Frequent Questions

Why is the maximum contaminant level (MCL) for asbestos in drinking water measured in terms of fibers greater than 10 micrometers in length?

EPA's standard of 7 million fibers/liter (for fibers greater than 10 micrometers in length) is based upon evidence of benign polyps occurring in male rats following oral administration of intermediate size chrysotile fibers (i.e., >10 micrometer range). The study did not indicate potential adverse health effects for short-range fibers (56 FR 3526, 3535; November 13, 1985).
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