How the 70-kg Man Impacts NIOSH-Recommended Exposure Limits

Details

• Personal Author:
  Lucas L ; Whittaker C
• Description:
  This study examines the impact of assuming a single human body weight value when developing occupational exposure limits. NIOSH uses quantitative risk assessment to evaluate the risks of chemical exposures in the workplace and as a basis of its occupational exposure limits, Recommended Exposure Limits (RELs). Simplifying assumptions are a necessary part of quantitative risk assessment and there are several key assumptions that go into occupational risk assessments - one, of note, is the assumption that the typical human body weight is 70 kg (typically also assumed to be male). In this investigation, the public draft proposed NIOSH REL for 1-bromopropane (1-BP) was used as a case study to explore the impact of this assumption. In the public draft risk assessment, NIOSH used data from a National Toxicology Program mouse 2-year bioassay to estimate the risk of cancer in workers exposed to 1-BP over a working lifetime. The risks were calculated using Bayesian model averaging of Benchmark Dose estimates of the mouse dose-response data. The BMDL (lower limit on the Benchmark Dose estimate) was extrapolated to humans, assuming dose equivalence in units of mg/kg-day scaled according to body weight to the 0.75 power to find the human equivalent BMDL at 70 kg. This value was then converted to ppm and adjusted to account for an 8-hour workday 5 days per week to derive the proposed REL of 0.3 ppm. At the draft REL, the risk of cancer was estimated to be 1 excess case per 1000 workers exposed to 1-BP every workday over a working lifetime of 45 years. In this study, the NHANES data for body weights by gender in the United States were used to create a distribution of weights for both adult male and adult female populations. From data collected in 2021, the mean body weight in the female population was 77.5 kg +/- 21.2. In the male population, mean body weight was 90.6 kg +/- 20.85. A simulation was run on a randomly selected body weight from the distribution of body weights and the risk of 1-BP was recalculated based on this selection. This experiment was repeated 10,000 times, each time using different randomly selected body weights. The results show how risks vary depending on body weight. Instead of a risk of 1/1000, for example, an 80 kg person exposed to 0.3 ppm 1-BP would have a risk of 0.91/1000 - a nearly 10% difference. Conversely, a lighter individual would have a higher risk when exposed to the same concentration of 1-BP. Since the mean body weights for males and females were higher than the assumption of 70 kg, the mean female risk was 0.99/1000 and the mean male risk was 0.87/1000. However, for more than 38% of the female population and 17% of the male population, the estimated risks were higher than the 1/1000 target risk level in the NIOSH public draft document. These results demonstrate the importance of understanding and explaining the impact of the assumptions used in quantitative risk assessment. The unbalanced impact of the assumption depending on gender also points out hidden potential gender bias in occupational risk assessment. Clearly identifying and discussing the assumptions used in a quantitative risk assessment is an important aspect of ensuring that the occupational exposure limit is appropriately used in the workplace. [Description provided by NIOSH]
• Subjects:
  Body Weight Occupational Exposure Occupational Health Risk Assessment Safety Sex Characteristics
• Keywords:
  Body Weight Exposure Limits Gender Factors Occupational Exposure Quantitative Risk Assessment Recommended Exposure Limits RELs
• ISSN:
  1096-6080
• Document Type:
  Text
• Genre:
  Abstract or Summary
• Place as Subject:
  Massachusetts ; Ohio ; OSHA Region 1 ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  DSI - Division of Science Integration
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Volume:
  192
• NIOSHTIC Number:
  nn:20067219
• Citation:
  Toxicologist 2023 Mar; 192(S1):277
• Federal Fiscal Year:
  2023
• Peer Reviewed:
  False
• Source Full Name:
  The Toxicologist. Society of Toxicology 62nd Annual Meeting & ToxExpo, March 19-23, 2023, Nashville, Tennessee
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:577920d7b64b06e9a0706d00c634493fe6db346958dfb03864925b571463dc81d79e42ebc9ab6f1da474d138a82245b627876de73d3ed847d8e67b1003b24361
• Download URL:
  https://stacks.cdc.gov/view/cdc/231346/cdc_231346_DS1.pdf
• File Type:
  [PDF - 1.09 MB ]