temperature diminishes. An analysis of the change in pressure of a saturated vapor in relation to temperature for chemically pure substances and certain mixtures was described by V. G. Matsak and L. K. Khotshonov (1959), who indicate that, "the farther the temperature of the substance departs from the boiling point (diminishing), then the faster the vapor pressure falls." One can postulate quite an important hygienic significance from the point of view of the possibilities of contamination by mercury of the air of industrial buildings which supports an earlier established (in connection with required norms) mandatory temperature regime. Thus, at an increase in temperature between 20 -30°C one can expect an increase in vapor pressure and consequently and increased concentration of mercury in the air by 2.32 times. Attention is called to the fact that at temperatures of 30 - 40°C at the surface of mercury a concentration of its vapors exceed the maximum permissible quantity for industrial sites 3,000 - 6,000 times, and at temperatures of 60 - 80°C the temperature of tool surfaces in shops using mercury, by thirty thousand-eighty thousand times. In connection with this, it becomes clear why in these enterprises, on surface structure in winter time, especially on surfaces of skylight outlets through which air leaves a workshop, mercury vapor often condenses. If mercury condensate is not removed, it will remain a self contained source for the introduction of mercury into the air at the beginning of the warm period. A condition of hyperthermia, arising in the body and accompanied by a series of functional changes, combines with the development, under the effects of mercury, of a toxic effect, which can aggravate the effects of mercury symptoms caused by this action. Through treatment of the following materials it will be shown that, in such combined simultaneous effect on the organism of toxic and temperature factors one can infer a circle in which disintegration and change, caused by mercury and high temperatures, reinforce each other causing the organism to become more susceptible to the action of each of these indicated factors. The concentration of mercury in the air depends not only on temperature but on a series of other conditions, such as the known relationship established between concentrations of mercury vapors and their distance from volatile surface of mercury. According to the data of Renk (according to A. N. L'vov, 1939), air found above 0.5M2 from the surface of metallic mercury at a height of 5 cm about the vaporizing surface contains 1.86 mg mercury vapor in one M3, at a height of 30 cm - 1.26 mg, at a height of 100cm - 0.85 mg. On looking at specific quantities which characterize the meaning of the coefficient of diffusion (D) for vapors and substances diffusing in the air, attention is called to the high coefficient of diffusion for mercury (D at zero degrees C equals 0.1124) in comparison with analogous parameters for volatile organic substances having the same molecular weight. Further, there is a relationship between the concentration of mercury vapor in the air and the purity of vaporizing mercury. Pure metallic mercury is easily pulverized and disintegrates into separate very fine globules, which, in toto, compose a significantly higher surface of evaporation than the same quantity occurring as an ordinary compact mass. This is the consequence of the high surface tension and low viscosity of mercury. Mercury belongs to the group of substances with high molecular weight - 200.61, the vapor of which is heavier than air (usually 7 times). IONIZATION POTENTIAL. Mercury has a high ionization potential (10.39 electron-volts.) From this is connected the property of mercury metal to separate from its various compounds, that is, to transform to its atomic form. This property is one of the most characteristic for mercury and explains cases of finding it in a native state in nature. The high ionization potential (10.39 electron volts) explains the capacity of mercury to form various compounds with active reagents, such as oxygen, acids, etc. INORGANIC MERCURY COMPOUNDS. From the hygienic point of view mercuric chloride is of greatest interest, also sulfides, and nitrates. Notice also that we discuss these compounds in order of their lethal toxic significance - from the most toxic to the least toxic. Mercuric chloride, corrosive sublimate - (HgCl2). This compound is a white crystalline powder. Its specific gravity is 5.44, melting point - about 277°C, boiling point -303°C. It has a metallic