Remember the Mad Hatter? He was one of the more rambunctious guests at the tea party in Alice’s Adventures in Wonderland, by Lewis Carroll. He greased his pocket watch with butter and dipped it in his tea when it wouldn’t keep time. He was rude and irrational, and he thoroughly frustrated Alice. No wonder — the Mad Hatter was not a well man. In the 1800s, when Carroll wrote about Alice, the hat makers used mercury nitrate in the felting process and were constantly exposed to it. Many developed mercury poisoning and suffered from dementias, thus the phrase “mad as a hatter.”

Mercury poisoning still threatens the health and lives of humans, and nurses have much to learn about potential sources of poisoning, prevention, and assessment.^1,2 Although there is no known treatment as yet to reverse the damage caused by this heavy metal element, found in liquid, solid, and vapor forms, sometimes chelating agents are used to attempt to reduce levels.

Because of its solubility in fatty tissues, methyl mercury, the form ingested by humans and animals, is one of the most toxic forms of mercury — five to 20 times more toxic than inorganic mercury. By inhibiting the processes in the brain involved in neuronal cell division and migration, it is thought methyl mercury causes a loss of neuronal cells in specific areas of the brain.³ If toxic levels are reached, irreversible neurological and renal damage may occur. According to Thomas Clarkson, PhD, chairman of the Department of Environmental Medicine at the University of Rochester in New York, a leader in studying the effects of mercury on humans for decades, stringent measures to prevent methyl mercury poisoning are necessary because of the slow onset of action and irreversible nature of the damage for both prenatal and adult poisoning.³ As a former member of the advisory committee for the World Health Organization (WHO), he followed many of the victims of the Minamata, Japan, poisoning for years. This disaster, caused by the ingestion of fish contaminated by tons of mercury-tainted industrial waste dumped into Minamata Bay, made worldwide headlines in the 1950s.

Mercury Poisoning — Infiltrating the Food Chain

In the general population, the presence of mercury in the food chain has become the most significant pathway for mercury exposure throughout the U.S. and the entire world. Since the industrial revolution and even more so since the 1950s, scientists have noticed increased levels of mercury in the environment. Air pollution and mercury emissions from human-related activities, such as the use of incinerators, are major culprits. As of May 22, 2007, all 50 states in the U.S. have issued health advisory warnings about mercury contamination in fish. We now have 100% of the states in this country with mercury fish advisory warnings. Each year the number of states with advisories has steadily risen rather than decrease. Hundreds of thousands of miles of our rivers and lakes are contaminated with mercury and that doesn’t include our coastlines. This problem has become so widespread that most of the U.S. coastline is covered by mercury fish consumption advisories. The advisories specify which fish are safe to eat and which to avoid; they also indicate safe consumption levels of contaminated fish.⁴

When mercury levels in the fish, the food most commonly involved, exceed 0.5 ppm, an advisory is issued by the state. Levels of mercury in the fish in some contaminated waters have been reported to be as high as 7 ppm to 8 ppm.^5,6,7 Moreover, contaminated fish cannot be trimmed of its mercury, since the toxic metal is found throughout the entire fish.

Some ocean fish that remain contaminated with high levels of methyl mercury include shark, swordfish, king mackerel, and tilefish.⁷ Canned light tuna contains less mercury than the canned white albacore tuna.⁴

Lakes, rivers, canals, and parts of the ocean all over the world contain varying levels of mercury. For example, in Florida, fish samples continue to show abnormally high levels of mercury and pose a threat to public health. For the first time, in 1992, 11 adults and three children who fished the canals in the Everglades were tested for the presence of mercury in their hair, an indicator of mercury in body tissue. All 14 showed some amount.⁸ Five had amounts above the WHO acceptable limit for mercury, which is 2 ppm, the same as the FDA’s acceptable limit.^9,10 Several years later, a study by the University of Miami researchers found even more people with elevated mercury levels.¹¹

Unfortunately, many people in the U.S. and throughout the world are unaware of mercury advisories or openly ignore them. Subsistence fishermen, in many instances, have no choice but to continue to use the fish to supplement their families’ diets.

