IMPACT OF DISINFECTION TREATMENT CHANGES ON SR ADSORPTION AND ACCUMULATION IN IRON DRINKING WATER PIPE: AN UNFORESEEN ADVERSE CONSEQUENCE TO HUMAN HEALTH

Ingestion of non-radioactive strontium (Sr²⁺) from drinking water has not been considered a significant threat to human health until recently, prompting the United States Environmental Protection Agency to consider it regulation in drinking water. This study examines the accumulation mechanisms of Sr in iron drinking water pipe corrosion products formed in the presence of free chlorine and chloramine disinfected waters. Samples were examined via synchrotron-based in-situ m-X-ray adsorption spectroscopy and traditional bulk X-ray diffraction and X-ray fluorescence analyses. Iron coupons were conditioned in free chlorine and chloramine disinfected waters, with Sr concentrations of 0.30 mg L^-1. Sr adsorption to iron corrosion was 113% greater in chloramine versus free chlorine disinfected water at the end of the 68 days. The iron corrosion products were subsequently exposed to a Sr-enriched water (100 mg L^-1) for 1-hour. Sr adsorption by the end of the one hour increased by 361% and 877% in chloramine and free chlorine disinfected waters, respectively. However, once the Sr-enriched water was flushed from the system, Sr desorbed by 77% and 85% over 24 hours, in chloramine and free chlorine disinfected waters respectively. Based on these finding short-term (24 hours) adsorption and desorption indicates Sr is likely adsorbed in weak outer surface complexes and does not differ regardless of the water disinfection. Long-term Sr adsorption (68 days) however is more pronounced in chloramine disinfected waters. This finding is intriguing because Sr adsorption should not differ in the two types of disinfections since Sr only has a single oxidation state. These results may reflects differences in the corrosion product morphologies, with iron corrosion formed in chloramine being more porous and thus likely a greater number of available adsorption sites. This porous nature makes the surface layers of these corrosion products more susceptible to hydraulic or chemical disturbances during which time mass desorption of Sr ions or iron particulate laden with Sr could be released into the drinking water exposing consumers to high concentrations of Sr and other conventional and emerging contaminants, know to accumulate in the surface layers of iron corrosion, at levels in excess of regulatory limits.