Effects of work schedule and period of exposure on changes in urinary chromium and nickel excretion among rotating shift workers in a stainless-steel plant

ABSTRACT

We investigated the association between the period of exposure and changes in urinary excretion of chromium and nickel among rotating shift workers in a stainless-steel plant. The study participants were composed of two groups: the workers who were occupationally exposed to metals (“exposed group”) and those who were not occupationally exposed to metals (“unexposed group”). The exposed and unexposed groups consisted of 56 and 40 male rotating shift workers, respectively. Urine samples were collected immediately before and immediately after the day shift, evening shift, and night shift. Urinary chromium and nickel were measured using inductively coupled plasma mass spectrometry. To correct for variations in urine dilution, urinary metal concentrations were expressed as a ratio to urinary creatinine concentration. In the exposed group, post-shift urinary excretion of chromium was significantly higher than pre-shift excretion. However, although urinary chromium excretion clearly increased after the day and night shift [63% (p < .0001) and 87% (p < .0001), respectively], urinary chromium excretion after the evening shift was only slightly higher than that measured before the evening shift (8%, p = .028). Similar patterns were found for urinary nickel excretion (p = .0001, 0.20, and 0.18 for the day, evening, and night shifts, respectively). Non-uniform urinary excretion of metals between the day shift, evening shift, and night shift were observed in the exposed group; specifically, urinary metal excretion increased only slightly during the evening shift. In the unexposed group, no significant increase or decrease was found in median urinary chromium or nickel excretion (p= .63–0.87). Work shift-specific permissible exposure level would be necessary.

KEYWORDS:

• Biological monitoring
• chronotoxicology
• circadian rhythm
• diurnal variation
• shift work

Acknowledgments

This study was supported by a research grant from the National Institute of Occupational Safety and Health, Japan (P21-01). Hiroaki Itoh, one of the authors, is an awardee of a postdoctoral fellowship from the Global Center of Excellence Program (E03), MEXT, Japan. We also thank Dr Peihong Nan for his help and support.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Additional information

Funding

This work was supported by the Ministry of Education, Culture, Sports, Science and Technology [a postdoctoral fellowship from the Global Center of Excellence Program (E03)]; National Institute of Occupational Safety and Health, Japan [P21-01].