Glyphosate and atrazine in rainfall and soils in agroproductive areas of the pampas region in Argentina

Highlights: • GLP, AMPA, and ATZ were found in 80% of the rainwater samples in the Argentine pampas. • Soils as a source of herbicides did not define a local atmospheric fingerprint. • Median GLP concentrations in rainwater were associated with precipitation dynamics. • ATZ levels followed no specific pattern for either rainwater or soil samples. The presence in the atmosphere of glyphosate (GLP) and atrazine (ATZ) was investigated—those pesticides dominating the market in Argentina—through rain, as the main climatic phenomenon associated with wet deposition, both through analyzing source-receptor relationships with soil along with the climatic influences that may condition that transport and through estimating the annual deposition on the surface of the Argentine pampas. Rainwater samples (n = 112) were collected throughout each rainfall in urban areas of the pampas having different degrees of land use and with extensive crop production plus subsurface-soil samples (n = 58) from the relevant periurban sites. The herbicides—analyzed by liquid-chromatography–mass-spectrometry—were detected in >80% of the rain samples at median-to-maximum concentrations of 1.24–67.3 μg·L⁻¹ (GLP) and 0.22–26.9 μg·L⁻¹(ATZ), while aminomethylphosphonic acid (AMPA) was detected at 34% (0.75–7.91 μg·L⁻¹). In soils, GLP was more frequently registered (41%; 102–323 μg·kg⁻¹) followed by ATZ (32%; 7–66 μg·kg⁻¹) and then AMPA (22%; 223–732 μg·kg⁻¹). The maximum GLP concentrations quantified in rainwater exceeded the previously reported levels for the USA and Canada. No associations were observed between soil and rainwater concentrations in the same monitoring areas—despite the soil's action as a source, as evidenced through the AMPA present in rainwater. Median GLP concentrations were significantly associated with isohyets, in an increasing gradient from the east to the west—as such in an inverse pattern to that of the annual rainfall volumes; whereas ATZ-rainwater levels exhibited no characteristic spatial configuration. The estimated annual deposition of GLP by rainfall indicated that more than onc source of a herbicide can lead to its presence in the atmosphere and points out the relevance of rainfall's contribution to the surface levels of a pollutant.