Comparison of renal function and psychomotor performance in workers exposed to elemental mercury

Summary Renal function and psychomotor performance (eye-hand coordination, arm-hand steadiness) of a group of 43 workers exposed to mercury vapor were examined. Their mean age and average duration of exposure to mercury were 38 and 5 years, respectively. The results were compared with those obtained in a matched group of 47 control workers. Increased proteinuria and albuminuria were found slightly more prevalent in the Hg-exposed group than in the control workers. These results are in agreement with those found during a previous study carried out in another group of workers also exposed to elemental mercury (Bucket et al. 1980). The scores of the psychomotor tests were less satisfactory in the Hg workers than in the control workers, the arm-hand steadiness test being more discriminative than the eye-hand coordination test. Preclinical changes in psychomotor function can be detected independently of the presence of signs of renal dysfunction. No clear-cut relationships were found between the prevalence of abnormal psychomotor scores and the level of mercury in blood (HgB) or in urine (HgU). Increased prevalences of abnormal psychomotor scores seem however to occur for HgB between 1 and 2 g/100 ml and for HgU between 50 and 100 g/g creatinine. Therefore, a biologic threshold limit value of 50 g/g creatinine is proposed for urinary mercury to prevent the development of preclinical effects on the central nervous system. A similar critical HgU level based on renal dysfunction prevalences has been suggested in a previous study.This study was supported by a grant from the Commission of the European Communities     

Introduction: scope and purpose of the multicenter project " Assessment of effects due to low doses in inorganic mercury following environmental and occupational exposure: human and in vitro studies on specific toxicity mechanisms"

The principal aims of the project financed by the Italian Ministry of University and Scientific and Technological Research were: to verify if at the current limit values early biological effects can be demonstrated; to identify the levels of internal dose that can cause early effects; to evaluate the non-occupational factors that can contribute to the levels of internal dose. In particular, the mercury intake derived from dental amalgams and fish consumption was considered. The internal dose was measured with the traditional biological indicators (urinary and blood mercury) and with the speciation of a large percentage of biological samples by ICP-MS. The central nervous system, neuroendocrine function, kidney and the immune system were considered as target organs and were examined using previously standardized indicators of effects. Two groups of subjects were included in the study: workers with occupational exposure to inorganic mercury in different industrial settings and control subjects identified from the general population. The first group was characterized by an exposure level to inorganic mercury clearly below the current limit values; whereas the HgU levels of a relevant number of control subjects were similar to those measured in the exposed subjects. The in vitro studies covered several issues: the percutaneous absorption of mercury using skin derived from human post-mortem samples in a standardized model; the release of the metal from dental amalgams in different physiological conditions of the oral cavity; the effects of increasing doses of mercury chloride on tubular renal cells. The project was realized with the cooperation of seven Research Units from six Italian Universities. Researchers belonging to Departments of Occupational Medicine, Industrial Hygiene, General Pathology, Biochemistry, Odontology, and Biostatistics were involved to achieve a multidisciplinary approach. The results of this research project are described and discussed in the following papers.     

Urinary and blood markers of internal mercury dose in workers from a chlorakali plant and in subjects not occupationally exposed: relation to dental amalgam and fish consumption

