Residual neurobehavioural effects associated with chronic exposure to mercury vapour

Epidemiology, clinical presentation, treatment, and follow-up of chronic mercury poisoning in China: a retrospective analysis

Background

There are no reports on the incidence of chronic mercury poisoning in a large population in China. This study investigated the epidemiology, clinical manifestations, treatment, and follow-up of Chinese patients with chronic mercury poisoning.

Methods

Data for 288 mercury poisoning patients were collected at our hospital from July 2014 to September 2019, including sex, age, admission time, blood mercury content, urine mercury content, creatinine, urinary mercury/creatinine ratio, 24-h urinary protein levels, electromyography (EMG) findings, renal biopsy, and follow-up. Patient characteristics were evaluated by statistical and correlation analyses.

Results

First, mercury poisoning in China mainly occurred through occupational exposure and the inappropriate use of mercury-containing cosmetics and Chinese folk remedies (CFRs). Second, the most common symptoms were nervous system (50.3 %), kidney (16.4 %) and breathing (8.0 %). Mercury poisoning-induced Nephrotic syndrome (NS) and peripheral neuropathy are common long-term complications. The complications of occupational and cosmetics-induced mercury poisoning are consistent with international belief. However, the NS caused by CFRs is mainly membranous nephropathy and the probability of peripheral neuropathy caused by CFRs is higher than other pathogens. Third, follow-up data shows that 13 patients with EMG-confirmed neurological injury, 10 showed full recovery after 38.50 ± 8.03 months. Furthermore, among 18 patients with NS, 15 had normal urine protein and serum albumin levels after 22.67 ± 10.26 months.

Conclusions

Regulation of skin-lightening cosmetic products, safety surveillance of CFRs, and prevention and control of occupational exposure must be improved to decrease the incidence of mercury poisoning in China.

Neurotoxicity of mercury: an old issue with contemporary significance

Mercury exerts a variety of toxic effects, depending on the specific compound and route of exposure. However, neurotoxicity in virtue of its consequence to health causes the greatest concern for toxicologists. This is particularly true regarding fetal development, where neurotoxic effects are much more severe than in adults, and the toxicity threshold is lower. Here, we review the major concepts regarding the neurotoxicity of mercury compounds (mercury vapor; methylmercury and ethylmercury), from exposure routes to toxicokinetic particularities leading to brain deposition and the development of neurotoxic effects. Albeit research on the neurotoxicity of mercury compounds has significantly advanced from the second half of the twentieth century onwards, several grey areas regarding the mechanism of toxicity still exist. Thus, we emphasize research advances during the last two decades concerning the molecular interactions of mercury which cause neurotoxic effects. Highlights include the disruption of glutamate signaling and excitotoxicity resulting from exposure to mercury and the interaction with redox active residues such as cysteines and selenocysteines which are the premise accounting for the disruption of redox homeostasis caused by mercurials. We also address how immunotoxic effects at the CNS, namely microglia and astrocyte activation modulate developmental neurotoxicity, a major topic in contemporary research.

Evolutionary perspective on sex differences in the expression of neurological diseases

Sex-specific brain and cognitive deficits emerge with malnutrition, some infectious and neurodegenerative diseases, and often with prenatal or postnatal toxin exposure. These deficits are described in disparate literatures and are generally not linked to one another. Sexual selection may provide a unifying framework that integrates our understanding of these deficits and provides direction for future studies of sex-specific vulnerabilities. Sexually selected traits are those that have evolved to facilitate competition for reproductive resources or that influence mate choices, and are often larger and more complex than other traits. Critically, malnutrition, disease, chronic social stress, and exposure to man-made toxins compromise the development and expression of sexually selected traits more strongly than that of other traits. The fundamental mechanism underlying vulnerability might be the efficiency of mitochondrial energy capture and control of oxidative stress that in turn links these traits to current advances in neuroenergetics, stress endocrinology, and toxicology. The key idea is that the elaboration of these cognitive abilities, with more underlying gray matter or more extensive inter-modular white matter connections, makes them particularly sensitive to disruptions in mitochondrial functioning and oxidative stress. A framework of human sexually selected cognitive abilities and underlying brain systems is proposed and used to organize what is currently known about sex-specific vulnerabilities.

