Faced with a child who has been exposed to mercury, would you recognize the signs and symptoms? Would you know what questions to ask, which lab tests to draw, and what treatment to initiate?
Faced with a child who has been exposed to mercury, would you recognize the signs and symptoms? Would you know what questions to ask, which lab tests to draw, and what treatment to initiate? Would you know what to advise parents about a mercury spill at home?
Mercury is an amusing and attractive silvery liquid that appeals to children, who love to play with the shiny beads. Even adults amuse themselves with mercuryboiling it so that it jumps in the pan, throwing it against walls to see it dribble down, and coating it on cigarettes to revel in the colorful sparks created. Mercury is especially attractive to adolescents, who have been known to rub it on their skin and hair to take on the physical appearance of the silvery villain in the motion picture Terminator 2. The fact remains, however, that mercury is a poison that can terminate human life.
Although no national statistics exist on the prevalence of mercury poisoning, what limited data are available suggest that mercury exposure occurs with considerable frequency among all age groups and in all geographic regions of the United States. In 1999, the most recent year for which reporting statistics are available, poison control centers in the United States received more than 19,000 calls from Americans whose thermometers broke, according to the Georgia Poison Center. The vast majority of those thermometers were believed to contain mercury.
Sporadic reports of spills of elemental mercury to federal public health authorities have increased dramatically in recent years (Figure 1), reflecting greater access to expert assistance in such cases. The precise number of incidents is unknown because reporting is not mandated by law. Hazardous Substances Emergency Events Surveillance, an ongoing event-based survey conducted in 14 states by the Department of Health and Human Service's Agency for Toxic Substances and Disease Registry (ATSDR), received reports of 405 mercury spills in the six-year period 1993 to 1998.
The ATSDR receives many inquiries from physicians who do not know how to evaluate exposed patients. Their questions take on great urgency when a mercury spill occurs: In a recent event, for example, more than 1,000 people were evacuated from their homes, many for several days, and more than 100 area children were examined at local hospitals and clinics and an unknown number at physicians' offices. This article was written to address questions most commonly asked by physicians about liquid mercury exposure, to raise awareness about this problem among pediatricians, and to provide information about initial management of spills.
People have been fascinated by mercury for thousands of years, using it in medicine, industry, and cultural practices.1 It has been used as a cathartic, diuretic, antipruritic, anti-inflammatory, antimicrobial, and antiparasitic agent. The term "quack" has its origin in the treatment of syphilis with quicksilver (mercury). The expression "mad as a hatter" came from the exposure of 19th century hat makers to mercury that was used as a fixative. According to legend, the first Chinese emperor, Qin Shi Huang (259210), was entombed with his sarcophagus afloat in a pool of mercury. Mercury was used to embalm corpses because of its antimicrobial and antifungal properties. It has also been used by Mexican-American and Asian populations in folk remedies, and by Latin-American and Caribbean natives in religious and cultural practices that still take place in certain communities in the United States.
Today, the many uses of elemental mercury make it easy for children and teenagers to find (Table 1). Elemental mercury is commonly used in electrical switches, fluorescent and mercury vapor lamps, thermometers, barometers, indoor gas meter regulators, equipment gauges, and hospital equipment such as blood pressure monitors, esophageal dilators, and weighted feeding tubes.2 Elemental mercury is also used in dental amalgam, which is generally not considered a clinically significant source of exposure.3,4
Fluorescent and mercury lamps
Indoor gas regulators
Medical equipment (e.g., sphygmomanometers)
Used equipment gauges
Common organic sources of mercury, although not the subject of this article, include methyl mercury, most commonly found in fish caught in contaminated waters, and thimerosal, a mercury-based preservative that was, until recently, used in some vaccines5 and that is metabolized to ethylmercury and thiosalicylate. Currently, all vaccines recommended for childhood immunizations are free of thimerosal as a preservative.6
Many of the mercury spills that are reported to authorities occur when teenagers or young adults find liquid mercury in school chemistry labs or at abandoned or operating industrial sites and take the mercury home. The mercury, which is often shared with other people, can contaminate many homes, schools, vehicle interiors, and other locations, exposing a considerable number of people to the risk of poisoning.
