Effects of methylmercury on the microvasculature of the developing brain

The study, undertaken with the aim of further investigating the effects of methylmercury (MeHg) exposure on the developing brain, was performed in the cerebellum of chick embryos, chronically treated with a MeHgCl solution dropped onto the chorioallantoic membrane, and in control embryo cerebella. Quantitative evaluations, performed by cold vapour atomic absorption spectrophotometry, demonstrated a high mercury content in the chorioallantoic membrane, encephalon, liver and kidney of the treated embryos. The morphological observations showed severe neuronal damage consisting of degenerative changes of the granules and Purkinje neurons. The effects on astrocytes were even more severe, since they were extremely rare both in the neuropil and around the vessel wall. Compared with the controls, the cerebellar vessels of MeHg-treated embryos showed immature morphology, poor differentiation of endothelial barrier devices, and high permeability to the exogenous protein horseradish peroxidase. These findings support the hypothesis that MeHg-related neuronal sufferance may be secondary to astrocytic damage and suggest that the developmental neurotoxicity of this compound could also be related to astrocyte loss-dependent impairment of blood-brain barrier (BBB) differentiation.

A new cutaneous sign of mercury poisoning?

Chronic mercury poisoning is becoming a health concern because of extensive pollution of water and fish, and the increasing consumption of fish in the human diet. Mercury is extremely toxic to the body, especially the central nervous system, but diagnosis is difficult because of the lack of specific signs. A total of 11 patients were observed to have a nonpruritic or mildly pruritic discreet papular and papulovesicular eruption that correlated with high blood mercury levels. The mercury evidently came from increased seafood consumption. All of the patients improved when they were placed on either a seafood-free diet or chelation therapy. Physicians should suspect mercury poisoning in patients who eat a high-seafood diet who present with an asymptomatic or mildly pruritic papular or papulovesicular eruption.

Environmental exposure to mercury and its toxicopathologic implications for public health

Mercury is a toxic and hazardous metal that occurs naturally in the earth's crust. Natural phenomena such as erosion and volcanic eruptions, and anthropogenic activities like metal smelting and industrial production and use may lead to substantial contamination of the environment with mercury. Through consumption of mercury in food, the populations of many areas, particularly in the developing world, have been confronted with catastrophic outbreaks of mercury-induced diseases and mortality. Countries such as Japan, Iraq, Ghana, the Seychelles, and the Faroe Islands have faced such epidemics, which have unraveled the insidious and debilitating nature of mercury poisoning. Its creeping neurotoxicity is highly devastating, particularly in the central and peripheral nervous systems of children. Central nervous system defects and erethism as well as arrythmias, cardiomyopathies, and kidney damage have been associated with mercury exposure. Necrotizing bronchitis and pneumonitis arising from inhalation of mercury vapor can result in respiratory failure. Mercury is also considered a potent immunostimulant and -suppressant, depending on exposure dose and individual susceptibility, producing a number of pathologic sequelae including lymphoproliferation, hypergammaglobulinemia, and total systemic hyper- and hyporeactivities. In this review we discuss the sources of mercury and the potential for human exposure; its biogeochemical cycling in the environment; its systemic, immunotoxic, genotoxic/carcinogenic, and teratogenic health effects; and the dietary influences on its toxicity; as well as the important considerations in risk assessment and management of mercury poisoning.

A whitened face woman with nephrotic syndrome

Skin whitening cream from developing countries is a recognized source of chronic mercury poisoning. The authors report on a 34-year-old Indonesian domestic helper who presented with nephrotic syndrome secondary to membranous nephropathy. It was subsequently found that she used a skin whitening cream regularly that was found to contain a mercury level of almost 2,000 times above the allowable limit. Her blood and urinary mercury levels were both grossly elevated. Her symptoms improved after she stopped using the cream. However, she returned to her home country before chelating therapy could be arranged. Because mercury-containing skin products are still widely available in developing countries, the use of these products should be considered a possible cause of membranous nephropathy in immigrants from those countries.

