Spatiotemporal Variability in N-Nitrosodimethylamine Precursor Levels in a Watershed Impacted by Agricultural Activities and Municipal Wastewater Discharges and Effects of Lime Softening

Effect of spring runoff on 2,6-dichloro-1,4-benzoquinone formation during water treatment

This study investigated the impacts of spring runoff on the formation of halobenzoquinones (HBQs) and their correlation with common water quality parameters (WQPs) and aromatic amino acids (AAs) in source water. Source water and treated water samples were collected at two drinking water treatment plants in 2021, 2022, and 2023. HBQs and aromatic AAs were analyzed using solid phase extraction with high performance liquid chromatography-tandem mass spectrometry methods. The only HBQs detected in treated water were 2,6-dichloro-1,4-benzoquinone (DCBQ) and hydroxy‑DCBQ (OH-DCBQ). The concentration of DCBQ was 3-4 times higher during spring runoff events than during non-spring-runoff periods, suggesting the impact of spring runoff on the formation of DCBQ. The DCBQ concentrations in finished water positively correlated with the color, dissolved organic carbon, total organic nitrogen, and specific ultraviolet absorbance WQPs of source water in 2021 and 2022. The temporal trend of the total aromatic AAs determined in source water was strongly and positively correlated to DCBQ in finished water. Finally, there was a significant positive correlation between the concentration of DCBQ determined immediately following the addition of chlorine and the presence of its transformation product, OH-DCBQ, in finished water. The results also showed that powdered activated carbon can remove some of the HBQ precursors in the source water to reduce DCBQ formation. This study demonstrated that WQPs and aromatic AAs are useful indicators for the removal of precursors to reduce HBQ formation during drinking water treatment.

Making Waves: Formulation components used in agriculture may serve as important precursors for nitrogenous disinfection byproducts

N-Nitrosamines, many of which are carcinogenic, mutagenic, and teratogenic, are disinfection byproducts (DBPs) formed from the reaction of chloramine with nitrogenous organic compounds during water disinfection. The identification of major nitrosamine precursors is important to understand and prevent nitrosamine formation. In this analysis, we propose that efforts to identify nitrosamine precursors must look beyond conventionally evaluated active agent chemicals to consider inert or inactive chemicals as potentially relevant precursors. Using agricultural chemicals applied in the US as an example, we demonstrate that amines widely used as inactive agents in herbicide formulations (i.e., dimethylamine [DMA], a known N-nitrosamine precursor) are potentially much more important than active agent herbicides previously evaluated as potential nitrosamine precursors (i.e., the herbicides diuron or trifluralin). Accounting for use rates and nitrosamine yields, amines used in herbicide formulations represent potential nitrosamine precursor inputs to the environment that are similar in magnitude to recognized precursors like the pharmaceuticals ranitidine and metformin. Because the amounts of amines used as inert agents in herbicide formulations have increased dramatically over recent decades, particularly in certain US regions, we suggest that identification of potential nitrosamine precursors should consider variation in the inputs of both active and inactive agents over time, as well as geographical variation in use that may alter the relative importance of specific precursors in certain locations.

Animal Feedlots and Domestic Wastewater Discharges are Likely Sources of N-Nitrosodimethylamine (NDMA) Precursors in Midwestern Watersheds

N-nitrosodimethylamine (NDMA) precursor concentrations along four major rivers in Minnesota, USA were quantified and correlated with watershed land cover types, anthropogenic activity, and organic matter characteristics. River water samples (36 in total) were chloraminated under uniform formation conditions (UFC) before and after lime-softening treatment, and the resulting NDMA concentrations were quantified (NDMAUFC). Regarding land cover, NDMAUFC in raw river water exhibited weak positive correlations with urban land (ρ = 0.33, p = 0.05) and cropland coverage (ρ = 0.35, p = 0.04). For anthropogenic activity, NDMAUFC in raw river water positively correlated with the number of feedlots (ρ = 0.57), total weight of animals (ρ = 0.68), and total number of domestic wastewater treatment plants (WWTPs; ρ = 0.63) with p < 0.01. NDMAUFC positively correlated with region IV fluorescence intensity from fluorescence excitation-emission spectra (ρ = 0.70, p < 0.01). Lime softening of river water typically increased NDMAUFC and preferentially removed organic matter that fluoresces in region V, suggesting that the organic matter in this region decreases NDMAUFC by competing for available chloramines. Overall, animal feedlots, along with domestic WWTPs, are predominant sources of NDMA precursors in the studied watersheds, while croplands and urban runoff are of lesser importance.