Thorium concentration in human tissues from two U.S. populations.

Area of Science:

• Environmental Science
• Radiochemistry
• Human Health

Background:

• Natural alpha-emitting isotopes of thorium, including 228Th, 230Th, and 232Th, are present in the environment.
• Exposure to these isotopes can occur through various pathways, including proximity to uranium mine tailings.
• Understanding thorium isotope concentrations in human tissues is crucial for assessing potential health risks.

Purpose of the Study:

• To determine and compare the concentrations of thorium isotopes (228Th, 230Th, 232Th) in various human tissues from Grand Junction, CO, and Washington, DC.
• To investigate potential differences in thorium isotope levels between populations with and without exposure to uranium mine tailings.
• To evaluate the accumulation patterns of 230Th in human tissues, particularly in relation to environmental exposure.

Main Methods:

• Human tissue samples (lung, lymph nodes, liver, kidney, bone, gonads, spleen, thyroid) were collected post-mortem from 22 individuals in Grand Junction, CO, and 10 in Washington, DC.
• Alpha-spectrometry was used to quantify the concentrations of 228Th, 230Th, and 232Th in the collected tissue samples.
• Personal data including age, sex, smoking history, and occupation were collected to control for confounding factors.

Main Results:

• Thorium isotope concentrations were highest in pulmonary lymph nodes for both populations.
• While lung 230Th concentrations were not elevated in Grand Junction residents compared to Washington, DC residents, bone 230Th concentrations were significantly higher (p < 0.1) in Grand Junction subjects after age adjustment.
• The study observed a higher-than-expected accumulation of 230Th in the skeleton.

Conclusions:

• Non-mining residents near uranium mine tailings in Grand Junction did not exhibit elevated lung 230Th concentrations compared to control populations.
• A statistically significant increase in bone 230Th concentration was observed in Grand Junction residents, indicating potential skeletal accumulation from environmental exposure.
• The findings suggest that 230Th may be more readily accumulated in the skeleton than previously assumed based on its geochemical abundance.