Five years of follow-up after elemental mercury self-poisoning

A case of attempted suicide by injection of elemental mercury is described. Radiographs demonstrated the presence of widespread opacities of metallic mercury in both the lungs and the abdomen. During a 5-year follow-up, even though the patient had high concentrations of mercury in the urine and blood, only mild clinical symptoms and moderate carbon monoxide diffusing capacity reduction appeared. No biochemical evidence of damage to any organ was found.

Investigation of intracellular factors involved in methylmercury toxicity

Methylmercury is a known pollutant that causes severe central nervous system disorders. It is capable of passing through the blood-brain barrier and accumulates in cerebral cells. However, little is known regarding the mechanism of its toxicity at the molecular level. Using yeast cells, we searched for the genes involved in the expression of methylmercury toxicity, and found that genes encoding L-glutamine.D-fructose-6-phosphate amidotransferase (GFAT) and ubiquitin transferase (Ubc3) confer methylmercury resistance on the cells. It has also been shown that GFAT is the target molecule of methylmercury in yeast cells. These findings provide important clues about the mechanism underlying methylmercury toxicity in mammals.

Pathology of "toxic oils" and selected metals in the MRL/lpr mouse

The Toxic Oil Syndrome epidemic that occurred in Spain in 1981 and affected nearly 20,000 people was caused by ingestion of oil mixtures that contained analine-denatured rapeseed oil. To date, an animal model in which to identify the actual etiologic agents(s) and to investigate the pathogenesis of the disease has not been discovered. In this study, the MRL/lpr was used to assess the histopathological response of 3 "toxic oils" and 3 metals. The oils tested were a denatured rapeseed oil collected from a family who were affected by the Toxic Oil Syndrome epidemic in Spain (CO756) plus two synthesized oils (RSD and RSA). Female mice, 7 weeks of age, received an undiluted (neat) or a 1:10 diluted dose of each oil; mercury (50 ppm), cadmium (100 ppm), or lead (50 ppm). Half of each group was killed after 5 weeks of exposure and the remaining mice after 10 weeks of exposure. Body and organ weights (liver, kidney, thymus, and spleen) were recorded and selected organs were collected for histopathology. Ten weeks after treatment, body weights (BW) of the cadmium and lead groups were significantly suppressed, and the body weight of the C0756-neat group was significantly increased compared to their respective controls. Kidney/BW were decreased in the RSA-neat and RSA 1:10 groups after 10 weeks of exposure, and the kidney/BW in the mercury and cadmium groups were increased. Spontaneous development (12 weeks of age) and progression (17 weeks of age) of histopathological lesions are described for selected organs examined in the naïve mice as are changes that resulted from exposure to the "toxic oils" and metals. C0756-neat, mercury, and lead suppressed progression of the glomerulonephritis that normally occurs in the MRL/lpr mouse. Also of interest were lesions that included mononuclear cuffing of hepatic bile ducts, progression of the granulomas that formed in the renal glomeruli, vessels in the lymphoid organs that contained tightly packed lymphocytes, and the presence of plasma cells in the thymus. All 3 oils stimulated early development of the lymphoproliferative syndrome characteristic of the MRL/lpr mouse as demonstrated by an increase in the thymus/BW and spleen/BW ratios after 5 weeks of treatment. These data contribute to our knowledge of spontaneous disease progression in the thymus, spleen, lymph nodes, and kidneys in the MRL/lpr mouse and the effects of 3 different "toxic oils" and metals on the development and progression of those lesions.

Necropsy findings and environmental contaminants in common loons from New York

Diagnostic and analytical findings are presented for 105 common loons (Gavia immer) found dead or debilitated in New York (USA) from 1972-99. Aspergillosis (23% of cases) and ingestion of lead fishing weights (21%) were the most common pathologies encountered. Stranding on land, shooting, other trauma, gill nets, air sacculitis and peritonitis, and emaciation of uncertain etiology accounted for most of the remaining causes of disease or death. Analysis for total mercury in the liver of 83 loons yielded a geometric mean (gm) of 10.3 mg/kg (wet basis) and range of 0.07 to 371 mg/kg, with emaciated birds generally showing higher levels. Organochlorine contaminant levels in brain were generally low, principally consisting of PCB's (gm = 2.02 mg/kg) and DDE (0.47 mg/kg).