Interestingly, in many if not most cases, the symptoms of those exposed are not readily linked to the mercury exposure. Without a careful history or high index of suspicion, it is easy to miss this diagnosis. In fact, many cases are diagnosed only after a sibling or other close associate develops similar signs, prompting the clinician to investigate further.79
Mercury occurs in three forms: elemental (also known as metallic or liquid mercury, azogue, or quicksilver); inorganic (mercurous or mercuric salts); and organic (methylmercury, ethylmercury, phenylmercury, and others) (Table 2). Adverse effects of mercury exposure depend on the form of mercury and route of exposure. Liquid mercury is the form found in accidental spills. Once spilled, mercury is difficult to contain and readily vaporizes at room temperature. It often gets tracked into vehicles, homes, and schools, where it can remain for years and silently affect the inhabitants, with potentially devastating results.10
Salts (mercurous or mercuric)
When a child breaks a thermometer and swallows the mercury inside, there is little immediate cause for concern. But, if the same amount of liquid mercury is heated or allowed to evaporate, the vapors pose a serious health threat. Swallowing elemental mercury is relatively harmless because the mercury is poorly absorbed from the gastrointestinal tract.11 Less than 0.01% is absorbed by this route, in the absence of enteric fistulae or intestinal perforation.12 Skin absorption is also minimal. Elemental mercury is very dangerous, though, when vapors are inhaled, because they are readily absorbed (75% to 80%) through the lungs.3 Therefore, the danger is not in swallowing mercury but in breathing its vapors.
Most people do not realize that liquid mercury is volatile even at room temperature. The inhaled vapors are readily absorbed through the alveolar membranes and transported by the blood throughout the body. Mercury oxidizes in the blood (primarily in the red blood cells) to its divalent cation, which can bind with proteins, and accumulates primarily in the kidneys. The high lipophilicity of elemental mercury in the body permits it to cross the blood-brain barrier.
In the brain, elemental mercury is oxidized to the divalent form. Divalent mercury does not easily cross the blood-brain barrier, and ion trapping can occur. Accumulation of mercury in the brain can produce irreversible damage to the basal ganglia, cerebellum, corpus callosum, and probably the temporal lobe of the cerebrum.13 These lesions can result in permanent neurologic dysfunction, including tremor, rigidity, truncal unsteadiness, impaired gait, and defects in memory.
Children are especially vulnerable to mercury toxicity. Their brains are still developing and the processes of brain maturation can be undermined. Moreover, because mercury is heavier than air, the vapors accumulate near the floor, where small children play and breathe. Compared with adults, children also have a faster respiratory rate and greater minute volumes per kilogram of body weight, and therefore are at greater risk of toxicity.
The symptoms and signs of mercury toxicity are seldom definitive, and the patient may or may not present with a history of playing with a silvery-gray liquid. Therefore, as with any patient, the clinician needs to ask the right questions. Perhaps the greatest challenge is to always be prepared to consider exposure to some type of toxic substance. In patients suspected of having mercury exposure or toxicity, a comprehensive environmental exposure history is indicated. Questions should cover the following12:
The physical exam should include a thorough neurologic exam. In young children, an assessment of developmental milestones and progression is essential to detect any neurodevelopmental impairment.14
Acute exposure. Consider this scenario: A 16-year-old cigarette smoker presents to the emergency department with shortness of breath, pain and tightness in his chest, and paroxysmal coughing. Other symptoms include fever, nausea, chills, and headache. The initial history reveals nothing to account for his symptoms. Upon further questioning, he says that he dipped his cigarettes in a shiny, silver liquid he obtained from a friend.
Symptoms of acute toxicity, as exhibited by this teenager, may occur within hours of exposure to high air concentrations of elemental mercury vapor. Respiratory symptoms, such as paroxysmal cough and shortness of breath, may predominate. Children are at increased risk of pulmonary toxicity, including chemical pneumonitis, necrotizing bronchiolitis, and pulmonary edema. Death can occur as a result of respiratory failure.
