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Mercury poisoning is a type of metal poisoning caused by Hg exposure. Mercury is a highly toxic element; however, only a few cases of Hg poisoning have been reported. Formerly, it has been used as a component of ointments, parasiticides, antiseptics, disinfectants, diuretics, and fungicides. When Hg is found in seed-dressing fungicides, anti-slime fungicides in the pulp and paper industry, by-products of coal combustion, mining tailings, and wastes from the chlorine-alkali industry, it can cause environmental contamination. Muscle weakness, poor coordination, numbness in the hands and feet, skin rashes, memory issues, difficulty speaking, hearing, or seeing are all possible symptoms.

The majority of exposure is attributed to eating fish, amalgam-based dental fillings, or workplace exposure. Chelation with dimercaptosuccinic acid or dimercaptopropane sulfonate, if given within a few hours of exposure, tends to improve outcomes in those who have been poisoned by inorganic Hg salts. Acrodynia, commonly known as Pink disease, is a condition in which the skin turns pink and peels because of mercury exposure in children. Hg comes in various different forms, including metallic mercury, a gleaming, silver-white, odourless liquid that, when heated, transforms into a colourless, odourless gas. Methylmercury is a compound composed of mercury and carbon mostly formed in water and soil by small organisms. When Hg reacts with elements such as chlorine, sulphur, or oxygen, it forms Hg salts that are either white powders or crystals. Metallic Hg and methylmercury are more toxic than mercury salts because they can promptly enter the brain.[1,2,3]

Symptoms

The symptoms of Hg poisoning vary as per the type of Hg used in the exposure. A metallic taste in the mouth, as well as numbness and tingling in the hands, feet, and face, are early signs of Hg poisoning. Hg can have adverse implications long before symptoms appear. If you think you have been exposed to mercury, regardless of your symptoms, you should see a doctor right away.[2,4]

Symptoms of methylmercury poisoning from fish

The majority of humans have some methylmercury in their tissues, although it is at a safe level. Excess methylmercury has a negative impact on the nervous system. This is particularly harmful to foetuses, infants, and children because their brains and nervous systems are still growing.

Methylmercury poisoning may lead to disturbances in speech, walking, and hearing. Muscular strength is affected by peripheral visual sensation, particularly on the hands, feet, and mouth.

Symptoms of poisoning from elemental Hg

If mercury spills from a thermometer or other Hg-containing instruments, this type of poisoning is most likely to occur. Inhaled Hg vapour is a common cause of poisoning, particularly in settings with poor ventilation. The signs and symptoms are listed below:

• Tumours/headaches


• Having problems in sleeping and having impaired senses


• Emotional changes, muscle weakness, and twitching (mood swings, irritability, nervousness)


• Kidney failure


• Death because of breathing difficulties

Symptoms of poisoning from inorganic Hg

Industrial exposure is more likely to cause this sort of poisoning. The following are signs and symptoms of inorganic Hg poisoning:

• Skin problems such as rashes and dermatitis


• Breathing difficulties


• Difficulty with memory mental health issues mood swings


• Muscle strength declines

Causes And Risk Factors

Causes

Hg toxicity can occur when you are exposed to dangerous levels of Hg because of a variety of factors.

• Breathing in Hg vapours from the air


• Consuming tainted food, particularly fish or shellfish—the highest levels of Hg are found in larger and older fish.


• Hg-contaminated drinking water (rare)


• Utilizing Hg in religious or folk medicine rituals.

Metallic Hg can be reported in a variety of consumer products, including compact fluorescent lamps, battery packs, heating systems, and old thermometers.

Hg, along with other elements, can be reported in certain dental fillings. This type of filling has not been shown in studies to be harmful to people. Some vaccines contain thimerosal as a preservative. It contains a trace amount of mercury, but many studies have shown that it is not harmful to humans.[2,4]

Risk Factors

The impact of Hg exposure varies as per the type of Hg. Hg, in general, has a negative impact on the nervous system. This puts unborn babies and children at greater risk because their nervous systems are still developing.

Mercury exposure puts the following people at a higher risk:

• Unborn children


• Toddlers and children up to the age of six years


• Workers in industrial settings where Hg is used or produced,


• People with kidney disease

People who were born before the 1950s and were exposed to Hg in baby products developed the pink disease

Tell your doctor if you have any of the following risk factors:

Working in:

• Dental field


• Health-care services


• Chemical manufacturing industry


• Other industries that make use of Hg include electric meter repair.


• Consuming more than 6 ounces of white albacore tuna per week


• Consuming more than 12 ounces of Hg-free fish and shellfish per weeks such as shrimp, canned light tuna, salmon, pollock, and catfish


• Performing rituals involving Hg

Furthermore, pregnant women, their unborn foetuses, and toddlers are especially vulnerable to Hg’s harmful effects.

Prevention

Below are the preventive measures that help to reduce the chances of Hg toxicity:[2]

• Any use of metallic Hg should be avoided.


