Mercury Poisoning

Picture of a blood sample about to be tested for mercury poisoning.

• Mercury is an element that is found all over the earth, in soil, rocks, and water. Even trace amounts can be found in the air. The largest deposits on earth are cinnabar (mercuric sulfide). Mercury exists in several forms such as a liquid metal (quicksilver), as a vapor, and in compounds (organic and inorganic). Scientifically, the symbol for mercury is Hg and its element number is 80.
• Mercury has been used for centuries as a medicine, to make amalgams, and in many industrial applications. Eventually, scientists, physicians, and others realized the various forms of mercury caused health problems. The phrase "Mad as a Hatter" originated in the 1800s from the observation that people (hatters) who used mercury to process felt for hats often developed mental changes.
• The problem with mercury is that if humans are exposed to it, depending on the amount (dose), route (ingestion, skin contact, inhalation), and duration (time) of exposure, mercury can be toxic to humans.
• Some elemental and chemical forms of mercury (vapor, methylmercury, inorganic mercury) are more toxic than other forms. The human fetus and medically compromised people (for example, patients with lung or kidney problems) are the most susceptible to the toxic effects of mercury.
• Although various forms of mercury can cause some different symptoms, the effects that are most toxic occur in the brain and nervous system.
• There are numerous items that contain mercury in various forms that can cause toxic exposure. They are present in many workplaces and in the home. For example, coal-burning power plants emit mercury (the highest source of mercury put into the air), home thermometers, "button" batteries, new energy-saving fluorescent light bulbs, and seafood (shellfish, tuna, marlin, and many others). Such items are all potential sources of mercury poisoning. However, guidelines are available for the prudent use, consumption, and disposal of items containing forms of mercury.
• Following guidelines can reduce or eliminate toxic mercury exposures.

Mercury binds to sulfhydryl groups in many tissue enzymes and proteins, and thereby causes direct damage to cells and their functions. This damage can be drastic and eventually precipitate failure of organ systems such as the lungs, kidneys or the nervous system.

Outbreaks of mercury poisoning usually occur when there is an industrial release of mercury or methylmercury into the environment. The classic example of such a disaster is the contamination of Minamata Bay in Japan, where the term Minamata disease originated. Studies from about 1956 to 1960 suggested the unusual symptoms (neurological) found in people in this area could be traced back to industrial wastewater containing methylmercury. Over 2,200 people were diagnosed and over 1,700 deaths were eventually attributed to methylmercury toxicity. Mercury has been used in skin creams. The most recent problem cream was identified in 1996 from Mexico named "Crèma de Belleza-Manning."

Mercury poisoning can be caused by all forms of mercury (elemental, vapor, inorganic, and organic). Poisoning of humans can occur from inhalation, ingestion, or skin contact with the various forms of mercury.

Inhalation Mercury Poisoning

Inhalation poisoning occurs when elemental mercury is vaporized, usually in a closed indoor space when products such as thermometers, medical equipment, valves, or other products are broken open and elemental mercury escapes. Any heating of elemental mercury increases its rate of vaporization (slow vaporization occurs at room temperature) which worsens inhalation exposure.

Ingestion and Skin Contact Mercury Poisoning

Ingestion is one of the most frequent ways in which people get mercury poisoning, and mercury is most frequently ingested in the organic methylmercury form of mercury. Methylmercury (also termed methyl mercury, monomethylmercury or monomethylmercuric cation) is generated by two general processes; as an industrial production byproduct and microbially produced when elemental and vaporized mercury eventually reaches the water.

Unfortunately, methylmercury enters the tissues of fish (and shellfish) where it remains. The more methylmercury that is present in the environment, the higher the concentration in the fish tissue. Methylmercury is not cleared out of fish tissue; the older and larger the fish, especially those fish that eat other fish (for example, shark, sailfish, tuna, and marlin) the higher the methylmercury levels can be in their tissue. People that eat a lot of these fish may get mercury poisoning.

Inorganic mercury (for example, mercury compounds in batteries) most frequently causes human toxicity when ingested or adsorbed by the skin. Many inorganic mercury compounds are caustic (dissolve tissue).

