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

Personalized Prevention in Mercury-Induced Amyotrophic Lateral Sclerosis: A Case Report

Chronic exposure to low levels of mercury is involved in the development of motor neuron diseases (MND). Genetic alterations may have a crucial role in the onset and progression. We presented a case of a TANK-binding kinase 1 (TBK1)-mutated 54-year-old male worker who developed a MND due to chronic mercury exposure at work. He was employed in a chlor-alkali plant in Central Italy. After two years of employment he had acute mercury intoxication with suggestive neurological symptoms and a high urinary level of the metal. Through years, many episodes of intoxication occurred, but he continued to perform the same job and be exposed to mercury. After yet another episode of intoxication in 2013, he showed fasciculations of the upper limbs and trunk, and electromyographic activity patterns were consistent with amyotrophic lateral sclerosis (ALS). In 2016, a genetic test revealed a mutation of TBK1, an ALS-related gene. This case highlights the important role of genetics in personalized occupational medicine. Occupational physicians should use genetic tests to identify conditions of individual susceptibility in workers with documented frequent episodes of mercury intoxication recorded during health surveillance programs to customize prevention measures in the workplace and act before damage appears.

Mercury-induced motor and sensory neurotoxicity: systematic review of workers currently exposed to mercury vapor

The neurotoxicity of elemental mercury (Hg0) is well-recognized, but it is uncertain whether and for how long neurotoxicity persists; among studies that evaluated previously exposed workers, only one examined workers during and also years after exposure ceased. The aim of this review is to document the type, frequency, and dose-relatedness of objective neurological effects in currently exposed mercury workers and thereby provide first approximations of the effects one would have expected in previously exposed workers evaluated during exposure. We systematically reviewed studies of neurotoxicity in currently exposed mercury workers identified by searching MEDLINE (1950-2015), government reports, textbook chapters, and references cited therein; dental cohorts were not included. Outcomes on physical examination (PE), neurobehavioral (NB) tests, and electrophysiological studies were extracted and evaluated for consistency and dose-relatedness. Forty-five eligible studies were identified, comprising over 3000 workers chronically exposed to a range of Hg0 concentrations (0.002-1.7 mg/m3). Effects that demonstrated consistency across studies and increased frequency across urine mercury levels (<50; 50-99; 100-199; ≥200 μg/L) included tremor, impaired coordination, and abnormal reflexes on PE, and reduced performance on NB tests of tremor, manual dexterity and motor speed. The data suggest response thresholds of UHg ≈275 μg/L for PE findings and ≈20 μg/L for NB outcomes. These results indicate that PE is of particular value for assessing workers with UHg >200 μg/L, while NB testing is more appropriate for those with lower UHg levels. They also provide benchmarks to which findings in workers with historical exposure can be compared.

Mercury and neuromotor function among children in a rural town in Chile

BACKGROUND

Mercury (Hg) exposure from artisanal gold mining has adverse effects on the neuromotor function in adults. However, few studies have examined this relationship in children.

OBJECTIVES

To investigate the impact of Hg exposure on children's neuromotor function.

METHODS

Cross-sectional data on Hg risk factors and demographics were collected from n = 288 children (response = 68.9%). Based on complete cases (CCs) (n = 130) and multiple imputations (n = 288), associations between fingernail Hg and four different neuromotor function components were calculated using multiple logistic regression adjusted for confounders.

RESULTS

Of the children, 11.1, 14.9, 63.9, and 10.4% had pathologic pure motor skills, adaptive fine motor skills, adaptive gross motor skills, and static balance, respectively. No significant association between fingernail Hg and any neuromotor component was found. However, Hg burning in the household was significantly associated with children's pathologic pure motor skills (OR 3.07 95% CI 1.03-9.18).

CONCLUSION

Elemental Hg exposure in the household might have adverse long-term effects on children's pure motor skills.

Reconsideration of the WHO NCTB strategy and test selection

The World Health Organization-recommended neurobehavioral core test battery (NCTB) became the international standard for identifying adverse human behavioral effects due to neurotoxic chemical exposure when it was first proposed in 1983. Since then the WHO NCTB has been repeatedly cited as the basis for test selection in human neurotoxicology research. A discussion group was held before the International Symposium on Neurobehavioral Methods and Effects in Occupational and Environmental Health to review the NCTB and reconsider its tests. The workshop made three consensus recommendations to the International Congress on Occupational Health (ICOH) Scientific Committee on Neurotoxicology and Psychophysiology (SCNP):. 1. A 'screening' battery of broadly sensitive tests is needed as guidance to the field of human neurotoxicology 2. The SCNP should convene a panel to reconsider the functions measured and the tests in the WHO NCTB 3. Three disciplines should be represented in the panel recommending a revised NCTB: neuropsychology; experimental psychology; neurology. This recommendation will be pursued at the next meeting of the International Congress on Occupational Health (ICOH) Scientific Committee on Neurotoxicology and Psychophysiology (SCNP).

Screening for action tremor in epidemiological field surveys: assessing the reliability of a semi-quantitative, visual, template-based scale for rating hand-drawn spirals

BACKGROUND

Population-based epidemiological studies of essential and other tremors have need of a rapid yet accurate means to assess tremor, especially mild tremors. Handwriting is often affected by tremor, and a hand-drawn spiral can provide investigators with objective rather than self-reported data. We present a semi-quantitative, ordinal scale to rate hand-drawn spirals. The scale, which includes values for mild tremor, is accompanied by photographic examples of spirals of each rating, providing a visual template for guidance.