Recent advances in recognition of low-level methylmercury poisoning

Clinically evident neurologic damage from methylmercury exposure was well described following poisoning episodes in Japan and Iraq several decades ago. Paresthesias have been considered to be an early effect; however, additional data raise questions about whether this is the most sensitive adverse effect among adults. Fetuses are considered the most sensitive subpopulation because of the vulnerability of the developing nervous system. Over the past 5 years questions have been raised about what is an appropriate level of exposure for sensitive groups. A recent evaluation by a committee for the US National Research Council found that 0.1 microg/kg body weight per day is a scientifically justified level of methylmercury exposure for maternal-fetal pairs. The conclusions of this report and other issues are discussed in the present review. Because of anthropogenic release of mercury into the environment, methylmercury exposure from fish consumption is a pathway that is of increasing concern.

Histologic, neurologic, and immunologic effects of methylmercury in captive great egrets

Captive great egret (Ardea albus) nestlings were maintained as controls or were dosed with methylmercury chloride at low (0.5), and high doses (5 mg/kg, wet weight) in fish. Low dosed birds were given methylmercury at concentrations comparable to current exposure of wild birds in the Everglades (Florida, USA). When compared with controls, low dosed birds had lower packed cell volumes, dingy feathers, increased lymphocytic cuffing in a skin test, increased bone marrow cellularity, decreased bursal wall thickness, decreased thymic lobule size, fewer lymphoid aggregates in lung, increased perivascular edema in lung, and decreased phagocytized carbon in lung. High dosed birds became severely ataxic and had severe hematologic, neurologic, and histologic changes. The most severe lesions were in immune and nervous system tissues. By comparing responses in captive and wild birds, we found that sublethal effects of mercury were detected at lower levels in captive than in wild birds, probably due to the reduced sources of variation characteristic of the highly controlled laboratory study. Conversely, thresholds for more severe changes (death, disease) occurred at lower concentrations in wild birds than in captive birds, probably because wild birds were exposed to multiple stressors. Thus caution should be used in applying lowest observed effect levels between captive and wild studies.

Perimortem fixation of the gastric and duodenal mucosa: a diagnostic indication for oral poisoning

Two cases of fatal oral poisoning are presented. In the first case, a 40-year-old man died due to a lethal dose of mercury (blood concentration 113.8 microg/ml) and in the second, a 34-year-old man died of chloralhydrate overdose with a lethal blood concentration of trichloroethanol (52 microg/ml), the active metabolite of chloralhydrate. In both cases gross examination and histology showed an unusually well preserved gastrointestinal mucosa in addition to unspecific signs of intoxication. The two cases demonstrate that the phenomenon of perimortal fixation is a useful indication for the forensic pathologist and should direct the suspicion to oral poisoning. The detection of fixation facilitates toxicology screening by indicating that the relevant substance must have the capability to precipitate proteins.

Apparent diffusion coefficient on rat brain and nerves intoxicated with methylmercury

The effects of methylmercury chloride (MMC) on the degenerative changes in rat brain and cranial nerves were studied. Twelve Wistar rats were divided into two equal groups. The rat model of methylmercury intoxication (MMC group) was made by subcutaneously administering 10 mg mercury/g body weight daily for 7 days. Control group rats were infused with the same amount of normal saline during this period. Magnetic resonance imaging (MRI) measurements were performed before and 14 days after the first MMC administration, using a 4.7-T MR system. No significant focal changes were observed on T1- and T2-weighted MR images regarding the internal structures of the brains of the MMC-intoxicated rats, atrophy of the cerebellum, and dilatation of the arachnoid space around the brain stem of MMC-treated rats, but were demonstrated without edematous change. The apparent diffusion coefficients (ADC) of the cortex, caudate-putamen, and trigeminal nerve were not significantly different between the MMC-treated and control rats. However, the ADC parallel to the optic nerves were significantly increased in the MMC group, in contrast to the unchanged ADC perpendicular to the optic nerves. An electron microscopy study revealed a marked decrease of microtubules and moderate decrease of neurofilaments in the axons of myelinated fibers of optic nerves of the MMC-treated rats. We have thus demonstrated a disturbance in the integrity of microtubules and neurofilaments as a toxic action of MMC in the rat nervous system in vivo, particularly in the optic nerves. The use of ADC values calculated by diffusion-weighted MRI is a promising approach for the evaluation of changes in brains and nerves in methylmercury intoxication research.