Symptoms of mercury poisoning can be numerous and may occur either rapidly or over long periods of time. In general, symptoms occur and progress more rapidly the higher the dose of mercury encountered. Exposure to the various forms of mercury can result in some similar and some different symptoms. Symptoms can be grouped into three categories based on the form of mercury toxicity:

1. elemental and vaporized mercury,
2. organic mercury, and
3. inorganic mercury

Elemental and Vaporized Mercury Poisoning Symptoms

Elemental mercury toxicity (which usually occurs in the vaporized form) can cause:

• mood swings, nervousness, irritability, and other emotional changes,
• insomnia,
• headache,
• abnormal sensations,
• muscle twitching,
• tremors,
• weakness,
• muscle atrophy, and
• decreased cognitive functions.

High exposure to elemental mercury can cause kidney malfunction, respiratory failure, and death.

Organic Mercury Poisoning Symptoms

Organic mercury toxicity (most frequently in the methylmercury form from ingestion), causes neurological malfunctions, and especially in a fetus, impaired neurological development. Other symptoms include:

• peripheral vision impairment,
• stinging or needle-like sensations in the extremities and mouth,
• loss of coordination,
• muscle weakness, and
• other impairments of speech and hearing.

Since many pregnant women have had methylmercury toxicity, the effects of this toxicity on their children were studied. Importantly, the fetal brain was shown to be very sensitive to methylmercury; developmental impairments such as reduced ability in thinking, attention span, memory, and most motor skills occurred in various degrees, often severe, even if the mother developed few if any symptoms.

Inorganic Mercury Poisoning Symptoms

Inorganic mercury toxicity often causes skin rashes and inflammation (dermatitis). If ingested, it can dissolve tissues and some may be absorbed by the intestinal tissue. Large amounts of ingested inorganic mercury may cause bloody diarrhea. Absorbed mercury can spread to other organ systems resulting in mental changes including mood swings and memory loss or renal damage. Muscle weakness may also occur.

Other Mercury Poisoning Symptoms

Many other symptoms and health problems have been attributed to mercury poisoning (for example, high blood pressure, endometriosis, headaches) in anecdotal reports in the popular press and in a few cases in scientific publications. Currently, there are no good studies to support these claims; however, if people have concerns about their symptoms and health problems related to mercury exposure, they should discuss their concerns with their doctor.

If any person suspects or knows that they have been exposed to any form of mercury, they should seek medical care immediately. If a child, teen, or adult is suspected or known to ingest a battery of any type, they should be brought to an emergency center. Early medical treatment may prevent or lessen the toxic effects of mercury poisoning.

Most physicians are urged to notify their local poison control center and a medical specialist in toxicology and use them as consultants. In the United States, the National Poison Control Center Hotline phone number is 1-800-222-1222.

Unfortunately, many people do not know they have been exposed to industrial or environmental sources of mercury. This makes the diagnosis difficult for the physician because many times the symptoms of mercury poisoning are subtle and may take weeks, months, or years to develop in some individuals. Consequently, physicians may order many different tests before, or at the same time as those listed below in an effort to diagnose the patient's condition from the many diseases [such as Parkinson's, amyotrophic lateral sclerosis (ALS, Lou Gehrig's Disease), dementia, and multiple sclerosis (MS)] and toxins (iron, arsenic, carbon monoxide) that produce one or more symptoms of mercury toxicity.

