Asbestos Fiber Preparation Methods Affect Fiber Toxicity

Abstract

To measure the toxic potential of asbestos fibers-a known cause of asbestosis, lung cancer, and malignant mesothelioma-asbestos minerals are generally first ground down to small fibers, but it is unknown whether the grinding condition itself changes the fiber toxicity. To evaluate this, we ground chrysotile ore with or without water for 5-30 min and quantified asbestos-induced reactive oxygen species generation in elicited murine peritoneal macrophages as an indicator of fiber toxicity. The toxicity of dry-ground fibers was higher than the toxicity of wet-ground fibers. Grinding with or without water did not materially alter the mineralogical properties. However, dry-ground fibers contained at least 7 times more iron than wet-ground fibers. 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. Therefore, fiber preparation conditions should be accounted for when comparing the toxicity of asbestos fibers between reported studies.

Figure 1

Grinding of chrysotile fiber bundles (A) with or without water affected the color of fibers produced. Dry grinding produced typical white fibers (B), whereas wet grinding produced gray fibers (C). The dry-ground fibers were soaked in water before the picture was taken.

Figure 2

X-ray diffraction result for chrysotile fibers exposed to wetand dry-grinding treatments for 5, 15, and 30 min. Fibers produced by 5 min of wet grinding were too large for XRD analysis. The vertical dashed lines indicate the characteristic peaks of chrysotile fibers.

Figure 3

Chrysotile fibers produced by 15 min of grinding in dry (left) and wet (right) conditions. Wet-grinding method created fibers with high aspect ratios and disassociated fiber bundles, whereas dry-grinding method produced fiber bundles with a shorter aspect ratio.

Figure 4

Effect of grinding method for chrysotile asbestos on the levels of asbestos-induced ROS in murine peritoneal macrophages, as assessed via the fluorescent probe, CellROX Green Reagent. Data are presented as mean ± standard deviation of the mean and **** indicates p < 0.0001.