Mortality studies of smelter workers

Area of Science:

• Occupational Medicine
• Environmental Health
• Epidemiology

Background:

• Limited data exists on smelter worker mortality, despite their historical significance in occupational medicine.
• Previous studies on smelter workers often lack precise identification of job roles and exposure types.
• Existing research suggests an excess of lung cancer in various smelter populations (lead, copper, cadmium, nickel).

Purpose of the Study:

• To present findings from a historical-prospective mortality study of male workers at a copper smelter in Tacoma, Washington.
• To investigate the association between occupational exposures at the smelter, particularly to arsenic, and mortality outcomes.
• To examine respiratory cancer incidence in relation to exposure duration and time since exposure.

Main Methods:

• A historical-prospective cohort study design was employed.
• The study population comprised males who worked at a copper smelter and refinery (high arsenic content ore) for at least one year between 1940 and 1964.
• Mortality follow-up was conducted through 1976, with high rates of tracing (97.2%) and death certificate acquisition (96%). Standardized Mortality Ratios (SMRs) were calculated.

Main Results:

• Overall mortality was 3.5% higher than expected for U.S. white males (SMR = 103.5).
• A significant excess of respiratory system cancers was observed: 104 cases versus 54.6 expected (SMR = 190.5, p < .05).
• Elevated respiratory cancer rates were noted in both smokers and nonsmokers, with risk increasing with exposure duration but not time since exposure, suggesting arsenic's effects may wane over time.

Conclusions:

• Workers at the Tacoma copper smelter experienced significantly elevated respiratory cancer rates, strongly suggesting a link to arsenic exposure.
• The observed pattern of risk, increasing with exposure duration but decreasing with time since exposure, aligns with findings for other carcinogens like arsenic and chromates.
• Further research on smelter worker cohorts, examining specific processes and co-exposures, is crucial for understanding occupational health risks in this industry.