Vulnerability associated with "symptoms similar to those of mercury poisoning" in communities from Xingu River, Amazon basin

The Brazilian Amazon is known to be a region with high levels of mercury (Hg) in the environment and studies point to an association between high levels of natural mercury in the mother rock and the vast number of clandestine gold mines. Other studies already report the contamination of fish in this region, as well as high levels of Hg in biological material from environmentally exposed populations. On the other hand, this is one of the least developed regions of the planet and it is necessary to understand the vulnerability factors in these populations that may be intoxicated by this element. The purpose of the present study was to investigate the vulnerability factors in communities from Xingu River-Amazon basin probably exposed to Hg. A cross-selection study in two cities localized in Xingu River was conducted, and the sample contained was 268 individuals. sociodemographic questions, lifestyle, diet habits and health conditions were collated. The majority of the sample was female, between 30 and 59 years old, had less than 3 years of educational level and lived in the local of study more than 240 months. There was regular fish consumption (95.9%), principally carnivorous species (80.5%). The visual problem has a highest prevalence (43.3%) between the health problems and about the symptoms of Hg intoxication, memory loss (42.9%), weakness (35.1%), fatigue (34.3%), mood changes (28.7%) and difficulties in concentration (27.2%) was most reported. The female sex, age over 60, educational level below 3 years of study, did not had flush toilet, smoke and least one chronic non-communicable disease represent higher probability to had symptoms of Hg intoxication. Lack of access to health services, low education level and income evidence the susceptibility of this community to diseases and injuries. The vulnerable groups identified in this study should be a priority in public health and environmental health policies.

Elemental mercury neurotoxicity and clinical recovery of function: A review of findings, and implications for occupational health

This paper assessed approximately 30 studies, mostly involving occupationally exposed subjects, concerning the extent to which those who developed elemental mercury (Hg)-induced central and/or peripheral neurotoxicities from chronic or acute exposures recover functionality and/or performance. While some recovery occurred in the vast majority of cases, the extent of such recoveries varied considerably by individual and endpoint. Factors accounting for the extensive inter-individual variation in toxicity and recovery were not specifically assessed such as age, gender, diet, environmental enrichment, chelation strategies and dose-rate. While the data indicate that psychomotor endpoints often show substantial and relatively rapid (i.e., 2-6 months) recovery and that neuropsychological endpoints display slower and less complete recovery, generalizations are difficult due to highly variable study designs, use of different endpoints measured between studies, different Hg exposures based on blood/urine concentrations and Hg dose-rates, the poor capacity for replicating findings due to the unpredictable/episodic nature of harmful exposures to elemental Hg, and the inconsistency of the initiation of studies after induced toxicities and the differing periods of follow up during recovery periods. Finally, there is strikingly limited animal model literature on the topic of recovery/reversibility of elemental Hg toxicity, a factor which significantly contributes to the overall marked uncertainties for predicting the rate and magnitude of recovery and the factors that affect it.

Persistence of mercury-induced motor and sensory neurotoxicity: systematic review of workers previously exposed to mercury vapor

Elemental mercury (Hg0) is a well-recognized neurotoxicant, but it is uncertain whether and for how long its neurotoxicity persists. Among studies that evaluated previously-exposed workers, only one examined workers during and also years after exposure had ceased. The objective of this review is to create a series of 'synthetic' longitudinal studies to address the question of persistence of Hg0 neurotoxicity in occupationally exposed workers. We systematically reviewed studies describing objective motor and sensory effects in previously-exposed mercury workers. Data from physical examination (PE), neurobehavioral (NB) tests, and electrophysiological studies (EPS) were extracted into structured tables and examined for their consistency and dose-relatedness and then compared with the corresponding results from studies of currently exposed workers. We identified six cohorts that described neurological findings in 1299 workers, examined an average of 4.8-30 years after the cessation of exposure. Historical group mean UHg levels ranged from 23 to >500 μg/L, with UHg levels >6000 μg/L in some individuals. Overall, few findings were significant; most were inconsistent across the previous-exposure studies, and in comparisons between studies of previously and currently exposed workers. The results of this systematic review indicate that Hg0-related neurotoxic effects detectable on PE, NB testing, and EPS are substantially reversed over time. To the extent that such effects do persist, they are reported principally in workers who have had very high-dose exposures. In addition, based on the limited available data, those effects reported to persist have been described as having little or no functional significance.

