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.     

铅作业工人神经行为功能分析

目的探讨和评价铅作业工人神经行为功能状况。方法使用WTO神经行为核心测验组合对接触组和对照组进行神经行为功能测试调查,同时测定铅作业工人尿铅浓度。结果接触组的各情感状态积分均明显高于对照组,差异有非常显著性(P<0.01);各行为功能指标积分均明显低于对照组,差异有显著性(P<0.01),且高工龄组低于低工龄组,差异有显著性(P<0.05,P<0.01)。结论铅对作业工人情感和神经行为功能存在有害影响,神经行为功能测定可作为铅作业工人接触反应的早期评价指标。     

Neuropsychological effects associated with exposure to mercury vapor among former chloralkali workers.

OBJECTIVES: This investigation studied possible neuropsychological effects among former chloralkali workers with past exposure to mercury vapor. METHODS: Seventy-five formerly exposed workers who had been examined with an extensive neuropsychological test battery were compared with 52 referents frequency-matched for age. The tests measured general cognitive function, motor and psychomotor function, attention, memory, and learning. The groups were similar in educational level, age, and verbal comprehension. The mean exposure time to mercury vapor in the index group was 7.9 (range 1.1-36.2) years with an annual mean urinary mercury concentration of 539 (range 41-2921) nmol/(l x year). The mean time since the cessation of exposure was 12.7 (range 1.0-35.0) years. RESULTS: Performance on the grooved pegboard (dominant hand 75.8 versus 70.9 seconds, P<0.05; nondominant hand 82.2 versus 76.3 seconds, P=0.02) and the Benton visual retention test (mean number of correct reproductions 6.9 versus 7.5, P<0.05) was poorer among the formerly exposed workers when compared with the referents. In addition the subjects who had experienced the highest intensity of exposure [cumulative urinary mercury index > or =550 nmol/(l x year)] had a poorer performance on the trailmaking test, part A and B, on the digit symbol test, and on the word pairs test (retention errors). CONCLUSIONS: The presented results suggest a slight persistent effect of mercury vapor exposure on the central nervous system, mainly involving motor functions and attention, but also possibly related to the visual system. Previous exposure does not seem to have affected the workers' general intellectual level or their ability to reason logically.     

Chronic psychological effects of exposure to mercury vapour among chlorine-alkali plant workers

BACKGROUND: Quantitative assessment of nervous system function is essential in characterising the nature and extent of impairment in individuals experiencing symptoms following work-place mercury vapour exposure. OBJECTIVES: The purpose of this study was the application of standardised tests of behavioural, psychomotor and memory function to understand the neuropsychological effects of mercury in occupationally exposed chlorine-alkali plant workers. SUBJECTS AND METHODS: The study comprised 45 workers at a chlorine-alkali plant with the mean age of 39.36 +/- 5.94 years, who had been exposed to daily inhalation of mercury vapour over long-term employment of 16.06 +/- 4.29 years. The cumulative mercury index was 155.32 +/- 95.02 micrograms/g creatinine, the mean of urinary mercury concentrations on the first day of the study was 119.50 +/- 157.24 micrograms/g creatinine, and the mean of urinary mercury concentrations 120 days after cessation of exposure was 21.70 +/- 26.07 micrograms/g creatinine. The analysis included tests of behavioural, psychomotor and memory function. The behavioural test battery consisted of: Environmental Worry Scale (EWS), Minnesota Modified Personal Inventory (MMPI-2), Purdue standard 25 minute test, and adapted, 10 minutes test, Bender's Visual-Motor Gestalt test (BGT), and Eysenck Personality Inventory (EPQ). The data were compared to a control group of 32 not directly exposed workers. RESULTS: In the mercury vapour exposed workers with relatively high level exposure to inorganic mercury vapour (TWA/TLV = 0.12 mg/m3/0.025 mg/m3) we identified somatic depression-hypochondria symptoms with higher scores for scales: hysteria (P < 0.001), schizoid and psycho-asthenia (MMPI-2). The mercury-exposed workers had introvert behaviour (EPQ, MMPI-2). The cognitive disturbances in mercury-exposed workers were identified as: concentration difficulty, psychomotor, perceptual and motor coordination disturbances, and brain effects. We identified fine tremor of the hands in 34 out of 45 mercury-exposed workers (BGT). CONCLUSIONS: The results point to a relationship between the duration of mercury exposure and the long-term, probably irreversible, psychological disturbances.     

Minimal immunological effects on workers with prolonged low exposure to inorganic mercury.

