Neuropsychological alterations in mercury intoxication persist several years after exposure

Mercury Exposure and Its Health Effects in Workers in the Artisanal and Small-Scale Gold Mining (ASGM) Sector—A Systematic Review

Gold is one of the most valuable materials but is frequently extracted under circumstances that are hazardous to artisanal and small-scale gold miners’ health. A common gold extraction method uses liquid mercury, leading to a high exposure in workers. Therefore, a systematic review according to the PRISMA criteria was conducted in order to examine the health effects of occupational mercury exposure. Researching the databases PubMed^®, EMBASE^® and Web of Science^TM yielded in a total of 10,589 results, which were screened by two independent reviewers. We included 19 studies in this review. According to the quantitative assessment, occupational mercury exposure may cause a great variety of signs and symptoms, in particular in the field of neuro-psychological disorders, such as ataxia, tremor or memory problems. However, many reported symptoms were largely unspecific, such as hair loss or pain. Most of the included studies had a low methodological quality with an overall high risk of bias rating. The results demonstrate that occupational mercury exposure seriously affects miners’ health and well-being.

Salivary biomarkers and neuropsychological outcomes: A non-invasive approach to investigate pollutants-associated neurotoxicity and its effects on cognition in vulnerable populations

The occurrence of neurotoxicity caused by xenobiotics such as pesticides (dichlorodiphenyltrichloroethane, organophosphates, pyrethroids, etc.) or metals (mercury, lead, aluminum, arsenic, etc.) is a growing concern around the world, particularly in vulnerable populations with difficulties on both detection and symptoms treatment, due to low economic status, remote access, poor infrastructure, and low educational level, among others features. Despite the numerous molecular markers and questionnaires/clinical evaluations, studying neurotoxicity and its effects on cognition in these populations faces problems with samples collection and processing, and information accuracy. Assessing cognitive changes caused by neurotoxicity, especially those that are subtle in the initial stages, is fundamentally challenging. Finding accurate, non-invasive, and low-cost strategies to detect the first signals of brain injury has the potential to support an accelerated development of the research with these populations. Saliva emerges as an ideal pool of biomarkers (with interleukins and neural damage-related proteins, among others) and potential alternative diagnostic fluid to molecularly investigate neurotoxicity. As a source of numerous neurological biomarkers, saliva has several advantages compared to blood, such as easier storage, requires less manipulation, and the procedure is cheaper, safer and well accepted by patients compared with drawing blood. Regarding cognitive dysfunction, neuropsychological batteries represent, with their friendly interface, a feasible and accurate method to evaluate the eventual cognitive deficits associated with neurotoxicity in people from diverse cultural and educational backgrounds. The association of these two tools, saliva and neuropsychological batteries, to cover the molecular and cognitive aspects of neurotoxicity in vulnerable populations, could potentially increase the prevalence of early intervention and successful treatment.

A Cross-Sectional Study of Blood Ethylmercury Levels and Cognitive Decline Among Older Adults and the Elderly in the United States

Cognitive health is an emerging public health concern for the aging American population. Mercury (Hg) is a toxic element that can cause nervous system damage. This hypothesis-testing study evaluated the relationship between blood ethyl-Hg levels and cognitive decline in an older adult and elderly American population. A total of 1,821,663 weighted-persons between 60-80 years old with detectable blood ethyl-Hg levels within the 2011-2012 National Health and Nutritional Examination Survey were examined. Those persons with blood ethyl-Hg levels greater than the median were deemed the higher ethyl-Hg exposure group and those with ethyl-Hg levels less than the median were deemed the lower ethyl-Hg exposure group. Three tests were utilized to measure cognitive function: 1) Consortium to Establish a Registry for Alzheimer's Disease - Word List Learning (CERAD W-L) delayed recall test, 2) animal fluency test, and 3) Digit Symbol Substitution Test. Each cognitive test score was categorized as higher for those with scores greater than the median and lower for those with scores less than the median. Survey logistic regression modeling with covariates was used to analyze the data for the relationship between blood ethyl-Hg levels and cognitive function scores. Significantly increased risks for lower animal fluency test (odds ratio (OR) = 13.652, p = 0.0029) and CERAD W-L delayed recall test (OR = 6.401, p = 0.0433) scores were observed among the higher ethyl-Hg exposure group as compared to the lower ethyl-Hg exposure group. This study supports the hypothesis that increased ethyl-Hg exposure is associated with significant cognitive decline in older adult and elderly Americans.

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.