Glyphosate transport through weathered granite soils under irrigated and non-irrigated conditions — Barcelona, Spain

The transport of Glyphosate ([N-phosphonomethyl] glycine), AMPA (aminomethylphosphonic acid, CH6NO3P), and Bromide (Br−) has been studied, in the Mediterranean Maresme area of Spain, north of Barcelona, where groundwater is located at a depth of 5.5 m. The unsaturated zone of weathered — granite soils was characterized in adjacent irrigated and non-irrigated experimental plots where 11 and 10 boreholes were drilled, respectively. At the non irrigated plot, the first half of the period was affected by a persistent and intense rainfall. After 69 days of application residues of Glyphosate up to 73.6 μgg− 1 were detected till a depth of 0.5 m under irrigated conditions, AMPA, analyzed only in the irrigated plot was detected till a depth of 0.5 m. According to the retardation coefficient of Glyphosate as compared to that of Br− for the topsoil and subsoil (80 and 83, respectively) and the maximum observed migration depth of Br− (2.9 m) Glyphosate and AMPA should have been detected till a depth of 0.05 m only. Such migration could be related to the low content of organic matter and clays in the soils; recharge generated by irrigation and heavy rain, and possible preferential solute transport and/or colloidal mediated transport.