Chronic inorganic mercury induced peripheral neuropathy

We report the clinical features, electrophysiological studies, and morphometric analysis of sural nerve pathology in a patient with polyneuropathy due to inorganic mercury intoxication. He developed slowly progressive generalized paralysis of all limbs after 3 months ingestion of herb drugs which contained mercuric sulfate. Electrophysiologic studies revealed axonal polyneuropathy involving both motor and sensory fibers. Sural nerve biopsy demonstrated axonal degeneration with demyelination and a predominant loss of large myelinated fibers. His muscle strength showed only mild improvement after 2 years' follow-up. We concluded that inorganic mercury exposure may induce severe axonal sensorimotor polyneuropathy in humans and that neurological deficits may persist in severe cases.

The present mercury contents of scalp hair and clinical symptoms in inhabitants of the Minamata area

A total of 191 fishermen and their family (32-82 years) living in some mercury-polluted areas along the Shiranui Sea volunteered for the present study. They made a living by fishery and had formerly eaten the methyl mercury-contaminated fish and shellfish caught there. The questionnaire on subjective symptoms, fish eating habits, and past living history was conducted on the subjects. In addition, they were clinically examined in detail by several neurologists and scalp hair was collected. With six exceptions, all the 185 subjects showed a normal total mercury level in hair (<10 ppm). The ratio of methyl mercury to total mercury was 79-94% on the average for each group examined, suggesting indirect contamination (perhaps through the food chain). Despite their low mercury level in scalp hair, however, the subjects showed various neurological symptoms, particularly, sensory disturbance (such as the glove and stocking type), at a very high rate. Thus, it seems fair to state that, in addition to officially recognized Minamata disease patients, there still exist many people with atypical, slight Minamata disease on the coast of the Shiranui Sea. The current hair mercury level is not necessarily useful as a criterion for diagnosing chronic Minamata disease because of the long lapse of time.

MR findings of Minamata disease--organic mercury poisoning

We describe MR findings in patients with Minamata disease who have been followed for a long time. All patients examined were affected after daily eating of a large quantity of methylmercury-contaminated seafood, from 1955 to 1958, and showed typical neurological findings. On MR images, the visual cortex, the cerebellar vermis and hemispheres, and the postcentral cortex are significantly atrophic in Minamata disease. The visual cortex is slightly hypointense on T1-weighted images and hyperintense on T2-weighted images, probably representing the pathologic changes of status spongiosus. MRI can demonstrate the lesions located in the calcarine area, cerebellum, and postcentral gyri, which are probably related to three of the characteristic manifestations of this disease: the constriction of the visual fields, ataxia, and sensory disturbance, respectively.

The chronic toxicity of inorganic mercury in goats: clinical signs, toxicopathological changes and residual concentrations

Chronic mercury toxicity was induced in goats by administering mercuric chloride at 100 micrograms/ml in deionized drinking water offered ad libitum for 90 days. Toxic signs of gastrointestinal disturbances and renal dysfunction developed from 43 days onwards without any mortality. The toxicity also induced nephrosis and tubular nephritis; centrilobular necrosis of liver; mild to moderate necrosis in spleen, intestine and lymph node; Zenker's degeneration of cardiac muscles; exudative pneumonia; and pial congestion, oedema and vacuolation in the brain. In addition, hyperaemia, oedema and tissue haemorrhages were evident in most of the organs. The kidneys contained the largest residues of mercury, followed by liver, spleen, intestine, lymph node, skeletal muscles, lungs, heart, brain and the omental fat. The intensity of the cytotoxic changes in the various organs was proportional to the amount of mercury accumulated.

