Is there an optimal sampling time and number of samples for assessing exposure to fast elimination endocrine disruptors with urinary biomarkers? F. Faÿs a,b, ⁎, P. Palazzi a , E.M. Hardy a , C. Schaeffer a , C. Phillipat c , E. Zeimet a , M. Vaillant d , C. Beausoleil e , C. Rousselle e , R. Slama c , B.M.R. Appenzeller a a Human Biomonitoring Research Unit, Department of Population Health, Luxembourg Institute of Health, 1 A-B rue Thomas Edison, 1445 Strassen, Luxembourg b University of Luxembourg, 2, avenue de l'Université, L-4365 Esch-sur-Alzette, Luxembourg c University Grenoble Alpes, Inserm, CNRS, Team of Environmental Epidemiology Applied to Reproduction and Respiratory Health, Institute for Advanced Biosciences (IAB), Site Santé - Allée des Alpes, 38700 La Tronche, France d Competence Center for Methodology and Statistics, Department of Population Health, Luxembourg Institute of Health, 1 A-B rue Thomas Edison, 1445 Strassen, Luxembourg e ANSES, Risk Assessment Department, 14 rue Pierre et Marie Curie, 94701 Maisons-Alfort, France HIGHLIGHTS • 805 urine samples were collected over 6 months from 16 volunteers. • 16 phthalate metabolites, 4 bisphenols and 9 pesticide metabolites were ana- lyzed. • 21 of the 29 fast elimination biomarkers were detected in N80% of samples. • No evidence to prefer a specific time of day for sample collection was observed. • High variability over time was observed for all the urinary biomarkers. GRAPHICAL ABSTRACT abstract article info Article history: Received 20 May 2020 Received in revised form 17 July 2020 Accepted 21 July 2020 Available online 25 July 2020 Editor: Adrian Covaci In studies investigating the effects of endocrine disruptors (ED) such as phthalates, bisphenols and some pesti- cides on human health, exposure is usually characterized with urinary metabolites. The variability of biomarkers concentration, due to rapid elimination from the body combined with frequent exposure is however pointed out as a major limitation to exposure assessment. This study was conducted to assess variability of urinary metabolites of ED, and to investigate how sampling time and number of samples analyzed impacts exposure assessment. Urine samples were collected over 6 months from 16 volunteers according to a random sampling design, and an- alyzed for 16 phthalate metabolites, 9 pesticide metabolites and 4 bisphenols. The amount of biomarkers ex- creted in urine at different times of the day were compared. In parallel, 2 algorithms were developed to investigate the effect of the number of urine samples analyzed per subject on exposure assessment reliability. In the 805 urine samples collected from the participants, all the biomarkers tested were detected, and 18 were present in N90% of the samples. Biomarkers variability was highlighted by the low intraclass correlation coeffi- cients (ICC) ranging from 0.09 to 0.51. Comparing the amount of biomarkers excreted in urine at different time did not allow to identify a preferred moment for urine collection between first day urine, morning, afternoon and evening. Algorithms demonstrated that between 10 (for monobenzyl (MBzP) phthalate) and 31 (for bisphenol S) samples were necessary to correctly classify 87.5% of the subjects into quartiles according to their level of exposure. Keywords: Urinary biomarkers Variability Exposure assessment Bisphenols Phthalates Sampling strategy Science of the Total Environment 747 (2020) 141185 ⁎ Corresponding author at: Human Biomonitoring Research Unit, Department of Population Health, Luxembourg Institute of Health, 1 A-B rue Thomas Edison, 1445 Strassen, Luxembourg. E-mail address: francois.fays@lih.lu (F. Faÿs). https://doi.org/10.1016/j.scitotenv.2020.141185 0048-9697/© 2020 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv