Dose-dependent elimination kinetics for mercury in urine: observations in subjects with brief but high-level exposure

Prenatal and postnatal mercury exposure and blood pressure in childhood

Elevated blood pressure in childhood is an important risk factor for hypertension in adulthood. Environmental exposures have been associated with elevated blood pressure over the life course and exposure to mercury (Hg) has been linked to cardiovascular effects in adults. As subclinical vascular changes begin early in life, Hg may play a role in altered blood pressure in children. However, the evidence linking early life Hg exposure to altered blood pressure in childhood has been largely inconsistent. In the ongoing New Hampshire Birth Cohort Study, we investigated prenatal and childhood Hg exposure at multiple time points and associations with blood pressure measurements in 395 young children (mean age 5.5 years, SD 0.4). Hg exposure was measured in children's toenail clippings at age 3 and in urine at age 5-6 years, as well as in maternal toenail samples collected at ∼28 weeks gestation and 6 weeks postpartum, the latter two samples reflecting early prenatal and mid-gestation exposures, respectively. Five measurements of systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were averaged for each child using a standardized technique. In covariate-adjusted linear regression analyses, we observed that a 0.1 μg/g increase in child toenail Hg at age 3 or a 0.1 μg/L urine Hg at age 5-6 were individually associated with greater DBP (toenail β: 0.53 mmHg; 95% CI: -0.02, 1.07; urine β: 0.48 mmHg; 95% CI: 0.10, 0.86) and MAP (toenail β: 0.67 mmHg; 95% CI: 0.002, 1.33; urine β: 0.55 mmHg; 95% CI: 0.10, 1.01). Neither early prenatal nor mid-gestation Hg exposure, as measured by maternal toenails, were related to any changes to child BP. Simultaneous inclusion of both child urine Hg and child toenail Hg in models suggested a potentially stronger relationship of urine Hg at age 5-6 with DBP and MAP, as compared to toenail Hg at age 3. Our findings suggest that Hg exposure during childhood is associated with alterations in BP. Childhood may be an important window of opportunity to reduce the impacts of Hg exposure on children's blood pressure, and in turn, long-term health.

Mercury exposures and symptoms in smelting workers of artisanal mercury mines in Wuchuan, Guizhou, China

Mercury exposures to smelting workers of artisanal mercury mines in Wuchuan, Guizhou, China were evaluated by urine and hair mercury survey. The mean urinary mercury (U-Hg), hair total mercury (T-Hg), and hair methyl mercury (Me-Hg) for smelting workers was 1060 microg/g creatinine (microg/g Cr), 69.3 and 2.32 microg/g, respectively. The results were significantly higher than that of control group, which is 1.30 microg/g Cr, 0.78 and 0.65 microg/g, correspondingly. The average urinary beta2-microglobulin (beta2-MG) was 248 microg/g Cr for the exposed group contrasting to 73.5 microg/g Cr for the control group and the data showed a serious adverse effect on renal system for the smelting workers. The workers were exposed to mercury vapor through inhalation, and the exposure route of Me-Hg may be through intake of polluted diet. The results indicate that age, alcohol drinking, and smoking are not crucial factors controlling the urine and hair mercury levels for the exposed and the control group. Clinical symptoms including finger and eyelid tremor, gingivitis, and typical dark-line on gums were observed in six workers. This study indicated that the smelting workers in Wuchuan were seriously exposed to mercury vapor.

The toxicology of mercury and its chemical compounds

This review covers the toxicology of mercury and its compounds. Special attention is paid to those forms of mercury of current public health concern. Human exposure to the vapor of metallic mercury dates back to antiquity but continues today in occupational settings and from dental amalgam. Health risks from methylmercury in edible tissues of fish have been the subject of several large epidemiological investigations and continue to be the subject of intense debate. Ethylmercury in the form of a preservative, thimerosal, added to certain vaccines, is the most recent form of mercury that has become a public health concern. The review leads to general discussion of evolutionary aspects of mercury, protective and toxic mechanisms, and ends on a note that mercury is still an "element of mystery."

