Effect of occupational mercury exposure on plasma lysosomal hydrolases

Update on Toxic Neuropathies

Purpose of Review

Toxic neuropathies are an important preventable and treatable form of peripheral neuropathy. While many forms of toxic neuropathies have been recognized for decades, an updated review is provided to increase vigilant in this area of neurology. A literature review was conducted to gather recent information about toxic neuropathies, which included the causes, clinical findings, and treatment options in these conditions.

Recent Findings

Toxic neuropathies continue to cause significant morbidity throughout the world and the causative agents, particularly with regards to medications, do not appear to be diminishing. A wide variety of causes of toxic neuropathies exist, which include alcohol, industrial chemicals, biotoxins, and medications. Unfortunately, no breakthrough treatments have been developed and prevention and symptom management remain the standard of care.

Summary

A detailed medication, occupational and hobby exposure history is critical to identifying toxic neuropathies. Increased research is warranted to identify mechanisms of neurotoxic susceptibility and potential common pathomechanistic pathways for treatment across diverse toxic neuropathies.

Concentration of mercury species in hair, blood and urine of individuals occupationally exposed to gaseous elemental mercury in Asturias (Spain) and its comparison with individuals from a control group formed by close relatives

Between November 19th, 2012 and December 3rd, 2012, 50 workers were intoxicated with gaseous Hg in San Juan de Nieva (Asturias, Spain) during the maintenance of a heat exchanger of a zinc manufacturer. We have quantified the concentration of methylmercury (MeHg), ethylmercury (EtHg) and Hg(II) in blood, hair and urine samples of those individuals taken three years after the accident. Blood, hair and urine of their closest relatives were also analyzed to assess whether the mercury burden present in the intoxicated individuals was due to the occupational exposure or to environmental or lifestyle-related factors. The determination of the mercury species in the samples was carried out applying multiple spiking Isotope Dilution GC-ICP-MS. This procedure corrects for possible interconversion reactions between the Hg species during the sample preparation procedure. Linear correlations were observed for both groups when plotting MeHg in blood vs MeHg in hair, and MeHg in hair vs Hg (II) in urine. The concentrations of Hg species in the intoxicated individuals were not significantly different from those obtained in the control group except for MeHg in blood. Significantly higher levels of MeHg in blood were obtained in some of the intoxicated individuals who had not consumed fish or seafood since the accident. A different correlation between MeHg in hair and MeHg in blood was obtained for these individuals compared to the control group who showed a hair-to-blood ratio consistent with the reported value for people exposed to Hg via fish consumption. Our results suggest that ingested MeHg followed the same pathway of deposition in hair in exposed and non-exposed individuals. However, the exposed individuals with high MeHg levels in blood showed a significantly different extent of MeHg deposition in hair compared to the control group.

Mercury toxicity and treatment: a review of the literature

Mercury is a toxic heavy metal which is widely dispersed in nature. Most human exposure results from fish consumption or dental amalgam. Mercury occurs in several chemical forms, with complex pharmacokinetics. Mercury is capable of inducing a wide range of clinical presentations. Diagnosis of mercury toxicity can be challenging but can be obtained with reasonable reliability. Effective therapies for clinical toxicity have been described.

Estimation and validation of mercury intake associated with fish consumption in an EPIC cohort of Spain

OBJECTIVE

To estimate mercury intake due to fish consumption among the individuals from Gipuzkoa participating in the European Prospective Investigation into Cancer (EPIC), and to validate the estimation of mercury exposure through diet, by measuring blood mercury level.

DESIGN AND SETTING

The population for the EPIC Gipuzkoa cohort was recruited from 1992 to 1995. Each individual's diet was assessed regarding habitual intake over the previous year, using the diet history method. Blood samples were taken at the time of the interview. The mercury content of the fish species consumed was supplied by the Food Chemical Surveillance Programme in the Basque Country.

SUBJECTS

For the estimation, 8417 volunteers, men and women, aged 35-65 years, of the EPIC cohort; for the validation, a random sample of 120 individuals stratified by fish intake was taken.

RESULTS

The validation study confirmed the relationship between fish consumption and mercury intake, as well as between fish consumption and mercury in erythrocytes. 99.9% of individuals have intakes below 75% of the Provisional Tolerable Weekly Intake (PTWI) of mercury established by the World Health Organization. But the limit dosage recommended by the United States Environmental Protection Agency, measured by the average risk index, would be exceeded often.

CONCLUSIONS

No individual from the cohort would exceed the PTWI of mercury. Nevertheless, owing to the amount of fish consumed, certain individuals would have mercury intakes approaching the recommended limits. With a view to the future, we believe mercury in fish must continue to be monitored closely in order to assess the risks for the population.

An estimation of the uptake of mercury from amalgam fillings based on urinary excretion of mercury in Swedish subjects

Mercury is released from amalgam fillings in several forms, i.e. as elemental vapour, ions and in fine particles. Despite many investigations there is still considerable uncertainty concerning the uptake of such mercury. Most available estimates have calculated the pulmonary uptake of mercury vapour based on measurements of concentrations intra-orally or in expired breath. Presented estimates vary by an order of magnitude from approximately 1 to 20 micrograms/day. The possibility of estimating this uptake based on levels of mercury in a biological index medium has received comparatively little attention. The purpose of the present work is to estimate the uptake of mercury from amalgam fillings based on urinary concentrations of mercury. It is estimated that the average uptake of mercury from amalgam fillings in Swedish subjects is within the interval 4-19 micrograms/day. This interval was arrived at after a detailed evaluation of the uncertainties in the data used and in the different assumptions. Notwithstanding the considerable range of this estimate it indicates a higher uptake than several other estimates, some of which have had a large impact on the scientific debate concerning this issue.

In vivo XRF analysis of mercury: the relation between concentrations in the kidney and the urine

The objective of this study was to determine the concentrations of mercury in organs of occupationally exposed workers using in vivo x-ray fluorescence analysis. Twenty mercury exposed workers and twelve occupationally unexposed referents participated in the study. Their mercury levels in kidney, liver and thyroid were measured using a technique based on excitation with partly plane polarized photons. The mercury levels in blood and urine were determined using atomic absorption spectrophotometry. The detection limit for mercury in the kidney was exceeded in nine of the exposed workers, but in none of the referents. The mean kidney mercury concentration (including estimates below the detection limits) was 24 micrograms g-1 in the exposed workers, and 1 microgram g-1 in the referents. The association between mercury in the kidney and in urine was statistically significant, but it was unclear whether the relation was linear. The measurements on liver (n = 10) and thyroid (n = 8) in the exposed workers showed mercury levels below the detection limit. The study shows that it is now possible to measure the mercury concentrations in kidneys of occupationally exposed persons, using in vivo x-ray fluorescence. The estimated concentrations are in reasonable agreement with the limited human autopsy data, and the results of animal studies.

Urinary mercury levels and early changes in kidney function in dentists and dental assistants

Mercury exposure and renal function parameters were examined in 68 dentists and 64 dental assistants. The levels of mercury in urine were low: only three individuals exceeded 20 micrograms/l. Increased excretion of urinary proteins and increased activity of urinary enzymes were observed. This enhanced prevalence of renal function changes appeared not to be related to the mercury urine level, age, sex, or smoking and drinking habits. Only for men was a positive relation between the level of mercury in urine and the activity of beta-galactosidase found. The proteinuria may be due to one or more potential nephrotoxic agents used in dental practice.