Thorium ingestion

When inhaled, ingested, or adsorbed through the skin, thorium isotopes are potentially harmful because of ionizing radiation and chemical toxicity. 

As thorium undergoes natural radioactive decay, a number of products, including gases, are emitted. These decay products are extremely dangerous radioactive poisons if inhaled or ingested. 

It was determined in several species of animals (mice, rats, rabbits) that more than 95% of the ingested amount is excreted in the feces within several days (approximately 2-4 days) (Patrick and Cross 1948 Scott et al. 1952 Sollmann and Brown 1907). Sollmann and Brown (1907) concluded that, since very little thorium was excreted in the feces following intravenous or intramuscular injection, and since very little thorium was excreted in the urine following ingestion, appreciable amounts of thorium were neither absorbed nor excreted from the gastrointestinal tract. 

Blood levels of thorium following oral exposure of humans to simulated radium dial paint demonstrated that approximately 0.02% of the ingested amount was absorbed by the gastrointestinal tract (Maletskos et al. 1969). This study was the basis for the ICRP (1979) recommendation of an oral absorption factor of 0.02% for thorium. 

Biomarkers of Exposure and Effect. The major route of excretion of inhaled or ingested thorium is in the feces. Exposure to thorium can be determined by measurement of thorium and/or its daughters in the feces, urine, blood, or expired air. The body burden of thorium may be estimated by the measurement of external gamma rays emitted from thorium daughters in the body. Further studies correlating thorium exposure with thorium and/or thorium daughters in the urine, feces, blood, and expired air would be helpful in more accurately quantifying thorium exposure. 

Bioavailability from Environmental Media. The absorption and distribution of thorium as a result of inhalation and ingestion exposures have been discussed in Sections 2.3.1 and 2.3.2. However,... 

Linsalata P, Eisenbud M, Franca EP. 1986. Ingestion estimates of thorium and the light rare earth elements based on measurements of human feces. Health Phys 50 163-167. 

Thorium nitrate is highly toxic by ingestion and other routes of exposure. The compound also is a radiation hazard. 

As the relative transfer coefficients from soil to plants and from diet to the blood increase, ingestion takes on more importance. This certainly appears to be the case for U. It may be that ingestion will be more important for Am and Cm than for Pu or thorium. Neptunium remains in enigma because of the paucity of data. 

DOT CLASSIFICATION 7 Label RADIOACTIVE, Oxidizer SAFETY PROFILE Poison by intraperitoneal, intravenous, and intratracheal routes. Moderately toxic by ingestion. Experimental reproductive effects. Radioactive. An oxidizing material when in contact with readily combustible substances will cause violent combustion or ignition. When heated to decomposition it emits toxic fumes of NOx. See also THORIUM and NITRATES. 

Internally deposited naturally occurring radionuclides also contribute to the natural radiation dose from inhalation and ingestion of these materials when contained in air, food, and water. Included are radionuclides of lead, polonium, bismuth, radium, potassium, carbon, hydrogen, uranium, and thorium. Potassium-40 is the most prominent radionuclide in normal foods and human tissues. The dose to the total body from these internally deposited radionuclides has been estimated to be 39mremyear. ... 

Hazard Flammable and explosive in powder form. Dusts of thorium have very low ignition points and may ignite at room temperature. Radioactive decay isotopes are dangerous when ingested. 

Relatively little Pu, Pu, Pu, americium and curium are formed in the irradiation of thorium-uranium fuel with fissUe makeup. However, when plutonium is used as fissile makeup for a thorium fuel cycle, considerable quantities of americium and curium are formed. As discussed in Sec. 2.4, these are the radionuclides that are the greatest contributors to radioactivity and ingestion toxicity after about 600 years of waste isolation, when the fission products have decayed. 

The toxicity of the high-level wastes from a uranium-thorium HTGR fuel cycle is initially smaller, after the fission-product decay period of 600 years, because of the relatively small quantities of americium, curium, Pu, and Pu formed in this thorium fuel cycle. However, after about 100,000 years of isolation the theoretical ingestion toxicity of the wastes is governed by Ra, formed by... 

Consequently, the actinide content and theoretical ingestion toxicity of the radioactive wastes from uranium-thorium fuel are relatively small for waste disposal times of lOCX) to... 

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