Mercury is a heavy metal found naturally in water, air, and soil. Excessive exposure to mercury through consumption of fish, through dental amalgam fillings or subjection to mercury gas may lead to toxic levels of the metal in the body – a condition called mercury toxicity or mercury poisoning. Exposure to industrial waste containing mercury with neurological impairment is called Minamata disease. Symptoms occur when normal kidney function is insufficient to remove mercury.
Definition & Facts
Certain fish and shellfish contain a very toxic form of mercury buildup, called methyl mercury. Methyl mercury is released into the atmosphere via coal burning, mining and chloralkali manufacturing. It then dissolves into fresh or sea water, where it is absorbed by marine life.
Sushi is prepared using fish likely to contain methyl mercury, such as swordfish, ahi, marlin, shark and mackerel. 80 to 90 percent of mercury poisoning cases occur from eating fish.
High levels of mercury retained in the body can harm the brain, heart, lungs, kidneys, and immune function. Unborn children are very susceptible to poisoning and may suffer brain damage leading to learning disabilities and impairment with social functioning. Mercury toxicity builds up very slowly in the adult body, so the poisoning symptoms are not recognized immediately.
Symptoms & Complaints
- Blurred vision
- Loss of hearing
- Unsteady gait
- Cognitive impairment
- Emotional lability (when a person cries or laughs uncontrollably)
Elemental mercury exposure, such as that from mercury fillings, may include vomiting, sore gums and a metallic taste in the mouth. The 'classic triad' of symptoms for elemental exposure include tremors, gingivitis and erethism. Erethism is common in the chronic phase of mercury toxicity and involves emotional lability, insomnia, and anxiety.
Mercury accumulates in the body via ingestion, inhalation, and direct contact with substances containing mercury. Improperly cleaning up after household items (batteries, barometers, for example) that contain mercury can be a source of mercury toxicity.
Mercury in dental amalgam fillings releases subtle emissions of mercury gas, which gradually accumulate in the body. Vulnerability will depend upon how many fillings are present and how old they are, as fillings will wear and leak in time. Cosmetic products also contain mercury.
In September 2016, a study was published determining that amalgam fillings contribute strongly to chronically high systemic mercury levels. The University of Georgia reported that individuals with eight or more amalgam fillings had 150 percent more mercury in their bloodstream than those who had no fillings. 25 percent of Americans have 11 amalgam fillings or more. Persons most at risk are those with several amalgam fillings and exposure to mercury through work environments or consumption of suspect seafood.
Diagnosis & Tests
A history of symptoms and physical examination is helpful in determining high levels of mercury. Clinical urine tests can be used to assess metallic or inorganic forms of mercury accumulation, but the urine test cannot determine exposure to methyl mercury. Whole blood mercury levels, with complete blood count (CBC) may be requested to determine anemia as result of kidney failure or gastrointestinal hemorrhage. Acute toxicity will be noted through high mercury blood levels. Paresthesias, or abnormal tingling and prickling in nerves, is expected with mercury blood levels higher than 20 mcg/dL.
Occasionally, nerve biopsies are ordered, due to the altered gait and postural unsteadiness sometimes present. Neuroimaging scans like magnetic resonance imaging (MRI) scans may be ordered for cognitive complaints. The MRI is more likely to rule out other cognitive disease than to determine mercury poisoning, but pathological findings due to mercury poisoning may be visualized. Patients with inorganic poisoning have presented with mild cortical atrophy.
Hair and toenail analysis can measure long-term mercury exposure, and cerebrospinal fluid may be obtained to measure mercury concentrations as well. The cerebrospinal fluid will measure chronic exposure, as abatement of exposure will clear the spinal fluid within several months.
Electrophysiology studies may show evidence of sensorimotor neuropathy or numbness people subjected to mercury vapors. Electrophysiology examines the electrical phenomena that determines nerve impulses and reactions.
Treatment & Therapy
Once toxicity is determined, immediate removal of an individual from the source of poisoning will be ordered. If symptoms are obvious, removal from sources of food or employment environment will be advised before extensive laboratory tests are completed.
Neurological symptoms of Minamata disease are not reversible. Management to reduce the burden of toxicity on the body and minimize further damage is the goal. Patients with critical symptoms are placed in an intensive care unit (ICU) to stabilize the illness and decontaminate the body. Renal function will be closely watched to determine if failure is possible due to ingestion of inorganic mercuric salts. Patients should be managed by physicians knowledgeable about mercury poisoning and toxicology.
Hemodialysis will be ordered in cases where renal function is no longer optimal. This form of dialysis has been successful to chelate, or remove, mercury toxins. Unfortunately, chelation removes only part of the body's toxic storage of mercury. Sometimes clinical deterioration of a patient may occur with chelation therapy. Surgery has been performed to remove subcutaneous mercury deposits successfully.
Prevention & Prophylaxis
One should should their state's department of environmental quality in order to determine what the safe procedure is in the event of a mercury spill. One should not dispose of a mercury container into a recycle bin.
Due to the devastating consequences of mercury poisoning, the World Health Organization has limited the amount of mercury content allowed in foods such as fish before they are marketed. Awareness of mercury and it's toxicity has lead to recommendations that consumption of certain fish be regulated to several times weekly, and not consumed as an everyday meal.