The Ecotoxicity of Sugarcane Pesticides to Non-target Soil Organisms as a Function of Soil Properties and Moisture Conditions

To attend the increasing demand for food and energy, vast monocultures such as sugarcane, soy, and corn, often adopts routinely intensive application of pesticides and chemical fertilizers, disregarding their potential effects on non-target soil organisms, which are crucial for soil functioning. In this study, we present the assessment of toxic effects of the commercial herbicide DMA® 806 BR (active ingredient: 2,4-D) and of the insecticide Regent® 800 WG (active ingredient: fipronil) to the non-target terrestrial plant Raphanus sativus var. acanthioformis (dicotyledon) and to the collembolan species Folsomia candida , in combination with different soil moisture conditions in natural and artificial tropical soils. Plant growth and biomass were severely affected by the presence of DMA alone, with significant differences from the control treatment already detected at 0.13 mg/kg/dw. Upon low soil moisture (20%, 40%, 60% WHC), the toxicity of DMA to plants was diminished, exhibiting an antagonistic pattern of interaction between DMA and soil moisture. Soil composition had a significant influence on survival and reproduction of collembola especially at high soil moisture content. In the natural soil, 80% of the water holding capacity (WHC) induced 100% collembola mortality whereas, in the tropical artificial soil (TAS), this same moisture condition had a negligible effect on survival. Reproduction was mainly affected by fipronil under drought conditions (20% WHC) at both soil types, possibly correlated with increased concentration of fipronil in the soil pore water at such conditions. Results herein presented highlight the requisite of including abiotic fluctuations in hazard assessment of pesticides to preserve soil function provided by biota.