• Medical history and exam: A thorough history and physical exam may alert the physician to the potential for mercury poisoning if tremors and erethism (several neuropsychiatric problems concurrently such as anxiety, depression, memory loss, excessive shyness, and irritability) are present. Acrodynia (rash, fever, irritability, splenomegaly, and muscle weakness) can be seen in patients, especially children, exposed to most forms of mercury poisoning. If the person knows or suspects mercury poisoning, the physician needs to be told immediately.
• Blood tests: Acute mercury poisoning can be detected by measuring mercury levels in the blood. This test is usually done in a specialized laboratory. A normal mercury level is less than 10 µg/L (micrograms/liter) and less than 20µg/L in urine. Higher levels suggest toxic exposure. However, there are two problems with this test. First, the test on blood or urine should be performed five days or more after a person has stopped eating fish; because such a meal can raise the blood level of mercury higher than normal for a short (up to five days) time period. Second, it does not usually provide any valuable information about a previous short or chronic exposure. Further, urine tests are not reliable for measuring methylmercury or other compounds such as short-chained alkyl mercury compounds because they are mainly excreted in the feces and bile, respectively.
  • Tests to measure the ratio of mercury in blood plasma versus red blood cells are performed to help distinguish organic mercury poisoning from inorganic. Red cells concentrate on organic mercury but not inorganic mercury compounds. The concentration of organic mercury in red cells is about 20 times that found in plasma; the concentration of inorganic mercury at maximum is only about twice that found in plasma.
  • Other tests that are usually ordered are a complete blood count (CBC) and a fecal blood detection test to help determine if anemia or gastrointestinal bleeding has occurred.
• Imaging tests: Some doctors request an MRI scan to determine the extent of brain atrophy. X-rays are generally ordered for individuals that have ingested elemental mercury (for example, a broken mercury thermometer). X-rays show the movement and excretion of the X-ray opaque mercury.

Other than avoiding potential sources of mercury poisoning, there is no major role for self-care at home. However, in the prevention section below, precautionary actions are listed to help prevent exposure to forms of mercury at home and elsewhere.

Suspected and known exposure to all forms of mercury should be treated as soon as possible. Suspected acute exposure is treated medically because often waiting for confirmatory tests may allow irreversible damage to occur. Early consultation with poison control and a medical toxin expert is advised. In large outbreaks, city, state or national toxin control personnel may need to be notified to limit further toxic exposures to people.

In acute exposures, the first step in treatment is to remove the person from the mercury source and at the same time, protect others from coming in contact with it. If possible, the person's contaminated clothing should be removed and bagged for disposal, and the person thoroughly cleaned.

Acute inhalation of mercury vapor may require emergency respiratory support (bronchodilators or intubation) if the person inhales a large amount. Ingestion of the caustic inorganic mercury forms should not be treated with medications that induce vomiting (emetics), as vomiting may increase tissue exposure to the caustic toxin. In chronic exposures, the mercury source needs to be identified and then isolated from human contact.

Treatment varies with the form of mercury poisoning. Ingestion of a caustic inorganic form of mercury usually begins with the removal of the source (for example, a battery), usually by an experienced surgeon:

• If the inorganic form is in a liquid or edible form (not encased like a battery), activated charcoal should be used to bind and inactivate the toxin. "Aggressive" gastric lavage (cathartic and fluid washout of the stomach) is also recommended to remove both unbound and charcoal-bound toxins. Patients undergoing such treatment often need intravenous (IV) fluids because of toxin damage to the intestinal tract cells and profuse diarrhea due to the toxin damage to tissue and cathartics.
• Acute organic forms are treated in the same manner as inorganic, except the toxin usually does not immediately affect intestinal cells, so the treatment may be less "aggressive" with charcoal and a cathartic (laxative).
• Ingestion of elemental mercury (for example from a broken thermometer) usually has no effects on gastrointestinal cells unless the gastrointestinal tract is damaged (for example, in people with ulcerative colitis, fistulas, or diverticulitis) and a laxative will remove the elemental mercury. If the intestinal tract is damaged, then more "aggressive" treatment may be needed.

Further medical treatment usually is done with chelating agents that bind most toxic forms by competing for sulfhydryl groups that toxic mercury forms bind to in tissue cells. The agent often used is dimercaprol (BAL in Oil). Mercury forms chelated with dimercaprol may also be removed from the blood with dialysis. Dimercaprol should not be used with methylmercury exposure as it may increase the toxicity of the brain and spinal cord. Another chelating agent used for both organic and inorganic forms of mercury exposure (chronic and mild exposures) is DMSA [also termed 2, 3 – dimercaptosuccinic acid, succimer, (Chemet)].

Other treatments used by specialists are neostigmine (Prostigmin Bromide) to help motor function and polythiol to bind methylmercury in bile secretions.

The use of these medications, their methods of administration, and the amounts used are best determined for each individual patient in consultation with a toxin expert (toxicologist).