The burden of chronic mercury intoxication in artisanal small-scale gold mining in Zimbabwe: data availability and preliminary estimates

BACKGROUND

Artisanal small-scale gold mining (ASGM) is a poverty-driven activity practiced in over 70 countries worldwide. Zimbabwe is amongst the top ten countries using large quantities of mercury to extract gold from ore. This analysis was performed to check data availability and derive a preliminary estimate of disability-adjusted life years (DALYs) due to mercury use in ASGM in Zimbabwe.

METHODS

Cases of chronic mercury intoxication were identified following an algorithm using mercury-related health effects and mercury in human specimens. The sample prevalence amongst miners and controls (surveyed by the United Nations Industrial Development Organization in 2004 and the University of Munich in 2006) was determined and extrapolated to the entire population of Zimbabwe. Further epidemiological and demographic data were taken from the literature and missing data modeled with DisMod II to quantify DALYs using the methods from the Global Burden of Disease (GBD) 2004 update published by the World Health Organization (WHO). While there was no disability weight (DW) available indicating the relative disease severity of chronic mercury intoxication, the DW of a comparable disease was assigned by following the criteria 1) chronic condition, 2) triggered by a substance, and 3) causing similar health symptoms.

RESULTS

Miners showed a sample prevalence of 72% while controls showed no cases of chronic mercury intoxication. Data availability is very limited why it was necessary to model data and make assumptions about the number of exposed population, the definition of chronic mercury intoxication, DW, and epidemiology. If these assumptions hold, the extrapolation would result in around 95,400 DALYs in Zimbabwe's total population in 2004.

CONCLUSIONS

This analysis provides a preliminary quantification of the mercury-related health burden from ASGM based on the limited data available. If the determined assumptions hold, chronic mercury intoxication is likely to have been one of the top 20 hazards for population health in Zimbabwe in 2004 when comparing with more than 130 categories of diseases and injuries quantified in the WHO's GBD 2004 update. Improving data quality would allow more accurate estimates. However, the results highlight the need to reduce a burden which could be entirely avoided.

Longitudinal analysis of the association between removal of dental amalgam, urine mercury and 14 self-reported health symptoms

BACKGROUND

Mercury vapor poses a known health risk with no clearly established safe level of exposure. Consequently there is debate over whether the level of prolonged exposure to mercury vapor from dental amalgam fillings, combining approximately 50% mercury with other metals, is sufficiently high to represent a risk to health. The objective of our study is to determine if mercury exposure from amalgam fillings is associated with risk of adverse health effects.

METHODS

In a large longitudinal non-blind sample of participants from a preventative health program in Calgary, Canada we compared number of amalgam fillings, urine mercury measures and changes in 14 self-reported health symptoms, proposed to be mercury dependent sub-clinical measures of mental and physical health. The likelihood of change over one year in a sample of persons who had their fillings removed was compared to a sample of persons who had not had their fillings removed. We use non-parametric statistical tests to determine if differences in urine mercury were statistically significant between sample groups. Logistic regression models were used to estimate the likelihood of observing symptom improvement or worsening in the sample groups.

RESULTS

At baseline, individuals with dental amalgam fillings have double the measured urine mercury compared to a control group of persons who have never had amalgam fillings. Removal of amalgam fillings decreases measured urine mercury to levels in persons without amalgam fillings. Although urine mercury levels in our sample are considered by Health Canada to be too low to pose health risks, removal of amalgam fillings reduced the likelihood of self-reported symptom deterioration and increased the likelihood of symptom improvement in comparison to people who retained their amalgam fillings.

CONCLUSIONS

Our findings suggest that mercury exposure from amalgam fillings adversely impact health and therefore are a health risk. The use of safer alternative materials for dental fillings should be encouraged to avoid the increased risk of health deterioration associated with unnecessary exposure to mercury.