Other acute health effects are sore throat, chills, fever, and a metallic taste. Gastrointestinal symptoms may include nausea, diarrhea, vomiting, increased salivation, and abdominal pain. At higher doses, mercury accumulates in the kidneys, prompting proteinuria, nephrotic syndrome, acute tubular necrosis, and oliguric renal failure. Tachycardia and hypertension may develop. Acrodynia (erythredema polyneuropathy or pink disease), a rare, delayed, idiosyncratic nonallergic hypersensitivity to mercury, is more common in children than in adults. It is characterized by irritability, sleeplessness, sweating, severe leg cramps, scarlet discoloration of the cheeks and tip of the nose, paresthesia, and a painful pink peeling rash on the hands, nose, and soles of the feet.15,16
Chronic exposure.Consider the following: An irritable 18-month-old is admitted with a history of anorexia, weight loss, malaise, and, most recently, difficulty walking. She also has generalized pruritic rash and swollen, red hands and feet with desquamation. Upon close questioning, the mother reports that about three months ago a mercury thermometer broke on the carpet in the infant's bedroom; the mother vacuumed the broken glass and the spilled mercury.
Continuous exposure to elemental mercury, as in the case of this infant, primarily affects the nervous system and kidneys. Symptoms of chronic mercury poisoning include neuropsychiatric effects and renal impairment. Patients may demonstrate an intention tremor, ataxia, and personality changes that include erethism (a psychic disturbance marked by irritability, emotional instability, depression, shyness, and fatigue), emotional lability, aggressiveness, nervousness, shyness, loss of self-confidence, anger, insomnia, anorexia, memory loss, and depression. Peripheral nervous system findings may include limb weakness, motor and sensory nerve conduction delay, exaggerated reflexes, and distal paresthesia. Mercury toxicity to the kidney may result in a nephrotic syndrome in which there is increased excretion of urinary protein, hematuria, oliguria, urinary casts, edema, and hypercholesterolemia. Other symptoms of chronic mercury exposure may be corneal or lens changes, excessive perspiration, or dermatitis.
Laboratory tests. Blood and urine mercury levels are useful to confirm exposure. However, no definite correlation has been established between levels in blood and urine and the degree of mercury toxicity.17 Metallic mercury has a half-life in blood of only three days. Blood mercury is a valid measure of acute high-level exposure, and samples should be collected in EDTA or heparinized blood collection tubes, then refrigerated. The most reliable and commonly used method to determine mercury levels is cold vapor atomic absorption.12 Although mercury analysis is unavailable in most hospital laboratories, a physician who knows exactly what to ask for (the cold vapor atomic absorption test) can usually get this analysis done at a commercial lab. In most cases, the test can be run in less than a day, although shipping, scheduling, and quality control may lengthen the time needed to obtain reliable results.
Background blood levels of mercury in children are not precisely known, but adult levels rarely exceed 1.5 µg/dL of whole blood.18 The most recently available population-based survey indicated a geometric mean of 0.3 µg/dL whole blood mercury level in children 1 to 5 years of age.19 In adults, symptoms of toxicity begin to appear at blood mercury levels greater than 5 µg/dL.16 The corresponding level in children is not precisely known. The duration of time since exposure must be considered because the blood level returns to normal one to two days after exposure ceases.20 Newer, faster, and more accurate analytical methods, such as inductively coupled plasma mass spectrometry, are currently being introduced. The lack of standards for these newer methods makes the results difficult to interpret, however.
Urine specimens should be obtained from patients with a history of chronic mercury exposure (Table 3). The half-life of mercury in the kidneys is 60 days. Urine specimens must be collected in a plastic acid-washed container and refrigerated. Great care must be taken to avoid contamination of the specimen and container from mercury present on the skin, especially the hands. Although a 24-hour urine specimen is preferred, a first-morning voided urine as a spot specimen can also be used. As with blood, cold vapor atomic absorption is used to analyze the specimen. A urinary mercury concentration of less than 20 µg/L is considered normal for the general adult population.18 No population-based urine levels for children have been published. If a spot specimen is obtained, creatinine should be measured in the same specimen to adjust for overall urinary concentration.
