NDMA formation during chlorination and chloramination of aqueous diuron solutions

Formation of the potent carcinogen N-nitrosodimethylamine (NDMA)during chlorine disinfection of water containing secondary amines is now generally acknowledged. The phenylurea herbicide diuron is one of the most widely used herbicides in California, has been frequently detected in California's water sources with a transient nature of appearance, and has a structure that suggests it might be an NOMA precursor. This study sought to quantify the potential for NOMA formation from aqueous diuron solutions under varied chlorine and chloramine conditions. NOMA formation was consistently observed even in the absence of added ammonia, which has usually been the source of the nitroso-nitrogen during chloramination of other precursors. It appears that both nitrogen atomsin NDMA are donated by diuron during chlorination in the absence of added ammonia. For a given chlorine and diuron dose, NOMA formation increased in the order OCl- < NH2Cl < NHCl2, a result consistent with previous NOMA formation studies. Significant quantities of NOMA (170 ng/L) were produced during dichloramination of diuron using a low dichloramine concentration and a diuron concentration at the upper end of typically detected concentrations in California (20 mu g/L), suggesting a need for further investigation to accurately assess the human health risks posed by diuron with respect to NOMA formation potential. A reaction pathway is proposed to provide a possible explanation for NOMA formation from diuron during chlorination or chloramination. The findings in this study identify a specific potential precursor of NDMA formation, one that arises from nonpoint sources. This further highlights the difficulties associated with determining the environmental safety of chemicals and their associated byproducts.