OBJECTIVES: This study was carried out to investigate possible immunological changes in workers with prolonged low exposure to inorganic mercury in a fluorescent light bulb factory. METHODS: 29 immunological variables were examined in 34 workers with prolonged low level exposure to inorganic mercury (exposed workers) and 35 unexposed workers as the controls. The selected indicator of mercury exposure was concentration of mercury in the urine (U-Hg), which declined progressively from 36.0 micrograms/l in 1978 to 6.0 micrograms/l in the study year 1994. RESULTS: None of the exposed workers had ever shown signs of either acute or chronic inorganic mercury toxicity or had shown any form of hypersensitivity. The only changes found in the exposed workers, compared with the controls, were a reduction of the cells that express cluster differentiation (CD25,(T activation antigen (Tac antigen))) and concentrations of tumour necrosis factor-alpha (TNF-alpha) in serum. However, the decrease of cells that express CD25 was unrelated to occupational exposure and was, in all likelihood a chance finding. Conversely, the decline in serum TNF-alpha was closely associated with occupational exposure. However, no dose-response relation was found between U-Hg and TNF-alpha concentrations; nor were TNF-alpha concentrations affected by cumulative occupational exposure to inorganic mercury in over 20 years. CONCLUSIONS: Tentatively, we suggest that reduced serum TNF-alpha concentrations might be indicative of an in vivo functional defect of the monocyte macrophage system in this particular group of workers even though they were clinically asymptomatic.     

Effects of occupational exposure to mercury vapour on the central nervous system.

Possible effects of mercury on the central nervous system (CNS) were examined in a group of chloralkali workers exposed to mercury (n = 89) and compared with a control group (n = 75), by registration of subjective symptoms, personality changes, forearm tremor, and performance on six computerised psychometric tests in the two groups. The groups were similar in age, education, verbal comprehension, and work tasks. In the chloralkali group, median blood mercury concentration (B-Hg) was 55 nmol/l, serum mercury concentration (S-Hg) 45 nmol/l, and urine mercury concentration (U-Hg) 14.3 nmol/mmol creatinine (25.4 micrograms/g creatinine). Corresponding concentrations in the control group were 15 nmol/l, 4 nmol/l, and 1.1 nmol/mmol creatinine (1.9 micrograms/g creatinine) respectively. The number of self reported symptoms, the scores for tiredness and confusion in the profile of mood states (POMS), and the degree of neuroticism in the Eysenck personality inventory (EPI), were significantly higher in the mercury exposed group compared with the controls. Performance on the psychometric tests and tremor frequency spectra did not differ significantly between the two groups. Dose-response calculations showed weak but statistically significant relations between symptom prevalence and current mercury concentrations in both blood and urine. The performance on three of the psychometric tests was negatively correlated with earlier peak exposures. The findings indicate a slight mercury induced effect on the CNS among the chloralkali workers.     

Effects of occupational exposure to mercury vapour on the central nervous system.

Possible effects of mercury on the central nervous system (CNS) were examined in a group of chloralkali workers exposed to mercury (n = 89) and compared with a control group (n = 75), by registration of subjective symptoms, personality changes, forearm tremor, and performance on six computerised psychometric tests in the two groups. The groups were similar in age, education, verbal comprehension, and work tasks. In the chloralkali group, median blood mercury concentration (B-Hg) was 55 nmol/l, serum mercury concentration (S-Hg) 45 nmol/l, and urine mercury concentration (U-Hg) 14.3 nmol/mmol creatinine (25.4 micrograms/g creatinine). Corresponding concentrations in the control group were 15 nmol/l, 4 nmol/l, and 1.1 nmol/mmol creatinine (1.9 micrograms/g creatinine) respectively. The number of self reported symptoms, the scores for tiredness and confusion in the profile of mood states (POMS), and the degree of neuroticism in the Eysenck personality inventory (EPI), were significantly higher in the mercury exposed group compared with the controls. Performance on the psychometric tests and tremor frequency spectra did not differ significantly between the two groups. Dose-response calculations showed weak but statistically significant relations between symptom prevalence and current mercury concentrations in both blood and urine. The performance on three of the psychometric tests was negatively correlated with earlier peak exposures. The findings indicate a slight mercury induced effect on the CNS among the chloralkali workers.     