OBJECTIVES: The aim of this paper was both to evaluate the internal dose of Hg in occupationally exposed workers (35 Chloralkali workers) compared to that of non occupationally exposed controls (40 workers of the same plant of Portotorres and 22 residents on the island of Carloforte, usual consumers of local fish, mostly tuna fish with relatively high Hg levels) and to assess the relevance of environmental and individual exposure factors linked to lifestyle, sea fish consumption and amalgam fillings. METHODS: All subjects filled out a questionnaire concerning the working history and lifestyle. The amalgam fillings area was measured by medical inspection using a standardised schedule attached to the questionnaire. Mercury in urine (HgU) was measured in all cases, while in a subgroup of our study total blood mercury (HgB) and its organic and inorganic component were also assessed. Furthermore, for 8 of the Carloforte group mercury in hair was also available. RESULTS: Values of urinary mercury excretion of the Chloralkali workers were significantly higher (median value of 15.4, range 4.8-35.0 micrograms/g creatinine, 94.3% of the cases having values > 5 micrograms/g creatinine) than those observed both among the reference group (median value of 1.9, range 0.4-5.6 micrograms/g creatinine, 12.5% of the cases having values a little greater than 5 micrograms/g creatinine) and among the residents in Carloforte (median value of 6.5, range 1.8-21.5 micrograms/g creatinine, 59.1% of the cases having values > 5 mcg/g creatinine). The HgU values observed in this group were in turn significantly higher than those of the non occupationally exposed workers living near Sassari (p = 0.03). Only in this last group were the HgU concentrations statistically significantly related to the extension of the amalgam fillings area (Pearson r = 0.53, p < 0.01). In the Carloforte group HgU was significantly related to the number of fish meal consumed per week (Pearson r = 0.48, p < 0.02). HgB (median value of 5.9, range 3.4-21.6 micrograms/l) as well as its inorganic component (median value of 2.4, range 1.8-4.6 micrograms/l) were significantly higher in the Chloralkali group compared to the other two groups. In all cases of the Carloforte group the ratio between the organic component and the total HgB was higher than 85%, while this ratio was significantly lower in the other two groups. The relationship between HgU and HgB was statistically significant, considering both total blood mercury and the inorganic and the organic components separately. A statistically significant relationship between the sea fish consumption per week and both total HgB (Pearson r = 0.82) and the organic component in this matrix (Pearson r = 0.84, p < 0.001) was observed among 16 non-occupationally exposed subjects. However, the significant relationship between organic blood mercury and sea fish consumption was almost entirely supported by the data observed in the Carloforte group. Total hair mercury levels analysed in 8 subjects of the Carloforte group were high (median value of 9.6, range 1.4-34.5 micrograms/g) and significantly related to sea fish consumption, and to both the individual Hg urinary excretion (Pearson r = 0.83) and to the organic component of blood mercury (Pearson r = 0.87). CONCLUSIONS: According to several experimental human and animal trials and to some recent studies on methylmercury toxicokinetic models, our results suggest that the organic compounds absorbed by usual sea fish consumption may be partially demethylated, increasing the inorganic Hg concentration in the kidney and consequently its urinary excretion, as was observed in the Carloforte group.     

Surveillance of workers exposed to mercury vapour:validation of a previously proposed biological threshold limit value for mercury concentration in urine

A cross-sectional epidemiological study was carried out among subjects exposed to mercury (Hg) vapour, ie, a group of 131 male workers (mean age: 30.9 yr; average duration of exposure, 4.8 yr) and a group of 54 female workers (mean age, 29.9 yr; average duration of exposure 7 yr). The results were compared with those obtained in well-matched control groups comprising 114 and 48 male and female workers, respectively. The intensity of current Hg vapour exposure was rather moderate as reflected by the levels of mercury in urine (HgU) (mean and 95th percentile: males 52 and 147 micrograms/g creatinine; females 37 and 63 micrograms/g creatinine) and of mercury in blood (mean and 95th percentile: males 1.4 and 3.7 micrograms/dl; females 0.9 and 1.4 microgram/dl). Several symptoms mainly related to the central nervous system (memory disturbances, depressive feelings, fatigue, irritability) were more prevalent in the Hg-exposed subjects. They were, however, not related to exposure parameters. In both male and female Hg-exposed workers no significant disturbances were found in short-term memory (audioverbal), simple reaction time (visual), critical flicker fusion, and colour discrimination ability. Only slight renal tubular effects were detected in Hg-exposed males and females, ie, an increased urinary beta-galactosidase activity and an increased urinary excretion of retinol-binding protein. The prevalence of these preclinical renal effects was more related to the current exposure intensity (HgU) than to the duration of exposure and was detected mainly when HgU exceeds 50 micrograms/g creatinine. Changes in hand tremor spectrum recorded with an accelerometer were found in the Hg-exposed males only. The prevalence of abnormal values for some hand tremor parameters (total velocity and total displacement in the 2-50-Hz band) was mainly increased in male workers exposed for more than 10 yr. Unlike the renal tubular effects, the preclinical signs of tremor were more related to the integrated exposure than to the current exposure. Since the female workers, who have been exposed to Hg vapour levels usually insufficient to increase their HgU levels above 50 micrograms/g creatinine, did not exhibit any change in hand tremor pattern, the results of the present study tend to validate our previously proposed biological threshold limit value of a HgU of 50 micrograms/g creatinine for workers chronically exposed to mercury vapour.     

