Background
Acrylonitrile is a widely used industrial chemical in the production of plastics, synthetic rubber, and polymers that was recently classified as a Group 1 carcinogen. Due to its volatility, exposure via inhalation can occur across multiple industries. This raises concerns about the adequacy of current occupational exposure limits (OELs), particularly as more protective limits are being introduced internationally.
Objectives
We aimed to characterize exposure to acrylonitrile in Ontario, Canada, and the United States (US) and identify high-risk industries and occupations.
Methods
Historical time-weighted average (TWA) area and personal air monitoring data were obtained from workplace regulatory inspections: the Medical Surveillance database (1984-1993) for Ontario and the Integrated Management Information System (1979-2019) for the US. Non-detects were handled using regression on order statistics, and data were checked for normality and log-transformed when applicable. Differences in exposure between Ontario and the US were assessed using the Wilcoxon rank-sum test. Exposure was characterized using descriptive statistics (e.g., geometric mean [GM]), temporal trends, exceedance fractions with 70% confidence intervals, and upper tolerance limits (UTL95,95). Compliance was evaluated using the current Ontario/US OEL (2 ppm) as well as two other more protective OELs: the impending European Union (EU) OEL (0.45 ppm) and the New Zealand OEL (0.05 ppm). Groups were classified as high-risk if the UTL95,95 exceeded the OEL or the 70% upper confidence bound of the exceedance fraction exceeded 5%.
Results
A total of 1,058 valid TWA samples were obtained (Ontario=659; US=399). Samples showed a high proportion of non-detects in both Ontario (90.4%) and the US (62.2%), and were log-transformed for analysis. Acrylonitrile exposures ranged widely and were significantly different between Ontario (GM=<0.01 ppm; range= <0.01-3.90 ppm) and the US (GM=0.01 ppm; range =<0.01-38.00 ppm), p < 0.05. Manufacturing industries accounted for the majority of the detectable exposures in both jurisdictions. Temporal analyses showed no consistent pattern over time, although greater variability and higher exposure levels were observed in earlier decades, particularly in the US.
Overall, the proportion of samples above the OEL (2/0.45/0.05 ppm) was lower in Ontario (1.67% / 5.16% / 11.84%) than in the US (1.75% / 12.03% / 32.58%). However, overall compliance differed at the 2-ppm OEL -Ontario remained compliant, whereas the US was non-compliant due to UTL95,95 exceeding the OEL. Non-compliance increased in both jurisdictions under more protective OELs, with similar patterns observed using exceedance fractions.
High-risk industries were consistently identified within chemical manufacturing, plastics and synthetic resins, motor vehicle manufacturing, paints and coatings, and selected food processing sectors, with some industry-specific exceedance fractions reaching approximately 40-50% under the most protective OELs. High-risk occupations included chemical plant and system operators, chemical equipment operators, mixing and blending machine operators, extruding and drawing machine operators, and other production-related roles.
Conclusions/Implications
Although average acrylonitrile exposures have declined over time, substantial variability persists, and specific industries and occupations may remain at elevated risk. These findings highlight the importance of targeted prevention strategies and inform occupational cancer prevention and regulatory decision-making, as more protective OELs may be developed following IARC reclassification.