Assessment of in vitro toxicity of chloronitramide anion (CNAM)

In 2024, Fairey and colleagues were able to finally identify the chloronitramide anion (CNAM) as the degradation product of inorganic chloramines after more than 40 years since its existence was suggested. However, since their seminal work, no experimental information about CNAM toxicity has been published. In the current manuscript, we evaluate CNAM in vitro toxicity using the CHO cells chronic cytotoxicity assay. CNAM has a LC50 value of 9.99 x 10-5 M (99.9 µM; 9.45 mg/L), with LC50 representing the concentration resulting in 50% cell death. This suggests that CNAM is more toxic than regulated DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs). Toxicity-weighted DBP concentration assessment also shows that CNAM could be the major driver in chloraminated drinking water cytotoxicity and also play an important role in chlorinated tap water systems. In waters treated with organic chloramines, toxicity-weighted concentration index values for CNAM were greater than all other DBP classes evaluated including haloacetonitriles (HANs), haloacetamides (HAMs), haloacetaldehydes (HALs), hanonitromethanes (HNMs), THMs, HAAs and haloketones (HKs). These data also suggest that CNAM can exert significant oxidative stress in CHO cells, while mitochondrial stress and DNA damage were not significant.