Proficiency testing for all fiber sizes in drinking water: The long and the short of it

The Environmental Laboratory Approval Program (ELAP) of the New York State Department of Health has administered a proficiency-testing (PT) program for asbestos in drinking water since 1992. While the United States Environmental Protection Agency requires that only fibers longer than 10 mu m be counted, FLAP continues to require that ail fibers longer than 0.5 mu m be analyzed. FLAP mandates the use of polycarbonate filters because short fibers are apparently lost in mixed-cellulose eater filters. Thirteen different waterborne asbestos samples have been distributed to approximately two to three dozen laboratories analyzing asbestos by transmission electron microscopy. Mean total fiber concentrations have ranged from 5.49 to 3340 million fibers per liter (MFL) while mean long (>10 mu m) fiber concentrations have ranged from 0.377 to 76.7 MFL. Failure rates have ranged from 3.5% to 21% of participating laboratories, with equivalent failure rates for total and long-fiber analyses. As laboratories gained experience in long-fiber analysis, they appeared to report results closer to consensus means.