Environmental Medicine Integrating a Missing Element into Medical Education (1995) / Chapter Skim
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Case Study 22: Mercury Toxicity
Case Study 22: Mercury Toxicity
Pages 450-472
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From page 450... ...
This monograph is one in a series of self-instructional publications designed to increase the primary care provider's knowledge of hazardous substances in the environment and to aid in the evaluation of potentially exposed patients. See page 23 for further information about continuing medical education credits and continuing education units.
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From page 451... ...
CASE STUDY 22: MERCURY TOXlCllY Case Study A 3-year-old boy with irritability, digital erythema, and leg pain A 3-yeaf-old boy is brought to your office by his parents, who state that the child refuses to play and prefers to lie on his bed. His parents note that about a month ago, he seemed to withdraw and become cranky.
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From page 452... ...
Elemental mercury vapor accounts for most occupational exposures. The intermediate oxidation state, Hg'', forms numerous mercurous salts; the best known is mercurous chloride or calomel, which was commonly used in teething powders and other medicines until its adverse effects were publicized in 1948.
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From page 453... ...
The mercury concentration in fish at the top of the food chain is typically biomagnified up to 100,000 times the concentration in surrounding waters. In the general population, diet is the major source of mercury exposure, primarily through fish consumption.
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From page 454... ...
About 200 million mercury restorations are performed in the United States each year; at least one-half of those use silver amalgam. The mechanical action of chewing on an occlusive filling releases trace quantities of mercury vapor, which are partially absorbed.
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From page 455... ...
Household members of occupationally exposed workers may also be at increased exposure risk because mercury can be brought into the home on contaminated clothes. Personnel potentially exposed to mercury include, but are not limited to, the following: chlorine and caustic soda production workers cosmetic producers dental personnel electroplators explosives manufacturers felt makers and leather tanners grinding machine operators paper millers hazardous waste site personnel ink manufacturers laboratory personnel manufacturers of batteries, fluorescent lamps, mercury vapor lamps, switches, rectifiers metallurgists miners and processors of cinnabar (HgS)
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From page 456... ...
The source of contamination was effluent discharged into the bay from a factory using a mercury catalyst to make vinyl chloride. Neurologic and behavioral disorders have been observed in persons afteringestion ordermal application of inorganic mercury-containing compounds in teething powders, skin-lightening ointments, and laxatives.
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From page 457... ...
Primary Secondary Effects Effects Inorganic Elemental Liquid Hgt HgO Thermometers, Dermal contact: minimal absorption § barometers Ingestion: poor absorption Mercury Vaport HgO Industrial Inhalation: 80% absorbed Percutaneous: minimalabsorption Lungs, CNSt, skin, eyes, kidneys gingiva Salts Mercurous Hg'. Medicines, Ingestion: -10% absorbed Kidneys, CNS antiseptics Dermal contact: lethal doses can be Gl tract' absorbed by animals Mercuric Hg2.
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From page 458... ...
. The tissue distribution and excretion pathways of mercury salts are similar to those of mercury vapor; however, mercuric and mercurous ions cross the blood-brain and placental barriers to a much lesser extent than inhaled elemental mercury.
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From page 459... ...
Renal Effects After inorganic salts or phenylmercury compounds are ingested, a large amount of mercury may accumulate in the kidneys, producing a generalized increase in the permeability of the tubular epithelium. Exposure to mercury vapor or to mercury salts produces an apparently dose-dependent proteinuria or nephrotic syndrome.
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From page 460... ...
Infants born to women who had ingested flour made from grain treated with a MeHg fungicide had brain damage manifested by mental retardation, ataxia, deafness, constriction of the visual fields, blindness, microcephaly, cerebral palsy, and disturbances in swallowing. In experimental animals, exposure to elemental mercury vapor or administration of mercury salts has produced developmental anomalies, but the relevance of these findings to humans is unknown.
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From page 461... ...
If mercury salts have been ingested and corrosive injury is suspected, endoscopic examination should be performed. If elemental mercury vapor has been inhaled, a chest X ray should be obtained.
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From page 462... ...
are similar to those of mercury salts. Chronic Exposure Elemental Mercury The most important effects of chronic exposure to elemental mercury vapor involve the nervous system.
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From page 463... ...
O Permanent CNS damage may result from chronic exposure to MeHg. O Blood is an appropriate specimen for analysis after acute mercury exposure; a 24-hour urine specimen is preferred in cases of chronic exposure.
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From page 464... ...
Relationship of urinary mercury concentration with effects Urinary Mercury Concentration (~L) Signs and Symptoms <20 20 to ~ 00 ~ 00 to 500 500 to 1000 None Decreased response on tests for nerve conduction, brain-wave activity, and verbal skills Early indication of tremor on testing Irritability, depression, memory loss, minor tremor, and other nervous system disturbances Early signs of disturbed kidney function Kidney inflammation Swollen gums Significant tremor and nervous system disturbances Indirect Biologic Indicators If acute inorganic mercury poisoning is suspected, baseline BUN, creatinine, electrolytes, and urinalysis should be obtained; these values should be monitored continually to evaluate renal toxicity.
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From page 465... ...
O Chelation therapy has been used successfully in treating patients who have ingested mercury salts or inhaled elemental mercury. O No antidote exists for patients poisoned with organic mercury; supportive care is recommended.
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From page 466... ...
Mercury Salts When a patient has ingested mercury salts, the goals of therapy are to remove mercury from the body and to prevent dehydration and shock. Inorganic mercury can be removed from the gastrointestinal tract by emesis, catharsis, or ravage.
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From page 467... ...
or O.05 milligrams per cubic meter of air (mg/m3) for inorganic mercury vapor, and 1.2 ppb or 0.01 mg/m3 for organomercury compounds.
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From page 468... ...
Environment Air The EPA National Emission Standards for mercury from various industrial sources include the following: mercury ore processing facilities 2300 9 mercury maximum per 24-hour period; mercury cell chlor-alkali plants, sludge incineration plants, other wastewater treatments 3200 9 mercury maximum per 24-hour period. Ambient air contains mercury at about 2.4 parts per trillion (ppt)
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From page 469... ...
Regulation; TWA Mercury vapor 6.1 ppb (0.05 mg/m3) Mercury (aryl and inorganic)
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From page 470... ...
Mercury exposure from interior latex paint.
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From page 471... ...
(c) The best test to confirm or rule out chronic mercury exposure is a 24-hour urinary mercury concentration and creatinine clearance.
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From page 472... ...
Although the adverse developmental effects of MeHg are known, the longterm necrologic consequences to the human fetus of chronic low-level exposure to mercury vapor have not been documented well.
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