Dissipation of the herbicide active ingredient glyphosate in natural water samples in the presence of biofilms

Abstract

Dissipation of the herbicide active ingredient glyphosate was investigated in natural waters. To assess combined effects, glyphosate was applied in its pure form (glyphosate isopropylammonium salt) and in preparation Roundup Classic® formulated with polyethoxylated tallowamines (POEA). Standing and running surface water samples originated from Lake Balaton and River Danube between early May and mid-June of 2015. The kinetics of dissipation of glyphosate, measured by high-performance liquid chromatography combined with UV-VIS absorbance detection or tandem mass spectrometry, was investigated under laboratory conditions in aquaria with or without the presence of biofilms. The quantity and the biofilm structure of algal biomass were determined by in vivo fluorimetry and scanning electron microscopy. The presence of POEA affected the dissipation of glyphosate, and dissipation profiles differed in the investigated natural waters. Significantly higher initial concentrations of glyphosate were measured in River Danube for treatment with formulated glyphosate (101.4 ± 6.2 µg L−1), than with glyphosate alone (79.9 ± 6.6 µg L−1), and dissipation to a residual level (57.6 ± 1.4 µg L−1) consequently took longer (approximately by 1 day). Degradation of glyphosate from the initial level (91.24 ± 5.9 µg L−1) in Lake Balaton was not detected. Phytotoxic effects of glyphosate, particularly if enhanced by a formulant on algal biomass, were observed. Thus, 5–18% and 11–33% of algal biomass reduction was determined in River Danube upon treatments with glyphosate and Roundup Classic®, respectively. Corresponding biomass decreases in Lake Balaton were 1.3–13% and 9–14%, respectively, accompanied by an overall decay in the algal biofilms. In River Danube, treatments resulted in the occurrence of 1.4–5.8% of green algae in the algal biomass in 28 days, while green algae were not detected in the untreated control. The results indicate that glyphosate is capable of modifying the structure of the algal community and to induce increased secretion of extracellular polymeric substances matrix in the biofilms assessed.