Is dental amalgam safe for humans? The opinion of the scientific committee of the European Commission

It was claimed by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)) in a report to the EU-Commission that "....no risks of adverse systemic effects exist and the current use of dental amalgam does not pose a risk of systemic disease..." [1, available from: http://ec.europa.eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_016.pdf].SCENIHR disregarded the toxicology of mercury and did not include most important scientific studies in their review. But the real scientific data show that:(a) Dental amalgam is by far the main source of human total mercury body burden. This is proven by autopsy studies which found 2-12 times more mercury in body tissues of individuals with dental amalgam. Autopsy studies are the most valuable and most important studies for examining the amalgam-caused mercury body burden.(b) These autopsy studies have shown consistently that many individuals with amalgam have toxic levels of mercury in their brains or kidneys.(c) There is no correlation between mercury levels in blood or urine, and the levels in body tissues or the severity of clinical symptoms. SCENIHR only relied on levels in urine or blood.(d) The half-life of mercury in the brain can last from several years to decades, thus mercury accumulates over time of amalgam exposure in body tissues to toxic levels. However, SCENIHR state that the half-life of mercury in the body is only "20-90 days".(e) Mercury vapor is about ten times more toxic than lead on human neurons and with synergistic toxicity to other metals.(f) Most studies cited by SCENIHR which conclude that amalgam fillings are safe have severe methodical flaws.

Symptoms of intoxication in dentists associated with exposure to low levels of mercury

The present study examined the effects of occupational exposure of a group of dentists to low levels of mercury. The study population consisted of 106 dentists and 94 general practitioners (referent group), from private and public clinics in Shiraz city. Subjects were requested to complete a questionnaire on demographic variables, suspicious symptoms of intoxication and work practices. Additionally, atmospheric and urinary concentrations of mercury were measured by Atomic Absorption Spectroscopy technique. The data were analysed by χ(2) test, independent sample t-test and multivariate logistic regression analysis, where applicable. Both groups were similar as far as most demographic and socioeconomic variables, but age and number of personal amalgam fillings, were concerned. Median of atmospheric concentration of mercury was found to be 3.35 μg/m(3). Likewise, the urinary concentration of mercury in dentists was estimated to be 3.16 μg/g creatinine. This value was significantly higher than that of the referent group. Similarly, analysis of the data revealed that neuropsychological, muscular, respiratory, cardiovascular and dermal symptoms were more prevalent in dentists. Our findings indicate that occupational exposure of dentists to mercury, even at low levels, is associated with a significant increase in the prevalence of symptoms of intoxication.

Comments on the Article “The Toxicology of Mercury and Its Chemical Compounds” by Clarkson and Magos (2006)

Clarkson and Magos (2006) provide their perspectives on the toxicology of mercury vapor and dental amalgam. As scientists who are involved in preparing a German federal guideline regarding dental amalgam, we welcome additional scientific data on this issue. However, Clarkson and Magos do not present all the relevant studies in their review. The additional data provided here show that: (a) Dental amalgam is the main source of human total mercury body burden, because individuals with amalgam have 2-12 times more mercury in their body tissues compared to individuals without amalgam; (b) there is not necessarily a correlation between mercury levels in blood, urine, or hair and in body tissues, and none of the parameters correlate with severity of symptoms; (c) the half-life of mercury deposits in brain and bone tissues could last from several years to decades, and thus mercury accumulates over time of exposure; (d) mercury, in particular mercury vapor, is known to be the most toxic nonradioactive element, and is toxic even in very low doses, and (e) some studies which conclude that amalgam fillings are safe for human beings have important methodogical flaws. Therefore, they have no value for assessing the safety of amalgam.

Neuropsychological alterations in mercury intoxication persist several years after exposure

Elemental mercury is a liquid toxic metal widely used in industry. Occupational exposure occurs mainly via inhalation. Previously, neuropsychological assessment detected deficits in former workers of a fluorescent lamp plant who had been exposed to elemental mercury vapor and were away from exposure for several years at the time of examination.

OBJECTIVES

The purpose of this work was to reexamine these functions after 18 months in order to evaluate their progression.

METHODS

Thirteen participants completed tests of attention, inhibitory control, verbal/visual memory, psychomotor speed, verbal fluency, visuomotor ability, executive function, semantic knowledge, and depression and anxiety inventories on 2 separate occasions.

RESULTS

At baseline, the former workers indicated slower psychomotor and information processing speed, verbal spontaneous recall memory impairment, and increased depression and anxiety symptoms compared to controls (P<0.05). Paired comparisons of neuropsychological functioning within the exposed group at baseline and 1.5 years later showed poorer immediate memory performance (P<0.05). There were no differences on other measures.