Mercury can also be measured in hair. Currently, the analysis of hair samples for mercury levels has not proven useful in the clinical evaluation of patients for mercury toxicity.16,21
The first and best treatment for children, teenagers, and adults exposed to mercury is finding and removing the source of the contamination to prevent further exposure. In an acute exposure, decontamination should be attempted whenever possible before transporting the patient. All visible contamination with elemental mercury must be removed from the skin, hair, and clothing to prevent contamination of vehicles and emergency care facilities and to minimize exposure of others. Clothing and personal belongings should be removed and placed in a double plastic bag. Exposed skin and hair should be washed in a shower with a mild soap and water and rinsed thoroughly. Exposed eyes should be flushed with plain water or saline for five minutes. If mercury has been ingested, vomiting should not be induced and activated charcoal is not indicated. Vomitus, where present, should be sealed in double plastic bags because it may contain elemental mercury.
Cleaning up spilled liquid mercury is much more difficult and complex than most people realize. Mercury can remain on carpets, furniture, and tiles for years unless these materials are properly decontaminated.22 See "Cleaning up a spill of mercury".
Although mercury exposure is not mandated as a reportable condition, it is often very beneficial to contact a poison center at the first hint of mercury exposure. These centers are an excellent point of triage for families and can advise them when to seek medical care. Poison centers can also provide physicians with valuable information on symptoms and treatment of mercury exposure. In addition, more accurate prevalence data will be available in the future if physicians take the time to report mercury exposures.
All patients exposed to mercury should be assessed for stridor, wheezing, and rales, and treated with an aerosolized bronchodilator and supplemental oxygen as appropriate. Respiratory distress, if present, should be managed aggressively. Symptomatic children with known mercury exposure must be monitored closely and may well require hospitalization depending on the severity of the symptoms and the level of mercury exposure. Symptomatic patients with a history that suggests inhalation of mercury vapor should be transported to a medical facility for evaluation.12
Once elemental mercury is in the body, it enters an oxidation-reduction cycle and is eliminated through urine, feces, and expired air. In the absence of continued exposure, body burden declines over time; half-life is one or two months. The exception is elemental mercury in the brain. Insufficient information exists to definitely establish the half-life of mercury in the brain, but it appears to be a biphasic process that lasts years. In Japan, workers exposed to elemental mercury vapors a decade before their deaths had a high residual brain mercury level on autopsy.23
Chelation is the only available intervention that reduces the body's burden of mercury.3 This treatment should be considered only for symptomatic patients with documented exposure. Asymptomatic patients who do not have laboratory confirmation of mercury exposure should not be chelated. Hemodialysis does not remove mercury from the body effectively, but may have a role as supportive therapy in patients with renal failure as a result of mercury toxicity.
Over the years, a number of chelators have been used in patients with elemental mercury exposure, with varying efficacy and side effects; for example, 2-3-dimercaptosuccinic acid (DMSA or succimer), D-penicillamine, and dimercaprol (BAL or British anti-Lewisite). Among the possible side effects are vomiting, headache, tachycardia, and allergic reactions. Moreover, these chelators are not specific for mercury and also remove iron, calcium, and other beneficial elements from the body. A transient, marked elevation of the blood mercury level may occur during chelation as mercury stores are mobilized, raising the concern that chelation may increase mercury ion trapping in the brain. (Dimercaprol is contraindicated for elemental and organic mercury for this reason.) Dimercaprol increases the brain level of mercury and can cause neurotoxicity in animals undergoing experimental treatment for exposure to phenylmercury, methoxyethylmercury compounds, or elemental mercury vapor.3
Little evidence exists to aid the physician in initiating or monitoring chelation by following the blood or urine mercury level. If no baseline level is obtained before chelation is started, it is difficult, if not impossible, to interpret subsequent levels. Until the efficacy of chelation therapy is better established,6,24,25 it should, first, be used only after serious consideration of the risks and benefits and, second, be reserved for symptomatic patients with known mercury exposure.