A multidisciplinary clinical study of patients suffering from illness associated with mercury release from dental restorations: psychiatric aspects

The aim of this study was to map the psychological/psychiatric, odontological and medical aspects of patients with symptoms allegedly related to the side-effects of mercury in dental fillings. A total of 67 consecutive patients and 64 controls matched for age, sex and residential area were included in the study. The most striking result was the high prevalence of psychiatric disorders in the patients (89%) compared to the controls (6%), predominantly somatoform disorders. The personality traits differentiating the patients according to the Karolinska Scales of Personality (KSP) were somatic anxiety, muscular tension, psychasthenia and low socialization. More patients than controls showed alexithymic traits. The prevalence of diagnosed somatic diseases was higher, but not sufficiently so to explain the large difference in perceived health. The multiple symptoms and signs of distress displayed by the patients could not be explained either by the odontological data or by the medical examination. Our data indicate that the patients show sociodemographic and clinical patterns similar to those of somatizing patients. The medicalization of the suffering of these patients and the neglect of psychiatric problems prevent the use of appropriate psychotherapeutic approaches.

A review of experimental methylmercury toxicity in rats: neuropathology and evidence for apoptosis

As an animal model for examining the pathogenicity of human organic mercury intoxication, rats have been used for the reproduction of human neurologic diseases. Rats experimentally exposed to methylmercury chloride showed clinical signs of neurologic dysfunction characterized by ataxic behavior. Neuropathology of the diseased animals consisted of lesions such as: (a) degeneration of the peripheral nerve and sensory root nerve with preservation of the motor root nerve; (b) degeneration of the posterior funiculus of the spinal cord; and (c) degeneration of cerebellar granule cells with preservation of Purkinje cells. These findings suggest the human neuropathology of this toxicity. The degeneration was characterized by nerve fiber damage or neuronal cell death accompanied by astrocytic gliosis and activated macrophages or microglias. For the cerebellar granule cells, the mechanism of neuronal cell death was shown to be apoptosis. This fact was verified by histologic and ultrastructural findings as well as by in situ nick-end labeling and electrophoretic methods. Evidence of apoptosis involvement in cerebellar degeneration would provide a new viewpoint from which to analyze the selected degeneration of the nervous system in neurotoxicology.

Pathology of Minamata disease

Minamata disease, or methylmercury poisoning, was first discovered in 1956 around Minamata Bay, Kumamoto Prefecture, Japan. A similar epidemic occurred in 1965 along the Agano River, Niigata Prefecture, Japan. The neuropathology of Minamata disease has been well studied; this review focuses on human cases of Minamata disease in Kumamoto Prefecture. Nervous system lesions associated with Minamata disease have a characteristic distribution. In the cerebral cortex, the calcarine cortex was found to be involved in all cases of Minamata disease, particularly along the calcarine fissure. The destruction of nerve tissue was prominent in the anterior portions of the calcarine cortex. Occasionally, the centrifugal route from the visual and visual association areas (internal sagittal stratum) showed secondary degeneration in prolonged cases after acute onset. Postcentral, precentral, and temporal transverse cortices showed similar changes, though they were less severe. Intense lesions in the precentral cortex caused the development of secondary bilateral degeneration of the pyramidal tracts. In the cerebellum, the lesions occurred deeper in the hemisphere. The granule cell population was most affected. In the peripheral nerves, sensory nerves were more affected than motor nerves. Secondary degeneration of Goll's tracts was occasionally seen in prolonged or chronic cases.

Acute mercury poisoning by intentional ingestion of mercuric chloride

A 26-year-old woman ingested 0.9 g of mercuric chloride in a suicide attempt and developed hematemesis, melena and acute renal failure. Anuria persisted for 14 days. She was treated by plasma exchange, hemodialysis and peritoneal dialysis in combination with continued dimercaprol chelation. While hemodialysis was ineffective in removing the mercury, plasma exchange effectively eliminated mercury. After two plasma exchange therapies, mercury concentration in the blood decreased linearly on a log scale with half-lives of 23.1 days for whole blood and 19.1 days for plasma, using first-order kinetics. One month after ingestion, renal function recovered to normal as judged by serum creatine and blood urea nitrogen levels, although the beta 2-microglobulin level in urine was still elevated. At a follow-up examination four months later, renal function was found to be completely normal. This indicates that the renal damage caused by acute mercuric chloride poisoning may not be permanent.