Risk assessment for o-toluidine and bladder cancer incidence.

Area of Science:

• Occupational Health
• Toxicology
• Epidemiology

Background:

• Elevated bladder cancer incidence observed in rubber industry chemical workers (1946-2006).
• o-Toluidine (OT), an aromatic amine, identified as a prime suspect agent.
• Aniline, also present, is an animal carcinogen but showed lower worker exposure markers than OT.

Purpose of the Study:

• To conduct a quantitative risk assessment for bladder cancer in rubber industry workers.
• To estimate cumulative o-toluidine (OT) exposures.
• To evaluate bladder cancer incidence models considering healthy worker survivor effects.

Main Methods:

• Quantitative risk assessment using historical environmental data and worker exposure records.
• Estimation of cumulative OT exposures based on exposure intensity ranks and direct environmental sampling.
• Analysis of bladder cancer incidence with adjustments for workforce turnover and survivor bias.

Main Results:

• Estimated excess lifetime risk of bladder cancer from OT exposure at 1 ppb ranged from 1 to 7 per thousand.
• Risk estimates were derived under various workforce turnover assumptions.

Conclusions:

• Current occupational exposure limits for OT (ACGIH TLV, OSHA standards) are significantly higher (1000-fold) than levels associated with a 1-7 per thousand excess lifetime risk.
• The findings suggest that existing occupational safety standards for o-toluidine may not adequately protect workers from bladder cancer.