Occupational exposure to metallic mercury in the dentist's office of a public primary health care clinic in the city of São Paulo

This paper discusses occupational exposure to metallic mercury among dentists and dental assistants, focusing on biological evaluation, effects on heaith, and environmental evaluation. Methods included visits to the clinic, hazard maps, urinary and environmental mercury measurements, and evaluation of health status. Results for the environment and work processes showed that mercury vapor concentrations impregnating surfaces and piping varied from 0.001 to 0.051 mg/m3 in air; occupational exposure with 62.5% of health workers having HgU ranging from 10 to 49 mg/l and 37.5% having HgU below 10 mg/l in 1994, while workers' previous measures (from 1992) were lower in every single case; an outflow of mercury and inadequate amalgamation due to a faulty amalgamator, the need for using a piece of chamois to obtain a homogeneous amalgam and remove excess mercury; the existence of combined hazards in the environment, and that all workers had been exposed since 1992. Results for workers' health showed a prevalence of symptoms from lesions to the central nervous system; central nervous system signs; and that mild-to-moderate chronic poisoning was found in 62.5% of workers.     

The inadequacy of threshold values for preventing lead poisoning in Brazil

This article reviews studies performed since 1975 on the occurrence of central and peripheral neurological manifestations in low-level lead exposure. The review shows that in many workers exposed to lead who present indications of both biological effects and exposure below the limits established by the Brazilian laws, abnormalities are found in peripheral nerve conduction velocity and also in several central nervous system functions. The study thus suggests that the threshold values used in Brazil to confirm lead poisoning should be revised.     

Immunologic effects of exposure to low levels of inorganic mercury

OBJECTIVE: The immune system is a target for the toxic effects of inorganic mercury, both in humans and animals. In humans it has been observed that occupational and environmental exposure to inorganic mercury may cause both clinical (autoimmunity, hypersensitivity) and subclinical effects (cellular and humoral immunologic variable modifications). To obtain a better definition of these effects with respect to the exposure levels, a multicentre study was performed on 117 workers exposed to very low doses of inorganic mercury and 172 subjects from the general population of the same geographical area with environmental exposure to mercury from dental amalgams and dietary fish intake. RESULTS: The white blood cell count was included in the normality range for all subjects and there was no difference between exposed and non exposed subjects. The immunologic variables studied showed an increase of the CD4+ and CD8+ number in exposed workers compared to non-exposed subjects, with a statistically significance only for CD4+, while no difference was observed regarding CD4+, CD8+, NK+ percentage and CD4+/CD8+ ratio. A significative decrease of serum IL-8 and an inverse correlation between serum levels of this cytokine and HgU were observed in exposed workers compared to non exposed subjects. No association between immunologic variables and both dental amalgams and dietary fish intake was found in subjects not occupationally exposed to inorganic mercury. DISCUSSION: The decrease in IL-8 serum levels observed in exposed workers might suggest an immunosuppressive effect of occupational exposure to very low doses of inorganic mercury. This result suggests the need to revise of current HgU BEI after further definition of its prognostic significance.     

Evaluation of the neurotoxic and nephrotoxic effects following long-term exposure to metallic mercury in employed at a chlorine/sodium-hydroxide plant

OBJECTIVES: Within the frame work of a wide multicentre study, a sub-study was developed in order to explore the occurrence of early effects on the central nervous system, on the kidney and on the neuro-immune system in the workers of a chloro-alkali production plant exposed to metallic mercury at airborne concentration levels lower than 0.025 mg/m3 (TLV-TWA). They were compared to a control population of employees of the same huge petrochemical plant with different job that did not implicate exposure to mercury vapors. Specifically, the study aimed at revealing the occurrence of early effects on the central nervous system related with mercury exposure, as can be assessed through neurophysiological and neurobehavioral tests. METHODS: The excretion of urinary mercury was measured by atomic absorption spectrometry. The study of renal function was assessed by measurement of the urinary excretion of some high and low molecular weight protein markers (albumin, beta 2-microglobulin, retinol-binding protein, fibronectin, specific proximal tubule brush border antigens, N-acetyl-beta-D-glucosaminidase). The neurobehavioral status of the study subjects was assessed by means of several test parameters (Simple Reaction Time, Color Word Vigilance Test, Symbol Digit, Finger Tapping, Mood Scale of Kjellberg and Iwanowski, Subjective symptoms questionnaire (QSS), Luria Nebraska Motor Scale, Branches Alternate Movement Task and Tremometry). RESULTS: The values of urinary excretion averaged 12 +/- 8 micrograms Hg/g of creatinine for the exposed workers group (n = 38), while for the reference group (n = 34 cases) urinary excretion was statistically lower, averaging 4 +/- 6 micrograms Hg/g of creatinine. Neither the parameters selected for the assessment of renal functions, nor those chosen to probe the neurobehavioral status of the probands revealed statistically reliable differences between the group of exposed workers (length of exposure: range 1-34 years) and the control group. Nevertheless, some minor but still statistically reliable correlations were found between some neurobehavioral parameters and some demographic variables describing the whole group of tested workers, but not to the level of occupational exposure to mercury. CONCLUSIONS: The results of the study confirm the lack of toxic effects of clinical importance on the central nervous system and on the kidney for values of mercury urinary excretion lower than the suggested index of biological exposure (IBE) of 35 micrograms Hg/gram of creatinine.     

