Thallium

Thallium is a bluish-white metal that is found in trace amounts in the earth's crust. It resembles tin but becomes discolored when exposed to air. In the Periodic Table, thallium has the symbol Tl and atomic number 81. It is present in base metal sulfide ores and is discharged in effluent from the ore industry. Thallium is toxic to humans. Due to thallium's toxicity, the Occupational Safety and Health Administration (OSHA) has set an exposure limit of 0.1 milligrams per cubic meter (0.1 mg/m³) for thallium in workplace air. The U.S. EPA does not permit thallium in drinking water above the concentration of 0.0005 mg/L or 0.5 parts per billion. Despite its toxicity, and although thallium has been found in sewage sludge and subsequently in the milk of cows fed on forage fertilized with sewage sludge, the U.S. EPA does not regulate the amount of thallium permitted in sewage sludge applied to land as fertilizer.

Uses
Thallium is used mostly in manufacturing electronic devices, switches, and closures, mostly for the semiconductor industry. It is also used in pharmaceuticals, glass manufacturing, infrared detectors. It has been used as an insecticide and rat poison.

In the Environment
Thallium also enters the environment from coal burning. Once in the environment, thallium stays in the air, water, and soil for a long time and does not break down. Thallium (I) hydroxide is highly soluble in water. It can also be transferred from soil to crops and thus accrues in food crops.

Presence in Sewage Sludge
In the Targeted National Sewage Sludge Survey, a 2009 test of 84 samples of sewage sludge from around the U.S., the EPA found thallium in 80 samples (95%) in concentrations ranging from 0.02 to 1.7 parts per million.

Although thallium is not often found in high concentrations in sewage sludge, it is also not regulated in the United States for sewage sludge applied to land. Thus, it was fully legal for a wastewater treatment plant to provide Georgia dairy farmer Andy McElmurray with sewage sludge tainted with thallium to spread on his fields. The source of the thallium was a Nutrasweet plant. McElmurray grew forage for his cattle and then sold their milk. Once McElmurray's cows began dying and the sewage sludge was identified as the source of the problem, scientists collected milk samples from the farm and from grocery stores in Georgia and surrounding states to test them for contaminants. In the milk, they found thallium at levels exceeding EPA's safe drinking water standards.

Toxicity
"Thallium is more toxic to humans than mercury, cadmium, lead, copper or zinc and has been responsible for many accidental, occupational, deliberate, and therapeutic poisonings since its discovery in 1861." According to the CDC, "Breathing high levels of thallium may result in effects on the nervous system, while ingesting high levels of it results in vomiting, diarrhea, temporary hair loss, and other effects." The U.S. EPA identifies hair loss, changes in blood, or problems with their kidneys, intestines, or liver problems as risks of drinking water contaminated with thallium. Additionally, chronic occupational exposure to thallium resulted in nervous system effects like numbness of fingers and toes from breathing thallium. According to the National Institute for Occupational Safety and Health (NIOSH), 15 mg/m³ of thallium is considered immediately dangerous to life and health, causing permanent health problems or death.

Related SourceWatch articles

 * Biosolids
 * Sewage sludge
 * Food Rights Network

External resources

 * Pesticide Action Network, Thallium (I) Sulfate

External articles

 * Josh Harkinson, "Sludge Happens", Mother Jones, May/June 2009
 * Jill Richardson, "Cattle Deaths, Milk Contamination", La Vida Locavore, June 5, 2010