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black lung continued strong mechanistic links between BAI content in coal and reactive oxygen species as well as inflammatory responses associated with CWP. Iron and quartz are proven inducers of fibrosis. Both are present in the U.S. Eastern and Western coal mines alike. This begs the question: why would these two compounds cause a health problem to the coal miners in the Eastern but not to those in the Western coal mines in the U.S.? Perhaps instead of further investigating mechanisms by which BAI and quartz cause CWP, a more pragmatic approach should be to find out what compound(s) in the mixed coal dust inhibits the toxicities of BAI and quartz, and thus prevents CWP from rising in the Western coal workers. We have found that BAI is stable only under acidic pH and, Western coals containing high levels of calcite (CaCO3) have high pH and, consequently low BAI and less toxicity. In addition to eliminating BAI in the mixed coal dust, calcite also reduced endogenous levels of cellular iron, diminishing an important source of iron that can be sequestered by silica and plays a critical role in silicosis and CWP. According to the calcium oxide (CaO) levels in high temperature ashes, calcite levels in Western coal mine regions have been estimated to be between 2%-5% (w/w). Conceivably, this calcite-mediated lower toxicity may partly account for the relatively low CWP prevalence observed among Western coal workers. Does the addition of calcite to Appalachian coals cause environmental concern to the coal industries? Calcite is the main constituent of rock dust that is widely used in underground coal mines for prevention of dust explosions and in the treatment of acid mine drainage. Pulverized calcite is added to the boilers of coal-fired power plants to absorb SO2 and NOx, important components of the air pollution that leads to acid rain. Given these existing uses, introduction of calcite into coal before or during mining should not cause substantial environmental concern, and may even have beneficial effects on acid rain and acid mine drainage. Now the questions remaining to be answered are whether it is safe and feasible to use calcite as a preventive agent in Appalachian coal mines. It is harmless to ingest calcite since calcium is an essential human nutrient required in substantial amounts. The dietary calcium recommendation was recently increased from 800 to 1,200 mg/day for persons older than 51 years April 2013 of age. In nutrition, calcite is the most common calcium supplement because it has the highest concentration of calcium by weight (40%), as compared to other common calcium supplements (e.g., calcium citrate, acetate, phosphate and gluconate). Calcite is also commonly taken orally as an over-thecounter treatment for heartburn and acid indigestion. Orally administered calcium decreases iron absorption, and thus BAI in the body. However, despite its presence at relatively high levels in Western coals, there is a lack of toxicological data on the inhalation of pure calcite. In laboratory experiments, mouse lung tissue indicated increased fibrogenic markers of epithelial mesenchymal transition after exposure to acidic and BAI-containing PA coal dust, but not after exposure to PA coal dust plus calcite or calcite alone. Markers of inflammation increased following exposure to www.coalage.com 55