无铅汽油对神经行为功能和单胺类神经递质代谢产物的影响

目的 探讨职业性无铅汽油接触以对神经功能和单胺类神经递质代谢的影响。方法 应用WHO推荐的神经行为检测组合（NCTB）对92名汽油作业工人和88名对照工人进行神经行为测试,同时用高效液相色谱法－电化学法联检测定其尿中高香草酸（HVA）和香草扁桃酸（VMA）的浓度。结果 接触组明显存在忧郁－沮丧的不良情绪状态,简单反应时慢于对照组,数字跨度、提转捷度、数字译码和目标追中学踪得分明显低于对照组,且行为功能得分随浓度的增高而降低;汽油接触工人尿中HVA和VMA浓度均降低。结论 提示职业性低浓度接触无铅汽油油可影响神经行为功能和单胺类神经递质代谢。     

Subjective symptoms and psychological performance of chlorine-alkali workers

Subjective symptoms and psychological performances on a computer-administered test battery were studied among a group of 60 chlorine-alkali workers and their matched referents. The exposure time of the group exposed to inorganic mercury vapor had been about 14 years, and the estimated long-term average exposure had been about 25 micrograms/m3 of air. The exposed workers had an actual mercury concentration of 51.9 (SD 25.0, range 15-150) nmol/l in blood and 84.1 (SD 56.6, range 15-260) nmol/l in urine. Neither perceptual motor nor memory nor learning abilities of the mercury-exposed workers showed any disturbances in a comparison with the referents. However, the exposed group reported statistically significantly more memory disturbances than the referents. Strain caused by three-shift work was a possible cofactor for other increased subjective symptoms, namely, for sleep disorders, fatigue, and confusion.     

Neuropsychological studies on lead workers in Singapore

The neuropsychological performance of a group of 49 workers occupationally exposed to lead was compared with a matched control group of 36 non-exposed workers. The psychometric measurements were composed of tests covering a broad range of different neuropsychological functions, particular emphasis being given to perceptual motor ability and attention concentration functioning. A questionnaire to assess subjective symptoms in mood, sleep disturbance, poor concentration and forgetfulness, somatic complaints, and social passivity was also included in the battery of tests. Compared with the controls, the performance of the lead workers was found to be significantly poorer for digit symbol, Bourdon-Wiersma, trail making test (part A), Santa Ana test, flicker fusion, and simple reaction time. In terms of subjective symptoms the exposed group also reported significantly more complaints of anxiety and depressed mood, poor concentration and forgetfulness, and other somatic complaints. These differences were observed among lead workers with a mean blood lead value of 2.35 mumol/l (SD 0.7).     

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.     

Peripheral neurotoxicity in workers exposed to inorganic mercury compounds

Nerve conduction velocity (NCV) of the median motor, median sensory, and sural nerves was assessed in 16 workers chronically exposed to various inorganic mercury compounds. Exposed workers were compared with an unexposed control group using t test analyses. Slowing of the median motor nerve NCV was found, which was correlated with both increased levels of mercury in blood and urine, and with increased number of neurologic symptoms. Sensitive evaluation of neural function was found to be practical and informative for investigating mercury toxicity. Such evaluation can help determine safe mercury levels at the workplace.     

Neuropsychological studies on lead workers in Singapore.

The neuropsychological performance of a group of 49 workers occupationally exposed to lead was compared with a matched control group of 36 non-exposed workers. The psychometric measurements were composed of tests covering a broad range of different neuropsychological functions, particular emphasis being given to perceptual motor ability and attention concentration functioning. A questionnaire to assess subjective symptoms in mood, sleep disturbance, poor concentration and forgetfulness, somatic complaints, and social passivity was also included in the battery of tests. Compared with the controls, the performance of the lead workers was found to be significantly poorer for digit symbol, Bourdon-Wiersma, trail making test (part A), Santa Ana test, flicker fusion, and simple reaction time. In terms of subjective symptoms the exposed group also reported significantly more complaints of anxiety and depressed mood, poor concentration and forgetfulness, and other somatic complaints. These differences were observed among lead workers with a mean blood lead value of 2.35 mumol/l (SD 0.7).     

Mobilization of mercury by DMPS in occupationally exposed workers and in model experiments on rats: evaluation of body burden

The aim of the study was to evaluate the efficacy of DMPS (sodium-2,3-dimercapto-1-propane sulfonate) (Dimaval) administration for mobilizing mercury from the body in occupationally exposed people and experimental animals. Two doses of DMPS were administered at a 24-h interval to: (a) groups of people occupationally exposed to merkury--workers of the chloralkali industry (n = 43), and dentists (n = 12), (b) non-exposed individuals (n = 20), and (c) rats chronically exposed to mercury vapour at the concentration of 0.8 mg/m3 Hg degree (6 h/day, 5 days/week) for 15 weeks. In an out-patient mobilizing test, the urinary excretion of mercury 48 h after the administration of the first dose reached 1513 micrograms in the group of industrial workers, 132.6 micrograms in dentists, and 3.78 micrograms in controls. In rats, two consecutive doses of DMPS decreased kidney content of mercury by about 30% and 50% after oral and intraperitoneal administration, respectively. Kidney mercury burden was calculated on the basis of the data from animal and human studies of the mobilization of mercury via urine after DMPS treatment: 61, 2800 and 28,000 ng/g in controls, dentists and workers, respectively. It was estimated that two doses of DMPS mobilized 17-20% (after oral administration) and 25-30% (after intramuscular administration) of kidney mercury burden, both in the control and exposed subjects.     

