A comparison of the chemo- and radiotoxicity of thorium and uranium at different enrichment grades

Abstract

Uranium and thorium are heavy metals, and all of their isotopes are radioactive, so it is impossible to study chemical effects entirely independent of the radiation effects. In the present study, we tried to compare the chemo- and radiotoxicity of both metals, taking into account deterministic radiation damages reflected by acute radiation sickness and stochastic radiation damages leading to long-term health impairments (e.g., tumor induction). We made at first a literature search on acute median lethal doses that may be expected to be caused by chemical effects, as even acute radiation sickness as a manifestation of acute radiotoxicity occurs with latency. By simulations based on the biokinetic models of the International Commission on Radiological Protection and using the Integrated Modules for Bioassay Analysis software, we determined the amounts of uranium at different enrichment grades and thorium-232 leading to a short-term red bone marrow equivalent dose of 3.5 Sv considered to cause 50% lethality in humans. Different intake pathways for incorporation were considered, and values were compared to the mean lethal doses by chemotoxicity. To assess stochastic radiotoxicity, we calculated the uranium and thorium amounts leading to a committed effective dose of 200 mSv that is often considered critical. Mean lethal values for uranium and thorium are in the same order of magnitude so that the data do not give evidence for substantial differences in acute chemical toxicity. When comparing radiotoxicity, the reference units (activity in Bq or weight in g) must always be taken into account. The mean lethal equivalent dose to the red bone marrow of 3.5 Sv is reached by lower activities of thorium compared to uranium in soluble compounds. However, for uranium as well as thorium-232, acute radiation sickness is expected only after incorporation of amounts exceeding the mean lethal doses by chemotoxicity. Thus, acute radiation sickness is not a relevant clinical issue for either metal. Concerning stochastic radiation damages, thorium-232 is more radiotoxic than uranium if incorporating the same activities. Using weight units for comparison show that for soluble compounds, thorium-232 is more radiotoxic than low-enriched uranium in the case of ingestion but even more toxic than high-enriched uranium after inhalation or intravenous administration. For insoluble compounds, the situation differs as the stochastic radiotoxicity of thorium-232 ranges between depleted and natural uranium. For acute effects, the chemotoxicity of uranium, even at high enrichment grades, as well as thorium-232 exceeds deterministic radiotoxicity. Simulations show that thorium-232 is more radiotoxic than uranium expressed in activity units. If the comparison is based on weight units, the rankings depend on the uranium enrichment grades and the route of intake.

Thorium Removal, Recovery and Recycling: A Membrane Challenge for Urban Mining

“…Thorium compounds are relatively few compared to other elements, even the less reactive ones [ 75 , 76 ]. Thus, thorium dioxide, halogens or a nitride are encountered, but the speciation of the thorium ion (Th 4+ ) in aqueous solutions is of practical importance, as countless hydroxylated chemical species can be generated: [ThOH] 3+ , [Th(OH) 2 ] 2+ , [Th(OH) 3 ] + , [Th(OH) 4 ], [Th(OH) 2 (CO 3 ) 2 ] 2− , [Th 2 (OH) 2 ] 6+ and [Th(H 2 O) 9 ] 4+ [ 77 , 78 , 79 ], hence the importance of the operational parameters (pH, ionic strength, temperature, contact ions in the aqueous solution [ 80 , 81 , 82 , 83 ]), which would be the object of the study of membrane processes.…”

Thorium Between Removing, Recovery and Recycling: A Membrane Challenge for Urban Mining

“…Thorium compounds are relatively few compared to other elements, even the less reactive ones [75,76]. Thus, thorium dioxide, halogens or a nitride are encountered, but the speciation of the thorium ion (Th 4+ ) in aqueous solutions is of practical importance, as countless hydroxylated chemical species can be generated: [ThOH] 3+ , [Th(OH)2] 2+ , [Th(OH)3] + , [Th(OH)4], [Th(OH)2 (CO3)2] 2-, [Th2(OH)2] 6+ and [Th(H2O)9] 4+ [77][78][79], hence the importance of the operational parameters (pH, ionic strength, temperature, contact ions in the aqueous solution [80][81][82][83]), which would be the object of the study of membrane processes.…”

Thorium Alters Lung Surfactant Protein Expression in Alveolar Epithelial Cells: In Vitro and In Vivo Investigation

“…Notably, it exhibits a higher tendency to form complexes with biomolecules (with coordination numbers ranging from 8 to 12) compared to other nonradioactive heavy metal ions such as Pb, Cd, and Hg. Consequently, thorium-232 poses toxicity risks stemming from both its radiological and chemical properties. , Upon inhalation, the deposition and absorption of actinides, including Thorium, along the respiratory pathway are influenced by their size (ranging from 1 to 20 μm) and chemical forms (soluble or insoluble). These factors predominantly determine their entry into the alveolar lumen, which consists of alveolar epithelial type-I and type-II cells (AEPT-I and AEPT-II).…”