Chronic Effects of Mercury on Organisms:

Some geochemical data on the content of mercury in objects in the environment


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Some Geochemical Data on the Content of Mercury in Objects in the Environment. Specialists, working in the field of Industrial studies in the geochemistry of determining chemical substances, concluded that the meaning of geochemical elements, that is, the laws determining distribution and dissemination in the earth's crust can be directed in more rational path by new discoveries and further analysis of the data on a given substance. According to V. I. Vernadskiy (1934), geochemistry studies the atoms of the earth's crust, their history, distribution and movement in space and time, their genetic relationships. A. A. Saukov (1940) undertook basic studies in the geochemistry of mercury, in the course of which he determined the concentration of mercury not only in various minerals, mine tailings, ores, soils, etc. The significance of these data are very important. In studying the distribution of mercury in nature, its content in various plants and animals, its absorption by highly dispersed systems, etc., A. A. Saukov made the foundation for the expansion of hygienic norms for the content of mercury vapor in the external environment, the truth about the occurrence of mercury in human and mammalian organisms, and about its presence in various organs and systems. As the chemical elements isolated from ores will increase, mercury lends itself to multiplex hygienic evaluation of it scale and route of migration which appears below: Data on the World Production of Mercury between 1500 and 1967. (Prepared by S. M. Mel'nikov.) As evident from the preceding data and also from later materials, the production of mercury, especially in later years, increased significantly so that truly one cannot deny the hygienic importance of it in our external environment. One of the most important problems in the hygienic evaluation of mercury content under natural environmental conditions is that the quantity of mercury present in the atmosphere of inhabited places. The continued presence of mercury in the atmosphere is caused by the high volatility of its vapors which we have explained in detail above. How do these direct sources contribute mercury to the atmosphere? What explains the fact that under natural conditions the air above forests and fields contains about 0.00001mg/m3 of mercury? First of all note that the occurrence in the atmosphere of mercury vapor occurs as the result of direct contact of native liquid mercury with the atmosphere. M. M. Saukov notes that often in cinnabar deposits native metallic mercury is not discovered not only because it is not observed, but because of its speed of vaporization is higher than its rate of formation. Also mercury occurs in the atmosphere through the eruption of volcanoes, because magma always contains some quantity of mercury. The presence of mercury in the atmosphere is connected with its isolation from mine sources of juvenile origin, and from jets, occurring at the surface of the earth. It is possible that it is discharged into the atmosphere together with water vapor during evaporation from the hydrosphere. A. Stock and S. Cucuel (1934) conducted experiments to determine mercury directly in atmospheric air and under conditions which excluded the possibility of contamination of the air by mercury used in industry. Towards this goal the authors carried out two experiments, using a system of cooling liquid air, on 3.5 cubic meters of air. In both the first and second case they detected 0.00003 mg mercury. They undertook a control (blind) experiment with these reagents and obtained the presence of 0.00001 - 0.00002 mg when each of these tests used a 300-600 liter air sample. From these data, A. Stock and F. Cucuel came to the conclusion that the content of mercury in the atmosphere approached the limits of sensitivity of the method and took up no more than 0.00002 mg/m3. An interesting connection based on this analysis was put forth by A. A. Saukov. Corresponding calculations made by the author indicated that if one takes as a basic proposition the unidirectional reaction formation of all mercury compounds of metallic mercury, then evaporate them into the atmosphere the content of them in the air would be: 1.57 1012T = 0.2 . 10-6 m/M3 = 2.105 y/M3 = 7.875.1013M3 = 200 y/π.