Neurotoxic effect of exposure to low doses of mercury

OBJECTIVES: To assess early effects on the Central Nervous System due to occupational exposure to low levels of inorganic mercury (Hg) in a multicenter nationwide cross-sectional study, including workers from chloro-alkali plants, chemical industry, thermometer and fluorescent lamp manufacturing. The contribution of non-occupational exposure to inorganic Hg from dental amalgams and to organic Hg from fish consumption was also considered. METHODS: Neuropsychological and neuroendocrine functions were examined in a population of 122 workers occupationally exposed to Hg, and 196 control subjects, not occupationally exposed to Hg. Neuropsychological functions were assessed with neurobehavioral testing including vigilance, motor and cognitive function, tremor measurements, and with symptoms concerning neuropsychological and mood assessment. Neuroendocrine functions were examined with the measurement of prolactin secretion. The target population was also characterized by the surface of dental amalgams and sea fish consumption. RESULTS: In the exposed workers the mean urinary Hg (HgU) was 10.4 +/- 6.9 (median 8.3, geometric mean 8.3, range 0.2-35.2) micrograms/g creatinine, whereas in the control group the mean HgU was 1.9 +/- 2.8 (median 1.2, geometric mean 1.2, range 0.1-33.2) micrograms/g creatinine. The results indicated homogeneous distribution of most neurobehavioral parameters among exposed and controls. On the contrary, finger tapping (p < 0.01) and the BAMT (Branches Alternate Movement Task) coordination test (p = 0.05) were associated with occupational exposure, indicating an impairment in the exposed subjects. Prolactin levels resulted significantly decreased among the exposed workers, and inversely related to HgU on an individual basis (p < 0.05). An inverse association was also observed between most neuropsychological symptoms and sea fish consumption, indicating a "beneficial effect" from eating sea fish. On the contrary, no effects were observed as a function of dental amalgams. CONCLUSIONS: In conclusion, this study supports the finding of early alterations of motor function and neuroendocrine secretion at very low exposure levels of inorganic Hg, below the current ACGIH BEI and below the most recent exposure levels reported in the literature.     

Effects of low exposure to inorganic mercury on psychological performance

The effects of low exposure to inorganic mercury on psychological performance was investigated: the study groups included eight chronically exposed workers and 20 who were only occasionally exposed. These were compared with a control group of 22 subjects from the same plant who were not exposed to mercury. All subjects were administered the WHO test battery to detect preclinical signs of central nervous system impairment: the battery includes the Santa Ana (Helsinki version) test, simple reaction time, the Benton test, and the Wechsler digit span and digit symbol. In addition, the Gordon test was used to study personality profiles and the clinical depression questionnaire. Urinary mercury was used as indicator for internal dose. To this effect, urinary mercury observed in workers examined from 1979 to 1987 was evaluated. Of the pyschic functions explored by behavioural tests, only short term auditory memory was found to be impaired in the chronically exposed workers (p less than 0.05 compared with the controls). The chronically exposed workers were also found to be more depressed than those in the two other groups. No changes of visual motor functions were observed. The personality of the occupationally exposed workers was found to be considerably changed compared with that of the control group. On the basis of the results obtained and in view of urinary mercury mean concentrations in the exposed group which were 30-40 micrograms/l over the years, it is suggested that the TLV-TWA for mercury should be lowered to 0.025 mg/m3 and that the biological urinary exposure indicator for biological monitoring should be 25 micrograms/l.     