taste. It precipitates protein. Various organic substances, especially under the effect of heat and light, react with mercuric chloride, yielding calomel. Mercuric chloride is mainly used as a strong antiseptic agent. Thanks to its good solubility and high degree of dissociation it is number one of all inorganic compounds of mercury which display a disinfectant power. Mercuric chloride dissolves in liquids, which makes it easy to penetrate tissues. Its antiseptic action is caused not only by the action of free mercury ions, but also by the effect of complex compounds, formed through the combination of metallic salts with polypeptides (W. Heubner. Appearing in E. Starkenstein, E. Rost, S. Pol. Toksikologiya, number 1 M. - L., 1931.) Mercuric chloride sublimes easily. It is soluble in cold (6.6% at 20°C) and hot (56.2% at 100°C) water, acids, especially acetic, and alcohol (33% to 25°C), ether, acetone, pyridine in salt solution with the formation of a complex compound HgC12. NaCl. Its water solutions give acid reactions but upon the addition of NaCl the reaction becomes neutral. It is weakly dissociated. In light, especially in the presence of organic compounds, it reacts easily with metallic mercury and calomel. The results of the reaction are a mixture of mercuric sulfates and sodium chloride (NaCl) which upon heating yeild: HgSO4 + 2NaCI ->Na2SO4 + HgCI2 To prevent the formation of Hg2CI2, a small quantity of manganese dioxide was added to the mixture. The calomel formed in this way sublimates. Another method of doing this is to dissolve mercuric oxide in an acid salt or react a surplus of chlorine with metallic mercury, heated almost to its boiling point. To the group of soluble inorganic compounds belong also the above mentioned oxides and suboxides of mercury salts of nitric acids. Nitric suboxide of mercury - Hg2(NO3)2 . 2H2O This compound is a white crystalline powder. Its specific gravity is 4.78, melting point - 70°C. It dissolves in water in small quantities, it hydrolyzes easily: Hg2(NO3)2 + H2O ->HNO3 + Hg2 (OH)NO3 It dissolves in nitric acid and hot carbon disulfide. It is obtained by the reaction of mercury with cold nitric acid. Nitric oxide of mercury is a colorless crystalline powder; soluble in nitric acid and acetone. Hydrolyzes in water, after which it forms the basic salts: Hg(NO3)2 + H2O <=>HNO3 +Hg(OH)NO3 2Hg(NO3)2 + 2H2O <=>Hg2O(OH)NO3 + 3HNO3 It is obtained by the reaction of mercury or mercuric oxide in hot nitric acid (concentrated). Its specific gravity is 4.3; its melting point - 79°C. Mercury Fulminate - [Hg C2 N2 O2] It is obtained by the solution of metallic mercury in nitric acid in the consequent reaction of the obtained solution with ethyl alcohol. It is a hard crystalline substance. It detonates easily upon heating, striking or friction. The decomposition of mercury fulminate proceeds according to the following equation: HgC2N2O2 ->Hg + 2CO + N2 It is used as an initiating substance in blasting caps. Mercuric sulfide, cinnabar - (HgS). Cinnabar occurs in nature as an ore, it is basically the most widely distributed mercuric material from which mercury is obtained. It contains 86.2% mercury and 13.8% sulfur; it commonly contains impurities of clay, iron oxides bituminous materials. Two forms are known; a black amorphous substance and a dark red crystal. Its specific weight is 8.0 - 8.2; hardness 2.0 - 2.5. Cinnabar is quite resistant to atmospheric agents, and even in rare cases transfers to native mercury, calomel or mercuric oxychloride. Its boiling point at normal pressure - 580°C. Its solubility in water is insignificant; in nitric acid salts it is insoluble. It dissolves in 2N HCI upon boiling. Artificial cinnabar is obtained in the process of prolonged grinding of corresponding quantities of mercury and sulfur or the precipitation of hydrogen sulfide from solutions of mercuric oxide salts (black sulfide), and also upon grinding mercury with sulfur or the precipitation of hydrogen sulfide from solutions of mercuric oxide salts (black sulfide), and also upon grinding mercury with sulfur or K2S5 with consequent treatment with alkali (red sulfide.) The heat of formation - 109,000 cal/gm - mol. Mercury monochloride, calomel - (Hg2CI2) Calomel is obtained by heating mercury and mercuric chloride; reacting the acid salt on the soluble salt of mercury suboxide: Hg2 ++ + 2CI- ->Hg2CI2 sublimation from the mixture of a sulfate of mercury suboxide and cooking salt with the consequent washing of the sublimate to remove the mercuric chloride. Hg2SO4 + 2NaCI ->Na2SO4 + Hg2CI2 