Seasonal patterns and degradation of glyphosate and AMPA in the Baltic Sea

Extensive application of the widely used herbicide glyphosate has made it a ubiquitous environmental pollutant. In our previous study in 2019, glyphosate and its metabolite aminomethylphosphonic acid (AMPA) were detected in Baltic Sea waters for the first time. Initial evidence from that study suggested that glyphosate might be more persistent than AMPA. Our goal was to expand upon these preliminary findings by providing a more comprehensive temporal and spatial assessment for the Baltic Sea. In order to examine glyphosate and AMPA seasonal fluctuations and spatial distribution, we analyzed surface water samples from (1) the Baltic Sea, taken during winter and summer of 2020, (2) from a coastal site over the course of a year, and (3) from two selected tributaries. Glyphosate and AMPA were detected at all study sites and concentrations varied seasonally and spatially. In winter 2020, Baltic Sea surface water median concentrations were 0.21 and 2.52 ng L^-1 for glyphosate and AMPA, respectively, while 0.53 and 1.03 ng L^-1 were determined in summer 2020; median concentrations at the coastal site were 0.96 and 2.81 ng L^-1, over the entire year. Measured glyphosate concentrations at the tributaries and the coastal site indicate potential for temporary medium risk to aquatic organisms. Results from a seawater degradation experiment using isotopically labelled substrates suggest that AMPA is removed faster than glyphosate. This supports the observed distribution pattern for both compounds in the Baltic Sea.