Perspectives on the relevance of the circadian time structure to workplace threshold limit values and employee biological monitoring

ABSTRACT

The circadian time structure (CTS) and its disruption by rotating and nightshift schedules relative to work performance, accident risk, and health/wellbeing have long been areas of occupational medicine research. Yet, there has been little exploration of the relevance of the CTS to setting short-term, time-weighted, and ceiling threshold limit values (TLVs); conducting employee biological monitoring (BM); and establishing normative reference biological exposure indices (BEIs). Numerous publications during the past six decades document the CTS substantially affects the disposition – absorption, distribution, metabolism, and elimination – and effects of medications. Additionally, laboratory animal and human studies verify the tolerance to chemical, biological (contagious), and physical agents can differ extensively according to the circadian time of exposure. Because of slow and usually incomplete CTS adjustment by rotating and permanent nightshift workers, occupational chemical and other contaminant encounters occur during a different circadian stage than for dayshift workers. Thus, the intended protection of some TLVs when working the nightshift compared to dayshift might be insufficient, especially in high-risk settings. The CTS is germane to employee BM in that large-amplitude predictable-in-time 24h variation can occur in the concentration of urine, blood, and saliva of monitored chemical contaminants and their metabolites plus biomarkers indicative of adverse xenobiotic exposure. The concept of biological time-qualified (for rhythms) reference values, currently of interest to clinical laboratory pathology practice, is seemingly applicable to industrial medicine as circadian time and workshift-specific BEIs to improve surveillance of night workers, in particular. Furthermore, BM as serial assessments performed frequently both during and off work, exemplified by employee self-measurement of lung function using a small portable peak expiratory flow meter, can easily identify intolerance before induction of pathology.

KEYWORDS:

• Circadian rhythm
• industrial hygiene
• occupational medicine
• threshold limit values
• human biological monitoring
• biological exposure indices

Acknowledgments

We gratefully acknowledge the contributions of pioneers of the field of chronobiology who through their insight and research during their lifetime established the foundation for the many translational applications in clinical and occupational medicine from which many, including us authors, now benefit; among them in alphabetical order are: Jürgen Aschoff, Israel Ashkenazi, William Colquhoun, Franz Halberg, Erhard Haus, Eugene Kanabrocki, Karl Klein, Nathaniel Kleitman, Heinz von Mayersbach, Joseph Rutenfranz, Larry Scheving, James Waterhouse, Hans Wegmann, and Elliot Weitzman.

Disclosure statement

The content of this review article represents the collective contributions of the listed authors. None of the authors have commercial interests of any kind to declare that are of relevance to the contents of the article.