N-Nitrosodimethylamine

N-Nitrosodimethylamine (NDMA), also known as dimethylnitrosamine (DMN), is a semi-volatile organic chemical that is highly toxic and is a suspected human carcinogen. The US Environmental Protection Agency has determined that the maximum admissible concentration of NDMA in drinking water is 7 ng L−1. At high doses, it is a "potent hepatotoxin that can cause fibrosis of the liver" in rats. The induction of liver tumors in rats after chronic exposure to low doses is well-documented. Its toxic effects on humans are inferred from animal experiments but not well-established experimentally.

NDMA is an industrial by-product or waste product of several industrial processes. It first came to attention as a groundwater contaminant in California in 1998 and 1999 at several sites that produced rocket fuel. Manufacturing of unsymmetrical dimethylhydrazine (UDMH), which is a component of rocket fuel that requires NDMA for its synthesis, proved to be the culprit in these cases. Of more general concern, water treatment via chlorination or chloramination of organic nitrogen-containing wastewater can lead to the production of NDMA at potentially harmful levels. Further, NDMA can form or be leached during treatment of water by anion exchange resins. Finally, NDMA is found at low levels in numerous items of human consumption including cured meat, fish, beer, and tobacco smoke It is, however, unlikely to bioaccumulate.

NDMA's contamination of drinking water is of particular concern due to the minute concentrations at which it is harmful, the difficulty in detecting it at these concentrations, and to the difficulty in removing it from drinking water. It does not readily biodegrade, adsorb, or volatilize. As such, it cannot be removed by activated carbon and travels easily through soils. Relatively high levels of UV radiation in the 200 to 260 nm breaks the N-N bond and can thus be used to degrade NDMA. Additionally, reverse osmosis is able to remove approximately 50% of NDMA.