(0,2 M*/π). * backward `s' Why is the actual content of mercury in the atmosphere much lower than calculated? This can be explained first of all by the presence of reversible processes as a result of which mercury is transformed from its vaporous state to the solid and in this way is removed from the atmosphere. For the hygienist the point of these processes have a determining interest, in that they determine to a significant degree, the content of mercury in such objects in the external environment, as the soil, water, and plants. These processes represent, in general, the solution of mercury in the water of the hydrosphere, in rain water, sorption of mercury vapor by highly dispersed systems, especially soils, etc. Analysis of the sorption of mercury vapor occurring under natural conditions has direct practical significance for hygienists. In a given case the relationships connected with the sorption of mercury vapors observed not only from the position of interest in the general characteristics of mercury distribution in objects of the external environment but also from the point of view of devising more active absorbents for mercury vapor. The research of Ye. V. Alekseyevskiy (1933) showed that one of the very powerful absorbents of mercury was active manganese dioxide -- Mn02. The grounds for undertaking these studies were the observation under natural condition of processes in which the sorption of mercury vapors occurs. It is especially intense in hydrated manganese oxides. From these results, Ye. V. Alekseyevskiy (1933, 1937) subsequently recommended activated manganese dioxide as a specific mercury vapor absorbent. Additionally, the author also studied the capacity and degree of mercury absorption of a series of substances (activated charcoal, activated alumina, cobalt oxide, hopcatlite and others). Consequently the mercury vapor absorption under ordinary natural conditions is one of the factors determining its occurrence in nature as a shifting ratio between mercury, found in the atmosphere, on the one hand, and mercury in the lithosphere on the other. An analogous event takes place between mercury, found in the atmosphere, on the one hand, and mercury in the lithosphere on the other. An analogous event takes place between mercury, found in the atmosphere and mercury contained in the hydrosphere. And here an important place is occupied by the sorption of mercury from solutions of certain highly dispersed (at the moment of formation) colloidal systems (clay deposits, iron and manganese ores, etc.). Besides that, portions of mercury, dissolved in water, enter the atmosphere by means of evaporation. At that time a reverse process is occurring: mercury, found in the atmosphere, dissolves in the water, and therefore enters the hydrosphere together with rain water. The preceding geochemical data on the occurrence of mercury in nature and on certain relationships connected with its migration and its content in various objects in the external environment, permits, on the one hand, a sufficient basis (from natural background) to treat the results of hygienic observations on the content of mercury in the atmosphere, drinking water, food products, the air of industrial premises, etc. Another would be controlled evaluation of the presence of mercury in the human body, quantities, characterizing its content as a micro-element. Only with the knowledge of these data can we see the whole problem of the effect on the organism of small concentrations of mercury, exposing its hygienic significance, determining principles for solving basic problems, clearly establishing limiting quantities, which, being "small", appear by no means indifferent fro the point of view of hygiene and toxicology. Finally, the above data in conjunction with materials of hygienic observations on the content of mercury in the surrounding human environment, are especially productive, permitting of "small" or "low" concentration, which cause those concrete quantities of mercury in the air which is signified by this term. In the atmosphere of big cities mercury vapor occurs significantly more often than in rural places. This is caused not only by all the sites using mercury in various aspects of production releasing it, but also by the burning in cities of large amounts of coal, fuel oil, and other types of fuel containing mercury. Coal contains about 0.000001% of mercury, oil shale, 0.0001%. The content of mercury in soot is significantly higher than in fuel. Significant quantities of mercury vapor enter the air when metallic mercury is extracted from its ores in metallurgical plants, and also through the treatment of iron ores and the ores of nonferrous metals. Each ton of these ores contains about one gram of mercury which can release into the atmosphere at metallurgical enterprises hundreds of grams of mercury daily (M. M. Tomson, 1949). The atmosphere is also contaminated by natural and illuminating gases in which mercury occurs in the quantities of 0.005 mg/m3. According to data of A. Stock (1936), mercury contained in street dust of cities amounts to 0.000087%. The mercury vapor content in the air of large cities in conditions where multiple sources of atmospheric contamination by mercury exist and purification of the effluents is practically nonexistent, varies from 0.0003 to 0.002 - 0.003 mg/m3. From the sources of such contamination of the atmosphere by mercury vapor, according to R. G. Leytes (1952), appear clouding gases from mercury furnaces, air from vacuum and vacuum flow pumps containing exhausts from mercury apparatus and instruments, air from exhaust hoods (closed) for the conduction of work with heated mercury, air from exhaust hoods in which