Even more halogenated disinfection byproducts discovered

Scientists in Hong Kong have discovered four new groups of disinfection byproducts (DBPs) that are formed in water when it is chlorinated to kill off bacteria and viruses. The specific groups of compounds might not have been anticipated but the fact that there are more DBPs did not come as a surprise because only about 50% of the total organic halogen formed during chlorination has been accounted for to date.

The DBPs contained both chlorine and bromine, as described in a new paper by Xiangru Zhang and Yang Pan from the Hong Kong University of Science and Technology. In experiments on simulated drinking water, the chlorine originates from the disinfection process but bromide was added because it is present in source water around the world, so gets caught up in the disinfection reactions.

The new products are dihalo-4-hydroxybenzaldehydes, dihalo-4-hydroxybenzoic acids, dihalosalicylic acids, and trihalophenols. They were identified by mass spectrometry in the precursor ion scanning mode while looking for ions that produced chlorine signals at m/z 35 and 37 and bromine ion signals at m/z 79 and 81. Mechanisms for their formation were proposed and they were found to be important intermediates that decompose to produce the common DBPs like trihalomethanes and haloacetic acids.

Although the experiments were conducted on simulated drinking water, the researchers fully expect the comounds to be formed in real drinking water. One of the next steps should be to examine the toxicological relevance of the compounds to discover their effects on human health.