Circadian rhythmicity of the urinary excretion of mercury, potassium and catecholamines in unconventional shift-work systems.

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Abstract
Round the clock urinary excretion rates of Hg were assessed for 2 series of unconventional patterns of activity and sleep in subjects who were not exposed to occupational medical or other obvious sources of Hg. In 1st series, urine was collected in 3 h periods from 6 subjects during 1st and last 2 days of a 4 wk, continuous 6 h shift (car ferry, watches either 08:00-14:00 and 20:00-02:00 or 14:00-20:00 and 02:00-08:00). In 2nd series, urine was collected in 4 h periods from 5 subjects working an 8 h experimental rotation shift compressed into 5 d (work 2 mornings, 8 h interval, work 2 nights, 8 h interval, work 2 afternoons). Mean daily excretion rate of 11 subjects (48 investigation days, 334 urine samples) was 14.5 pmol Hg/min (range 5.5-24.4 pmol Hg/min). Hg excretion oscillated regularly during 24 h by .+-. 20-25% of individuals daily mean excretion rates. Peak excretion rates were found at 06:52 in 1st and 06:42 in 2nd series (cosinor treatment). Due to circadian rhythm, mean 24 h excretion rates were best represented (r = 0.92) by analyses of urine produced around noon (spot samples, collection periods 11:00-14:00 and 10:00-14:00, respectively). Circadian oscillations of Hg excretion were not influenced by widely different and varying activity-sleep patterns of the 2 series. Rhythmicity of K excretion (peaks at around 14:00) was more irregular. Stable oscillations of Hg excretion contrasted most with excretion of adrenaline and noradrenaline which without losing the basic 24 h rhythmicity, closely followed unconventional patterns of activity and sleep.

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