work with uncovered mercury is undertaken, exhaust from general shop ventilation systems from places where "open" and "closed" work with mercury occurs. The indicated materials pertaining to the significant sorption of mercury by the soil leads to the conclusion that, in the determined conditions the soil can be a source of secondary contamination by mercury of the atmosphere, water sources, ground water and plants. Secondary contamination by mercury of various objects in the environment and the subsequent desorption determines the possibility of a mercury cycle between industrial sites and the surrounding atmosphere. In the present chapter not that at various distances (up to 3,000 meters) from industrial source of mercury in the air along with the contamination of soil, researchers observed the absorption of mercury onto building walls, the contamination of air of various dwellings, the presence of mercury in paints on internal walls of these houses, on roof surfaces, and in the leaves of trees. In speaking of the contamination of external objects with mercury from industrial discharges, it is very pertinent, so to speak, to note the comparatively low concentrations, on the order of 0.0003 to 0.002 -0.003 mg/m3. At the same time it is vital to clearly establish that such quantities of mercury contained in the air are by no means the "natural" concentrations of mercury, to establish corresponding hygienic norms for he content of mercury in the environment. The generalization by hygienists of contemporary data on the geochemistry of elements and the acquaintance of geochemistry of elements and the acquaintance of geochemists with materials on the content and presence of these elements in the environment, obtained by hygienists, can facilitate a real attempt towards the development of a new branch of hygienic science -- geohygiene. In arguing and propagandizing the idea of geohygiene, N. V. Lazarev (1959, 1956) set forth its task as the study of all the changes in chemical composition and physical characteristics of the external layer of the earth's crust which has or could have in the future "significance for the hygienic properties on the surface of the earth as a medium of habitation for man". In the opinion of N. V. Lazarev, hygienists must frequently know the scale and route of migration of toxic elements produced in connection with the removal of these elements from minerals. The author explains this fact, that the absolute dimensions of a mixed mass in the external layer of the earth's crust under the effect of the industrial activity of man at the present time is such that it is possible to change significantly the characteristics of all regions of the earth. In developing the conception espoused by N. V. Lazarev on the geohygienic significance of chemical factors in the human habitat by our use of mercury, it has been shown that at the present time the correct study of mercury and its hygienic and toxicological evaluation is from the point of view of geohygiene (I. M. Trakhtenberg, V. P. Yerogov, M. N. Korshun, 1968). Particular attention should be focused on mercury as a factor exercising influence on the state of health of the population under conditions of the mercury biogeochemical province. We come now to the data of V. P. Yerogov (1966, 1967) obtained as a result of studies undertaken in t he Gorno-Altay Autonomous Region where many ore bodies are located and there is intensive extraction of mercury from ores. According to his data examples of different soil types from this province contain mercury within the limits 0./03 -1.2 mg/100g., and in the control region, 0.004 - 0.12 mg/100 g. The mercury level in water sources is indicative of its concentration in the external medium and is about 0.002 - 0.03 mg/1. The quantity of mercury in the atmosphere also exceeds significantly its content within the limits of mercury deposits and composes 0.007 - 0.13 mg/m3. Upon analysis of general morbidity (based on published data) it was established that among people who had lived a long time within this region, indicators were significantly higher than among persons living in control regions (from 10.7 - 27.5%). There was a higher morbidity level in a majority of nosological forms: infectious diseases, ear, nose and throat diseases, diseases of the respiratory and hemotopoietic organs, of the kidneys and urinary tract and of the mouth and teeth. The number of people with dental caries in the region studied is also up to 10.4% higher than in the control region; the difference in susceptibility of the groups to caries increases with age: from 4.0% in preschool age children, to 8.6% in school children and to 18.7% in adults. Interesting data have been obtained on the state of the thyroid gland. The study was done because most of the Gorno-Altay Region is known for the low concentration of iodine in its soil and water. This exclusion constitutes a geochemical province. A high percentage of goiter is noted in both iodine poor and iodine rich regions of the biogeochemical province. In contrast to