Does serpentine rock or asbestos-cement pipe (AC Pipe) pose any problems for MMWD drinking water?
Serpentine (our official state rock) is common in Marin and many other places and contains naturally-occurring asbestos. Asbestos has been shown to be a human carcinogen through inhalation, but the short fibers typically found in drinking water are not a health problem. Regulations limit drinking water to 7 million fibers per liter of asbestos fibers longer than 10 microns. There is no regulatory limit or health concern for fibers smaller than 10 microns. A micron is 1/25,400 of an inch. The regulation is based on evidence of benign polyps in male rats following oral administration of elevated doses of asbestos fibers 10 microns and larger. A parallel study using fibers less than 10 microns produced no polyps in either female or male rats. The EPA also noted the findings of the National Research Council which concluded that health affects of asbestos in water “have not been confirmed in animal studies and has not been observed consistently in human studies.” A more recent (2003) toxico
