Glyphosate bioavailability in soil

Abstract

Biodegradation of glyphosate in sod-podzol soil by both the indigenous micro flora and the introduced strain Ochrobactrum anthropi GPK 3 was studied with respect to its sorption and mobility. The experiments were carried out in columns simulating the vertical soil profile. Soil samples studied were taken from soil horizons 0-10, 10-20, and 20-30 cm deep. It was found out that the most of the herbicide (up to 84%) was adsorbed by soil during the first 24 h; the rest (16%) remained in the soluble fraction. The adsorbed glyphosate was completely extractable by alkali. No irreversible binding of glyphosate was observed. By the end of the experiment (21st day), glyphosate was only found in extractable fractions. The comparison of the effect of the introduced O. anthropi GPK 3 and indigenous microbial community on the total toxicant content (both soluble and absorbed) in the upper 10 cm soil layer showed its reduction by 42% (21 mg/kg soil) and 10-12% (5 mg/kg soil), respectively. Simultaneously, 14-18% glyphosate moved to a lower 10-20 cm layer. Watering (that simulated rainfall) resulted in a 20% increase of its content at this depth; 6-8% of herbicide was further washed down to the 20-30 cm layer. The glyphosate mobility down the soil profile reduced its density in the upper layer, where it was available for biodegradation, and resulted in its concentration in lower horizons characterized by the absence (or low level) of biodegradative processes. It was shown for the first time how the herbicide biodegradation in soil can be increased manifold by introduction of the selected strain O. anthropi GPK 3.

Decay characteristics and erosion-related transport of glyphosate in Chinese loess soil under field conditions

“…Bergstrom et al (2011) reported that the residues of glyphosate and AMPA were mainly detected in topsoil (0-30 cm), despite the application of glyphosate 748 d earlier, and Shushkova et al (2010) reported that 57% of the glyphosate was concentrated in the 0-10 cm soil layer after 7 d. Studies also showed that glyphosate is initially absorbed mostly in the upper 2 cm of soil rather than transported and absorbed after a few days in deeper soil horizons (Rampazzo et al, 2013) which is similar to Yang et al (2015) and our results (Tables 2 and 3). Glyphosate and AMPA content then correspondingly decreased significantly in deeper soil layers (2-10 cm) and were even below the limit of detection in some layers.…”

“…The biodegradation of glyphosate in soil follows two pathways: the oxidative cleavage of the C-N bond to yield aminomethylphosphonic acid (AMPA) and the breaking of the C-P bond to generate sarcosine (Borggaard and Gimsing, 2008). The efficiency of biodegradation can be enhanced by providing suitable conditions for the reproduction of introduced microorganisms (Shushkova et al, 2010). The factors that determine the occurrence and degree of decay of glyphosate in the environment, however, remain to be clarified (Borggaard and Gimsing, 2008).…”

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“…The use of insecticides in agriculture has been incriminated in the emergence of insecticide in insect vectors (Akogbéto et al, 2005). Glyphosate can bind to soil particles under certain conditions (Shushkova et al, 2009), especially in clay soils. It can be quickly leached in sandy soil, while it may persist for over a year in soils which contain clay (Bergström et al, 2011).…”

Glyphosate biodegradation and potential soil bioremediation by Bacillus subtilis strain Bs-15

“…The most active glyphosate-degrading microorganisms were isolated from soils polluted by organophosphonates (Shushkova et al, 2010). In soil, glyphosate is primarily decomposed by bacteria and fungi, which utilize glyphosate as carbon source, leading to the production of aminomethylphosphonic acid, or as a phosphorus source, producing glycine (Solomon et al, 2007).…”