other places in the Gorno-Altay where a diffuse form of goiter prevails, populations at points in the mercury province are most often affected by nodal and mixed forms (72.9%). Another feature of endemic goiter in this location as opposed to endemic goiter in the rest of the Gorno-Altay is the unusual number of people afflicted with hyperthyroid goiter. Note also that as a result of iodine prophylaxis among schoolchildren who lived in regions with a low iodine content, the number of persons with goiter decreased from 54.0% to 29.8% in three years at the same time that analogous measures among schoolchildren of the geochemical province were almost ineffective: The percent of persons suffering from goiter rose from 40.0% to 43.9% in that time. In determining the mercury content in the urine of persons living in the biogeochemical province, it was established among preschool children -- 0.014 mg/1. This leads us to state that indicated quantities exceed by far the mercury content in the urine of persons having no contact with mercury or its compounds. Thus, under the conditions of the mercury biogeochemical province and increased content of mercury in objects in the external environment determines the state of health of the population inhabiting these regions. Mercury as a Bioelement. The presence, continual circulation and migration of mercury in the human environment determines its continued presence in a variety of biological substrates. Mercury belongs to the series of trace elements that is, those chemical substances which are found in plant and animal organisms in concentration on the order of thousandths or hundred thousandths of a percent. It is known that of 70 trace elements discovered up to the present time we have data on the biological significance of only 35. The discovery of the possible physiological significance of mercury as a trace element or the effect of its absence from the hygienic point of view is an extremely important task. The necessity of solving this dictates the principal need of determining the "physiological norm" for mercury content in various biological substrates of the organism (organs, blood, saliva, urine, feces, etc.), food products, plants and so on. Knowledge of this "norm" allows hygienists a more basic orientation for the evaluation of the degree of risk of concentrations of mercury in the bodies of workers and to characterize the effects of a series of quantities which come to mind as "diagnostic". An attempt at such analysis has been undertaken already by A. Stock (1934). It agrees with data obtained by the author and his co-workers together with cooperating laboratories that man takes in about 0.005 mg Hg daily. About the same amount is excreted daily by the healthy person. A. Stock and F. Cucuel (1934) found relatively high concentrations of mercury in the bodies of estruating and marine fish and in marine algae. After many observations A. Stock (1940) stated that traces of mercury occur in excreta of persons who have never had contact with mercury and that their blood, urine and feces contain insignificant quantities of mercury (on the order of 0.003 - 0.007 mg/1 of blood). In his conclusions the author noted that the total mercury content in the human organism varies within the limits of 0.0001 - 0.001 mg/100g of fresh tissue. According to A. Stock, under ordinary conditions the mercury sources for the body are food products and dust discharges which contain traces of this metal. According to his data, persons who have not had daily contact with mercury excrete urine containing up to 0.0005 mg mercury and feces containing up to 0.01mg. S. Teisinger (1953) and other workers observed the healthy man can excrete 0.008 - 0.017 mg Hg/1 of urine. I. Bodnar, Od. Szep and B. Wespremy (1939) having determined mercury in organs taken from human cadavers who in life had had no contact with mercury commented on the insignificant quantities of mercury in human organs and tissues. L. Brigatti (1949) stated that the limits of normal mercury content in the human body were ). 05 mg/100 g. According to the author the largest quantity of mercury occurs in the liver, less in the lungs and brain and still less in the heart. Spectrometric studies revealed that in dry tissue from humans who have had no contact with mercury, the following concentrations occur: in the kidneys -- 0.05 mg%, in the liver -- 0.37 mg%, in the spleen -- 0.12 mg% (G. C. Griffith, E. M. Butt, I. Walker, 1954). According to I. G. Fridlyand, insignificant quantities of mercury in excreta of healthy humans are caused by its uptake along with certain food products by the body. Interesting materials were obtained by P. Borinskiy (1931). He studied urine and feces of persons who had had no contact with mercury and in 51% of the cases found mercury present in quantities varying from 0.005 - 0.01 mg. In twelve of the eighteen children studied, the daily voidance of urine and feces yielded from 0.00008 - 0.0007 mg mercury. P. Borinskiy also studied food products and found mercury in them. The author concluded