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Quartz Toxicity on Clayart


This material was taken from the Clayart discussion group and I am embarrassed to admit that I have lost the name of its author. Due to the importance of this issue and the informative nature of this material I have posted it anyway. If you are the author please contact me so we can credit you.

When Silica (SiO2) combines with other cations to form Silicates, then the SiO2 is no longer "free". Free Silica exists in three forms, amorphous, cryptocrystalline and polymorphic crystalline.

Mining or quarrying of any rock that contains siliceous material may produce hazardous exposures to "free" Silica. Thus, the mining of copper, gold, platinum, tin, uranium or even coal may produce high exposures. Tunneling in rock containing high concentrations of quartz may produce severe exposures. The quarrying of granite, sandstone and slate may produce exposures from the quarry face where modern flame cutters may have increased exposure through all aspects of cutting, dressing, and polishing the quarried stone. Abrasive blasting and other uses such as scouring and polishing where Silica flows may be used may cause rapidly progressive disease. Other significant exposures may occur in glass manufacture, production of pottery, porcelain and lining bricks, boiler scaling, and enameling.

The production and use of refractory brick containing Silica may pose significant health hazards particularly after they have been exposed to high temperatures as a significant major proportion of the Silica is transformed to cristobalite or tridymite. Bricklayers and others who maintain and dismantle the refractory brick of ovens, furnaces and other similar devices are exposed to a serious silica hazard.

Foundry work is still a major source of "free" Silica exposure. In all stages of the foundry process from core making through "shake-out" to maintenance and repair, "free" Silica exposures occur along with other potentially hazardous exposures to metal fumes, asbestos and toxic gases. As the quartz-containing sand used in the molds is exposed to hot metal, formation of cristobalite may occur. It is not uncommon for such sand to be used on a repeated basis leading to further increases in the concentration of cristobalite.

Silica related diseases

Silicosis in its chronic and accelerated forms varies in it s symptoms. It is not uncommon for relatively severe radiological changes to be present. Coughing may develop as the disease advances and in the later stages may be long and stressful. In the early stages of the disease there is usually very little sputum, but as the disease advances, recurrent bronchial infections occur and sputum becomes common. Dypsnea is perhaps the most significant problem of established Silicosis and this is usually associated with massive changes within the lungs and contraction of lobes. Respiratory failure is the most important consequence of complicated Silicosis. In accelerated Silicosis, the major features of the disease are identical, but changes occur more quickly.

The most important aspect of diagnosis is a history of exposure to "free" Silica. The x-ray changes of silicosis provide in many cases the definitive diagnosis. Classically rounded nodules are the basic elements but in complicated forms, massive densities predominate.

There is no treatment for Silicosis, and previous treatments of miners with inhalation of aluminum dust have not been effective. In fact, aluminum dust itself may be fibrogenic. The only treatment for silicosis is prevention of exposure by reduction of the Silica content of the air.

Conclusion

Silicosis has been known to the general medical and scientific community since the 1930 s. The risk of contracting silicosis in the sandblasting occupations, foundry industry, and masonry trades, (bricklayers, helpers, etc.) has been well documented. In fact, current literature indicates that persons who are exposed to "free" Silica in certain occupational environments are at a greater risk of developing lung cancer.

NIST/ACerS Crystalline Silica Workshop

NIST and The American Ceramic Society held a workshop on Crystalline Silica in Gaithersburg, Maryland, September 2001 to establish the current state of scientific understanding regarding the relationship between surface characteristics, crystal structure and crystal perfection, and other chemical and mineral aspects, and the potential health hazards associated with crystalline silica. The Occupational Safety and Health Administration (OSHA) has created a Special Emphasis Program, which is considering a 50% reduction in the permissible exposure limit (PEL) for crystalline silica.  Such a reduction in the PEL would, at the very least, result in many companies having to invest large sums of money in upgrading their dust collection capabilities, require increased monitoring of air quality within the plants and lead to increased surveillance by OSHA and MSHA. Following are some contact people.
  • Bice Fubini, University of Turin
  • Vincent Castranova, National Institute for Occupational Safety and Health (NIOSH)
  • Marthe Kent, OSHA
  • William Wallace, NIOSH
  • Jim Cline, NIST
  • Bill Moll, William F. Moll Associates
  • Sarkis Ampian, Ampian & Associates

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By Tony Hansen




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