METHODS

This study, conducted within the framework of a population-based epidemiological study of 5,000 individuals aged 60 and older in Shanghai, asked enrollees to draw an Archimedes spiral with each hand. Spirals were rated using an ordinal scale (0, 0.5, 1, 1.5, 2, and 3). Three raters rated an initial set of 548 spirals. Four raters rated a subsequent set of 200 spirals using a visual template for guidance.

RESULTS

Initial agreement (548 spirals) was good (r values ranged from 0.49 to 0.62, all p<0.001). Subsequent agreement (200 spirals and using visual template) improved (r values ranged from 0.67 to -0.91, all p<0.001).

DISCUSSION

This tool will be useful to researchers who are attempting to rapidly assess action tremor in their field surveys.

Exposure and toxic effects of elemental mercury in gold-mining activities in Ecuador

Traditional gold mining, using metallic mercury (Hg(0)) to form gold amalgam, followed by burning to remove the Hg(0), is widely used in South America, Africa and Asia. The gold is sold to merchants who burn it again to eliminate remaining Hg(0). In Ecuador, 200 gold miners, 37 gold merchants and 72 referents were studied. The median Hg concentrations in urine (U-Hg) were 3.3 (range 0.23-170), 37 (3.2-420), and 1.6 (0.2-13)μg/g creatinine, respectively, and in whole blood (B-Hg) were 5.2, 30, and 5.0 μg/L, respectively. Biomarker concentrations among merchants were statistically significantly higher than among miners and referents; also the miners differed from the referents. Burning of gold amalgam among miners was intermittent; U-Hg decreased in the burning-free period. In computerized neuromotor examinations, B-Hg and U-Hg concentrations were associated with increases in the centre frequency of the tremor, as well as in reaction time and postural stability.Retention of Hg (B-Hg), and the elimination rate (U-Hg) appears to be modified by polymorphism in a gene of an enzyme in the glutathione synthesis (GCLM), but there were no significant genetic modifications for the associations between exposure and neurotoxicity.Thus, the gold merchants have a much higher exposure and risk than the miners, in whom the exposure varies over time. The metabolism of Hg is modified by genetic traits. The present exposure to Hg had limited neurotoxic effects.

Evaluation of multiple neurotoxic outcomes in cancer chemotherapy

Although it is now clear that cognitive dysfunction is a common accompaniment of cancer chemotherapy, its implications await further research and direction. Most of the clinical research relies on standard neuropsychological tests that were developed to diagnose stable traits. Cognitive dysfunction in patients undergoing treatment varies with time, however. Its dimensions will vary during the course of treatment, which generally consists of cycles of drug administration followed by recovery periods. To effectively determine the connection between chemotherapy and cognitive function requires neuropsychological tests based on performance, so that they can be administered repeatedly at specified times during the entire course of treatment and beyond. A number of computerized test batteries, many of which have been developed for environmental neurotoxicology, are now available that fit such criteria. Moreover, cognitive impairment is only one aspect of chemotherapy-induced neurotoxicity. A full appreciation of its scope requires assessment of sensory functions such as vision, audition and somatosensory properties and assessment of motor function. A program of research based on animal models is also essential. Only with animal models is it possible to determine dose-response relationships and to couple behavioral with mechanistic indices such as neuroplasticity. Animal behavior models play a vital role in environmental toxicology because, from them, it is possible to derive some index of exposure that limits adverse effects. However, as in human testing, it is critical to choose situations whose properties remain stable over long periods of time so as to trace the time course of neurotoxicity. Schedule-controlled operant behavior offers the most promising source of animal models.

Neurological tremor: sensors, signal processing and emerging applications

Neurological tremor is the most common movement disorder, affecting more than 4% of elderly people. Tremor is a non linear and non stationary phenomenon, which is increasingly recognized. The issue of selection of sensors is central in the characterization of tremor. This paper reviews the state-of-the-art instrumentation and methods of signal processing for tremor occurring in humans. We describe the advantages and disadvantages of the most commonly used sensors, as well as the emerging wearable sensors being developed to assess tremor instantaneously. We discuss the current limitations and the future applications such as the integration of tremor sensors in BCIs (brain-computer interfaces) and the need for sensor fusion approaches for wearable solutions.

Neurodevelopmental toxicity risks due to occupational exposure to industrial chemicals during pregnancy

Exposure to neurotoxic chemicals is of particular concern when it occurs during early development. The immature brain is highly vulnerable prenatally and is therefore at risk due to occupational exposures incurred by pregnant women. A systematic search of the literature has been performed with emphasis on epidemiological studies on female workers and the neurodevelopment of their children. The majority of recent occupational studies focused on organic solvents and pesticides, which were associated with neurobehavioral impairments in the progeny. Additional evidence on environmental exposures demonstrates the vulnerability of the developing brain to substances like lead and methylmercury. Despite the evident hazards involved, the number of occupational cohort studies carried out in this field is very low. However, the lack of evidence for assumed neurotoxicants should not divert the attention by occupational health researchers and practitioners from the need to protect pregnant workers. Due to the vulnerability of the brain during early development, a precautionary approach to neurodevelopmental toxicity needs to be applied in occupational health.