Is There a Cure for Thallium Poisoning?

Thallium is a highly toxic heavy metal with no known biological function. It is widely used in the manufacturing, chemical, and fireworks industries, as well as in medical imaging. Pure thallium is a bluish-white metal found in trace amounts in the earth's crust. 

• In the past, thallium salts were used to treat syphilis, gonorrhea, tuberculosis, and tinea corporis (ringworm)
• Other applications included being used as a hair removal agent for excess hair and in formulations such as rat poison and ant killer. 

However, in the early 1930s, numerous cases of thallium poisoning were reported, with some resulting in death. The commercial use of thallium in the United States was prohibited by the mid-1970s. The lethal dose for adults is about 12 mg/kg.

Present-day applications for thallium include:

• Electronics manufacturing
• Optical glass manufacturing
• Medical imaging

Thallium is largely utilized in the production of electrical devices and switches, primarily for the semiconductor industry.

Thallium is primarily released into the environment by burning and smelting coal, wherein it is a trace contaminant of the raw materials. It does not degrade and persists for a very long time in the soil, water, and air. Rain and snow remove some thallium compounds from the atmosphere. As it enters the food chain, it is absorbed by plants. Moreover, it gets accumulated in fish and shellfish.

The exact mechanism of thallium poisoning is unclear, but it usually results from toxic or prolonged exposure to this heavy metal. Thallium is easily absorbed through the skin and inhalation. Even nonlethal doses of thallium cause toxic effects; however, prolonged exposure may result in accumulation and chronic poisoning.

The following are the safe limits of thallium for the human body:

• The occupational limit for thallium exposure to the skin is 0.1 mg/m3 for eight hours per day.
• Levels above 15 mg/m3 are considered immediately hazardous to health.
• The lethal dose is approximately 15 to 20 mg/kg body weight and is rapidly distributed throughout the body's tissues.

The kidneys may excrete up to 35 percent of thallium, but the majority is eliminated through feces. Nevertheless, chronic toxicity and buildup may result from prolonged exposure.

Potential causes of prolonged exposure include:

• Eating food contaminated with thallium, such as fish and shellfish (a major source of exposure for most people)
• Breathing workplace air in industries that use thallium
• Smoking cigarettes
• Living near hazardous waste sites containing thallium
• Accidental ingestion of rat poison
• Deliberate poisoning

The industrial wastes released by factories contain harmful metallic compounds, such as arsenic and thallium, which are consumed by fish and other living organisms in river water. Humans consume these fish, which is harmful to their health. It's also illegally sold and mixed with drugs, such as cocaine and heroin.

The triad of gastroenteritis, polyneuralgia, and alopecia is the classic syndrome of thallium poisoning. Thallium poisoning can be acute, subacute, or chronic. Acute thallium poisoning, which is the most common form, develops quickly and is caused by short exposures to high doses.

The following is the timeline of symptoms:

• Gastrointestinal and/or renal symptoms: Appear one to five days after ingestion.
  • Nausea
  • Vomiting
  • Abdominal pain
  • Diarrhea
  • Stomatitis
  • Liver and kidney dysfunction
• Neurologic symptoms: May develop two days after ingestion.
  • Pain and paresthesias of the lower extremities
  • Motor weakness
  • Respiratory paralysis
  • Nystagmus
  • Ophthalmoplegia
  • Visual loss
  • Convulsions
  • Ataxia 
  • Confusion
  • Hallucinations
  • Coma
• Dermatologic symptoms: Develop 15 days after exposure.
  • Alopecia or hair loss (may appear within one to three weeks of thallium poisoning)
  • Most significant hair loss is seen on the scalp but may also involve the lateral eyebrows
  • Mees' lines on the nails
  • Scaling and acne-like lesions

Other symptoms may include:

• Anxiety
• Anemia
• Delirium
• Psychosis
• Agitation and aggression
• Personality changes
• Depression
• Apathy
• Abnormal color vision
• Shortness of breath
• Pleuritic chest pain
• Renal injury
• Tachycardia

Respiratory failure can lead to death. Chronic thallium poisoning is uncommon and usually results from a low level of exposure sustained over time. Symptoms may include:

• Tiredness
• Headaches
• Depression
• Lack of appetite
• Leg pains
• Hair loss
• Disturbances of vision
• Symptoms of neuropathy

Patients who receive appropriate treatment may recover significantly from the effects of thallium poisoning. Even with treatment, some patients may experience residual paresthesias.

