A biochar-loess granular formulation for reducing abamectin mobility under laboratory soil-column conditions

This study evaluated the leaching behavior and soil-column transport–retention of abamectin using a loess–biochar carrier formulation under laboratory-controlled conditions. The formulation uses biochar as an adsorptive component contributing to reduced abamectin mobility in soil systems, while loess serves as a structural mineral component supporting granule formation. Phytotoxicity assessments using oriental melon ( Cucumis melo L.) seedlings showed no significant inhibition of shoot and root development at concentrations up to 10 µg mL⁻¹. In vitro nematode bioassays indicated that egg hatching was the most sensitive endpoint, with near-complete inhibition at ≥0.8 µg mL⁻¹ (IC₅₀ = 0.84 µg mL⁻¹), demonstrating greater sensitivity compared to the shoot-growth IC₅₀ (31.92 µg mL⁻¹). Laboratory column experiments, combined with Gaussian-fitted transport modeling, indicated that the loess–biochar formulation was associated with reduced abamectin mobility, likely due to retention processes within the soil matrix. Formulation ratios of 2% and 4% (w/w) biochar showed the most favorable performance for nursery substrates and upland soil columns, respectively, in terms of cumulative leaching reductions (23.3% and 39.2% compared to the control). While these findings establish the loess–biochar composite as a framework for reducing mobility, further investigations into mass balance, degradation kinetics, and field-scale efficacy are essential to fully characterize the long-term environmental behavior of this formulation under relevant conditions.