Exploring the half-life of glyphosate in human urine samples

Background: The International Agency for Research on Cancer (IARC) has recently classified glyphosate as a Group 2A 'probably carcinogenic to humans'. Due to this carcinogenic classification and resulting international debate, there is an increased demand for studies evaluating human health effects from glyphosate exposures. There is currently limited information on human exposures to glyphosate and a paucity of data regarding glyphosate's biological half-life in humans. Objective: This study aims to estimate the human half-life of glyphosate from human urine samples collected from amenity horticulture workers using glyphosate based pesticide products. Methods: Full void urine spot samples were collected over a period of approximately 24 h for eight work tasks involving seven workers. The elimination time and estimation of the half-life of glyphosate using three different measurement metrics: the unadjusted glyphosate concentrations, creatinine corrected concentrations and by using Urinary Excretion Rates (UER) (mu g L-1, mu mol/mol creatinine and UER mu g L-1) was calculated by summary and linear interpolation using regression analysis. Results: This study estimates the human biological half-life of glyphosate as approximately 5 1/2, 10 and 7 1/4 hours for unadjusted samples, creatinine corrected concentrations and by using UER (mu g L-1, pmol/mol creatinine, UER mu g L-1), respectively. The approximated glyphosate half-life calculations seem to have less variability when using the UER compared to the other measuring metrics. Conclusion This study provides new information on the elimination rate of glyphosate and an approximate biological half-life range for humans. This information can help optimise the design of sampling strategies, as well as assisting in the interpretation of results for human biomonitoring studies involving this active ingredient. The data could also contribute to the development or refinement of Physiologically Based PharmacoKinetic (PBPK) models for glyphosate.