To assess the toxic potential of asbestos fibers, the most common cause of malignant mesothelioma, asbestos-containing materials are first broken into small fibers. In a recent study, researchers at the University of Pennsylvania Perelman School of Medicine have shown that the method employed to break down the asbestos fibers may markedly influence the fibers’ toxicity.
The study, “Asbestos Fiber Preparation Methods Affect Fiber Toxicity,” published in Environmental Science and Technology Letters, shows that breaking down the fibers in water is associated with lower toxicity than that found in dry-ground fibers, suggesting that the asbestos preparation conditions should be taken into account when comparing toxicity of asbestos between different studies.
Exposure to asbestos, a naturally occurring mineral, is known to pose serious health effects, such as increased risk for malignant mesothelioma and pleural disorders, as well as development of lung and stomach cancer.
To study the toxic potential of asbestos fibers, researchers needed to break them into small fibers by mechanical grinding or by ultrasonic treatment for long periods of time. However, despite the evidence that the different grinding methods can change the fibers’ shape, size, and structure, it is unknown whether the methods affect the toxicity of the asbestos.
To assess the toxicity of asbestos prepared in different ways, the researchers ground chrysotile ore with or without water for five to 30 minutes, and applied the resulting fibers in macrophage cultures. These macrophages, which are specific immune cells, had been taken from the peritoneal membranes of mice, the membranes that surround the abdominal organs and where peritoneal mesothelioma develops.
Results revealed that macrophages reacted more negatively to dry-ground than to wet-ground fibers, producing increased amounts of toxic reactive oxygen species (ROS). ROS are molecules that induce damage to proteins and DNA molecules, promoting the development of cancer.
“These results indicate that grinding methods significantly affect the surface concentration of iron, resulting in changes in fiber-induced reactive oxygen species generation or toxicity,” wrote author Ashkan Salamatipour with the Division of Pulmonary, Allergy and Critical Care Medicine at Penn.
The researchers say the difference in both techniques is the iron concentration, as dry-ground fibers had seven times more iron than wet-ground fibers. Although scientists are still not entirely sure how asbestos triggers malignant mesothelioma, iron concentration is believed to be an important factor, with increased iron levels often leading to increased ROS and damage to cellular structures.
The investigators believe that while grinding asbestos fibers in water removes a fraction of total iron from fibers, decreasing their toxicity, dry-grounding preserves or exposes the fibers to even more iron, thereby increasing toxicity.
“Thus, it is important to consider the fiber preparation method and resulting changes in surface chemical properties when conducting future research examining toxicity of asbestos fibers or comparing asbestos toxicity between reported studies,” the authors wrote.