Pure thallium is a bluish-white metal that is found in trace amounts in the earth’s crust. In the past, thallium was obtained as a by-product from smelting other metals; however, it has not been produced in the United States since 1984. Currently, all the thallium is obtained from imports and from thallium reserves.
In its pure form, thallium is odorless and tasteless. It can also be found combined with other substances such as bromine, chlorine, fluorine, and iodine. When it’s combined, it appears colorless-to-white or yellow.
Thallium is used mostly in manufacturing electronic devices, switches, and closures, primarily for the semiconductor industry. It also has limited use in the manufacture of special glass and for certain medical procedures.
What happens to thallium when it enters the environment?
Thallium enters the environment primarily from coal-burning and smelting, in which it is a trace contaminant of the raw materials.
It stays in the air, water, and soil for a long time and is not broken down. Some thallium compounds are removed from the atmosphere in rain and snow. It’s absorbed by plants and enters the food chain.
It builds up in fish and shellfish.
How might I be exposed to thallium?
- Eating food contaminated with thallium may be 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 (may result in higher than normal exposures).
- Touching or, for children, eating soil contaminated with thallium.
- Breathing low levels in air and water.
How can thallium affect my health?
Exposure to high levels of thallium can result in harmful health effects. A study on workers exposed on the job over several years reported nervous system effects, such as numbness of fingers and toes, from breathing thallium.
Studies in people who ingested large amounts of thallium over a short time have reported vomiting, diarrhea, temporary hair loss, and effects on the nervous system, lungs, heart, liver, and kidneys.
It has caused death. It is not known what the effects are from ingesting low levels of thallium over a long time.
Birth defects were not reported in the children of mothers exposed to low levels from eating vegetables and fruits contaminated with thallium.
Studies in rats, however, exposed to high levels of thallium, showed adverse developmental effects.
It is not known if breathing or ingesting thallium affects human reproduction. Studies showed that rats that ingested thallium for several weeks had some adverse reproductive effects.
Animal data suggest that the male reproductive system may be susceptible to damage by low levels of thallium.
There is no information available on the health effects of skin contact with thallium in people or animals.
How likely is thallium to cause cancer?
The Department of Health and Human Services, the International Agency for Research on Cancer, and the Environmental Protection Agency (EPA) have not classified thallium as to its human carcinogenicity.
No studies are available in people or animals on the carcinogenic effects of breathing, ingesting, or touching thallium.
Is there a medical test to show whether I’ve been exposed to thallium?
There are medical tests available to measure levels of thallium in urine and hair. In addition, thallium can also be measured in blood; however, this is not a good indicator of exposure since thallium only stays in blood a very short time.
These tests require special equipment that is not usually available in most doctor’s offices. In addition, these tests cannot determine if adverse health effects will occur from the exposure to thallium.
Has the federal government made recommendations to protect human health?
The EPA requires that discharges or accidental spills into the environment of 1,000 pounds or more of thallium be reported.
The Occupational Safety and Health Administration (OSHA) has set an exposure limit of 0.1 milligrams per cubic meter (0.1 mg/m) for thallium in workplace air.
The American Conference of Governmental Industrial Hygienists (ACGIH) has established the same guidelines as OSHA for the workplace.
The National Institute for Occupational Safety and Health (NIOSH) has recommended that 15 mg/m of thallium be considered immediately dangerous to life and health.
This is the exposure level of a chemical that is likely to cause permanent health problems or death.
- Remove from the source of exposure if possible. Remove contaminated clothing but be careful not to become exposed too.
- Assess airways, breathing and circulation. With inhalation, possible respiratory failure is a great concern and IV access and administration of oxygen is advised.
- If ingestion has occurred in the last 30 minutes, induce vomiting. In an A&E department gastric lavage can be performed if within an hour of ingestion.
- With ingestion, activated charcoal and Prussian blue (potassium ferric hexacyanoferrate) are recommended.
- Prussian blue is better than charcoal at keeping thallium out of the enterohepatic circulation and enhancing faecal excretion but it is not often available.
- Prussian blue is better than chelating agents such as penicillamine, and the latter may cause redistribution of thallium into the central nervous system.
- Forced diuresis aids renal excretion and adding potassium seems to enhance this.
- Haemoperfusion or haemodialysis, if employed, should be performed as early as possible. Its efficacy is low.
- All patients with significant signs and symptoms of thallium poisoning require hospital admission
- Measure thallium levels in blood and urine 3 times per week to confirm a decreasing trend.
- Prussian blue should be continued until the 24-hour urine thallium concentration returns to the reference range (0-24 μg/d).
- Physiotherapy may reduce or prevent muscle contractures.
- Of those who survive poisoning, about a third to a half have residual neurological or visual disability.
- Exposure during pregnancy can lead to fetal abnormalities.
- Chronic cases may lead to dementia, depression and psychosis.