Chelation techniques are provided in Medical Management Guidelines for Acute Chemical Exposures,12 published by the ATSDR. ATSDR also maintains a toll-free number for information on mercury and other toxic substances888-422-8737as well as a 24-hour emergency response line: 404-498-0120. In addition, clinical consultations for patients exposed to mercury or other toxic substances are available through a national network of pediatric environmental health specialty units (PEHSUs). These units are located in children's hospitals and leading academic medical centers throughout the United States (Figure 2). PEHSUs also accept clinical referrals from physicians whose patients have had environmental exposures or whose illnesses may have been triggered by environmental factors.
The lack of a definitive treatment for mercury toxicity makes a strong case for public education to eliminate opportunities for exposure. For example, thermometers that contain mercury could be replaced with equipment that is mercury-free. It is important for pediatricians to use all available opportunities to educate teenagers, parents, and teachers on the many possible sources of mercury exposure and attendant health risks.
Liquid mercuryeasy to find and fun to play withis quite volatile at room temperature, and exposure to its vapors can have serious consequences. Children are especially vulnerable to mercury toxicity. Mercury can remain for years in contaminated homes, schools, and vehicles, acting as a silent poison.
Other than acrodynia, no unique constellation of symptoms defines mercury toxicity. Therefore, obtaining a careful exposure history is essential. Because the history of mercury exposure may not be known in every case, a high level of suspicion is always necessary. Consider the possibility of mercury toxicity and ask questions about any exposure to this toxic silvery liquid whenever a child or teenager exhibits symptoms that are not easily explained.
The author is indebted to Dr. Michael Allred, Dr. Robert Amler, Dr. Eric Auf der Heide, Dr. Christopher T. De Rosa, Dr. John Risher, Richard Nickle, and other staff members in the division of toxicology at the Agency for Toxic Substances and Disease Registry for reviewing the manuscript of this article. In addition, George Prince provided a literature review and Anne A. Olin edited the manuscript before submission.
1. American Academy of Pediatrics: Handbook of Pediatric Environmental Health, Elk Grove Village, Ill., American Academy of Pediatrics, 1999
2. Weiss J, Trip L, Mahaffrey KR: Human exposures to inorganic mercury. Public Health Rep 1999;114:400
3. Agency for Toxic Substances and Disease Registry: Toxicological Profile for Mercury (update). Atlanta, US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 1999
4. Weiner JA, Nylander M, Berglund F: Does mercury from amalgam restorations constitute a health hazard? Sci Total Environ 1990;99:1
5. American Academy of Pediatrics and the United States Public Health Service: Joint statement of the American Academy of Pediatrics (AAP) and the United States Public Health Service (USPHS) (RE9937). Pediatrics 1999;104:568
6. Goldman LR, Shannon MW, Committee on Environmental Health: Technical report: Mercury in the environment: Implications for pediatricians. Pediatrics 2001;108:197
7. Bonhomme C, Gladyszaczak-Kholer J, Cadou A, et al: Mercury poisoning by vacuum-cleaner aerosol. Lancet 1996;347:1044
8. Velzeboer SC, Frenkel J, de Wolff FA: A hypertensive toddler. Lancet 1997;349:1810
9. Rennie AC, Robinson C, McWilliam R, et al: Mercury poisoning after spillage at home from a sphygmomanometer on loan from hospital. Br Med J 1999; 319:366
10. Yates KO, Mortensen ME: Acute and chronic neuropsychological consequences of mercury vapor poisoning in two early adolescents. J Clin Exp Neuropsychol 1994;16:209
11. Wright N, Yeoman WB, Carter GF: Massive oral ingestion of elemental mercury without poisoning (letter). Lancet 1980;1(8161):206
12. Agency for Toxic Substances and Disease Registry: Medical Management Guidelines for Acute Chemical Exposures. Atlanta, US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry, 1997
13. Ellenhorn MJ: Metals and related compounds, in Medical Toxicology: Diagnosis and Treatment of Human Poisoning. New York, Williams and Wilkins,1997, pp 15881599
14. Amler RW, Rice DA, Johnson BL: Assessment of mercury neurotoxicity through psychometric and neurobehavioral testing. Neurotoxicology 1996;17(1):237
15. Warkany J, Hubbard DM: Acrodynia and mercury. J Pediatr 1953;42:365
