Cancer mortality among electrolysis workers: where have all the cancers gone? A challenge to occupational epidemiologists and regulatory boards
本文质疑加拿大Port Colborne精炼厂电解工人癌症死亡率未升高的结论，指出研究存在工人排除、死亡漏报和预期数膨胀等问题，导致风险被低估，并呼吁重新审视监管决策。
<h3>Objectives</h3> The alleged absence of increased cancer mortality among electrolysis workers at the Port Colborne refinery (Canada) contrasts the excess incidence of lung cancer and nasal cancer seen among workers engaged in electrolytic production of nickel and copper at the Kristiansand refinery (Norway) and the Harjavalta nickel refinery (Finland). The latter hazards have been ascribed to soluble nickel compounds. <h3>Methods</h3> Epidemiological reports and published papers issued 1959–1992 from Port Colborne were reviewed. <h3>Results</h3> In 1977, the U.S. National Institute of Occupational Safety and Health (NIOSH) reported 80 lung cancer deaths and 27 nasal cancer deaths (1950–1976) among long-term workers (5 years or more) from Port Colborne furnace and electrolysis departments. In a new enlarged cohort – subsequently established by the company – some 25% of the old workers and relevant respiratory cancer deaths seemed to disappear. The nasal cancer mortality never exceeded 19 deaths despite another 8 years of follow-up. By the end of the last update (1950–1984), 42% of Port Colborn workers had unknown vital status but were taken to be alive throughout the observation period, thereby inflating the expected numbers of deaths. <h3>Conclusions</h3> Exclusion of long-term workers from the cohort, a general loss of deaths in the linkage procedure, and artificially high expected numbers all contribute to a downward bias in the observed-to-expected mortality ratios. Epidemiological papers after 1980 and reviews relying on Port Colborne workers may have flaws in the data that seriously question the reliability of the risk estimates. Some regulatory decisions may need to be reconsidered.