Human experimental exposure to glyphosate and biomonitoring of young Swedish adults

Glyphosate (GLY), N-(phosphonomethyl) glycine, is the most widely used herbicide in the world. It is a broad-spectrum herbicide, also used in crop desiccation. Agricultural workers may be occupationally exposed and general populations may be exposed to GLY mainly through diet. We studied the kinetics of GLY by measuring the parent compound and its metabolite aminomethylphosphonic acid (AMPA) in urine samples of three volunteers after an experimental oral exposure. We further examined GLY exposure by measuring GLY and AMPA in spot urine samples of 197 young adults in the general population in Scania, southern Sweden. Urine samples were analyzed using LC-MS/MS. In the experimental exposure, three healthy volunteers received an oral dose equivalent to 50% of the ADI for GLY. Urinary samples were collected up to 100 h after the exposure. The excretion of GLY to urine seemed to follow first-order kinetics and a two-phase excretion. The excretion half-life of GLY (density adjusted) was 6-9 h in the rapid phase and 18-33 h in the slower phase. The total dose recovered as unchanged GLY in the urine samples of volunteers was 1-6%. The metabolite AMPA was found to be 0.01-0.04% of the total dose of GLY. In the population of young adults, the median concentration was below 0.1 μg/L and a maximum concentration being 3.39 μg/L (density adjusted). AMPA was generally detected in lower concentrations (maximum = 0.99 μg/L). A moderate correlation (Spearman's ρ = 0.56) was observed between GLY and AMPA concentrations. Overall, the results may suggest that GLY and AMPA partly originate from separate exposures and that unchanged GLY is a more suitable biomarker of exposure.