Uptake of mercury vapour in blood in vivo and in vitro from Hg-containing air

Scopoli's work in the field of mercurialism in light of today's knowledge: past and present perspectives

The Idrija Mercury Mine (1490-1994) appointed its first physician, Joannes Antonius Scopoli, in 1754. Most of his descriptions of mercurialism are still relevant today. This study highlights Scopoli's observations on the interaction between elemental mercury (Hg degrees ) and alcohol, on the appearance of lung impairment, insomnia, and depressive mood in mercurialism. This presentation is based on Scopoli's experiences presented in his book, De Hydrargyro Idriensi Tentamina (1761), current knowledge, and our own experience acquired through health monitoring of occupational Hg degrees exposure. Some studies have confirmed Scopoli's observation that alcohol enhances mercurialism and his hypothesis that exposure to high Hg degrees concentrations causes serious lung impairment. Neurobiological studies have highlighted the influence of Hg degrees on sleep disorder and depressive mood observed by Scopoli. Although today's knowledge provides new perspectives of Scopoli's work on mercurialism, his work is still very important and can be considered a part of occupational medicine heritage.

The inhibition of mercury absorption by dietary ethanol in humans: cross-sectional and case-control studies

BACKGROUND

Since the inhibition of mercury absorption by ethanol was serendipitously discovered in 1965,(1) a limited number of small number studies with both animal and human subjects have reported results consistent with this finding.

AIMS

To investigate this phenomenon in a large scale human study with low level Hg exposed dentists.

METHODS

Data were collected for a sample of 1171 dentists, and both cross sectional and case-control methods were utilised to examine the data.

RESULTS

Abstainers (n = 345) had significantly higher urinary mercury concentrations (HgU) than drinkers (n = 826): 5.4 microg/l v 4.8 microg/l. Multiple linear regression showed a significant effect of ethanol dose on HgU after adjusting for potential confounders. A case-control analysis in which cases were defined as those individuals with urinary Hg concentrations of > or =15 microg/l (approximately top 5%), and controls as those with concentrations of <1.0 microg/l ( approximately bottom 5%), showed a clear protective dose-response relation; there was a decreasing risk of being a "case" (having an HgU > or =15 microg/l) with increasing ethanol consumption. The significance of the adjusted model is p<0.001, and the chi2 test for trend across ethanol consumption categories in the adjusted model is p<0.05, confirming the dose-response relation.

CONCLUSION

We believe that this straightforward investigation provides the first specific confirmation in a large scale human study of the inhibitory effect of ethanol on urinary mercury concentration, and by inference, on mercury absorption.

The effect of selenium on the localization of autometallographic mercury in dorsal root ganglia of rats

The autometallographic technique was used to demonstrate the localization of mercury in dorsal root ganglia of adult Wistar rats. The animals were either exposed to mercury vapour, 100 micrograms Hg m-3, 6 h day-1, 5 days per week, or treated with organic mercury in the drinking water, 20 mg CH3HgCl per litre, for 4 weeks. The effect of orally administered sodium selenite on the pattern of intracellular distribution of mercury in these two situations was investigated. In rats exposed to mercury vapour alone, faint staining was present in ganglion cells. The selenite induced a conspicuous increase in the number of stained cells and in the intracellular staining intensity. In rats treated with organic mercury, mercury deposits were detected within ganglion cells and macrophages. The number of mercury-containing cells was increased by co-administration of selenite. In addition, satellite cells, the capsule and vessel walls were faintly stained. Twenty weeks after cessation of the organic mercury treatment, mercury staining was reduced. Again, selenite treatment enhanced staining intensity. When studied using the electron microscope, mercury was restricted to lysosomes, irrespective of treatments. The present study shows that the deposition of autometallographic mercury in the dorsal root ganglia depends on the chemical type of mercury, the co-administration of selenite and the length of the survival period.

Localization of mercury in CNS of the rat. V. Inhalation exposure to metallic mercury

