N-Functionalized Carbon Nanotubes As a Source and Precursor of N-Nitrosodimethylamine: Implications for Environmental Fate, Transport, and Toxicity.

Hazardous byproducts may be generated during the environmental processing of engineered nanomaterials. Here, we explore the ability of carbon nanotubes with nitrogen-contg. surface groups (N-CNTs) to generate N-nitrosodimethylamine (NDMA) during chem. disinfection. Unexpectedly, we obsd. that com. N-CNTs with amine, amide, or N-contg. polymer (PABS) surface groups are a source of NDMA. As-received powders can leach up to 50 ng of NDMA per mg of N-CNT in aq. suspension; presumably NDMA originates as a residue from N-CNT manufg. Furthermore, reaction of N-CNTs with free chlorine, monochloramine, and ozone generated byproduct NDMA at yields comparable to those reported for natural org. matter. Chlorination also altered N-CNT surface chem., with XPS indicating addn. of Cl, loss of N, and an increase in surface O. Although these changes can increase N-CNT suspension stability, they do not enhance their acute toxicity in E. coli bioassays above that obsd. for as-received powders. Notably, however, dechlorination of reacted N-CNTs with sulfite completely suppresses N-CNT toxicity. Collectively, our work demonstrates that N-CNTs are both a source and precursor of NDMA, a probable human carcinogen, while chem. disinfection can produce CNTs exhibiting surface chem. and environmental behavior distinct from that of native (i.e., as-received) materials. [on SciFinder(R)]