Neonicotinoid and s-triazine pesticide transport dynamics in a small karst agricultural watershed

Authors: KIBUYE, HENRY - Pennsylvania State University; Veith, Tameria; GROH, TYLER - Pennsylvania State University; PREISENDANZ, HEATHER - Pennsylvania State University

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2026
Publication Date: 2/23/2026
Citation: Kibuye, H.J., Veith, T.L., Groh, T.A., Preisendanz, H.E. 2026. Neonicotinoid and s-triazine pesticide transport dynamics in a small karst agricultural watershed. Journal of Environmental Quality. 55. Article e70155. https://doi.org/10.1002/jeq2.70155.
DOI: https://doi.org/10.1002/jeq2.70155

Interpretive Summary: Forested and vegetative buffers along agricultural streams are currently designed and implemented, in part, to protect streams from sediment and nutrients transported by overland runoff. Two types of pesticides, surface applied and applied as a coating on plant seeds, are commonly used in crop fields and, despite careful management, can transport from fields to streams through surface and ground water. The extent to which nutrient and sediment buffers also trap pesticides is unclear, particularly in areas with sinkholes and other karst topographic features. We collected in-stream water samples at five locations within a karst agricultural watershed every two weeks from April through October of 2023. We analyzed the samples for three types of surface applied pesticides and four types of seed-coating applied pesticides. We compared the results to the type of landuse near each stream monitoring site and to the types of landuse upstream of each monitoring site. We found that vegetative and forested buffers appear to help prevent surface applied pesticides from reaching the streams. However, seed-coating applied pesticides, which are covered by soil, move down into the groundwater instead of being carried by surface runoff into the buffer. This study highlights the importance of considering both surface and groundwater transport pathways to mitigate pesticide transport, particularly in karst watersheds.

Technical Abstract: The potential ecological and human health risks posed by agricultural pesticides to nearby surface waters necessitate a comprehensive understanding of pesticide transport dynamics to guide effective management. Field-edge and riparian buffers are often implemented to mitigate nutrients and sediment transported via surface runoff. However, co-benefits they may offer in mitigating pesticides are not well understood, especially in karst watersheds. We monitored nested watersheds in a small (62 km2), agriculturally influenced, karst watershed in the Ridge and Valley physiographic province of Eastern United States to compare transport dynamics of two, surface applied, s-triazine herbicides to four, sub-surface applied, neonicotinoids. In-stream grab samples were collected and analyzed every two weeks from five sites over the 2023 growing season. Simazine, atrazine, and clothianidin were the most frequently detected compounds, found in 93%, 92% and 75% of samples collected, respectively. Concentration-discharge relationships indicated that clothianidin and atrazine were mobilized in surface runoff, implying that buffers targeting overland flow could mitigate their transport. Simazine was transported in groundwater, highlighting an uncertainty of treatment by overland flow buffers. Due to the karst topography, upstream pesticide inputs were found to influence downstream concentrations, indicating that for karst watersheds with agricultural land use distributed across the entire watershed, a watershed-wide approach to managing both nutrient and pesticide transport is necessary. Such hydrological connectivity between sub-watersheds presents challenges to the common approach of targeting “hot spots” for intensive implementation of control practices and may require extended implementation across all sub-watersheds to effectively mitigate pesticide transport and improve water quality.