A Comprehensive Assessment of the Pesticide Leaching: Insights from the Hindon River Basin, India

Pesticide leaching into groundwater poses a significant risk related to water security and public health, particularly in intensively cultivated, overexploited and contaminated regions. Farmers in most developing nations select pesticides based on their pest-killing efficiency and cost to increase crop yield and economic benefits rather than their potential environmental impacts. Therefore, this study estimated the leaching potential of 31 commonly used pesticides in the upstream (US), midstream (MS), and downstream (DS) regions of the Hindon River basin (HRB), India. The leaching indices such as the Groundwater Ubiquity Score, LEACH Index, Modified LEACH Index, Hornsby Index, LIX Index, LIN Index, and Global Leachability Index were employed. Key pesticide properties, such as water solubility, carbon-water partition coefficient, half-life, vapor pressure, and Henry's law constant, were used to calculate all the indices. In addition, pesticide consumption patterns and hydrogeological data—such as soil type, rainfall, aquifer hydraulic conductivity, and groundwater levels—were incorporated into the analysis to pinpoint the location and specific pesticides. The results indicate that pesticides like sulfosulfuron, metsulfuron methyl, imidacloprid, atrazine, carbendazim, dimethoate, and glyphosate are major contributors to groundwater contamination due to their mobility, persistence, and widespread usage. Specifically, the US regions, with shallow groundwater levels (< 8 mbgl) and high annual rainfall (~1100 mm), showed elevated leaching risks from carbendazim and dimethoate pesticides. However, the MS and DS regions, characterized by moderate rainfall (600–800 mm), moderate groundwater levels (> 12 mbgl) and higher aquifer hydraulic conductivity (33 m/day), exhibited significant leaching risks from pesticides like sulfosulfuron, metsulfuron methyl, imidacloprid, and atrazine. Instead of the low leaching potential of pesticides, such as fipronil, chlorpyrifos, and lambda-cyhalothrin, their residues may be detectable in groundwater due to high application rates. This study highlights the complex interplay between pesticide leaching risks based on the HRB consumption pattern and hydrogeological conditions. The results of this study would be helpful for pesticide regulation, the adoption of less persistent compounds, enhanced monitoring programs, safeguarding public health, and identifying potential recharge locations for agriculturally managed aquifer recharge (AgMAR). The findings suggest that future studies should focus on regular field monitoring of pesticide residues, evaluating aquifer vulnerability under varying pesticide consumption and climatic conditions, and incorporating advanced modeling tools to predict long-term contamination risks to ensure groundwater sustainability in the HRB.