Mercury exposure can also occur in other ways. In the dentist office, those who constantly work with mercury products, such as amalgam fillings, can be at risk. In addition, those involved in religious rites for healing or purification that incorporate metallic mercury are in danger. Practices might include heating mercury on a stove and sprinkling it around the house or automobile, or burning it in candles for good luck. Some might ingest mercury to treat conditions such as constipation or colic, or carry or wear it in the form of a charm, such as a small vial that can easily break open.^6,9,12

Controversy has existed for some time on the safety of a mercury compound called thimerosal, a preservative used in common vaccines administered to children and adults. Thimerosal is metabolized to ethyl mercury that might be equivalent to the toxicity of methyl mercury.^9,13 A 2000 joint policy statement of the American Academy of Pediatrics, the American Academy of Family Physicians, and other organizations reiterates the AAP’s 1999 policy statement and recommends continuation of the policy of moving rapidly to vaccines that are free of thimerosal as a preservative. In fact, many manufacturers now supply a number of thimerosal-free vaccines. The joint statement also indicates that until an adequate supply of each vaccine is available, use of vaccines containing thimerosal as a preservative is acceptable. Moreover, the AAP has stressed the need to continue vaccinating infants because of the known serious risk of many childhood diseases.¹⁴

On April 2, 2004, H.R. bill 4169 was introduced to the Committee on Energy and Commerce to amend the Federal Food, Drug, and Cosmetic Act to reduce human exposure to mercury through vaccines.  This act is cited as the “Mercury-Free Vaccines Act of 2004.”¹⁵ However, as of May 2007, there are still six major vaccines that contain mercury.¹⁶ In three years, since that bill was passed, we have not resolved entirely the problem with mercury in our vaccines.

Testing for mercury

Levels of mercury in hair and blood are the best indices of exposure to methyl mercury.⁹ Blood levels are predictive of levels in the brain, the main organ the mercury is seeking.³

Hair sampling, a proven, reliable method for mercury detection, is easier and less invasive than blood sampling. Hair is also easily stored and transported. Scalp hair is an excellent indicator of blood levels of methyl mercury and can also determine blood levels acquired months or years before the collection of the hair sample. The hair levels can be used to assess past exposures and maternal exposure after the birth of an affected infant. Transient increases become apparent from measurements of mercury levels in the hair.³ Once the mercury is incorporated into the hair, its concentration remains constant; its concentration in cord blood and maternal hair correlate.³

An insidious invader

Mercury poisoning received little attention until data became available about the illness and deaths of children and adults in Minamata in the 1950s and 1960s, and in Iraq in the 1970s. Hundreds died, and thousands became ill when they ate food highly contaminated with mercury.⁵ Studies from the Minamata poisoning epidemic showed that a prolonged period of 10 years or more could occur between exposure to methyl mercury and the appearance of symptoms and effects of poisoning, particularly the neurological symptoms, which can progress over a period of years after exposure ends.⁹

Methyl mercury toxicity from ingestion of contaminated fish builds up rapidly in the brain. After ingestion, about 90% to 95% of methyl mercury is absorbed through the gastrointestinal tract in humans.⁹ The methyl mercury binds with red blood cells rather than plasma. Because it is also lipid soluble, methyl mercury diffuses through cells in the brain. In humans, at high blood-mercury concentrations, there is evidence that approximately 10% of the ingested methyl mercury accumulates in the brain, 5% in the blood, and the rest is evenly distributed throughout other tissues.⁹

Children’s nervous systems continue to develop until about the age of 14 years old.⁴ Children, and especially fetuses, may be particularly vulnerable to methyl mercury.^5,9 Methyl mercury compounds pass easily through the blood barrier and the placenta, causing damage both pre- and postnatally.^6,9 Subtle neurological impairments may occur even at low to moderate levels.

Since the methyl mercury readily crosses the human placenta, levels have been shown to be 30% higher in fetal red blood cells than in the mother’s red cells. This might be due to accumulation of methyl mercury in cord erythrocytes or possibly to the different chemical structure of fetal and adult hemoglobin.⁹ The brain is methyl mercury’s principal target in the fetus.

