Iodo-acids were recently identified for the first time as DBPs in drinking water disinfected with chloramines. The iodo-acids identified included iodoacetic acid (IAA), bromoiodoacetic acid, (E)-3-bromo-3-iodo-propenoic acid,  (Z)-3-bromo-3-iodo-propenoic acid and (E)-2-iodo-3-methylbutenedioic acid. There is concern about these new iodo-acid DBPs because mammalian cell toxicity studies have revealed that IAA is highly cytotoxic and genotoxic—with a genotoxicity 2X that of regulated bromoacetic acid. New evidence indicates that iodinated DBPs may be increased in formation in chloraminated vs. chlorinated drinking water and this is of concern because many water utilities are switching from chlorine to chloramines. We developed a negative chemical ionization mass spectrometry method to measure these iodo-acids in drinking water and are conducting a large occurrence study of these iodo-acids in chloraminated drinking waters across the U.S.  Although this work was reviewed by EPA and approved for publication, it may not necessarily reflect official Agency policy.