Effects of low exposure to inorganic mercury on psychological performance.

The effects of low exposure to inorganic mercury on psychological performance was investigated: the study groups included eight chronically exposed workers and 20 who were only occasionally exposed. These were compared with a control group of 22 subjects from the same plant who were not exposed to mercury. All subjects were administered the WHO test battery to detect preclinical signs of central nervous system impairment: the battery includes the Santa Ana (Helsinki version) test, simple reaction time, the Benton test, and the Wechsler digit span and digit symbol. In addition, the Gordon test was used to study personality profiles and the clinical depression questionnaire. Urinary mercury was used as indicator for internal dose. To this effect, urinary mercury observed in workers examined from 1979 to 1987 was evaluated. Of the pyschic functions explored by behavioural tests, only short term auditory memory was found to be impaired in the chronically exposed workers (p less than 0.05 compared with the controls). The chronically exposed workers were also found to be more depressed than those in the two other groups. No changes of visual motor functions were observed. The personality of the occupationally exposed workers was found to be considerably changed compared with that of the control group. On the basis of the results obtained and in view of urinary mercury mean concentrations in the exposed group which were 30-40 micrograms/l over the years, it is suggested that the TLV-TWA for mercury should be lowered to 0.025 mg/m3 and that the biological urinary exposure indicator for biological monitoring should be 25 micrograms/l.     

Neuroendocrine and neurobehavioral effects associated with exposure to low doses of mercury from habitual consumption of marine fish

OBJECTIVES: To evaluate neuroendocrine and neurobehavioral effects possibly associated with increased dietary intake of organic mercury (Hg), a group of 22 subjects living on the island of Carloforte (south-west Sardinia) was examined, who were regular consumers of tuna fish with relatively high Hg content. This group, never exposed occupationally to either Hg or to other neurotoxic substances, was compared with 22 age-matched controls employed at a chemical plant in Portotorres (northern Sardinia). METHODS: Hg in urine (HgU) and serum prolactin (PRL) were measured in all cases, whereas measurements of total (HgB) and organic blood mercury were available only for 10 subjects from Carloforte and 6 controls. Data about working history and lifestyle (education, smoking habit, alcohol and sea fish consumption) were collected by an interviewer using a standardised questionnaire. Neurotoxic symptoms were evaluated by a self-administered questionnaire, whereas a test battery, including some computerised tests of the Swedish Performance Evaluation System (SPES) to assess vigilance and psychomotor performance, some tests on motor coordination (Luria-Nebraska and Branches Alternate Movement Task) and one memory test for numbers (Digit Span) was administered to assess neurobehavioral changes associated with exposure to dietary intake of organic mercury. In all cases, characteristics of hand tremor were evaluated by the CATSYS System 7.0. RESULTS: HgU values were significantly higher in the Carloforte group (median 6.5, range 1.8-21.5 micrograms/g creatinine) compared with controls (median 1.5, range 0.5-5.3 micrograms/g creatinine). Serum PRL was significantly higher among subjects from Carloforte and correlated with both urine and blood Hg levels. The scores of each item of the questionnaire investigating neurological symptoms were not statistically different in the two groups. In some tests of the SPES battery (Color Word Vigilance, Digit Symbol and Finger Tapping) the performance of the Carloforte group was significantly worse than that of controls, whereas in the other neurobehavioral tests poorer performances by the Carloforte group were not statistically significant. None of the tremor parameters was significantly different comparing the two groups. Multivariate analysis--controlling for education level and other covariates--carried out for the Symbol-Digit Reaction Time and for the Branches Alternate Movement Task (BAMT) showed that organic Hg concentration in blood was the most significant factor negatively affecting individual performance in these tests. Serum PRL was correlated with some neurobehavioral tests (Digit Symbol, Finger Tapping and BAMT). CONCLUSIONS: Some of the neurobehavioral tests were sensitive enough to discriminate groups with different Hg body burden, even in the low-dose range. However, the pattern of results suggests adverse neurobehavioral effects, especially on psycho-motor coordination, with a significant dose-effect relationship, mostly associated with long-term exposure to low levels of organic mercury due to the usual consumption of large fish with relatively high levels of Hg in the flash.     

