Human antibiotics are a trace component of wastewater treatment plant (WWTP) effluents. These can impact downstream drinking water treatment plants, where they can produce nitrosamines during chloramination. Similarly, in some watersheds impacted by contained animal feeding operations or other agricultural operations, veterinary antibiotics may be a source of nitrosamine precursors. Veterinary antibiotics are used in large quantities and have been found in watersheds impacted by agricultural run-off and WWTP effluents. In this study, the formation potential of nine veterinary antibiotics to form nitrosamines under chloramination was tested. It was expected that the deprotonated species would react more to form nitrosamines. Two antibiotics were tested, which had been previously identified as NDMA precursors, and molar conversions were comparable to previous studies. Antibiotics were tested at varying pH, temperature, chlorine to ammonia ratio, and with pre-formed mono- and dichloramine to elucidate the effect of water quality, chloramination conditions and structure of the molecule on NDMA formation. Average molar conversions to N-nitrosodimethylamine (NDMA) ranged from 0.03 to 4.9 percent. Antibiotics with two dimethylamine functional groups had one to two orders of magnitude higher molar conversion than those with one dimethylamine. One antibiotic with diethylamine functionality was found to produce N-nitrosodiethylamine upon chloramination. Initial tests suggest the highest formation occurred at pH 8 for most of the antibiotics regardless of pKa. In water stability tests, certain antibiotics were shown to decrease in concentration at high pH over time. In this case, conversion to NDMA was reduced. These initial results suggest veterinary antibiotics have the potential to be important contributors to NDMA formation in drinking water. In occurrence studies where NDMA formation has been high, but human wastewater contribution has been low, agricultural wastewater may be an important source of precursors.

Veterinary antibiotics as a source of nitrosamine precursors

248th National Meeting (2014)

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