Pathological changes in the fetus, like the adult, consist of cortical damage and damage to the granular layer of the cerebellum. But the infant brain shows developmental deficiencies in actual brain structure, such as hypoplasia and malformations. In Minamata, fetal brain lesions appeared more diffuse than in the adult, and in Iraq, abnormal neuronal migration in the cerebellum and cerebrum was evident.³

In the fetus, it is not known for certain if inorganic mercury or methyl mercury is more acutely toxic. For the unborn, methyl mercury is by far the most hazardous form of mercury for chronic exposure. Some studies suggest that duration of exposure to methyl mercury is extremely important to the development of toxic effects in both the adult and fetus.

A report released to the public in December of 2000 by the Environmental Protection Agency (EPA) estimated that 60,000 children in the U.S. were at risk of developing nervous system damage because of their mothers’ exposure to mercury.⁵ Now it is estimated that one in six women of childbearing age in the U.S. has levels of mercury in her blood sufficiently high enough to cause potential problems. That puts four million babies at risk of health problems.⁵ Unlike most other poisons, methyl mercury penetrates the blood-brain barrier, making it more toxic for the developing fetus.^7,9,16 Mercury poisoning epidemics in the past have had disastrous outcomes, such as stillbirths, prenatal mortality, and severe infant neurological disabilities.

Methyl mercury is excreted into breast milk. However, the concentration in breast milk is approximately 5% of the blood concentration.⁹ It is important to know an exposed mother’s mercury level before she begins to breastfeed. In Iraq, it was found that the infants’ blood-mercury levels were higher than their mothers’ levels for over four months after birth. Blood-mercury levels in the breastfed infants were maintained by the passage of methyl mercury via maternal milk.¹⁷

Children poisoned prenatally resemble those with cerebral palsy; they can be spastic, blind, deaf, and severely mentally impaired. Even at relatively low exposure levels, children may be affected with developmental retardation and mild neurological abnormalities.^6,17

In Minamata, 6% of the children who developed cerebral palsy were born to mothers who generally had no overt symptoms of methyl mercury poisoning during pregnancy or at the birth of their children, although some experienced mild paresthesia.³ Microcephaly was observed in 60% of congenital Minamata disease cases.³ Beginning in the sixth month postnatally, the affected infants began to show instability of the neck, experienced seizures, and were unable to track an object with their eyes. Common symptoms included intellectual impairment, appearance of primitive reflexes, dysarthria, hyperkinesia, and hypersalivation. These signs occur with cerebral palsy in general, but these children exhibited a more marked degree of impairment of intelligence and cerebellar symptoms.

Another study from Iraq showed that many of the infants initially noted as being free of symptoms subsequently developed neurological signs and had delays in psychomotor development. Since there was no case-matched control group of infant-mother pairs, the abnormalities could not be conclusively attributed to in utero methyl mercury poisoning. The authors reported the infants with prenatal exposure suffered permanent damage.³

In chronic exposure for children and adults, the onset of symptoms is insidious and vague. Paresthesias with numbness and a tingling sensation around the mouth, lips, fingers, and toes are usually the first clinical symptoms noted in adults. Ataxia is the next progressive symptom, along with dysarthria, constriction of the visual fields leading to tunnel vision, and impaired hearing. Generalized muscle weakness, fatigue, headache, irritability, and inability to concentrate often occur. Dementia can develop. In severe cases, myoclonic tremors occur, often followed by coma and death.