Mercury levels in urine and hair of children in an Andean gold-mining settlement

This field study investigated mercury (Hg) levels in urine and hair of Andean children of indigenous Saraguro and Metizo gold miners in the Nambija, Ecuador gold mining settlement. Spot samples of urine and hair samples were collected concurrently from 80 children each. Urine samples were used to determine the inorganic Hg burden, while hair samples were used as an index of methylmercury (MeHg) exposure from consumption of Hg contaminated fish. The mean level of Hg in urine (HgU) was 10.9 microg/L, and the mean level in hair (HgH) was 6.0 microg/g. Regression analysis showed a significant association (r = 0.404, p = 0.0007) between matched HgU and HgH samples. Mean HgU and HgU levels tended to be higher for children aged 6-14 years than for a younger group. The wide range of Hg levels in the urine and hair of Andean children of gold miners may place them at risk for neurodevelopmental and learning disorders.     

Renal effects of low doses of mercury

OBJECTIVES: The present study was aimed at investigating early markers of renal damage and dysfunction in subjects exposed to low doses of mercury from different sources. Different groups of subjects were examined with urinary Hg excretion (HgU) ranging from 0.1 to 35.0 micrograms/g creatinine: 122 occupationally exposed workers, 22 subjects living in a non-polluted area, but consuming large amounts of tuna and sword fish, and 197 controls. METHODS: Several markers of renal changes were measured in urine (albumin, fibronectin, beta 2-microglobulin, retinol-binding protein, tubular antigens, N-acetyl-beta-D-glucosaminidase activity) and serum (beta 2-microglobulin and cystatin C). Serum autoantibodies towards collagen, laminin and tubular antigens were assessed in subjects with abnormal renal markers. The role of glutathione-S-tranferases GSTT1 and GSTM1 polymorphisms in the inter-individual variability of biological response to Hg was also investigated. RESULTS: Renal markers were not correlated with HgU. None of such markers differed significantly between exposed workers and controls, except for urinary beta 2-microglobulin, which was decreased in Hg-exposed workers (GM = 55.8 vs 86.6 micrograms/g creatinine), in the absence of any changes in serum concentration. Subjects usually eating tuna and sword fish showed an increased urinary excretion of beta 2-microglobulin, albumin and fibronectin. Serum titres of auto-antibodies did not differ between the groups. Neither in controls nor in exposed workers were the observed differences modified by the GSTM1 and GSTT1 genotypes. CONCLUSION: The present study did not provide evidence of any changes in kidney integrity and function in subjects exposed to very low levels of inorganic Hg resulting in urinary Hg lower than 35 micrograms/g creatinine. Nor did we obtain evidence of Hg-induced autoimmunity towards kidney components. The potential modifying role of GST polymorphisms could not be clarified in the absence of effects associated with exposure to the risk factor, i.e., to inorganic Hg. Preliminary data suggesting nephrotoxic effects of organic Hg from a diet rich in large fish resulting in increased levels of both blood and urinary Hg--which however did not exceed 20 micrograms/g creatinine--deserves further investigation.     

Environmental Mercury and Its Toxic Effects

Mercury exists naturally and as a man-made contaminant. The release of processed mercury can lead to a progressive increase in the amount of atmospheric mercury, which enters the atmospheric-soil-water distribution cycles where it can remain in circulation for years. Mercury poisoning is the result of exposure to mercury or mercury compounds resulting in various toxic effects depend on its chemical form and route of exposure. The major route of human exposure to methylmercury (MeHg) is largely through eating contaminated fish, seafood, and wildlife which have been exposed to mercury through ingestion of contaminated lower organisms. MeHg toxicity is associated with nervous system damage in adults and impaired neurological development in infants and children. Ingested mercury may undergo bioaccumulation leading to progressive increases in body burdens. This review addresses the systemic pathophysiology of individual organ systems associated with mercury poisoning. Mercury has profound cellular, cardiovascular, hematological, pulmonary, renal, immunological, neurological, endocrine, reproductive, and embryonic toxicological effects.     

