Abstract
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.
Highlights
Regardless of the aging time, the mean juvenile production per vessel in the control at 25 ◦ C (135.8 ± 31.4 for 0 d and 125.0 ± 25.5 for seven days) was always significantly higher than that observed at 20 ◦ C
Glyphosate have been known to be toxicologically and environmentally benign, but our study showed that glyphosate can have negative effects on the juvenile production of A. kimi depending on the temperature and aging time
Glyphosate toxicity is largely determined by the amount of residue in the soil, which is dependent on the soil temperature
Summary
Glyphosate-based herbicides are systemic herbicides widely used worldwide, and are known to be environmentally benign [1]. This is because glyphosate is known to be safe for non-target species [2], and to be rapidly degraded by microorganisms under environmental conditions [3]. Along with these properties, the introduction of transgenic glyphosate-resistant crops (GRCs) has made glyphosate the most popular and effective herbicide [1]. Because of the increase in glyphosate-resistant weed species [8], the glyphosate application amount and frequency are subsequently increasing [4], suggesting strongly that the actual glyphosate concentrations in soil could be much higher than those measured or estimated in previous studies
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