Mercury monochloride is a white crystalline powder. Externally it is almost identical with mercuric chloride. However, on grinding it takes on a yellow color, while mercuric chloride remains white. The specific gravity is 7.15; the melting point - 302°C. ; the sublimation point - about 31-°C; the boiling point 383.7°C. Mercury monochloride is insoluble in water, alcohol, ether and dilute acids. I dissolves in boiling hydrochloric acid with the formation of mercuric chloride, and also in nitric and sulfuric acids. It decomposes in alkali releasing mercuric oxide. To the water insoluble inorganic mercury compounds belongs mercury iodides and bromides, and also a series of other suboxides of mercury. Solubility of the salts: From the hygienic and toxicological point of view the problem of the degree of solubility and dissociation is extremely important to the understanding of the effect on the organism of mercury salts because this property determines penetration and the degree of the subsequent toxic effect. The degree of toxicity depends directly upon the solubility, the degree of dissociation and the concentration of free mercury ions. The toxic effect of mercury salts depends also in relative degree on the content in the surrounding medium of protein substances, in combination with which (these substances bind or precipitate mercury) mercury salts are absorbed. Cooking salt to a significant degree can dissolve these compounds, forming mercury soluble albuninates. Cooking salt can also convert insoluble mercury compounds to soluble ones. In conclusion, inorganic mercury salts are comparatively unstable. Metallic mercury can be separated from them by contact with a series of metals, for example, iron and reaction with various agents. ORGANIC MERCURY COMPOUNDS. Mercury is an element distinguished by its abundant organic derivatives. Generally it displays, in comparison with the majority of metals, the closest relationship to carbon. This indicates the fact that organic derivatives of mercury are obtained most easily compared to organic derivatives of other metals and they are much stabler in comparison with the majority of known organometallic compounds. Among organic compounds of mercury one must note only those in which one atom of mercury binds directly (with the aid of one or two bonds) with a carbon atom. Organic derivatives of mercury differ from inorganic in that in their masking the actions of mercury ions; they do not precipitate protein and do not immediately react with ammonium sulfate. Organic mercury compounds have a significant bacterial effect. Further, the simplest of them, for example, mercurophene, in its effect on bacteria does not yield mercury chloride. P.P. Shorygin (1910) stated that the toxicity of organic mercury compounds for higher animals were weaker according to their capacity to give typical mercury reactions. The author characterized organo-mercury compounds as "atoms of mercury, assigned to organic molecules." F. Withmor (1921) noted the presence of a relationship between a strong toxic effect and the characteristic of addition of organic residues to the valency of mercury. The author stated that so called symmetrical compounds, in which both valences of mercury bind with carbon, are less toxic than compounds having one carbon bond, and another -- with hydroxylcyan --, chlorine, and thiosulfate groups. This explains why symmetrical organomercury compounds are very stable. The toxic effect of introducing them into the organism is connected with a splitting off of one radical and its subsequent transfer to the chlorine. The marked toxicity of diethylmercury, for example, lies in its formation in the organism of a new compound --ethylmercuric chloride. Evidently, symmetrical mercury compounds ought to be unstable to a degree in order to produce their toxic effect. In the process of studying the chemical toxic properties of a variety of organomercuricals it has been shown that the most active are compounds of the type RHgX, where R is a benzene ring with or without substituted groups. X is a hydroxyl (OH), or a cyano (CN) group, or, possibly a halogen atom. In the latter case the activity of the compound increases from chlorine to iodine. There is a relation between the chemical structure of various organomercury derivatives and their degree of toxicity. Among them the most significance is attached to the structure of the radical characterizing the acid residue. Thus, among methyl-and ethylmercury compounds, the most toxic are the phosphates. After them come the chloride