Evaluation of the dose of mercury in exposed and control subjects

OBJECTIVES: The aim of this paper was to analyse the concentrations of HgU and HgB in three different groups: 122 workers exposed, 18 workers formerly exposed and 196 subjects not occupationally or environmentally exposed to mercury. METHODS: All the subjects filled out a questionnaire concerning personal data, lifestyle, occupational or non-occupational exposure to Hg and medical history. The amalgam fillings area was measured by a standardised method. RESULTS: Urinary mercury excretion was significantly greater in the group of the exposed workers respect to the group of subjects not occupationally exposed (Median value of 8.3 micrograms/g creatinine and the 5 degrees and 95 degrees percentile respectively of 2.66 e 23.50 micrograms/g creatinine against Median value of 1.2 micrograms/g creatinine and the 5 degrees and 95 degrees percentile respectively of 0.18 and 5.42 micrograms/g creatinine). U-Hg in formerly exposed workers were comparable to U-Hg in non-occupationally exposed subjects, with a median value of 1.6 micrograms/g creatinine. B-Hg values were similar in the three groups: the median value was 3.1 micrograms/l in the non-occupationally exposed, 4.0 micrograms/l in the exposed workers and 3.9 micrograms/l in the past exposed. These value were not significantly different. Among the considered variables (amalgam fillings, fish consumption, age, sex, alcohol intake, chewing-gum and smoking) dental amalgam and fish consumption were significantly related with the Hg urinary excretion and the B-Hg levels. This is particularly true considering the subjects altogether: for the exposed workers, indeed, the occupational exposure was the most relevant variable. CONCLUSIONS: The results of the present research confirmed that the U-Hg excretion in non-occupationally exposed subjects is influenced by amalgam dental fillings. Furthermore, in our study Hg urinary excretion was significantly related with fish consumption. This fact can be explained, according to several recent experimental human and animal trials, considering that methylmercury contained in fish is partially converted, through breakage of the carbon-Hg bond, into Hg inorganic forms, which accumulate in the kidney and have a urinary excretion pathway.     

Significance of biological indicators of mercury exposure

BACKGROUND: It was considered appropriate to update of the significance and use of the different mercury exposure indicators. OBJECTIVE: The aim of the this paper was to correctly select biological media and sampling time and to understand the toxic kinetics of mercury for assessment of accurate biological monitoring. RESULTS: It was confirmed that mercury in blood (B-Hg) is a good indicator of recent exposure, while urinary mercury (U-Hg) indicates current exposure when mercury reaches the renal steady state. B-Hg values are greatly influenced by fish consumption, while the variables influencing U-Hg values are amalgam fillings, commercial gamma-globulin preparations, vaccines, topical remedies, environmental pollution and hobbies, occupational exposure and, partly, fish consumption. The speciation of mercury (Hg0, Hg++, methylmercury and ethylmercury) in biological media, should provide additional and important information in evaluating mercury toxicity. CONCLUSION: It was stressed that the appropriate choice of exposure indicators has to take account of the different variability factors and the characteristics of the toxic kinetics of mercury. The results of biological monitoring must be compared with references values, which are generally in the order of several micrograms/g creatinine, and limit values such as ACGIH BEI (U-Hg 35 micrograms/g creatinine and B-Hg 15 micrograms/l) or the DFG BAT (U-Hg 100 micrograms/l and B-Hg 25 micrograms/l).     

Methylmercury Exposure and Health Effects

Methylmercury is a hazardous substance that is of interest with regard to environmental health, as inorganic mercury circulating in the general environment is dissolved into freshwater and seawater, condensed through the food chain, ingested by humans, and consequently affects human health. Recently, there has been much interest and discussion regarding the toxicity of methylmercury, the correlation with fish and shellfish intake, and methods of long-term management of the human health effects of methylmercury. What effects chronic exposure to a low concentration of methylmercury has on human health remains controversial. Although the possibility of methylmercury poisoning the heart and blood vessel system, the reproductive system, and the immune system is continuously raised and discussed, and the carcinogenicity of methylmercury is also under discussion, a clear conclusion regarding the human health effects according to exposure level has not yet been drawn. The Joint FAO/WHO Expert Committee on Food Additives proposed to prepare additional fish and shellfish intake recommendations for consumers based on the quantified evaluation of the hazardousness of methylmercury contained in fish and shellfish, methylmercury management in the Korea has not yet caught up with this international trend. Currently, the methylmercury exposure level of Koreans is known to be very high. The starting point of methylmercury exposure management is inorganic mercury in the general environment, but food intake through methylation is the main exposure source. Along with efforts to reduce mercury in the general environment, food intake management should be undertaken to reduce the human exposure to methylmercury in Korea.     

