Hydrogeological features affecting spatial distribution of glyphosate and AMPA in groundwater and surface water in an agroecosystem. Córdoba, Argentina

LUTRI, V.F.; MATTEODA, E.; BLARASIN, M.; APARICIO, V.; GIACOBONE, D.; MALDONADO, L.; BECHER QUINODOZ, F.; CABRERA, A.; GIULIANO ALBO, J.

THE SCIENCE OF TOTAL ENVIRONMENT

Elsiever

Año: 2020 vol. 711

0048-9697

The study area is located in the eastern slope of Las Peñas Mountain and its adjacentoriental fluvio-aeolian-plain. Agriculture is the main activity (soybean, maize, wheat, peanutsand alfalfa) with no-tillage farming and intensive use of agrochemicals (pesticides-fertilizers).Glyphosate (N-phosphono-methylglycine) is the most common used herbicide which suffersmicrobial biodegradation giving aminomethylphosphonic acid (AMPA), its main metabolite.The objective of this work is to evaluate hydrogeological features which influence thepresence of glyphosate and AMPA in waters. In the study area, the main flow direction ofsurface and groundwater is NW-SE. The unsaturated zone thickness decreases in the same direction from 60 to 0 m, so groundwater surges in low areas in the eastern sector. From thetotal water samples collected, glyphosate was detected in 66% of surface water samples(0.2 to 167.4 μg/L), in 15.8% of the groundwater samples (1.3 to 2 μg/L) and in the harvestedprecipitation sample (0.2 μg/L). AMPA was found in 33% of surface water and 15.8% ofgroundwater. The herbicide detection was related to areas with the shallowest water table(< 4 m), low hydraulic conductivity in the aquifer (K= 1.5 m/d), low hydraulic gradient (i=0.16%) and very low flow velocity (0.02 m/d). The most outstanding result is that thegroundwater presents higher values in comparison with the surface water samples, whichcan be explained by the greater dilution capacity of streams. The detection of glyphosateand AMPA in the unconfined aquifer shows that the application for decades under theprevailing agricultural model exceeds the degradation potential of the soil and theunsaturated zone, causing groundwater contamination.