Treatment options in patients with thallium poisoning depend on signs and symptoms and the level of thallium toxicity.

Emergency and supportive measures

• Maintain an open airway and assist with ventilation as needed.
• Seizures and comas should be treated if they occur.
• Intravenous (IV) blood transfusion is recommended for anemic patients.
• Fluid replacement through IV is used to treat gastroenteritis.
• Treat hypotension and symptoms of shock with IV fluids and vasopressors (only if necessary).
• IV electrolytes are recommended if electrolytes, such as potassium, are low.
• Maximize hydration to increase renal thallium clearance.
• Maintain oral hygiene.
• Hemodialysis along with hemoperfusion and/or forced diuresis can be done in case of a massive overdose. However, it is usually not recommended due to severe side effects.
• At a later stage of the treatment, additional potassium is used to mobilize thallium from the tissue. However, it is usually not recommended due to severe side effects.

Drugs and antidotes

• Radiogardase, also called Prussian blue (ferric ferrocyanide)
  • This compound binds thallium ions and disrupts enterohepatic recycling (a feedback mechanism resulting from the combined roles of the liver and intestine).
  • Radiogardase (insoluble Prussian blue) is available in 500 mg tablets, and the recommended dose for adults is three grams orally three times per day. Prussian blue appears to be nontoxic at these concentrations.
  • A stomach wash may also be done using Prussian blue.
• Activated charcoal
  • It is widely available and has been reported to bind to thallium in vitro. 
  • Because thallium appears to undergo enterohepatic recirculation, multiple doses of charcoal are recommended. 
  • In one study, charcoal was reported to be more effective than Prussian blue at removing thallium.
• Decontamination process
  • If the conditions are right, administer activated charcoal orally. If given within a few minutes of exposure, induced vomiting may be helpful as an initial treatment.
  • For large recent ingestions, consider gastric lavage.
• Enhanced elimination process
  • Repeated administration of activated charcoal may improve fecal elimination by binding thallium secreted into the gut lumen or through the biliary system.
• Role of oral zinc sulfate
  • Thallium poisoning is commonly associated with dermatological symptoms similar to zinc deficiency.
  • Oral zinc sulfate appears to be an effective and safe treatment for thallium poisoning, particularly for skin and hair features. Moreover, it slows the poison's lethal progression and complications.
• Others
  • In severe cases where individuals experience excessive hair loss, the head is shaved.
  • Physiotherapists advise patients with thallium poisoning to engage in certain physical activities that will keep their muscles from contracting.

Thallium poisoning can be successfully treated with potassium ferric hexacyanoferrate (Prussian blue). Gastric lavage (within six hours of ingestion) and induced emesis may help prevent thallium absorption.

The most accurate way to diagnose thallium poisoning is through a 24-hour urine thallium concentration. If the thallium concentration in the urine is greater than 0.3 mg/L, it confirms thallium poisoning.

Other diagnostic tests include:

• Blood tests (used to determine eosinophilic levels)
• Optic nerve examination (for any significant changes or abnormalities)
• Microscopic examination of hair (which may reveal the presence of dark pigments)
• ECG (used to constantly monitor heart conditions)
• Liver and gastrointestinal tract imaging (may be recommended to view potential opacities).

Urine thallium levels are generally less than 0.8 mcg/L. Concentrations higher than 20 mcg/L indicate excessive exposure and may be linked to subclinical toxicity during workplace exposures.

Blood thallium levels are not considered accurate indicators of exposure unless significant exposures occur. Thallium levels in hair are only marginally useful; they are primarily used in forensic cases to demonstrate past exposure.

Thallium poisoning causes damage to the gastrointestinal system, eyes, skin, and nervous system. Prompt diagnosis and aggressive treatment of acute thallium poisoning may be an effective therapy as it quickly reduces the thallium concentration.

• Few survivors of thallium poisoning may still have neurological or visual impairment.
• Delay in medical care increases the risk of the persistence of neurological issues. Peripheral neuropathy symptoms and signs can appear in patients up to six years after toxication.
• During pregnancy, exposure can result in abnormalities in the fetus.
• Dementia, depression, and psychosis can all develop in chronic cases.

According to scientists, thallium and other dangerous heavy metallic compounds should be kept away from humans. The government should require industrial plants to release these substances after adequate purification so they do not affect the environment. It should be used at a low concentration or forbidden for all industrial applications.