First hydrological study on the seasonal occurrence of glyphosate, glufosinate, and their metabolites in the Red River system, North Vietnam

Abstract

We report the spatial and seasonal distribution of organophosphorus herbicides, namely glyphosate (GLYP), glufosinate (GLUF), and their respective metabolites aminomethyl phosphonic acid (AMPA) and 3-(methylphosphinico)-propionic acid (MPPA), in the Red River system (North Vietnam), a major water body in Southeast Asia. The four compounds were measured at 34 sampling stations located from upstream to the estuary during the dry (March) and wet (July) seasons in 2019. Large seasonal variations in herbicide concentrations were measured for the four analytes from upstream to the estuary, with the highest range of variations observed during the wet season. In the surface waters of the Red River, the maximum concentrations of GLUF (234 ng L–1), GLYP (565 ng L–1) and its metabolite AMPA (1329 ng L–1), occurred in the wet season. These values however, are lower than reported in other rivers worldwide. In contrast, the estimated fluxes of these compounds in the Red River water basin were very high during the wet season, i.e., up to 121, 50.2, 284, and 186 kg d–1 for GLYP, GLUF, AMPA, and MPPA, respectively. During both seasons, we observed correlations between the four compounds and ammonium (NH4+), suggesting that both nitrogen containing fertilizers and herbicides were applied in areas close to the river shore. The concentrations and fluxes of the herbicides GLYP, GLUF, and their metabolites determined in the Red River were compared to those recorded in other world river systems, such as the Garonne River (France), thus highlighting the importance of monitoring these compounds in surface waters.