The autometallographical technique has been used to determine the distribution and cellular localization of mercury deposits in the Wistar rat CNS after exposure to elemental mercury vapor (50-550 micrograms Hg/m3 of air for 4-24 h). In animals exposed to 50 micrograms Hg/m3 for 8 h, silver-enhanced mercury grains were confined to the capillary walls. Increasing the concentration of mercury to 500 micrograms Hg/m3 caused mercury staining to appear in neurons in the corpus striatum, mesencephalic nucleus of the trigeminal nerve and cerebellar deep nuclei. In the spinal cord, mercury appeared primarily in the motoneurons of lamina IX. Following exposure to 550 micrograms Hg/m3 for 12 h mercury was additionally detected in the ependyma. Animal exposure to 550 micrograms Hg/m3 for 24 h resulted in visible mercury deposits in the cerebellar and cerebral cortices. In the cerebral cortex, mercury was present in neurons populating lamina III in the isocortex. No mercury was detected in the allocortex. In the cerebellar cortex, mercury staining was limited to the Purkinje cells. Neurons in the thalamus contained heavy accumulations of mercury. Heavy staining for mercury was detected in lung alveolar macrophages in sections prepared from animals exposed to 550 micrograms Hg/m3 for 24 h. In animals exposed to 500 micrograms Hg/m3 or more, the primary target cells were the neurons, but glia cells also contained scattered mercury deposits. Ultrastructurally, mercury deposits were detected in the lysosomes.

Mercury vapor uptake and hydrogen peroxide detoxification in human and mouse red blood cells

The uptake of Hg vapor (Hg0) by suspensions of human and BALB-c mouse erythrocytes was studied in a closed exposure system. The formation of catalase-compound-I and thereby the oxidation of Hg0 was initiated by microinfusion of hydrogen peroxide. The degradation of H2O2 by the glutathione (GSH)/GSH peroxidase system was reduced by t-butyl-hydroperoxide (t-BOOH) or by 1-chloro-2,4-dinitrobenzene (CDNB). In human red blood cells, CDNB and t-BOOH increased the rate of Hg vapor oxidation at the low and intermediate H2O2 supplementation rates. In mouse erythrocytes, Hg uptake was increased by CDNB over the entire H2O2 infusion range. In human cells, t-BOOH (0.1 mM) produced a remarkably high Hg uptake even without added H2O2. This Hg uptake in absence of exogenous H2O2 was inhibited by aminotriazole as was the activity of catalase. Hence, the Hg uptake was likely to have been induced by endogenous hydrogen peroxide. These findings support the view that the intact GSH/GSH peroxidase system can diminish the efficiency of compound-I-induced Hg vapor oxidation in erythrocytes.

In vitro oxidation of mercury by the blood

A method is described for studying the in vitro oxidation of mercury vapour by red blood cells at short times and with diminishing mercury vapour concentrations. It is found that for 40% red blood cell suspensions and 37 degrees at concentrations greater than about 6 ng mercury vapour/ml, the oxidation rate is zero order, and that at lower concentrations the rate changes to first order. The effect of temperature and of added hydrogen peroxide are studied. Results are considered in terms of the generally accepted belief that the catalase-compound I system is the main path of oxidation. If the results obtained in vitro in these experiments apply in vivo to man, it follows that inhaled mercury is carried in the blood to the brain and other organs primarily as dissolved vapour rather than as inorganic mercury ions.

Partition coefficients of mercury (203Hg) vapor between air and biological fluids

Ostwald partition coefficients for mercury (Hg203) vapor (ng Hg per ml fluid/ng Hg vapor per ml air) were determined for human whole blood, 10.50 (10 degrees C), 6.62 (22 degrees C); 4.20 (37 degrees C); for human plasma, 5.56 (10 degrees C), 3.63 (22 degrees C), 2.40 (37 degrees C); for 0.9% NaCl; 2.65 (22 degrees C); and for sunflower oil, 80.8 (22 degrees C). It was shown that the uptake of mercury vapor by whole blood can not be accounted for as the sum of the solubilities of the saline and lipid components, but that when the uptake by hemoglobin is included the agreement is satisfactory. Using the solubility of mercury vapor as determined in this paper, consideration was given to various mechanisms for mobilization of mercury vapor from the lung. The method used for these determinations is recommended for similar studies because of its simplicity and precision.

Interactions between selenium and mercury in mice: marked retention in the lung after inhalation of metallic mercury

