Non-point source pollution of glyphosate and AMPA in a rural basin from the southeast Pampas, Argentina

Abstract

We measured the occurrence and seasonal variations of glyphosate and its metabolite, aminomethylphosphonic acid (AMPA), in different environmental compartments within the limits of an agricultural basin. This topic is of high relevance since glyphosate is the most applied pesticide in agricultural systems worldwide. We were able to quantify the seasonal variations of glyphosate that result mainly from endo-drift inputs, that is, from direct spraying either onto genetically modified (GM) crops (i.e., soybean and maize) or onto weeds in no-till practices. We found that both glyphosate and AMPA accumulate in soil, but the metabolite accumulates to a greater extent due to its higher persistence. Knowing that glyphosate and AMPA were present in soils (> 93% of detection for both compounds), we aimed to study the dispersion to other environmental compartments (surface water, stream sediments, and groundwater), in order to establish the degree of non-point source pollution. Also, we assessed the relationship between the water-table depth and glyphosate and AMPA levels in groundwater. All of the studied compartments had variable levels of glyphosate and AMPA. The highest frequency of detections was found in the stream sediments samples (glyphosate 95%, AMPA 100%), followed by surface water (glyphosate 28%, AMPA 50%) and then groundwater (glyphosate 24%, AMPA 33%). Despite glyphosate being considered a molecule with low vertical mobility in soils, we found that its detection in groundwater was strongly associated with the month where glyphosate concentration in soil was the highest. However, we did not find a direct relation between groundwater table depth and glyphosate or AMPA detections. This is the first simultaneous study of glyphosate and AMPA seasonal variations in soil, groundwater, surface water, and sediments within a rural basin.

Ecological Risk Assessment (ERA) of pesticides from freshwater ecosystems in the Pampas region of Argentina: Legacy and current use chemicals contribution

“…This explains the prevalence of herbicides in monitoring studies, given their wide use in extensive agriculture in the Pampas region; the most used chemicals within this group are glyphosate and atrazine (Leguizamón, 2014). This widespread use has led to finding them not only in the water column of freshwater ecosystems, but also in soils, sediments, groundwater and even in rainfall (Aparicio et al, 2013;Alonso et al, 2018;Okada et al, 2018).…”

Pesticides in water sources used for human consumption in the semiarid region of Argentina

“…Frequencies reported by other authors in watercourses of agricultural regions were generally lower but concentrations were several times higher [31,45,46]. Okada et al [47] monitored a stream southeast of the province of Buenos Aires (Argentina) and found glyphosate and AMPA in 28% and 50% of the samples, with a maximum concentration of 8.2 μg L −1 and 3.7 μg L −1 , respectively. On the other hand, Mac Loughlin et al [48] detected glyphosate and AMPA in a water body passing through a horticultural region in the Carnaval basin at concentrations up to 17.0 µg L −1 for glyphosate and 4.5 µg L −1 for AMPA, with a non-distinguishable behavior between seasons like our case.…”

“…In groundwater from southeast of Buenos Aires, Okada et al [47] detected glyphosate and AMPA in 24% and 33% of the samples, with maximum levels of 8.5 μg L −1 and 1.9 μg L −1 , respectively. The lower frequencies and concentrations found in boreholes coincide with other studies [16,31], although Primost et al [46] did not detect these compounds in aquifers of the province of Entre Ríos with depths similar to Sachayoj, and Okada et al [47] did not find an association between depth and presence of glyphosate or AMPA.…”

“…In groundwater from southeast of Buenos Aires, Okada et al [47] detected glyphosate and AMPA in 24% and 33% of the samples, with maximum levels of 8.5 μg L −1 and 1.9 μg L −1 , respectively. The lower frequencies and concentrations found in boreholes coincide with other studies [16,31], although Primost et al [46] did not detect these compounds in aquifers of the province of Entre Ríos with depths similar to Sachayoj, and Okada et al [47] did not find an association between depth and presence of glyphosate or AMPA. Lutri et al [52] detected glyphosate (1.2-2.0 µg L −1 ) and AMPA (1.5-3.1 µg L −1 ) in 15.8% of groundwater samples, pointing out that their detection was related to areas with shallow water table (< 4 m), low hydraulic conductivity (1.5 m d −1 ), low hydraulic gradient (0.16%) and very low flow rate (0.024 m d −1 ).…”

Interactions among Glyphosate and Phosphate in Soils: Laboratory Retention and Transport Studies

“…Typical ranges of GPS and PO 4 in soils are highly dependent on soil type and land use management. Maximum levels of GPS in soils from agriculturally intensive areas of Argentina range from 1.2 to 8.1 mg kg −1 soil (Primost et al, 2017; Okada et al, 2018), whereas total soil P typically ranges from 10 1 to 10 3 g P kg −1 soil (Kruse et al, 2015). Several studies demonstrated that GPS sorption by soils decreased in the presence of PO 4 .…”