Prevention — it’s elementary

The risk of mercury poisoning and especially congenital methyl mercury poisoning in newborn infants has definitely increased, especially in the United States and other countries known to have a problem with excessive levels of mercury in the food chain for humans.^1,2 A recent study done in Baltimore, Maryland showed that 9% of the tested subjects had blood mercury levels exceeding the EPA recommended levels.¹⁸

To safeguard public health, aggressive programs must be started to inform the public of the hazard that exists. This can be difficult since the advisories, which are not standardized, from the EPA and HRS change, depending upon the level of mercury in the fish and the creation of new contaminated waterways. The number of advisories in the U.S. has steadily increased over the last three years. But, it remains very difficult to obtain current state advisory lists. Plus, in some states, the guidelines continue to be difficult to understand. In their role as advocates, nurses may need to lobby their lawmakers and insist on clear and available guidelines for the public and healthcare providers. Guidelines produced by the Agency for Toxic Substances and Disease Registry (ATSDR) and the EPA include “Should I Eat The Fish I Catch?” (EPA document # 823F97009) and “Guide to Healthy Eating of the Fish You Catch” (EPA document # 823F02005), and the EPA’s Roadmap for Mercury, July 2006. The general public can obtain them by contacting the EPA’s National Service Center for Environmental Publications (see the “Resources” sidebar).

Health Care Without Harm, a position statement published by an international coalition of 28 organizations, including physicians, nurses, environmental organizations, and many others, urges nurses to eliminate sources of environmental harm in healthcare practice.¹⁹ For example, proper disposal of mercury-laden products, such as mercury and fluorescent light bulbs, can decrease pollution. Since mercury vaporizes, increasing exposure, vacuuming a spill from a thermometer is not recommended. Likewise, children should never play with the mercury.

According to the EPA, the health care sector ranks as the fourth-largest source of mercury air emissions. The Hospitals for a Healthy Environment program had set a goal to almost eliminate mercury from its waste by the year 2005.²⁰ Unfortunately, this hasn’t happened yet.

Power plants are the major contributors to mercury pollution. The mercury emissions from coal-fired power plants need to be decreased, as they are contributors to a large share of the U.S. mercury emissions. However, power plants continue to be the only major mercury polluters yet to be regulated under the federal clean air standards.⁵

The latest EPA mercury report states that one in six women of childbearing age (i.e., ages 15 to 44) are at risk.¹ For these women, in particular, screening for the presence of mercury can be important. “Do you use or work with mercury products, such as a dentist’s assistant mixing amalgam material?” and “Do you eat fish caught from local waterways?” are two key questions nurses should include in initial prenatal assessments. In particular, as part of all obstetrical/medical histories, caregivers should ask if women eat any fish from local contaminated zones. A list of these zones is available through the local health department.

If possible exposure to mercury exists, hair samples and/or blood samples for mercury levels are essential. Likewise, the medical history can include more questions about potential exposure related to occupation, eating habits, or religious practices. People with abnormal findings through history and/or testing require close follow-up and a neurological exam.

Infants whose mothers have been exposed to mercury require postnatal testing of their levels through hair, blood, or cord-blood samples. Supportive care including developmental follow-up exams for adults or older children with any of the signs and symptoms of mercury poisoning must be readily available.

Although the public must become aware of their local health advisory to limit their consumption of contaminated fish, and in some cases, not to eat the fish at all, this cannot be the final answer to prevent mercury poisoning. Many who fish the contaminated waterways depend on this source of food to supplement their nutritional needs. In the meantime, warning signs along the contaminated waterways must be posted and visible.

One other potential source of mercury exposure could be the new energy-efficient compact fluorescent light bulbs that are becoming more common to use in our homes.  These bulbs have about five milligrams of mercury sealed inside. Considered safe to use in the home, used bulbs should be recycled or placed in a  sealed plastic bag,  and disposed of in the local hazardous waste disposal site. If one breaks, do not allow children or pets in the area and open the window for at least 15 minutes. Use disposable gloves and scoop up the material with stiff paper or cardboard. Use sticky tape to pick up small pieces and powder, then clean the area with a damp paper towel and dispose of the debris in the outside trash can. Never use a vacuum to clean the spill. The vacuum will only disperse the mercury vapor and leave the particles trapped inside the cleaner bag.²¹

Aggressive programs need to be initiated to eliminate known mercury point sources as soon as possible. As protectors of the public health, nurses are in a position to educate the public, especially pregnant women, and prospective new mothers about the dangers of mercury poisoning.