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.     

职业性汞接触对作业工人神经行为功能的影响

目的探讨汞对人体神经行为功能的影响。方法采用世界卫生组织推荐的神经行为核心测试组合,于2009年9月对60名汞作业工人和60名对照人员进行神经行为功能测试。结果接触组在情感状态、简单反应时、数字跨度、视觉保留及数字译码、手提转捷度较对照组均有显著变化。结论汞接触可导致工人神经行为功能明显降低,神经行为功能测试可用于汞作业的早期评价指标。     

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.     

Effects of elemental mercury exposure at a thermometer plant

This study compares 84 mercury-exposed workers at a thermometer manufacturing facility with 79 unexposed workers for evidence of chronic mercury toxicity. Personal breathing-zone air concentrations of mercury ranged from 25.6 to 270.6 micrograms/m3 for thermometer workers. Urinary mercury levels in the study population ranged from 1.3 to 344.5 micrograms/g creatinine, with eight (10%) participants exceeding 150 micrograms/g creatinine and three workers exceeding 300 micrograms/g creatinine, which indicates increased absorption of mercury among the thermometer workers. All urine mercury levels in the comparison group were compatible with normal background levels in unexposed adults (less than 10 micrograms/g creatinine). Thermometer plant workers reported more symptoms than did controls; in general, these differences were not statistically significant and could not be specifically associated with mercury exposure. Static tremor, abnormal Romberg test, dysdiadochokinesia, and difficulty with heel-to-toe gait were more prevalent among thermometer workers than control workers, which could not be associated with recent mercury exposure; there was some suggestion of an association with chronic exposure. There were no intergroup differences for the standard clinical tests of renal function except for a significantly higher mean specific gravity among the thermometer workers. A positive correlation was found, however, between urinary N-acetyl-b-D-glucosaminidase (NAG) and urinary mercury. There was no consistent evidence for intergroup differences in proximal renal tubule function, as measured by urinary beta 2-microglobulin (B2M) or retinol binding protein (RBP).     

甲苯作业对工人神经行为功能的影响

对接触甲苯工人(暴露组)和对照组工人采用神经行为核心测试组合(NCTB)进行神经行为测试。结果暴露组在目标追踪、数字译码、数字跨度及视觉记忆测试等方面与对照组相比差异有显著性(P<0.05)。说明接触甲苯对作业工人的神经行为功能可产生一定的影响。     

Renal and immunological effects of occupational exposure to inorganic mercury.

Seven parameters of renal dysfunction (urinary excretion of albumin, orosomucoid, beta 2-microglobulin, N-acetyl-beta-glucosaminidase (NAG), and copper; serum creatinine concentration, and relative clearance of beta 2-microglobulin) were examined in a group of chloralkali workers exposed to mercury vapour (n = 89) and in an unexposed control group (n = 75). Serum concentrations of immunoglobulins (IgA, IgG, IgM) and auto-antibodies towards glomeruli and other tissues were also determined. The parameters examined were compared between the two groups and related to different exposure parameters. In the chloralkali group median blood mercury concentration (B-Hg) was 55 nmol/l, serum mercury (S-Hg) 45 nmol/l, and urine mercury concentration (U-Hg) 14.3 nmol/mmol creatinine (25.4 micrograms/g creatinine). Corresponding concentrations for the control group were 15 nmol/l, 4 nmol/l, and 1.1 nmol/mmol creatinine (1.9 micrograms/g creatinine) respectively. None of the parameters of renal dysfunction differed significantly between the two groups, but there was a tendency to increased excretion of NAG in the exposed group compared with the controls. Also, a statistically significant relation existed between U-Hg and U-NAG (p less than 0.001). Serum immunoglobulin concentrations did not differ between the groups, and serum titres of autoantibodies (including antiglomerular basement membrane and antilaminin antibodies) were low in both groups. Thus the results gave no evidence of glomerular damage or of a tubular reabsorption defect at the current relatively low exposures. The findings still indicate slight, dose related tubular cell damage in the mercury exposed group. There were no signs of a mercury induced effect on the immune system.