Mercury (inorganic Mercury): Xiaoyu Chen

Mercury (inorganic mercury) Xiaoyu

Chen

Professor

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Properties (general considerations)

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Mercury is a heavy, silvery—white metal that is a liquid at room temperature.  Its high vapor pressure presents the constant inhalation hazard in settings where elemental mercury is handled.  Mercury is present in numerous classes of rocks and is recovered primarily from cinnabar ore (HgS). Since ancient times, HgS has been used as a pigment. 

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cinnabar ore (HgS)

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Mercury may evaporate at room temperature, the rate depends on the surface area, temperature and ventilation. Thus ,increased amounts(surface area)of mercury will evaporate if it is scattered on the floor as small droplets. (if your thermometers is broken, clean up immediately ). The amount that evaporates at 40℃ is four times the amounts that evaporates at 20℃. 6

At saturation the air at 20℃ contains 15mg/m3( milligram , cubic meter ), which is more than 100 times the occupational exposure limit(USA).

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The toxicity of mercury has been known since antiquity , but therapeutic effects also were used in a variety of drugs. In particular ,mercury become an important drug from the sixteenth century when syphilis( 梅毒 ) were treated with mercury chloride. Such treatment invariably cause intoxications .

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Use and exposure

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Mercury is used for a variety of instruments (a major use of mercury is in the manufacture of control instrument), including thermometers, 温度计 manometers 压力计 , sphygmanometers 血压计 and electrical equipment (electrical devices).

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Mercury also is used tubes 电子管 , rectifiers 整流器， 纠正 , 矫正， batteries ,for the production of fluorescent light tubes ,as a catalyst in the chemical industry, including the production of chlorine ,and in 汞合金， 汞齐 for dentistry. (with expensive metal, gold ， silver ）

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Mercury is used in plating( 金属镀层 e.g gold)

jewelry, tanning 鞣革 ,and taxidermy

剥制动物标本 . Use in the felt 毛毡 industry (for example treatment of felt for hats.) in the 19th century led to extensive poisoning (“mad as a hatter”),and such use has been discontinued also.

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Inorganic mercury compounds are used for the production of certain pharmacentricals 药物 , including mercurious bromide 溴 , certain inorganic pesticides , antifouling agents for marine paints. Foul: 难闻的，恶臭的，船底沾满海藻贝壳的 A ship with a foul bottom . （海洋生物 halobios ）

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The various used and production of mercury and mercury compounds result in occupational exposure in a range of occupations. All workers involved in the extraction and recovery 回收 of mercury are at high risk for exposure to mercury vapor. Maintenance 维修 work on furnaces 火 炉 ,flues 烟道 ,and retorts （蒸馏器） is an important potential source of exposure.

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Workers engaged in the manufacture of electrical equipment requiring mercury may be exposed through spillage 散落 or careless handing. Metal—reclaiming workers may be exposed to mercury as well as other heavy metals. In production area where mercury is used as catalyst ,workers may be exposed through improper storing and handing or during maintenance operations.

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Workers in chlorine plants are also at risk though most operate using closed systems. Dentists , dental technicians ,and other laboratory workers may be exposed if mercury is not handled carefully.

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amalgams

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A miner tries to protect himself from vapors as he blowtorches a ball of purloined gold ore and mercury. However, covering his nose and mouth with his shirt provides no effective protection from the poisonous fumes.

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A miner (left) displays a 'pot of gold' that has been separated from rock and sediment with the help of mercury.

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Absorption Metabolism Excretion

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Elemental mercury is absorbed after the inhalation of mercury vapor. Ingested elemental mercury forms globules that are poorly absorbed from the gastrointestinal tract. Soluble mercurial salts (Hg++ ) are absorbed after inhalation and after ingestion.

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Inorganic mercury compounds distributed to many tissues, primarily the brain and kidney. There they bind to sulfhydryl groups (--SH)and may interfere with numerous cellular enzyme systems. Metallothionein(a low-molecular weight protein rich in sulfhydryl groups) production is increased after mercury exposure and may exert a protective effect in the kidney.

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Both organic and elemental mercury compounds readily cross the bloodbarrier and the placenta and are secreted in breast milk.(it’ dangerous for unborn and offspring). After inhalation, elemental mercury is rapidly oxidized by red blood cells, protecting the nervous system.(elemental mercury is easier cross the blood-brain than mercury ion, 100 times). Perk exposure may be more hazardous ,since the rate of oxidation may be inadequate 不充分

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All mercury compound are eliminated slowly in the urine, feces , saliva ,and sweat. The average half-life in humans is about 60 days for inorganic mercury. If the kidney is injured by mercury ,the mercury will be eliminated slowly.

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Clinical Findings 

A. Symptoms and signs:

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Acute: Inhalation of high concentration of mercury vapor or soluble mercury salts usually is a result of work in enclosed space. Cough , dyspnea 呼吸困难 , inflammation of the oral cavity ,and gastrointestinal complaints occur shortly after exposure. These may be followed by the development of a chemical pneumonitis with cyanosis 发绀 , tachypnea 呼吸急促 ,and pulmonary 肺水肿 edema 水肿 . Renal injury is a particular concern after exposure to mercury chloride and presente as an initial 初期的 diuresis 多尿 followed by proteinuria, and oliguric 少尿 ,renal failure. 32

After recovery from the acute illness , neurological symptoms （ similar to those seen with chronic overexposure ） may develop. Ingestion of soluble mercury compounds results in gastrointestinal complaints of nausea, vomiting, diarrhea, and abdominal pain, which may be followed by renal and neurological sequelae .