on the basis of his obtained data that the 0.01 mg mercury content in the daily urine output was normal and therefore was not significant. From the preceding data it follows that mercury, even in extremely minute quantities, is, as a rule, found in human organs and tissues. What kind of a biological role does it have as a trace element? In light of the well-known theory of the dissemination of trace elements (V. I. Vernadskiy, 1934; A. N. Vinogradov, 1950) it is difficult to conceive that the mercury found in the biosphere as a trace element penetrates the human body with air, water and food and remains for a long time in the blood, organs and tissues, does not have a biological significance. Interesting studies in that direction have been undertaken in recent years by A.A. Nepesov (1955, 1958). He undertook the study of the principles and processes underlying the "physiological properties of mercury" in those concentrations encountered under normal environmental conditions and in the human body. In the opinion of A. I. Venchikov, (1947, 1957) which he expressed in the study of the physiological properties of trace elements one can distinguish two possible forms by their action in the living organism. One of these is the "pharmacotoxicological, having the property in relation to the intake concentration of either damaging protoplasm or denaturing proteins, and blocking various steps of enzyme processes", and the other, "biotypic, continually participating in the metabolism of substances necessary to the normal life function of the organism". What are the results of the study of mercury as a bioelement? Research indicates that a really minute quantity of mercury (solutions of mercury dichloride, 0.003 - 0.125 mg%) has the capability of stimulating phagocytic activity of blood leucocytes in vitro and in vivo and to increase the intensity of heat exchange. In experiments on isolated frog hearts, mercury in the indicated concentrations has the property of "rendering toxic liquids(As a "toxic liquid" they used an extract obtained from products formed by "decomposing muscle".) harmless on tissue and the same time could accelerate restoration of disturbed cardiac function". Simultaneously they noted increased viability of the frogs who had been poisoned by toxic liquids and who had subsequently received 0.125 mg% solutions of mercury chloride. Further experiments on guinea pigs poisoned with diphtheria toxin showed the detoxifying properties of mercury chloride administered every two hours for two days and then hourly for the following three days (0.001 mg). At the same time all guinea pigs who had received a lethal dose of diphtheria toxin died, but among animals who had received simultaneous doses of mercuric chloride, no deaths occurred. Experimental evidence on mercury as a bioelement published by A. A. Nepesov indicates that it is an agent that stimulates phagocytic activity and metabolic intensity. Based on this data one can theorize that mercury as a bioelement participates in physiological processes connected with detoxication. Separate observations on the detoxifying capability of heavy metal salts (copper, zinc in microelement concentration indicate that they participate in intracellular redox processes (A. I. Venchikov). One should be cautious in attributing the same properties to "physiological" concentrations of mercury. Yet the proceeding materials indicate that mercury can exert a beneficial stimulating effect on the course of certain physiological processes. In recent years there has been more and more data on the effects of metals as trace elements on enzyme reactions in nucleic metabolism. It has been established frequently that mercury ions and ions of a series of other metals (Mg++, Ag++, Co++, Ni++) protect messenger RNA from the effects of RNAase (B. Singer, H. Frankel-Conrat, 1962; S. Nishimura, G. D. Novelli, 1963). The effect of mercury on the thermal stability of RNAase has also been established (S. Stocks, 1961). Changes in viscosity and absorption spectra of high polymer DNA solutions depend on the presence of certain metal ions, in this case, mercury. It is known that DNA molecules in reactions with HgCl2 decrease significantly and, under the effect of bound mercury reagents, increase (S. Katz, 1956). Accordingly one can say that complexed metal ions, particularly mercury, in reactions with nucleic acids produce reversible changes in the physical properties of the latter and that study of these reversible reactions "can have great significance in explaining the biological function of nucleic acids" (M. Ya. Shkol'nik, 1963) and can additionally elucidate the role of metals as bioelements. Mercury has another character in concentrations which exceed those normal for human organs and tissues. In these cases the border between the "physiological" and nonphysiological" effect of mercury gradually begins to disappear in its concentration in the environment. It rises and it gradually loses its significance as a trace element and begins to exert its effect as a toxic substance.