• If you must use metallic Hg, put it in a leak-proof container in a secure location such as a locked closet.


• Handle and dispose Hg-containing goods with care such as thermometers and fluorescent light bulbs.


• Spilled Hg should not be vacuumed or heated.


• Teach your kids not to experiment with silver liquids.


• Dispose of old Hg-containing medicines properly.


• Keep Hg-containing medicines out of the reach of kids.


• Inquire with your local public health or natural resources agency about animal and fish advisories in your region.


• Limit your fish intake to the prescribed amounts and avoid fish that have been shown to be tainted with Hg.


• Shark, swordfish, king mackerel, and tilefish should not be eaten.


• Consume up to 12 ounces of Hg-free fish and shellfish each week. Shrimp, canned light tuna, salmon, pollock, and catfish are examples of these fish.


• Consume no more than 6 ounces of white albacore tuna each week.

If you intend to consume local fish, ensure that the water is not polluted. Limit your consumption of local fish to 6 ounces in general.

Even if a little quantity of metallic Hg is spilled:

• Remove children from the area


• Do not use a vacuum cleaner


• Carefully roll the Hg bead onto a sheet of paper or suck it up with an eyedropper.


• Place the bead in an airtight bag or container.


• Identify how to properly dispose of Hg, paper, or eye dropper by contacting your local health agency.


• Ventilate the room by opening the windows.


• For at least 1 h, use fans to increase ventilation.

Diagnosis

Hg levels may be determined in both whole blood and urine. Hg levels in whole blood can be used to detect acute exposure; however, when Hg redistributes into tissues, blood levels will fall even as organ damage develops. Hg levels in whole blood are reported to be <10 µg/L. Urinary Hg levels can indicate acute exposure but are more effective in determining chronic exposure compared to whole blood. Urine samples are collected on the spot and every 24 h. Your doctor will inquire about your probable exposure history and may monitor your temperature, heart rate, blood pressure, and respiration. Hg values (<20 µg/L) in urine are considered normal. Because organic Hg is removed through faeces rather than urine, urine testing plays a minimal role in the workup of individuals who may be poisoned from organic Hg. Furthermore, “normal” blood and urine Hg levels should be interpreted with care. There is no consistent relationship between levels and toxicity. Some people can have very increased levels with no symptoms; however, others will develop toxicity with only moderately elevated amounts. Furthermore, falsely high levels from recent seafood consumption or herbal treatments might make blood level interpretation problematic. Organic and inorganic Hg can be distinguished, although this is not done on a regular basis.[4,5]

Treatment

Because absorption from the stomach is so fast, treating persons is typically problematic. When therapy is available, the stomach should be emptied and milk or raw egg white should be administered to precipitate Hg. Dimercaprol (BAL) is the preferred therapy, which is combined with substantial quantities of intravenous fluids to avoid dehydration. If Hg poisoning is suspected in severely ill patients, your doctor would most likely treat you with chelation treatment, regardless of the type of Hg that caused poisoning. Chelation treatment entails injecting a substance called a chelating agent into the circulation. The chelating agent binds to Hg and helps in its removal from the body. Chelating drugs can be orally or intravenously administered.[1,4]

Activated charcoal, sodium thiosulphate (to bind Hg), saline cathartic, and oral d-penicillamine are used in treatment. D-penicillamine is only effective if the gut is devoid of substantial absorbed Hg and if the renal function is normal. After persistent exposure to organic mercurials, BAL is ineffective.[2,6]

References

1. Mercury Poisoning. Michigan.gov. Available at: https://www.michigan.gov/dnr/0,4570,7-350-79136_79608_85016-26953--,00.html. Last Accessed: 16 August 2021. (https://www.michigan.gov/dnr/0,4570,7-350-79136_79608_85016-26953--,00.html)


2. Mercury toxicity. WinchesterHospital. Available at: https://www.winchesterhospital.org/health-library/article?id=120797. (https://www.winchesterhospital.org/health-library/article?id=120797)


3. Mercury Poisoning. Osmosis. Available at: https://www.osmosis.org/learn/Mercury_poisoning. (https://www.osmosis.org/learn/Mercury_poisoning)


4. Mercury exposure and poisoning. BetterHealth. Available at: https://www.betterhealth.vic.gov.au/health/HealthyLiving/mercury-exposure-and-poisoning. (https://www.betterhealth.vic.gov.au/health/HealthyLiving/mercury-exposure-and-poisoning)


5. Mercury. California Poison Control System. Available at: https://calpoison.org/news/mercury. (https://calpoison.org/news/mercury. Last Accessed: 16 August 2021)


6. Mercury Poisoning. NDVSU. Available at: https://www.ndvsu.org/images/StudyMaterials/Pharma/Mercury-poisoning.pdf. (https://www.ndvsu.org/images/StudyMaterials/Pharma/Mercury-poisoning.pdf)