CONCLUSIONS

Although the literature show signs of recovery of functions, the neuropsychological effects related to mercury exposure are found to persist for many years.

Quantitative assessment of neuromotor function in workers with current low exposure to mercury vapor

Evaluation of neuromotor function has been used in several epidemiological studies of workers with long-term exposure to mercury vapor (Hg 0). Some recent studies indicate adverse effects at relatively low exposure levels. In the present study, we used sensitive quantitative methods, developed specifically to detect subtle effects of exposure to toxins on motor function. After exclusion of individuals with neurological diseases or other conditions that may affect performance, 43 chloralkali workers with current low exposure to Hg 0, and 22 age-matched referents remained for further analysis. The median urinary mercury concentration in exposed workers was 5.9 microg/g (range 1.3-25) creatinine (microg/gC), while that in referents was 0.7 microg/gC (range 0.2-4.1). The mean exposure time was 15 years, and the median cumulative mercury index was 161 years x microg/gC in exposed workers. A eurythmokinesimeter (EKM) was used to quantify eye-hand coordination, and a diadochokinesimeter, to measure rapid alternating rotation of the forearms. In general, the differences in performance between the exposed workers and the referents were small. Age was associated with a decrease in speed, more tremor, and longer contact duration between the stylus and the metal targets in performance of rapid pointing movements. Smokers had significantly more tremor, and more contacts per event in the EKM test, than nonsmokers. Taking age, shift work, and smoking habits into account, no significant associations with current or cumulative mercury exposure were found for the majority of the outcome variables from the quantitative tests. In general, this study indicates no significant adverse effects of Hg 0 on neuromotor function at the exposure levels studied.

Dental amalgam exposure and urinary mercury levels in children: the New England Children's Amalgam Trial

BACKGROUND

Urinary mercury (U-Hg) excretion is a commonly used biomarker for mercury exposure from dental amalgam restorations.

OBJECTIVES

Our goal was to determine the most efficient measure of dental amalgam exposure for use in analyses concerning U-Hg in children.

METHODS

We analyzed time-sensitive longitudinal amalgam exposure data in children randomized to amalgam restorations (n = 267) during the 5-year New England Children's Amalgam Trial. We calculated 8 measures of amalgam, evaluating current versus cumulative exposure, teeth versus surfaces, and total versus posterior occlusal amalgams. Urine samples collected during follow-up years 3-5 were analyzed for mercury excretion. Multivariate models for current and cumulative U-Hg excretion estimated associations between exposures and U-Hg.

RESULTS

At the end of follow-up, the average (+/- SD) cumulative exposure was 10.3 +/- 6.1 surfaces and 5.7 +/- 2.9 teeth ever filled with amalgam, corresponding to 30 +/- 21 surface-years. Amalgam measures and U-Hg were moderately correlated. Of amalgam exposure measures, the current total of amalgam surfaces was the most robust predictor of current U-Hg, whereas posterior occlusal surface-years was best for cumulative U-Hg. In multivariate models, each additional amalgam surface present was associated with a 9% increase in current U-Hg, and each additional posterior occlusal surface-year was associated with a 3% increase in cumulative U-Hg excretion (p < 0.001).

CONCLUSIONS

One single measure of amalgam exposure is insufficient. Studies of cumulative effects of mercury from amalgam exposure in children are likely to have improved validity and precision if time-sensitive amalgam exposure measures are used. In contrast, simple counts of current amalgam fillings are adequate to capture amalgam-related current U-Hg.

Consensus paper of the WFSBP Task Force on Biological Markers: biological markers in depression

Biological markers for depression are of great interest to aid in elucidating the causes of major depression. We assess currently available biological markers to query their validity for aiding in the diagnosis of major depression. We specifically focus on neurotrophic factors, serotonergic markers, biochemical markers, immunological markers, neuroimaging, neurophysiological findings, and neuropsychological markers. We delineate the most robust biological markers of major depression. These include decreased platelet imipramine binding, decreased 5-HT1A receptor expression, increase of soluble interleukin-2 receptor and interleukin-6 in serum, decreased brain-derived neurotrophic factor in serum, hypocholesterolemia, low blood folate levels, and impaired suppression of the dexamethasone suppression test. To date, however, none of these markers are sufficiently specific to contribute to the diagnosis of major depression. Thus, with regard to new diagnostic manuals such as DSM-V and ICD-11 which are currently assessing whether biological markers may be included in diagnostic criteria, no biological markers for major depression are currently available for inclusion in the diagnostic criteria.