16. Agency for Toxic Substances and Disease Registry: Case Studies in Environmental Medicine: Mercury Toxicity. Atlanta: US Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, 1992
17. Berlin M: Dose-response relations and diagnostic indices of mercury concentrations in critical organs upon exposure to mercury and mercurials, in Nordberg GF (ed): Effects and Dose-Response Relationships of Toxic Metals. Amsterdam, Elsevier Scientific Publishing Company, 1976, pp 235245
18. Goldwater LJ: Normal mercury in man, in Mercury: A History of Quicksilver. Baltimore, York Press, 1972, pp 135150
19. Centers for Disease Control and Prevention: National Report on Human Exposure to Environmental Chemicals, Atlanta, US Department of Health and Human Services, CDC, March 2001, pp 1718
20. Sandborgh-Englund G, Elinder CG, Johanson G, et al: The absorption, blood levels, and excretion of mercury after a single dose of mercury vapors in humans. Toxicol Appl Pharmacol 1998;150:146
21. Eastern Research Group: Summary Report. Hair Analysis Panel Discussion: Exploring the State of the Science, June 1213, 2001. Atlanta, US Department of Health and Human Services, Agency for Toxic Substances and Disease Registry
22. Centers for Disease Control and Prevention: Mercury exposure among residents of a building formerly used for industrial purposes, New Jersey, 1995. Morbidity Mortality Weekly Report 1996;45:422
23. Takahata N, Hayash H, Watanabe B, et al: Accumulation of mercury in brains of two autopsy cases with chronic inorganic mercury poisoning. Folia Psychiatr Neurol Jpn 1970;24:59
24. Kosnett KJ: Unanswered questions in metal chelation. Clinical Toxicology 1992;30:529
25. Rogan WJ, Dietrich KN, Ware JH, et al: The effect of chelation therapy with succimer on neuropsychological development in children exposed to lead. N Engl J Med 2001;344:1421
Extreme care must be taken to properly dispose of the mercury after a spill. Sweeping the mercury with a broom or attempting to blot it with a paper towel may result in smaller, harder to clean droplets. Removing the mercury with an ordinary household vacuum cleaner can vaporize the mercury, increasing the airborne mercury concentration.1,2 Mercury vapor adsorbs to porous surfaces, such as clothing, cloth upholstery, bedding, and stuffed animals. If such items are affected, they must not be removed from the contaminated area. Instead, they must be left behind and removed when the area is cleaned up.
An eyedropper or stiff paper can be used to gather the mercury droplets into an airtight container, such as a jar with a lid or a zipper-lock plastic bag. The eyedropper or paper, as well as any contaminated carpet, tile, and other material, should be discardedbut only after the local health department or environmental agency is consulted and an appropriate disposal method is decided upon. A close inspection should be made for any remaining mercury beads by shining a flashlight on the surface in a dimly lit room. The light will reflect from any remaining beads. It is important not to step on the mercury and track it to other parts of the house.
Care should be taken to ventilate any area of contamination during the cleanup and for several days after. Anyone not essential to the cleanup should leave the area until cleanup is complete. Decontamination measures should result in an ambient mercury vapor concentration in the living area of the home of less than 1 µg/m3.
Help from the local health department or environmental agency is often needed to ensure thorough cleanup. Professional cleanup kits with self-contained vacuum systems are available commercially and must be used. Settings other than the home, such as schools and workplaces, represent a different exposure scenario and should be evaluated on a case-by-case basis.
1. Schwartz JG, Snider TE, Montiel MM: Toxicity of a family from vacuumed mercury. Am J Emerg Med 1992;10(3):258
2. Bonhomme C, Gladyszaczak-Kholer J, Cadou A, et al: Mercury poisoning by vacuum-cleaner aerosol. Lancet 1996;347:1044
Q. What should parents do if they want to get rid of their liquid mercury thermometers?
A. Many communities have hazardous waste collection programs, where thermometers and other household waste can be dropped off on certain days. Community-specific information and locations to dispose of hazardous household waste can be found at www.earth911.org . Parents can also call their local health department for information on proper disposal of their thermometers.
Sherlita Amler. Liquid mercury: A poisonous plaything. Contemporary Pediatrics 2002;8:37.