Glyphosate is the most used herbicide worldwide, but enormous use of glyphosate has raised concerned about its environmental loadings. Although glyphosate is considered non-toxic, toxicity data for soil non-target organisms according to temperature and aging are scarce. This study examined the toxicity of glyphosate with the temperature (20 °C and 25 °C) and aging times (0 day and 7 days) in soil using a collembolan species, Allonychiurus kimi (Lee). The degradation of glyphosate was investigated. Fatty acid composition of A. kimi was also investigated. The half-life of glyphosate was 2.38 days at 20 °C and 1.69 days at 25 °C. At 20 °C with 0 day of aging, the EC50 was estimated to be 93.5 mg kg-1. However, as the temperature and aging time increased, the glyphosate degradation increased, so no significant toxicity was observed on juvenile production. The proportions of the arachidonic acid and stearic acid decreased and increased with the glyphosate treatment, respectively, even at 37.1 mg kg-1, at which no significant effects on juvenile production were observed. Our results showed that the changes in the glyphosate toxicity with temperature and aging time were mostly dependent on the soil residual concentration. Furthermore, the changes in the fatty acid compositions suggest that glyphosate could have a chronic effect on soil organisms.
Keywords: arachidonic acid; degradation; herbicide; microorganism; risk assessment.