[My experience in mercury toxicology: behavioral teratology study of the effects of prenatal exposure to environmental pollutants]

I would like to express sincere thanks to all the people involved in awarding the 2005 Congress Award. It is a great honor to be given the prize. I have been interested in mercury toxicology since I was a graduate student and mercury toxicology has been my main subject of focus for 30 years. I am proud to continue the research in this field. In this presentation I would like to summarize some of my research works and to talk anecdotes related to the research works. Soon after I became involved in this research field, I came across "behavioral teratology", which is a novel field of study whose focus is understanding the postnatal consequences of exposure to harmful agents in utero. Spyker and her colleagues clearly showed postnatal behavioral deviations in mouse offspring exposed to a low dose of methylmercury prenatally. In various animal experiments, I elucidated the subtle consequences that appear postnatally. I found that these consequences are modified by many factors such as selenium status, PCBs, and heat, because the degree of exposure to produce these consequences can be extremely small. These experiments simulate actual human life and the results will be useful to assess the risk of methylmercury exposure through fish consumption in the human population, since fish eating populations are exposed to these factors at a low dose. Recently, cohort studies elucidating the possible effects of prenatal exposure to environmental pollutants in the postnatal period have been established and ongoing. When a conclusion is drawn, it is expected to serve as basic information that is useful for the risk assessment of methylmercury and other environmental pollutants. This will give great gratification to scientists in environmental health and preventive medicine.

Neuropsychological dysfunction related to earlier occupational exposure to mercury vapor

We assessed the neuropsychological test performances of 26 patients (mean age = 41.5 +/- 6.1 years; mean years of education = 9.8 +/- 1.8; 20 males) diagnosed with chronic occupational mercurialism who were former workers at a fluorescent lamp factory. They had been exposed to elemental mercury for an average of 10.2 +/- 3.8 years and had been away from this work for 6 +/- 4.7 years. Mean urinary mercury concentrations 1 year after cessation of work were 1.8 +/- 0.9 microg/g creatinine. Twenty control subjects matched for age, gender, and education (18 males) were used for comparison. Neuropsychological assessment included attention, inhibitory control, verbal and visual memory, verbal fluency, manual dexterity, visual-spatial function, executive function, and semantic knowledge tests. The Beck Depression Inventory and the State and Trait Inventory were used to assess depression and anxiety symptoms, respectively. The raw score for the group exposed to mercury indicated slower information processing speed, inferior performance in psychomotor speed, verbal spontaneous recall memory, and manual dexterity of the dominant hand and non-dominant hand (P < 0.05). In addition, the patients showed increased depression and anxiety symptoms (P < 0.001). A statistically significant correlation (Pearson) was demonstrable between mean urinary mercury and anxiety trait (r = 0.75, P = 0.03). The neuropsychological performances of the former workers suggest that occupational exposure to elemental mercury has long-term effects on information processing and psychomotor function, with increased depression and anxiety also possibly reflecting the psychosocial context.

A Meta-Analysis of the Neuropsychological Effects of Occupational Exposure to Mercury

This paper reports a meta-analysis of 36 peer-reviewed published studies of the neuropsychological effects of occupational exposure to mercury, which yielded 43 independent samples. These studies included 2,512 exposed participants and 1,846 controls, for a total sample size of 4,358. Because the independent variables defining mercury exposure varied across studies, effect sizes were calculated for exposed versus non-exposed workers. Dose-response relations were considered for measures of mercury levels in urine (81% of studies reported), blood (42% of studies reported), and air samples (33% of studies reported). Level of exposure was also estimated by reported years of exposure (M = 11.3, SD = 5.6). Cohen's d statistic yielded a statistically significant weighted study-mean effect size of -.23, p < .0001 for occupational mercury exposure. However, an effect this small is typically undetectable when evaluating individuals because it is smaller than the typical 95% confidence interval used for most neuropsychological measures. None of the exposure variables analyzed reached statistical significance. The magnitude of self-reported symptoms (-.30) was slightly larger than that obtained from objective test scores (-.22), though the difference was not statistically significant. Also, the weighted mean effect size for psychomotor skills (-.34) was the largest in magnitude, whereas the weighted mean effect size for verbal comprehension measures had the smallest (-.06). However, an analysis of the differential effects of mercury exposure across cognitive domains found significant differences between verbal comprehension measures and all other domains. None of the other domains were significantly different from one another. The weighted study-mean effect size suggests that the prevalence of neuropsychological deficits due to occupational exposure to mercury is small and difficult to detect on an individual case-by-case basis.