and cyano derivatives, and finally the toluolsulfates. Among the phenylmercuric compounds, the acetates are less and the nitrates more toxigenic than the chlorides. The substitution of a methyl or ethyl radical increases toxicity, and the substitution of a methyl for a phenyl lowers toxicity (about four to five times) (L. I. Medved', 1954). In modern times organomercuric compounds are synthesized from hydrazones, aldehydes, and ketones, which react easily with mercuric acetate in aqueous solution at a temperature of 70-90°C (A. N. Nesmeyanov, O. A. Reutov, A. S. Loseva, 1956). Of compounds of this type the most important in a hygienic context are the ethylmercuric chlorides, mehoxyethylmercuric acetate, phenylmercuric bromide, and phynylmercuric acetate. The wide use of these compounds as pesticides and fungicides (granosan, radosan, agronal and others), and complex acting compounds (mercuran, mercurhazane, have stimulated the most interest in them by domestic (S. I. Ashbel, 1964; V. Ye. Balashov, 1964; G. A. Belonovkho and co-authors, 1967; N. F. Borisenko, 1967; L. I. Medved', 1961; N. D. Mukhtarova, 1967; I. M. Trakhtenberg and co-authors 1966; A. R. Uvarenko, 1968; and others) and foreign scientists (I. Barnes, L. Margos, 1968; I. Gage, 1964; and others). Ethylmercuric chloride (C2H5) is a white crystalline substance with a boiling point of 192.3°C. Its solubility in water at 20°C is 1.4 x 10-4 grams in 100 grams H20; it dissolves easily in hot alcohol and in 10% NAOH solution (in cold to 20%). It is quite volatile, as a result of which at room temperature of lower it can escape into the air as vapor. According to the data of M. A. Trotsenko (1958), the volatility of vapor of ethylmercuric chloride at 20 degrees and 21.5 degrees is about 11mg/m3 and 21mg/m3. Almost identical results (12mg/m3) at 20°C were obtained by Charley and Skinner (1955), who determined ethylmercuric chloride according to the frequency of vibration of a quartz crystal in vacuum. According to the data of A. Swensson (1952), vapor pressure of ethylmercuric chloride at 20°C is equal to 300 x 10-5 MmHg. standard. This explains the initial effectiveness of a group of pesticides --granosan (NIVIF-2), mercurane, cerezane and others. Ethylmercuric Phosphate (C2H5Hg). (3PO4) is a white crystalline substance with a melting point of 178-179°C. It dissolves well in water and alcohol. It is somewhat hydroscopic. It decomposes under the influence of acid rather more slowly than through ignition. Splitting off an organic residue occurs only after prolonged heating with nitric acid. The specific gravity is 1.5. Ethylmercuric phosphate can be decomposed by halogens, reactions with which occur in the cold in the course of one to two hours. Reaction can be represented according to the following equation: 2(C2H5Hg)3PO4 + 6x2 ->3HgX + Hg3(PO4)2 Ethylmercuric phosphate volatilizes and mixes with air even at room temperature. Methoxyethlymercuric acetate CH3OCH2CH2 HgOCOCH3 is a white crystalline substance containing 62.8% mercury. The vapor pressure of methoxethylmercuric acetate at 20°C is 13 x 10-6 mmHg. standard. It is the active principle of the fungicide radosan. Phenylmercuric bromide C6H5HgBr Phenylmercuric Acetate C6H5HgOCOCH3 are white crystalline powders which contain about 56 and 60% mercury. The vapor pressure at 20°C is 6 x 10-7 mm Hg. standard. They are the active principal in the fungisides argronal, ruburone and leytosan. Diethylmercury Hg (C2H5)2 is a colorless liquid with an unpleasant odor. Its specific gravity is 2.55; its boiling point is 195°C. This compound is almost insoluble in water, is weakly soluble in alcohol, and dissolves easily in ether. It is obtained by the reaction of sodium amalgam in ethyl bromide. In connection with a survey of these properties common to the organic derivatives of mercury, one should pay attention to the process of their industrial vapors of organomercuricals and vapors of metallic mercury. Often in the air of industrial premises vapors of mercury dichloride are detected. This occurs on the one hand from peculiarities of the technology and synthesis of the indicated compounds and on the other from their definite volability. This is a very brief survey of the physical and chemical properties of mercury, its inorganic and organic derivatives, which we consider advisable to discuss before dealing with basic data on the toxicology of mercury, industrial hygiene for its production and laboratory uses, of the presence of mercury in biological substrates and its distribution in the environment.