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The efficiencies with which chrysotile fibers in water are retained by polycarbonate (PC) and mixed cellulose ester (MCE) filters have been measured. The studies demonstrate that, for filtration of water samples, PC filters of 0.2 μm pore size or less and MCE filters of 0.22 μm porosity or less are satisfactory filters for determination of the concentrations of asbestos fibers of all lengths in water samples, but that the presence of surfactant may introduce a negative bias in the shorter fiber sizes. The results show that the observed fiber densities on 0.22 μm porosity MCE filters increase with plasma etching, and also exhibit a positive bias due to a variable degree of shrinkage which occurs during the filter collapsing procedure. In a second series of measurements, using a procedure similar to that used by the pharmaceutical industry for testing the retention of bacteria by membrane filters, it was found that all of the filters tested were capable of yielding reduction factors of better than approximately 107. However, for 0.22 μm porosity MCE filters, sporadic reduction factors as low as 102 occurred, and when surfactant was added to the water, these low reduction factors were observed consistently, and measurable proportions of the fibers up to approximately 2 μm long passed through the filters.
Asbestos analysis, fiber, water, polycarbonate, mixed cellulose ester, membrane filter, filtration efficiency, retention, surface tension, parenteral
Chatfield, Eric J.
President, Chatfield Technical Consulting Limited, Mississauga, Ontario