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| Fig. 1: Fig. 1: A picture of thorium-covered mantle. (Source: Wikimedia Commons) |
For nearly a hundred years, kerosene lamps have changed the world of camping and provided a bright light that allows activities to carry on deep into the night. However as the gas lamp burns away, this may be more dangerous than we once thought. Thorium, a radioactive element that gives the white glow to the light, has been identified in these common everyday lanterns that were once sold. [1]
Thorium is a naturally occurring radioactive element that was discovered in 1828 by J. J. Berzelius. [1] It is considered to be "fertile", due to its ability to be converted into a fissile material from neutron absorption and later nuclear decay. Most of the natural thorium exists in isotope form as Th-232. [2] This unstable isotope is found almost everywhere - in the rocks, the soil, the water, and even the air. There is approximately 6 parts per million of thorium in soil. [3] The amount of thorium naturally in the environment does not increase with time, but rather decreases due to its radioactive decay. However though thorium is noted to be surrounding us almost everywhere, it still is a dangerous radioactive element that can lead to increased chances of lung, bone, and pancreas cancer. Many authors have noted that thorium will sit in the body for many years before causing symptoms or showing signs of disease. [1]
The radioactive properties that lanterns possess come about in the manufacturing process when the mantles are being made and coated with various things to make it glow brighter and longer. The mantle is the bag looking object that sits in the middle of the lantern and produces a bright light when heated by flame. (See fig. 1.) This piece is dipped into thorium nitrate where it dries and is later coated with other substances that affect the light's brightness. [4] Once the lamp is lit, the heat leads to the glow of the thorium along with the conversion of thorium to thorium oxide releasing numerous products of the radioactive decay of thorium. Thorium is a radioactive atom that emits both alpha and beta particles. [2] Though escaping bits of thorium particles are mostly blocked by the glass that surround the lantern, consuming or even smelling thorium can result in health problems, such as lung and bone cancer if consumed in large amounts that surpasses the natural thorium exposure limit. The chances of consumption or ingestion are much greater when a particle of the mantle falls out into the open. [4]
Over many years companies have grown aware of the thorium inside of the lanterns and therefore the production has significantly decreased. In the mid 1950s nearly 70 percent of the thorium that was being produced in the United States was used for the coating of mantles in camping lanterns. [5] Each mantle contained nearly 250 mg of thorium. [6] Though kerosene lanterns made with thorium are beginning to slowly decrease in number due to danger there are still many people who use them and are unaware of the dangers that they can cause.
© Duke Kinamon. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] C. H. Breedlove, "Some Illuminating Chemistry Provided by a Camping Lantern," J. Chem. Educ. 69, 621 (1992).
[2] K. Griggs, "Toxic Metal Fumes From Mantle-Type Camp Lanterns," Science 181, 842 (1973).
[3] R. Jamison, Thorium: Chemical Properties, Uses and Environmental Effects (Nova Science, 2014).
[4] E. K. Hyde, "The Radiochemistry of Thorium," Lawrence Radiation Laboratory, UCRL-8703, April 1959.
[5] M. A. H. I. A. Bhatti and I. Munawar, "Assessment of Thorium in the Environment (A Review)," J. Chem. Soc. Pak 34, 1012 (2012).
[6] J. W. Luetzelschwab and S. W. Googins. "Radioactivity Released from Burning Gas Lantern Mantles," Health Phys. 46, 873 (1984).
