Under the Microscope: Formaldehyde Exposure in National Health Service Pathology Departments in the United Kingdom

Technical Summary: Formaldehyde Exposure in National Health Service Pathology Departments

Problem Statement
Formaldehyde is a known human carcinogen and a potent irritant associated with severe short- and long-term deleterious effects on the respiratory, female reproductive, and nervous systems. While the United States Environmental Protection Agency (EPA) has recently classified formaldehyde as presenting an "unreasonable risk of injury to human health," the United Kingdom (UK) maintains the world's highest defined permissible occupational exposure limits (WELs): 2 ppm for both long-term (8-hour time-weighted average) and short-term (15-minute) exposure. In contrast, the European Union (EU) has mandated stricter limits (0.3 ppm long-term; 0.6 ppm short-term).

Under UK Control of Substances Hazardous to Health (COSHH) regulations, exposure to carcinogens must be reduced to "as low as is reasonably practicable" (ALARP). Pathology departments, which utilize formaldehyde (formalin) for tissue preservation, represent high-risk occupational environments. However, the extent of formaldehyde exposure among UK National Health Service (NHS) pathology workers had not been previously investigated. This study addresses the gap in empirical data regarding airborne formaldehyde concentrations and the adequacy of exposure controls within NHS cell pathology departments.

Methodology
The authors utilized the UK Freedom of Information Act (2000) to request 12 months of formaldehyde airborne monitoring data (covering the period 2024–2025) from cell pathology departments across 122 NHS Trusts in England, Scotland, Wales, and Northern Ireland. The request sought data categorized into specific concentration bins (ranging from >0 ppm to >2 ppm) rather than raw data, to facilitate disclosure while avoiding excessive administrative burden on Trusts.

The study cohort included 117 cell pathology departments that successfully disclosed suitable records, representing over 1.7 million distinct monitoring events. The analysis employed two primary statistical approaches:

1. Empirical Analysis: The proportion of monitoring events exceeding EU and UK WELs was calculated. Percentile estimates (50th and 95th) were derived using Monte Carlo simulations with uniform distributions to reconstruct datasets from the binned frequency data, avoiding parametric bias.
2. EN 689:2018 Statistical Evaluation: For departments where the empirical 95th percentile exceeded 0.3 ppm, the authors applied the statistical strategy outlined in Annex F of the European standard EN 689:2018. This involved calculating the geometric mean (GM) and geometric standard deviation (GSD) to determine the Upper Tolerance Limit (UTL95,70), a conservative estimate ensuring 70% confidence that the true 95th percentile does not exceed the calculated limit.

Key Results

• Monitoring Frequency: Monitoring was infrequent across the majority of sites. Only 27% of departments monitored daily or continuously. The remaining 73% monitored weekly or less (19% weekly, 34% monthly, 15% quarterly, 4% annually).
• Exposure Levels vs. EU WELs:
  • Long-term (0.3 ppm): 70% of sites (82/117) had a 95th percentile exceeding the EU long-term WEL. The average proportion of monitoring events exceeding this limit was 23.6%.
  • Short-term (0.6 ppm): 43% of sites (50/117) had a 95th percentile exceeding the EU short-term WEL. The average proportion of events exceeding this limit was 8.5%.
  • EN 689 Evaluation: The UTL95,70 exceeded the EU short-term WEL (0.6 ppm) at 68% of the assessed sites (79/117).
• Exposure Levels vs. UK WELs: No department had a 95th percentile exceeding the UK WEL of 2 ppm. However, 30% of sites recorded at least one event exceeding 2 ppm in the preceding 12 months.
• Compliance with "Adequate Control": Only 11% of departments demonstrated frequent (daily or continuous) monitoring with a 95th percentile below the EU long-term WEL. Only 17% met this criterion for the EU short-term WEL.

Significance and Claims
The paper asserts that formaldehyde exposure in NHS cell pathology departments is infrequently monitored and inadequately controlled. The authors argue that the current reliance on UK WELs (2 ppm) is insufficient to meet the ALARP principle, given the substantial body of evidence linking formaldehyde to health risks at concentrations significantly below the UK limit but above the EU limit.

The study claims that the data provides robust evidence that:

1. Current controls are insufficient: The high frequency of exceedances of EU WELs, combined with infrequent monitoring, suggests that thousands of NHS employees are exposed to concentrations associated with deleterious health effects.
2. Regulatory intervention is urgent: The authors call for national regulatory intervention to align UK standards with EU Directive 2019/983, upgrade infrastructure (specifically moving from open down-draught tables to purpose-built enclosed cabinets), and mandate more frequent personal exposure monitoring.
3. Governance gaps exist: The findings highlight a lack of management accountability and external oversight regarding occupational health in these departments.

The authors conclude that while the data is derived from public records and not direct measurement by the authors, the consistency of elevated concentrations across a large, diverse cohort over a 12-month period indicates a systemic issue requiring immediate attention to protect worker health.