Rusty iron pipes can react with residual disinfectants in drinking water distribution systems and form carcinogenic hexavalent chromium.
Chromium is a metal found in soil and groundwater. Minor amounts of trivalent chromium can occur in drinking water, and food and are believed to have a neutral health effect.
Certain chemical reactions can convert chromium atoms into a hexavalent form: this chemical can create genetic mutations in cells that cause cancer.
Haizhou Liu, professor of chemical engineering and environmental engineering at the Marlan and Rosemary Bourns College of Engineering, studied the chemical process of water purification and was convinced that some of the chromium that gets into drinking water might be the result of chemical reactions between water disinfectants and chromium rusting pipes.
Together with a group of scientists, Liu studied sections of two pipes, which were in operation for about five. They then scraped off the rust, ground it into powder, and measured the amount and types of chromium present in it. They then placed the samples in hypochlorous acid, a form of chlorine commonly used in municipal drinking water treatment plants and drinking water distribution systems.
As a result of the experiment, chromium, which was found in rusty iron pipes, turned into its toxic hexavalent form.
Our findings are changing our traditional belief that we control hexavalent chromium in drinking water. It also highlights how important it is to manage the drinking water distribution infrastructure to control toxic substances in tap water.
Haizhou Liu, Professor of Chemical Engineering and Environmental Engineering at Marlan and Rosemary Bourns College of Engineering,
The research team is calling for a reduction in the laying of pipes with a high chromium alloy content and the use of disinfectants that are less reactive to chromium, such as monochloramine.