Personality traits in miners with past occupational elemental mercury exposure

In this study, we evaluated the impact of long-term occupational exposure to elemental mercury vapor (Hg0) on the personality traits of ex-mercury miners. Study groups included 53 ex-miners previously exposed to Hg0 and 53 age-matched controls. Miners and controls completed the self-reporting Eysenck Personality Questionnaire and the Emotional States Questionnaire. The relationship between the indices of past occupational exposure and the observed personality traits was evaluated using Pearson's correlation coefficient and on a subgroup level by machine learning methods (regression trees). The ex-mercury miners were intermittently exposed to Hg0 for a period of 7-31 years. The means of exposure-cycle urine mercury (U-Hg) concentrations ranged from 20 to 120 microg/L. The results obtained indicate that ex-miners tend to be more introverted and sincere, more depressive, more rigid in expressing their emotions and are likely to have more negative self-concepts than controls, but no correlations were found with the indices of past occupational exposure. Despite certain limitations, results obtained by the regression tree suggest that higher alcohol consumption per se and long-term intermittent, moderate exposure to Hg0 (exposure cycle mean U-Hg concentrations > 38.7 < 53.5 microg/L) in interaction with alcohol remain a plausible explanation for the depression associated with negative self-concept found in subgroups of ex-mercury miners. This could be one of the reason for the higher risk of suicide among miners of the Idrija Mercury Mine in the last 45 years.

A aplicação da neuropsicologia na pesquisa experimental: o exemplo da intoxicação por vapor de mercúrio

O desenvolvimento da neuropsicologia acompanhou a evolução do estudo do cérebro desde os registros mais antigos. A ciência neuropsicológica faz uso de medidas quantitativas de desempenho e tecnologias para produção de neuroimagem que, em conjunto, permitem a observação das relações cérebro-comportamento. No âmbito experimental, a neuropsicologia tem revelado novos conhecimentos na investigação de alterações cognitivas, psicomotoras ou comportamentais associadas a patologias congênitas ou adquiridas. No presente artigo são abordados aspectos históricos da neuropsicologia experimental e apresentados os principais resultados de um estudo referente às alterações neuropsicológicas de pacientes com histórico de intoxicação por vapor de mercúrio, presentes anos após o período de exposição ao metal.

Elevated blood mercury and neuro-otological observations in children of the Ecuadorian gold mines

The prevalence of mercury (Hg) intoxication was investigated in 114 Andean Saraguro and non-Saraguro (Mestizo) children living in remote gold-mining settlements in Nambija and Portovelo, Ecuador. Venous blood samples showed a mean total blood mercury (B-Hg) level of 18.2 microg/L (SD 15.5; range 2-89.) for 77 Saraguro and non-Saraguro children in the Nambija settlement, which was significantly higher than that of children in the Portovelo and reference groups. Comparison of groups showed mean B-Hg levels of 26.4 microg/L (range 4-89 microg/L) for 32 indigenous/Saraguro children; 12.3 microg/L (range 2-33 microg/L) for 45 non-Saraguro children; 4.9 microg/L (range 1-10 microg/L) for 37 children in Portovelo; and 2.4 microg/L (range 1-6 microg/L) for a reference group of 15 children. Fisher's post hoc analysis revealed significant differences among groups, except between the Portovelo and the reference groups. Neuro-otological symptoms and abnormalities were observed in Saraguro, non-Saraguro, and Portovelo children. Samples of soil collected at sites near the local school were found to contain Hg levels ranging from 0. 1 to 38 ppm, cadmium (Cd) levels from 0.07 to 0.82 ppm and arsenic (As) levels from < 1 to 3.9 ppm. in conclusion, the children of Nambija, particularly the Saraguro "Amer-Indians," exhibited elevated B-Hg levels from exposure to Hg used in the gold-mining process, and are at risk for neurological impairment. The children of Portovelo who reported neuro-otological symptoms but had low B-Hg levels (<10 microg/L) may be affected by exposure to sodium cyanide, which is used extensively in the local gold-mining operations.

