Effects of Pesticide Co-occurrence on the Leaching Behaviour of Fipronil and Imidacloprid in Sugarcane-Growing Soils of Northern India

Abstract

The emerging trend of pesticide mixtures use in modern agriculture necessitates a deeper understanding on their environmental fate, particularly under diverse soil and agro-climatic conditions. The present study investigated the effect of co-occurrence of fipronil (FP) and imidacloprid (IM) on their leaching behaviour in three representative sugarcane-growing soils (sandy clay loam, loam and silty clay loam) of Northern India under simulated continuous and discontinuous rainfall regimes. The soil column leaching experiment revealed that imidacloprid exhibited moderate mobility, redistributing up to 15–20 cm depth depending on soil type and water flow conditions, while no breakthrough into the leachate was observed. However, fipronil showed strong sorption-driven immobility, with over 85–90% of residues retained within top 0–5 cm soil layer across all treatments. The co-presence of fipronil caused only minor competitive effects on imidacloprid mobility, suggesting limited interaction at the test concentrations. Soil texture and organic carbon content played a key role in restricting the pesticide movement. The present findings indicate a low immediate risk of groundwater contamination, while highlighting the importance of evaluating pesticide mixture behaviour for more precise environmental risk assessment.