Fig. 1.

Branched reaction scheme with the first-order rate coefficients k 1 and k 3 for the degradation of glyphosate to aminomethylphosphonic acid (AMPA) and sarcosine, respectively, and k 2 for the degradation of AMPA

 


Fig. 2.

Best fits (A) to Eq. [2] of data on glyphosate and (B) to Eq. [4] of data on aminomethylphosphonic acid (AMPA) concentrations for sand topsoil (•), sand subsoil (○), clay topsoil (▾), and clay subsoil (▵) (mean ± SE, n = 2). dw = dry weight.

 


Fig. 3.

Relationship between half-life (t 1/2) for glyphosate and Freundlich adsorption coefficient (K f), and between t 1/2 for aminomethylphosphonic acid (AMPA) and % organic matter.

 


Fig. 4.

Average daily temperature (upper graph) and daily precipitation (lower graph) at the lysimeter site during the experimental period.

 


Fig. 5.

Weekly amounts of leachate from the lysimeters (mean + SD, n = 2 for sand and n = 3 for clay).

 


Fig. 6.

Average concentrations of bromide in the leachate (mean ± SD, n = 2 for sand and n = 3 for clay), (A) over time and (B) in response to cumulative leachate, and (C) the normalized cumulative tracer mass as a function of effective pore volume for both soils. Open symbols (□) refer to the clay soil and filled symbols (▪) to the sand.

 


Fig. 7.

Average concentrations of glyphosate (▪) and aminomethylphosphonic acid (AMPA) (○) in the leachate (mean + SD, n = 2 for sand and n = 3 for clay). No AMPA was found in the leachate from sand.

 


Fig. 8.

Residues of glyphosate and aminomethylphosphonic acid (AMPA) in the 0- to 30-, 30- to 60-, and 60- to 90-cm soil layers 748 d after application. dw = dry weight.