“Chemical disinfection of drinking water is an extremely important practice, and one that has prevented millions of illnesses and premature deaths. It is most certainly among the most impactful public health interventions of the last century. It is well known that all chemical disinfectants, including chlorine and chloramines, lead to the production of disinfection byproducts. It is also widely accepted that we don’t know the precise identity of all disinfection byproducts that are formed. Chloronitramide anion is one such disinfection byproduct which has not, until now, been specifically identified. This research provides us with a little more of the full picture of disinfection byproducts formed following chloramine disinfection of drinking water. Knowing the identity is helpful since it will enable future research aimed at minimising or controlling the formation of disinfection byproducts.

While the precise identity of this disinfection byproduct is new information, it doesn’t change what we know about the safety of chlorinated or chloraminated drinking water. Many studies have been undertaken to directly assess the toxicity of drinking water samples, and these have been undertaken using methods that do not require the identity of specific chemical substances to be known. While there are almost always low levels of toxicity associated with any reactive chemicals, chlorinated and chloraminated drinking water have been shown to be extremely safe when treated in accordance with Australian and international guidelines and standards.

Chloramination is an important drinking water disinfectant, used in several Australian cities. In some systems, it has certain advantages over the other most common disinfectant, chlorine. The most important advantage of chloramination is chemical stability, which means that the quality of the drinking water is protected all the way from the water treatment plant to the customer tap, even over long distances or travel times.”

“This is a wonderful bit of chemical detective work. It’s long been known that there is an imbalance between the substances that go into water disinfection with chloramine, and those known to be present in the treated water.

Something was missing. A phantom substance. Now the books have been balanced and the phantom has been revealed as a new substance, hitherto unknown to science. It’s a negatively charged particle consisting of one chlorine atom, two nitrogen atoms and two oxygen atoms. Who would have thought that such a simple combination would have remained undiscovered over several centuries of chemical research in which tens of thousands of chemicals have been put on the books, so to speak?

The deep background to this story is a reminder that chlorine is a rogue element. We use it in a number of ways, but it’s very hard to control and it has a history of ‘getting off the leash’.

Used as chlorine gas, Cl2, it’s a very effective disinfectant – killing bacteria, fungi and other organisms – and it is reactive enough to destroy other chemicals, hence its use as a bleach. If chlorine is added to contaminated water, it mops up the contaminants and forms substances like chloroform. If there is any bromide in the water, it is converted to elemental bromine, which itself forms impurities like bromoform.

The use of the gas in warfare is notorious – a rogue element used by rogues!

Ways to keep chlorine on the leash were found, however. For example, by attaching the chlorine atom to oxygen as in hypochlorite, a common household and industrial bleach and disinfectant. Another strategy is to attach the chlorine to nitrogen, to form chloramines, which we don’t find on our shelves at home but are used industrially. Further in that direction, much of the ‘pool chlorine’ we use has chlorine attached to nitrogen in more complex substances.

Back to the recent research. The unusual feature of chloronitramide, and probably one that contributed to it hiding in the shadows for so long, is that it contains a nitro (NO2) group. Where did that come from? Plausibly, it is the result of active chlorine ripping apart substances like ammonia or another chloramine molecule, leaving their nitrogen attached to two oxygens. It’s a process that chemists refer to as ‘oxidation’ but in this case, the driving force is not oxygen, but active chlorine.

Finally, is chloronitramide toxic? We don’t know yet, but you can bet that toxicologists are working hard to find out. It’s not often that they are confronted with a totally new chemical.”

“This is a very interesting and detailed study that uses some very elegant chemistry to solve the identity of a previously unknown disinfection by-product. I am quite convinced by their analytical evidence, which is exceptionally thorough, that the unknown compound is indeed the chloronitramide anion (NB: an anion is an atom or molecule with more electrons than protons, thus having an overall negative charge).

The question then becomes whether chloronitramide is of concern or not?

Disinfection by-products are interesting pollutants as they are not present in the original water but rather are formed when chemicals used for disinfection react with organic matter in the water. They have been known about since the 1970s, and the more common ones are carefully monitored, although I have often thought water companies might need to pay more attention to potential new disinfection by-products. I agree that a toxicological investigation of this anion would be useful now that we know its identity, but  I am not overly worried about my tap water. The compound in question is not newly discovered, just newly defined. Its presence in some (not all) drinking waters has been known for over thirty years.

We should remember that the presence of a compound does not automatically mean it is causing harm. The question is not – is something toxic or not – because everything is toxic at the right amount, even water. The question is whether the substance is toxic at the amount we are exposed to. I think here the answer is probably not. Only 40 samples were tested in this study, which is not enough to be representative of all tap water in the USA and the concentration of chloronitramide was well below the regulatory limits for most disinfection by-products in the majority of samples.”