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Renal tubular epithelial cells from the urinary sediment of a patient with acute tubular necrosis caused by mercury poisoning. The patient took mercuric chloride in a suicide attempt. The cells have degenerated greatly and are much larger than usual. Sternheimer stain, X400. 34

Chronic: chronic exposure to inorganic mercury compounds results primarily in effects on the nervous system. (Mercury may damage both the peripheral and the central nervous systems.) In exposure to mercury vapor, the CNS is the critical organ. The classic triad of symptoms includes erethism , intention tremor and the gingivitis:

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Erethism : They are psychological effects caused by mercury on CNS. The manifestation include changes in restlessness ,irritability 易怒 , insomnia , 失眠 concentration difficulties , decreased memory(memory loss),depression 压抑 , shyness ,anxiety 忧虑 and emotional 情绪 的 stability , sometimes unusual psychological vulnerability 脆弱的 total neglect concerning economic problems and daily needs. In some cases a toxic psychosis develops.

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Tremor: Tremor is an early sign of neurotoxity . Initially the tremor is fine and is intention tremor 意向性震颤 , including fingers ,eyelids ,lips ,and tongue. The tremor may progress to spasms 痉挛 痉挛 of arms and legs. The tremor may be coarse 粗鲁的 jerking movement 反射 . A jerky micrographia （ ? ） is typical as well. Head tremor and skeletal ataxia 运动失调 .

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Along with the tremor ,disturbances in the autonomic nervous system may cause excess perspiration 出汗 and flushing 潮红 of the skin. Pains in arms and legs and paresthesias 感觉异常 may be related to a toxic polyneuritis 神经炎 . Hallucination 幻 觉 and dementia 痴呆 are late manifestations.

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Inflammation of the oral cavity: Other findings after excessive chronic exposure include inflammation of oral mucous and gingivitis , which become tender and bleed easily. Salivation is increased. If the inflammation develops further ,the teeth may loosen, dental erosion ,the salivary glands swell. Often the patient complains of metallic taste in the mouth. Especially when oral hygiene is bad, a gray border is formed on the gingival edges.

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Other: Renal injury usually results in proteinuria without frank renal failure. Eczematous 湿疹 skin eruption may also be present.

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The classic triad of symptoms includes erethism , intention tremor ,and the gingivitis

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B.

Laboratory Findings:

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Both acute and chronic exposure , measurement of mercury in blood and urine will confirm the diagnosis. It should be mentioned that urine levels usually are prefered as an indicator of occupational exposure, but if the kidney injured, the mercury may be eliminated slowly in the urine, and may not reflect toxicity symptoms.

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Normal concentration in nonexposed individuals are less than 0.01mg/L whole blood and less than 10 μg/g creatinine in urine. Substantial seafood consumption may result in higher levels.

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Biological monitoring is useful in the diagnosis of mercury exposure and in the control of occupational exposure levels. In the blood, inorganic mercury has a half-life of about 30 days, and methyl-mercury has a half-life about twice as long. Unfortunately , blood levels do not reflect mercury retained in the brain, where mercury after vapor inhalation has a halflife of several years. Thereby the effects on nervous system caused by mercury may recovery very slowly.

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After acute inhalation ,there may be hypoxemia ( 血氧过少，低氧血 shown by arterial blood gas measurements) and diffuse 弥散 infiltrates 浸润 on chest X-ray. Proteinuria indicates renal injury. The earliest manifestation of renal effects are increased excretion of low-molecular-weight protein , including N-acetyl 乙酰 -βglucosaminidase,β2microglobulin,and retinol 视网膜 -binding protein.

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Treatment

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After acute exposure to mercury ,prompt 立即 treatment with dimercaprol ( 二巯基丙醇 5 mg/kg intravenously)should be instituted. Respiratory distress 悲痛，忧伤，不幸 and renal failure should be treated appropriately. Penicillamine is also effective for acute poisoning.

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Individuals manifesting symptoms of chronic mercury toxicity should be removel from further exposure. The decision to give treatment in such cases depends on the severity of the symptoms and whether evidence of neurologic or renal toxicity is present. Suit the treatment to manifestation ,as internal medicine dose.

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Prevention

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1.Awareness of the constant hazard of mercury vapor exposure along with proper handing of material and meticulous attention to workplace hygiene will reduce potential exposure For example, the temperature in the workplace should not very high, reducing the evaporation of mercury. The working surface should be smooth, and easy cleaning, the slipped mercury can be collected easily. 51

2.Use of proper ventilation and respiratory protection is required in all operation that use mercury compounds. Special attention should focus on maintenance workers. The specific gravity of mercury vapor is heavier than that of air. So the ventilation measure should be on the lower position.

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3.Care in the handing and disposal of mercury compounds will prevent inadvertent contamination of the workplace. 4.Cntrol of industrial emissions will prevent contamination of waterways and seafood. Preventive measures should include the limitation of mercury released from industrial operation into the environment. 5.One of the important nonindustrial sources is in discard batteries (for cameras and watches ) and thermometers. 53