Important follow-up for all people exposed to mercury poisoning is to make sure that the source of mercury poisoning is completely removed or made inaccessible to everyone. This is sometimes difficult to accomplish if the source is industrial or environmental. Governmental regulatory agencies such as the EPA (Environmental Protection Agency) or OSHA (Occupational Safety and Health Administration) may need to be contacted to insure public safety from mercury poisoning.

Many patients that get mercury poisoning, especially organic mercury poisoning, develop neurological deficits. These patients may be referred to a neurologist for additional follow-up care and rehabilitation.

Prevention of mercury poisoning is difficult if the source of the mercury is unknown. Consequently, prevention of mercury poisoning begins with identifying the potential or known sources and stopping production or isolating the toxin so none will come in contact with people. These situations are usually found in industrial or environmental sources of mercury and may require both industrial and governmental assistance to design ways to prevent exposure to forms of mercury.

At home, there are a few mercury-containing items (for example, thermometers, medical devices, some disinfectants, and fluorescent light bulbs) that potentially can be the source of mercury poisoning. People are advised to read the labels on products to see if they contain mercury, have warning labels about potential toxicity, or have directions about how to dispose of a broken or non-useable product. The EPA has a detailed set of instructions about what to do and what not to do if mercury is spilled or a fluorescent bulb breaks in the home. The instructions also tell how to dispose of mercury-containing products.

Mercury Poisoning Prevention: Amalgam Fillings

People are also concerned about mercury found in dental amalgam fillings. However, the CDC has stated there is no good evidence that the small amount of mercury in amalgam fillings causes harm and that removing amalgam fillings does not benefit people. However, there are several other types of dental filling material that can be used so individuals are urged to discuss choices for dental fillings with their dentist.

Mercury Poisoning Prevention: Fish and Shellfish

Fish and shellfish are usually considered to be part of a healthy diet, but almost all contain traces of methylmercury. To prevent people from getting toxic methylmercury levels from eating seafood the FDA made these recommendations:

• Do not eat shark, swordfish, king mackerel, or tilefish because they contain high levels of mercury.
• Eat up to 12 ounces (two average meals) a week of a variety of fish and shellfish that are lower in mercury.
• Five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish.
• Another commonly eaten fish, albacore ("white") tuna has more mercury than canned light tuna. So, when choosing your two meals of fish and shellfish, you may eat up to 6 ounces (one average meal) of albacore tuna per week.
• Check local advisories about the safety of fish caught by family and friends in your local lakes, rivers, and coastal areas. If no advice is available, eat up to 6 ounces (one average meal) per week of fish you catch from local waters, but don't consume any other fish during that week.

Women who are trying to become pregnant, who are pregnant, or are breastfeeding should be especially careful about following these suggestions as the fetus, neonate, and infant brain and spinal cord seem especially sensitive to all forms of mercury poisoning.

Mercury Poisoning Prevention: Vaccines

Another source of concern for people is the use of thimerosal, a mercury-containing preservative used in vaccine preparations. Except for some influenza vaccines, it is not being used in most vaccines. However, the amount of mercury in thimerosal is very low. In 2008, the CDC recommended that current flu vaccines are safe to use in pregnant women and children because they contain very little mercury.

The prognosis for mercury poisoning depends on many factors:

• The chemical form of mercury (inhalation of vapor is worse than inorganic which may be worse than organic)
• The dose or amount of mercury poisoning (more leads to poor outcomes or death)
• Age of person (fetus, neonate, and infants more susceptible to lower doses of mercury)
• Length of exposure (longer exposures result in poor outcomes or death)
• Route of exposure (inhalation is worst, followed by ingestion, and then skin exposure)
• Person's overall health before exposure (people with preexisting medical problems do worse than healthy people)

Early treatment of any form of mercury poisoning has a good chance of improving the prognosis (reducing tissue damage and neurological effects of the toxins). Unfortunately, if the diagnosis and subsequent treatment are delayed, which has happened often in the past, many outcomes are only fair to poor with the patient experiencing residual or profound neurological deficits. This outcome is often seen with organic mercury poisoning because exposure usually occurs over a long length of time before characteristic signs and symptoms develop.