Circadian Rhythms in the Urinary Excretion of Cadmium: Consequences for Biological Monitoring

Abstract

The measurement of cadmium concentrations in urine, adjusted to creatinine, can vary widely for a given person depending on the collection time during the day. This article attempts to describe these variations for a group of moderately exposed workers. Fifteen foundry workers collected all of their urine for a week, without changing their daily habits. Each sample was characterized by its time of emission, volume, and cadmium and creatinine content. A total of 813 samples were collected. The data obtained are grouped into four 6-hour periods: morning, afternoon (working time), evening, and night. The cadmium concentrations adjusted to creatinine and urinary flow are computed. Cyclical daily fluctuations are confirmed using nonparametric statistical Friedman's test. Maxima are observed in the morning and minima in the evening. To avoid statistical distortion resulting from large level differences between individuals, the concentrations are expressed as variations from the median value for each person. The statistical results show that the amplitude of daily cycles and the scattering are at a minimum when the concentrations are adjusted to creatinine. For these reasons, it appears reasonable to collect spot urines at fixed hours in the evening and to adjust the concentrations to creatinine when studying cadmium excretion. Perret, D.; Bilat, D.; Schenk, O.; Maillard, J.-M.: Circadian Rhythms in the Urinary Excretion of Cadmium: Consequences for Biological Monitoring. Appl. Occup. Environ. Hyg. 9(1):36–39;1994.

Key Words:

• biological monitoring
• circadian rhythms
• creatinine adjustment
• foundry workers
• spot urine sampling
• urinary excretion of cadmium
• urinary flow adjustment