The distribution of 203Hg after inhalation of radioactive metallic mercury (4.3 mumol 203Hg0/kg body wt. for 1 h) was studied in saline (control) and selenite (10 mumol/kg body wt. intraperitoneally, i.p.) pretreated male C57BL mice by means of whole-body autoradiography and scintillation counting. Selenite pretreatment did not apparently change the immediate uptake and distribution of 203Hg (presumably inorganic Hg after oxidation in the different organs) but markedly increased the retention time in the whole body. The most marked retention was seen in the lungs where the selenite-pretreated animals had 200 times higher concentration as compared to control animals 14 days after inhalation. In other organs the corresponding value ranged between 1 (brain) and 12 (spleen). Selenite-pretreated and control animals showed the same low rate of exhalation of 203Hg after the inhalation period, while the latter animals eliminated significantly more through the urine and faeces (measured only during the first 24 h). When inversely radioactive selenite (75Se-selenite) was injected i.v. into animals 1 h earlier exposed to non-radioactive Hg0 (by inhalation), the lung concentration of 75Se after 24 h was 4 times higher than that of control animals. When radioactive mercury was injected i.v. in the form of 203HgCl2 (4.3 mumol/kg body wt.), selenite (10 mumol/kg body wt., i.p.) increased the retention time in the body, more so than after 203Hg0 inhalation. In this case the mercury was retained especially in the serum, red pulp of the spleen and liver (reticulo-endothelial system). 75Se-selenite injected i.v. after i.p. administration of non-radioactive HgCl2 in the same doses as above similarly accumulated more in serum, spleen and liver as compared to control animals. It is presumed that while injected selenite and inorganic mercury (Hg2+) interact strongly in the serum, increasing each other's uptake and retention especially in the reticulo-endothelial system, inorganic mercury retained in various organs after oxidation of Hg0 upon inhalation interacts with selenium mainly intracellularly. This occurs especially in the lungs, where initially high concentrations of mercury are found after inhalation.

Oxidation of mercury by catalase and peroxidase in homogeneous solution

Experiments in homogeneous solution confirm previous findings that catalase is an effective oxidant for Hg0 leads to Hg2+. Peroxidase also effects the oxidation, and in both oxidations the co-substrate hydrogen peroxide is not essential for mercury oxidation, although the oxidation is enhanced by the presence of hydrogen peroxide.

Whole body and liver distribution of inhaled mercury vapor in the mouse: influence of ethanol and aminotriazole pretreatment

Inhalation of radioactive metallic mercury vapor (203Hg0) in the mouse resulted in an accumulation of mercury in several organs where no specific uptake was observed after i.v. injection of inorganic mercury (203Hg2+). This was true for the whole respiratory epithelium (including the lung parenchyma), myocardium, brain, retina of the eye, adrenal cortex, corpora lutea of the ovary, epididymis, brown fat and thyroid gland. It is assumed that these organs have a high capacity for oxidizing Hg0 to Hg2+, which will then be retained in the tissues. Ethanol and aminotriazole (catalase inhibitors) decreased the concentration in several of these organs, although not in an exactly similar pattern. In the livers of non-treated animals, most of the inhaled mercury accumulated in the hepatocytes in the periphery of the lobuli (periportal region), close to where the blood vessels enter the liver parenchyma. Treatment with ethanol or aminotriazole increased the liver mercury content, with more or less all the hepatocytes apparently engaged in the oxidation of Hg0.

Selective determination of elemental mercury in blood and urine exposed to mercury vapor in vitro

A method is described to ensure quantitative measurement of dissolved mercury vapor (Hg0) in blood and urine. Room air passed through samples of blood and urine carries with it all the dissolved Hg0 but leaves behind all the ionic mercury (Hg++). Oxidation of Hg0 to Hg++ in blood samples is completely inhibited by addition of ethanol (0.5% v/v). To minimize error due to evaporation of Hg0, it is suggested that samples should be stored at 0 degree C and Hg0 should be determined within 60 min of collection of blood samples and within 10 min of urine samples.

Enzymatic oxidation of mercury vapor by erythrocytes

The formation of glutathione radicals, the evolution of nascent oxygen or the peroxidatic reaction with catalase complex I are considered as possible mechanisms for the oxidation of mercury vapor by red blood cells. To select among these, the uptake of atomic mercury by erythrocytes from different species was studied and related to their various activities of catalase (hydrogenperoxide : hydrogen-peroxide oxidoreductase, EC 1.11.1.6) and glutathione peroxidase (glutathione : hydrogen-peroxide oxidoreductase, EC 1.11.1.9). A slow and continuous infusion of diluted H2O2 was used to maintain steady concentrations of complex I. 1% red cell supsensions were found most suitable showing high rates of Hg uptake and yielding still enough cells for subsequent determinations. The results indicate that the oxidation of mercury depends upon the H2O2-generation rate and upon the specific acticity of red-cell catalase. The oxidation occurred in a range of the catalase-H2O2 reaction where the evolution of oxygen could be excluded. Compounds reacting with complex I were shown to be effective inhibitors of the mercury uptake. GSH-peroxidase did not participate in the oxidation but rather, was found to inhibit it by competing with catalase for hydrogen peroxide. These findings support the view that elemental mercury is oxidized in erythrocytes by a peroxidatic reaction with complex I only.