Glyphosate Effects on Earthworms: Active Ingredients vs. Commercial Herbicides at Different Temperature and Soil Organic Matter Levels

Little is known about the non-target effects of glyphosate active ingredients (GLY) versus glyphosate-based herbicide (GBH) formulations on soil organisms, and whether effects are influenced by environmental conditions. We investigated the avoidance behavior, biomass growth, and reproduction of earthworms (Eisenia fetida, E. andrei) in response to two GLYs (glyphosate ammonium and potassium salt), the corresponding GBHs (Touchdown Quattro, Roundup PowerFlex) containing these GLYs, and the “inert” co-formulant alkylpolyglycoside (APG) at two temperature (15 °C vs. 20 °C) and soil organic matter levels (3.2% vs. 4.3%). Earthworm avoidance was lower at high soil organic matter content, but remained unaffected by substances and temperature. Earthworm biomass growth and reproduction (cocoons and juveniles) were significantly affected by substances and temperature; reproduction was also affected by a substance and temperature interaction. Biomass growth was almost zero at higher temperature; reproduction was generally higher at higher temperature. More cocoons were produced under Roundup PowerFlex than under the corresponding AI, due to the impact of the co-formulant APG. No other differences were observed between GBH and the corresponding AIs. We conclude that the non-target effects of pesticides can only be fully assessed if all ingredients in a formulation are known and environmental parameters are included in environmental risk assessments.