Asbestos is the general name for a group of six naturally occurring silicate minerals composed of thin, durable fibers. Due to its resistance to heat, fire, and chemical breakdown, the material was historically used in thousands of commercial products, including building materials and water pipes. Concerns about the presence of these fibers in drinking water stem from the fact that inhaling them can lead to severe health issues, raising the question of water contamination.
The Physical Interaction with Water
Asbestos does not dissolve in water in the same way that salt or sugar does. Dissolution is a chemical process where a solid integrates completely into a liquid to form a homogeneous solution. The fibrous mineral structure of asbestos is highly resistant to this chemical integration and does not break down easily in a neutral aqueous environment.
Instead of dissolving, microscopic asbestos fibers become dispersed or suspended throughout the water column, forming a colloidal mixture where they remain as distinct, solid particles. While the fibers are chemically stable, some types, like chrysotile, can undergo slight chemical alteration in acidic water. This process involves the leaching of magnesium ions from the fiber’s surface, leaving behind a silica-like structure, but the fiber’s solid form remains intact.
Common Sources of Water Contamination
Asbestos fibers primarily enter the water supply through two pathways: the natural environment and aging infrastructure. Naturally occurring asbestos (NOA) is present in certain rock formations, such as serpentine rock, where natural erosion releases fibers into surface water and groundwater sources.
The second, and often more significant, source is the deterioration of asbestos-cement (AC) water pipes. Municipal systems widely used these pipes, which can contain up to 20% asbestos, from the 1940s to the 1970s. Over time, factors like age, corrosive water chemistry, and high flow rates can cause the cement matrix to break down, releasing microscopic fibers directly into the water supply.
Health Implications of Ingested Asbestos
The health danger of asbestos is associated with the inhalation of airborne fibers, which can lead to diseases like lung cancer and mesothelioma. The risk associated with ingesting asbestos fibers through drinking water is less clear and remains a subject of scientific debate. The digestive system is believed to be effective at passing most ingested fibers out of the body through feces.
Some epidemiological studies have suggested a potential link between high concentrations of asbestos in drinking water and an increased risk of specific cancers, including those of the esophagus, stomach, and intestines. Other research, such as animal feeding studies, has offered inconsistent results, failing to establish a conclusive link between ingested asbestos and tumor formation in the gastrointestinal tract.
Despite the inconclusive data, regulatory bodies have established standards to limit exposure from water. The United States Environmental Protection Agency (EPA) set a Maximum Contaminant Level (MCL) for asbestos in drinking water at seven million fibers per liter (7 MFL). This standard applies specifically to fibers longer than 10 micrometers, treating the presence of asbestos in water as a monitored public health concern.