The Potential Adverse Health Effects of Dental Amalgam

There is significant public concern about the potential health effects of exposure to mercury vapour (Hg(0)) released from dental amalgam restorations. The purpose of this article is to provide information about the toxicokinetics of Hg(0), evaluate the findings from the recent scientific and medical literature, and identify research gaps that when filled may definitively support or refute the hypothesis that dental amalgam causes adverse health effects. Dental amalgam is a widely used restorative dental material that was introduced over 150 years ago. Most standard dental amalgam formulations contain approximately 50% elemental mercury. Experimental evidence consistently demonstrates that Hg(0) is released from dental amalgam restorations and is absorbed by the human body. Numerous studies report positive correlations between the number of dental amalgam restorations or surfaces and urine mercury concentrations in non-occupationally exposed individuals. Although of public concern, it is currently unclear what adverse health effects are caused by the levels of Hg(0) released from this restoration material. Historically, studies of occupationally exposed individuals have provided consistent information about the relationship between exposure to Hg(0) and adverse effects reflecting both nervous system and renal dysfunction. Workers are usually exposed to substantially higher Hg(0) levels than individuals with dental amalgam restorations and are typically exposed 8 hours per day for 20-30 years, whereas persons with dental amalgam restorations are exposed 24 hours per day over some portion of a lifetime. This review has uncovered no convincing evidence pointing to any adverse health effects that are attributable to dental amalgam restorations besides hypersensitivity in some individuals.

Childhood urine mercury excretion: dental amalgam and fish consumption as exposure factors

The authors investigated the effect of amalgam fillings and fish consumption on urine mercury level (UHg), in children aged 4-8 years old inclusive. Using a sample of 60 children, we found that children with amalgam fillings had significantly higher UHg levels than children without amalgams (geometric mean=1.412microg Hg/g versus 0.436 microg Hg/g, respectively, P = 0.0001). Subjects with reported higher fish consumption also had significantly higher UHgs (P = 0.004). Univariate analyses provide evidence of an association between elevated UHg level and young age (P = 0.009), short height (P = 0.024), and low weight (P = 0.049) in children with amalgam chewing surfaces. We also found a negative correlation between urine mercury and age (-0.378), height (-0.418), and weight (-0.391). A multiple logistic regression model shows that the presence of amalgam fillings leads to increased odds of high UHg in children (OR=47.18), even after adjusting for high fish consumption (OR=8.66) and height (OR=11.36).

The impact of long-term past exposure to elemental mercury on antioxidative capacity and lipid peroxidation in mercury miners

Limited information is available on the effects of chronic mercury exposure in relation to the risk of cardiovascular disease (CVD). It is known from in vitro and in vivo studies that Hg can promote lipid peroxidation through promotion of free radical generation, and interaction with antioxidative enzymes and reduction of bioavailable selenium. The objective of the study was to test the hypothesis that long-term past occupational exposure to elemental Hg (Hg0) can modify antioxidative capacity and promote lipid peroxidation in miners. The study population comprised 54 mercury miners and 58 workers as the control group. The miners were examined in the post-exposure period. We evaluated their previous exposure to Hg0, the putative appearance of certain nonspecific symptoms and signs of micromercurialism, as well as the main behavioural and biological risk factors for CVD, and determined: 1) Hg and Se levels in blood and urine, 2) antioxidative enzymes, Cu/Zn superoxide dismutase (CuZn-SOD), catalase (CAT), and selenoenzyme glutathione peroxidase (GSH-Px) activity in erythrocytes as indirect indices of free radical activity, 3) pineal hormone melatonin (MEL) in blood and urine, and 4) lipid hydroperoxides (LOOHs) and malondialdehyde (MDA) as lipid peroxidation products. The mercury miners were intermittently exposed to Hg0 for periods of 7 to 31 years. The total number of exposure periods varied from 13 to 119. The cumulative U-Hg peak level varied from 794-11,365 microg/L. The current blood and urine Hg concentrations were practically on the same level in miners and controls. Miners showed some neurotoxic and nephrotoxic sequels of micromercurialism. No significant differences in behavioural and biological risk factors for CVD were found between miners and controls. A weak correlation (r = 0.36, p < 0.01) between systolic blood pressure and average past exposure U-Hg level was found. The mean P-Se in miners (71.4 microg/L) was significantly lower (p < 0.05) than in the controls (77.3 microg/L), while the mean U-Se tended to be higher (p < 0.05) in miners (16.5 microg/g creatinine) than in the controls (14.0 microg/g creatinine). Among antioxidative enzyme activities, only CAT in erythrocytes was significantly higher (p < 0.01) in miners (3.14 MU/g Hb) than in the controls (2.65 MU/g Hb). The mean concentration of B-MEL in miners (44.3 ng/L) was significantly higher (p < 0.01) than in the controls (14.9 ng/L). The mean value of U-MEL sulphate (31.8 microg/L) in miners was significantly lower (p < 0.01) than in the control group (46.9 microg/L). Among the observed lipid peroxidative products, the mean concentration of U-MDA was statistically higher (p < 0.01) in miners (0.21 micromol/mmol creatinine) than in the controls (0.17 micromol/mmol creatinine). In the group of miners with high mercury accumulation and the presence of some nonspecific symptoms and signs of micromercurialism, the results of our study partly support the assumption that long-term occupational exposure to Hg0 enhances the formation of free radicals even several years after termination of occupational exposure. Therefore, long-term occupational exposure to Hg0 could be one of the risk factors for increased lipid peroxidation and increased mortality due to ischaemic heart disease (ICH) found among the mercury miners of the Idrija Mine.