Urinary excretion of mercury after occupational exposure to mercury vapour and influence of the chelating agent meso-2,3-dimercaptosuccinic acid (DMSA).

The spontaneous and chelator mediated excretion of mercury in urine was investigated in male subjects occupationally exposed to mercury vapour (alkaline battery and chloralkali plants) who did not exhibit any sign of kidney damage. The time course of the spontaneous elimination of mercury in urine was examined in seven workers (age 22-40) who had been removed from exposure to mercury vapour (average duration of exposure 4.4 years) because their urinary mercury concentrations repeatedly exceeded 100 micrograms/g creatinine. The post exposure observation period started 10 to 29 days after the date of removal and lasted about 300 days (slow HgU elimination phase). For each worker, the kinetics of the spontaneous HgU decline followed a first order process; the biological half life ranged from 69 to 109 days (mean 90 days). The increased urinary excretion of mercury after a single oral administration of 2 g meso-2,3-dimercaptosuccinic acid (DMSA) was investigated in 16 control workers (group A; age 23 to 49), in 11 workers removed from exposure for at least two years (group B; age 27 to 41), and in 16 workers currently exposed to mercury vapour (group C; age 21 to 58). In group C, the DMSA experiment was repeated twice (three weeks before and three weeks after a holiday) after measures had been taken to reduce the mercury emission. The urinary mercury excretion was significantly higher during the 24 hours after DMSA administration in all groups compared with that in the 24 hours before. The bulk (50-70%) of the DMSA stimulated mercury excretion appeared within the first eight hours. In each group, the amount of mercury (microgram Hg/24h) excreted after DMSA was significantly correlated with that before administration of DMSA. The groups whose exposure had ceased, however, exhibited much higher correlation for coefficients (r=0.97 for group B and 0.86 for group C after three weeks of holiday) than those currently exposed to mercury vapour (r-0.66 for group C before and 9.58 after reduction of exposure). The data suggest that after a few days of cessation of occupational exposure to mercury vapour the HgU before and after administration of DMSA mainly reflects the amount of mercury stored in the kidney, which represents a mercury pool with a slow turnover.     

Urinary excretion of mercury after occupational exposure to mercury vapour and influence of the chelating agent meso-2,3-dimercaptosuccinic acid (DMSA).

The spontaneous and chelator mediated excretion of mercury in urine was investigated in male subjects occupationally exposed to mercury vapour (alkaline battery and chloralkali plants) who did not exhibit any sign of kidney damage. The time course of the spontaneous elimination of mercury in urine was examined in seven workers (age 22-40) who had been removed from exposure to mercury vapour (average duration of exposure 4.4 years) because their urinary mercury concentrations repeatedly exceeded 100 micrograms/g creatinine. The post exposure observation period started 10 to 29 days after the date of removal and lasted about 300 days (slow HgU elimination phase). For each worker, the kinetics of the spontaneous HgU decline followed a first order process; the biological half life ranged from 69 to 109 days (mean 90 days). The increased urinary excretion of mercury after a single oral administration of 2 g meso-2,3-dimercaptosuccinic acid (DMSA) was investigated in 16 control workers (group A; age 23 to 49), in 11 workers removed from exposure for at least two years (group B; age 27 to 41), and in 16 workers currently exposed to mercury vapour (group C; age 21 to 58). In group C, the DMSA experiment was repeated twice (three weeks before and three weeks after a holiday) after measures had been taken to reduce the mercury emission. The urinary mercury excretion was significantly higher during the 24 hours after DMSA administration in all groups compared with that in the 24 hours before. The bulk (50-70%) of the DMSA stimulated mercury excretion appeared within the first eight hours. In each group, the amount of mercury (microgram Hg/24h) excreted after DMSA was significantly correlated with that before administration of DMSA. The groups whose exposure had ceased, however, exhibited much higher correlation for coefficients (r=0.97 for group B and 0.86 for group C after three weeks of holiday) than those currently exposed to mercury vapour (r-0.66 for group C before and 9.58 after reduction of exposure). The data suggest that after a few days of cessation of occupational exposure to mercury vapour the HgU before and after administration of DMSA mainly reflects the amount of mercury stored in the kidney, which represents a mercury pool with a slow turnover.