Main content area

Glyphosate sorption to soils and sediments predicted by pedotransfer functions

Dollinger, Jeanne, Dagès, Cécile, Voltz, Marc
Environmental chemistry letters 2015 v.13 no.3 pp. 293-307
carbon, cation exchange capacity, cations, clay, clay fraction, environmental factors, freshwater, glyphosate, groundwater, models, pH, pedotransfer functions, prediction, regression analysis, risk assessment, sediments, sorption, water pollution, weed control
Glyphosate is the most applied herbicide for weed control in agriculture worldwide. Excessive application of glyphosate induces water pollution. The transfer of glyphosate to freshwater and groundwater is largely controlled by glyphosate sorption to soils and sediments. Sorption coefficients are therefore the most sensitive parameters in models used for risk assessment. However, the variations in glyphosate sorption among soils and sediments are poorly understood. Here we review glyphosate sorption parameters and their variation with selected soils and sediment. We use this knowledge to build pedotransfer functions that allow predicting sorption parameters, Kd, Kf and n, for a wide range of soils and sediments. We gathered glyphosate sorption parameters, 101 Kf, n and equivalent Kd, and associated soil properties. These data were then used to perform stepwise multiple regression analyses to build the pedotransfer functions. The linear (Kd) and Freundlich (Kf, n) pedotransfer functions were benchmarked against experimental data. We found the following major points: (1) Under current environmental conditions, sorption is best predicted by the Kd pedotransfer function. (2) The pedotransfer function is Kd = 7.20*CEC − 1.31*Clay + 24.82 (Kd in L kg⁻¹, CEC in cmol kg⁻¹ and clay in %). (3) Cation exchange capacity (CEC) and clay content are the main drivers of Kd variability across soils and sediments. Freundlich parameters are additionally influenced by pH and organic carbon. This suggests that the formation of complexes between glyphosate phosphonate groups and soil-exchanged polyvalent cations dominates sorption across the range of analyzed soils.