Sherlita Amler

Liquid mercury:    A poisonous plaything 

 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 mercuryboiling   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 

 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.

 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 (259210), 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.

 Elemental   mercury is also used in dental amalgam, which is generally not considered a   clinically significant source of exposure.

Where can children commonly find elemental mercury?

 Medical equipment (e.g., sphygmomanometers)       

 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 vaccines

 and that is metabolized to ethylmercury and thiosalicylate.   Currently, all vaccines recommended for childhood immunizations are free of   thimerosal as a preservative.

 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.

 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.

 Ethylmercurithiosalicylate (thimerosal)       

 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.

 Less than 0.01% is absorbed   by this route, in the absence of enteric fistulae or intestinal perforation.

   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.

 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.

 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 following

 Any history of playing with liquid mercury 

Use of elemental mercury in school or work 

Use of mercury-containing cosmetics or skin lightening creams Use of folk     remedies or mercury in religious or cultural practices 

Recent use of mercury-containing paints or similar materials in the home     (Starting in 1990, mercury was eliminated from interior paints sold in the     United States.) 

Occupation and hobbies of all members of the household 

 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.

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.

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. 

 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.

 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.

   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.

 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.

   In adults, symptoms of toxicity begin to appear at blood mercury levels greater   than 5 µg/dL.

 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.

   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.

 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. 

Relationship of urinary mercury concentration to health effects         in adults

Urinary mercury
        concentration (µg/L

 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.

 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.

 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.

 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.

 Chelation is the only available intervention that reduces the body's burden   of mercury.

 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.

 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,

   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. 

Medical Management Guidelines for   Acute Chemical Exposures

 published by the ATSDR. ATSDR also   maintains a toll-free number for information on mercury and other toxic substances888-422-8737as   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 mercuryeasy to find and fun to play withis 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. 

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. 

Articles

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?