Neuropsychological effects of low mercury vapor exposure in chloralkali workers

Neuropsychological effects were examined in 47 mercury vapor exposed male chloralkali workers with current low concentrations of urinary mercury (mean U-Hg 5.9 nmol/mmol creatinine (Cr)). Their average duration of exposure was 13.3 years, and the calculated mean concentration of U-Hg was 9.0 nmol Hg/mmol Cr per year (exposure intensity) during their time of exposure. They were compared with 47 age-matched male referents in a cross-sectional study. The two groups were not statistically significantly different with respect to neuropsychological test performance or number of self-reported subjective symptoms. The test results of the Static Steadiness Test, which assesses tremor, were not associated with exposure to mercury vapor. However current smokers had more hand tremor than non-smokers. Statistically significant associations were found between indices of current exposure (the concentration of inorganic mercury in whole blood) and the results of the WAIS Digit Symbol Test and the Benton Visual Retention Test (number of correct responses). This could indicate a small effect of current exposure on visuomotor/psychomotor speed and attention, and immediate visual memory. Whether the association found between the historical exposure intensity and the Digit Symbol Test results may represent long-term consequences of exposure cannot be determined in this study.

Workers' health and colonial mercury mining at Hhuancavelica, Peru

Mining had far-reaching ecological consequences throughout much of colonial Spanish America. It deformed the landscape, introduced pollutants such as sulfur, mercury and salt into the biosphere, and caused human settlement of sparsely populated or uninhabited regions. Forests succumbed to the charcoal makers' axes. Workers' lungs filled with silicosis-causing dust. Cave-ins snuffed out lives or crippled those they spared.

As unhealthy as mining was elsewhere in Spanish America, it was reported to have been especially harmful in the central Andes at Huancavelica. Workers there suffered the common diseases and injuries associated with the industry such as respiratory disease and broken limbs. They also had to overcome the challenges of arduous labor at high altitude. Most pernicious of all was the toxic nature of the mercury they were mining. Colonial critics asserted that Huancavelica was an environmental tragedy that placed workers in exceptionally dangerous conditions in order to produce the mercury needed by silver refiners to amalgamate and refine their ores. The critics claimed that the mercury mines' human cost was immoral, yet their cries of despair and outrage could not overcome quicksilver's crucial importance to the imperial economy. Killing and maiming, Huancavelica earned for itself an infamous reputation as themina de la muerte(the mine of death).

Neurobehavioral effects of acute exposure to inorganic mercury vapor

Mercury has well-established toxic effects on the central nervous system. This article describes comprehensive neuropsychological and emotional functioning of a group of 13 workers exposed to inorganic mercury vapor compared to that of a normal control group. The exposed group was exposed over a 2- to 4-week period and had elevated blood mercury levels. The evaluations were conducted between 10 and 15 months after exposure was terminated. Observed cognitive deficits included impairment in the following domains: motor coordination, speeded processing with and without a motor component, cognitive flexibility, verbal fluency, verbal memory, and visual problem solving and conceptualization. Emotional problems included increased focus on physical functioning, depression, anxiety, and social withdrawal. Cognitive deficits were, for the most part, not significantly associated with the degree of depression present.

Role of human neurobehavioural tests in regulatory activity on chemicals

Psychological performance tests have been used since the mid-1960s in occupational and environmental health toxicology. The interpretation of significantly different test scores in neurobehavioural studies is not straightforward in the regulation of chemicals. This paper sets out some issues which emerged from discussions at an international workshop, organised by the United Kingdom Health and Safety Executive (HSE), to discuss differences in interpretation of human neurobehavioural test data in regulatory risk assessments. The difficulties encountered by regulators confronted with neurobehavioural studies seem to be twofold; some studies lack scientific rigor; other studies, although scientifically sound, are problematic because it is not clear what interpretation to place on the results. Issues relating to each of these points are discussed. Next, scenarios within which to consider the outcomes of neurobehavioural studies are presented. Finally, conclusions and recommendations for further work are put forward.