Evaluation of Seasonal Variability of Toxic and Essential Elements in Urine Analyzed by Inductively Coupled Plasma Mass Spectrometry

Human exposure to elements is a process difficult to control and monitor. Studies on this topic usually rely on single spot urine sample to assess exposure, with the risk of ignoring variability over a longer period. In this work, we measured the urinary excretion of toxic and essential elements during 1 year with the overall goal of exploring the variability caused by seasonality on their concentration. Seven participants were recruited, and first morning urines were collected three times for each season, during November, January, April and July. Participants followed the same balanced diet during the week of collection. We then monitored nineteen essential and toxic elements in urines by inductively coupled plasma mass spectrometry. Unsupervised multivariate statistical analysis separated samples collected during summer from the ones collected during other seasons. Twelve elements had a significant seasonal variation (ANOVA test, p < 0.05) and their levels resulted increased during summer. These elements were both contaminants, such as Ni, Hg, Cd and Tl, and essential elements such as Se and Cu. However, none of these elements was detected at toxic concentration. In this study, we point out for the first time the variability of urine element concentration due to seasonality and we propose that the season of collection should be considered when providing urinary reference values of elements.