The absorption, blood levels, and excretion of mercury after a single dose of mercury vapor in humans

Nine healthy volunteers without amalgam fillings were exposed to 400 micrograms/m3 mercury vapor (Hg0) for 15 min, corresponding to 5.5 nmol Hg0/kg body wt (median range: 4.4-7.2). Frequent sampling of blood, urine, and exhaled air was performed for 30 days after exposure. The median retention of Hg0 was 69% of the inhaled dose. During the first 3 days after exposure 7.5-12% of the absorbed dose was lost by exhalation, with the median half time of Hg0 in expired breath being 2.0 days. In blood and plasma, a rapid absorption phase of Hg was seen, followed by a biexponential decline of the curves in both media. A substantial interindividual variation was observed in the area under the concentration-time curves of Hg in blood and plasma. In plasma the median half time of the second phase was 10 days. About 1.0% of the absorbed Hg was excreted via urine during the first 3 days after exposure, whereas the estimated amount excreted during 30 days ranged from 8 to 40%. In order to evaluate the chronic exposure to mercury from dental amalgam in the general population, the daily Hg dose from the fillings were estimated based on the plasma Hg levels found in subjects with amalgam fillings and on the plasma Hg clearance obtained in the present study. The daily Hg dose was estimated to 5-9 micrograms/day in subjects with an ordinary number of amalgam fillings.

The toxicology of mercury

The major physical forms of mercury to which humans are exposed are mercury vapor, Hg0, and methylmercury compounds, Ch3HgX. Mercury vapor emitted from both natural and anthropogenic sources is globally distributed in the atmosphere. It is returned as a water-soluble form in precipitation and finds its way into bodies of fresh and ocean water. Land run-off also accounts for further input into lakes and oceans. Inorganic mercury, present in water sediments, is subject to bacterial conversion to methylmercury compounds that are bioaccumulated in the aquatic food chain to reach the highest concentration in predatory fish. Human exposure to mercury vapor is from dental amalgam and industries using mercury. Methylmercury compounds are found exclusively in seafood and freshwater fish. The health effects of mercury vapor have been known since ancient times. Severe exposure results in a triad of symptoms, erethism, tremor, and gingivitis. Today, we are concerned with more subtle effects such as preclinical changes in kidney function and behavioral and cognitive changes associated with effects on the central nervous system. Methylmercury is a neurological poison affecting primarily brain tissue. In adults, brain damage is focal affecting the function of such areas as the cerebellum (ataxia) and the visual cortex (constricted visual fields). Methylmercury also at high doses can cause severe damage to the developing brain. Today the chief concern is with the more subtle effects arising from prenatal exposure such as delayed development and cognitive changes in children.