Environmental risk associated with glyphosate and 2,4-D based herbicides: the case of earthworms in agroecosystems

Herbicides, are becoming the most widely used weed management method worldwide due to their numerous advantages, such as labor time reduction, and workforce requirements as well as improving crop yields. The recurrent use of glyphosate and 2,4-D needs an assessment of their environmental risks. The objective of the study was to evaluate the impact of glyphosate and 2,4-D based herbicides on earthworms in tropical agroecosystems, using Eudrilus eugeniae as a model species. Two experimental plots A and B, each measuring 15 m × 15 m (225 m²), were used as experimental units for glyphosate and 2,4-D based herbicides respectively. In each experimental plot, glyphosate or 2,4-D residues in the soil, were monitored using high-performance liquid chromatography (HPLC). The ratios “predicted environmental concentration/herbicide concentration in the soil” (PEC/CS) were used to characterize the risk posed to earthworm communities. Evaluation of earthworm exposure to 2,4-D resulted in PEC ₅₀ /CS and PEC _rep /CS ratios of below 1 during the 28 days after application of this herbicide. In contrast, for glyphosate, the PEC ₅₀ /CS and PEC _rep /CS ratios were greater than 1. Based on these results, 2,4-D based herbicide is an herbicide able to reduce earthworm populations, whereas glyphosate application in agroecosystem does not represent significant risk of lethality or reproduction towards earthworms.