Inactive Ingredients in Herbicides May Contribute to Drinking Water Contamination

New findings at Washington University in St. Louis indicate that inactive ingredients found in farm pesticides, long assumed to be non-toxic, play a very important part in poisonous byproducts formed during the purification of water. The study, led by graduate researcher Jean Brownell and supervised by Associate Professor Kimberly Parker at the McKelvey School of Engineering, highlights how stabilizers known as amines, which are employed to enhance the efficacy of herbicides, might be major forerunners to nitrosamines. Nitrosamines are disinfection byproducts (DBPs) that have been associated with health threats at low doses and are formed when certain chemicals react during the disinfection of water. While previous assumptions pointed to pharmaceuticals and consumer products as primary sources of nitrosamines, this study challenges that view by showing how agricultural runoff, especially from herbicides containing amines, may be an underrecognized contributor.

Brownell’s research focused on analyzing the role of amines in herbicide formulations and how their increased usage over the past two decades correlates with the potential for DBP formation. Her research suggests that these inactive agents may now be competing with known nitrosamine precursors like ranitidine and metformin, both of which are drug-related and find their way into water supplies via municipal wastewater. The study pointed out that amines are being used in massive quantities, particularly in agricultural regions like the U.S. Midwest. Their prevalence guarantees that their runoff into water bodies is comparable to that of more familiar sources, posing a risk that may have been underestimated by regulators and water quality managers.

The implications of these findings are significant for environmental protection and public health. As agricultural practices evolve, the composition of commonly used products like herbicides also changes. These changes are not, however, accompanied by updated risk assessments, especially in terms of water safety. Brownell's work underscores the importance of looking not only at active ingredients but also so-called inert ingredients potentially having an indirect function in contributing to environmental and health risks. This would mean that existing water treatment facilities may have to be updated to account for the presence of such lesser-documented precursors.

Additionally, Brownell compared statistics on annual use of farm amines with use patterns of other chemicals and discovered that their occurrence in the environment can be seasonally or regionally highest depending on farming cycles and herbicide application schedules. This finding implies the need for local studies and monitoring procedures that can detect such space-time variations. Agricultural runoff has usually been treated as a diffuse pollution source, and regulation is accordingly problematic. But with such special studies as this one, it is possible to trace specific chemical agents and track their possible impact more closely.

The second significant implication of the study is the necessity for enhanced data gathering and cooperation between regions. Following herbicide formulation trends and information gathering from farmers and regulatory bodies can lead to enhanced future policy-making and allow for more efficient water treatment procedures. Without standard and region-specific data, generalization of findings or confirmation that water safety regulations are being maintained current in diverse agricultural environments becomes problematic.

The research suggests that assumptions about the environmental impact of agriculture, particularly as it relates to DBP precursors, need to be adjusted. Because chemicals used in agriculture continue to advance, evaluations of environmental risk also need to evolve. Brownell's work is among the first to estimate the potential contribution of agricultural formulation components like amines to the formation of nitrogenous DBPs in treated water. These findings are supported by additional field research to determine how these inactive components interact in real-world environments and how they may be mitigated by reformulation changes or water treatment practices.

The study also implies the broader imperative for more integrated approaches to environmental monitoring and chemical regulation. Because food production and safe drinking water are both required, inclusive strategies that account for the entire chemical profile of agricultural products and their downstream effects on ecosystems and public health must be developed. Rather than looking at agricultural chemicals as separate from water treatment issues, this study demands holistic thinking in environmental policy and management.

Source/Credits:
Shawn Ballard, Washington University in St. Louis | Study: Jean M. Brownell et al., Water Research (2025), DOI: 10.1016/j.watres.2025.123116 | Photo Credit: Pixabay / CC0 Public Domain