Researchers at New Mexico Institute of Mining and Technology (New Mexico Tech) theorized that the inactive mines are a source of dust that contained trace amounts of uranium. This harmful dust is carried upon the wind to nearby Navajo settlements, who reported far more cases of heart diseases than they historically experienced.
Uranium ore gives off a small amount of radiation, just enough to harm genetic data and increase the risks of ailments. But the researchers are much more worried about the chemical toxicity of the ore, a deadly characteristic that endures even after the radioactive isotopes have been extracted.
Earlier studies tested samples of depleted ore that no longer contained the most radioactive of uranium isotopes. They found that the ore was still capable of causing cellular apoptosis and DNA injuries. (Related: New study finds that toxic chemicals found in nail polish enter women’s bodies just hours after application.)
This is the first investigation on the health risk posed by uranium in respirable dust. Before this New Mexico Tech study, there was no information on whether or not the toxic element could dissolve into the bloodstream and the fluids that filled the lungs.
Researcher Gayan Rubasinghege led a team to the Grants Mining District in New Mexico. They obtained samples of airborne dust from five separate spots near the Jackpile and St. Anthony uranium mine, both of which were situated beside Navajo communities.
Analysis of the samples revealed different concentrations of minerals depending on the site that produced the respirable dust. However, all of the samples had at least one mineral that served as a uranium ore. The most commonly appearing ores were uraninite (previously called pitchblende) and carnotite (which also contained potassium and vanadium).
Next, the researchers exposed the samples to two liquids that replicated the fluids found in the lungs. One, Gamble's solution (GS), simulated pleural effusion, the protective fluid that envelops lung cells. The other liquid, artificial lysosomal fluid (ALF), copied the astringent environment found inside alveolar macrophage cells that engulf and dissolve pathogenic substances.
They performed chemical analyses that determined the concentration of uranium that leached into each fluid. They also determined which sample and mineral combination posed a greater threat to the simulated lung fluid.
The uranium minerals produced a number of uranium ions (species) that could dissolve in the fluids. The most common species was UO22+, a cation or positively charged ion. All of these were toxic to humans.
The mineral composition of the respirable dust affected its solubility in a fluid. Samples that contained large amounts of both carnotite and uraninite proved to be more soluble in GS. By extension, the uranium-laced dust would easily spread through the pleural effusion that encases all lung cells.
Meanwhile, dust with low amounts of uraninite and high levels of kaolinite (a clay mineral) dissolved more readily in ALF. That means the alveolar macrophages that engulf this dust end up absorbing uranium ions.
Based on their findings, the researchers recommended that future toxicological assessments of uranium mining sites target specific sites. Doing so will increase the accuracy of the evaluation, making it easier to determine what kind of health risk is prevalent in the local population.