Unrecognized risks of nickel-related respiratory cancer among Canadian electrolysis workers.

Objectives Nickel compounds, inclusive of water-soluble salts, have been classified as human carcinogens by the International Agency for Research on Cancer (IARC). Nickel producers have disputed the classification of soluble nickel compounds for three decades with reference to an alleged absence of excess respiratory cancer among Canadian nickel-exposed electrolysis workers. We evaluated historical data from two electrolytic refineries in Ontario, both included in prominent Canadian reports on occupational nickel-related cancer.Methods For Port Colborne nickel refinery (PCNR) and Copper Cliff copper refinery (CCCR), we identified process descriptions, exposure estimates, and original reports on cancer mortality using reference lists, libraries, and state archives. The documents were written or published between 1930 and 1992.Results For PCNR, a 1977 US National Institute of Occupational Safety and Health criteria document demonstrated an excess nasal cancer risk among electrolysis workers independent of furnace exposure. PCNR studies published after 1980 excluded 26% of long-term refiners who died from respiratory cancer according to earlier reports, and 42% of the workers had unknown vital status at the end of follow-up, biasing the standardized observed-to-expected mortality ratios downwards, most pronounced in recent reports and for workers without pension or company benefits. CCCR reports did not adequately address soluble nickel exposure in the evaluation of an observed occupational lung cancer excess.Conclusions While acknowledging important contributions to the recognition of nickel carcinogenicity from highly exposed Canadian refiners, we conclude that the claimed absence of nickel-related respiratory cancer among electrolysis workers has resulted from an arbitrary overemphasis of biased and inconclusive findings.Key terms Canada; carcinogen; copper; epidemiology; exposure; lung cancer; mortality; nasal cancer; Norway; refinery; review; sinonasal cancer.Nickel is widely distributed in nature and is a common component in industrial products and consumer merchandise (1). The refining of nickel ore has been linked to cancer excess at a Welsh refinery (UK) for 80 years (2). Case reports on nasal (sinonasal) cancer and lung cancer emerged during the 1930s and 1940s (3-5), and a company investigation was conducted by Austin Bradford Hill in 1939 [referred to in (6)]. By 1958, the first epidemiological paper appeared in a medical journal (7), and, one year later, a report to Canadian health authorities was the first to demonstrate similar risks among furnace workers at a refinery outside the UK (8). Based on a new study and a mortality update from the British and Canadian refineries (9, 10), and some case reports from other countries, a working group at the International Agency for Research on Cancer (IARC) ascribed the effect to nickel "in some form" in 1972 (11).Somewhat surprisingly, a subsequent study from a refinery in Kristiansand, Norway, (12) showed high risks of respiratory cancer among electrolysis workers, suggesting a carcinogenic effect from water-soluble nickel compounds, which is the main exposure in such departments. Increased risks of respiratory cancer had now been found in three groups of nickel workers: (i) those engaged in furnace departments (roasting, sintering, smelting, and calcining) (6, 7, 12); (ii) those producing water-soluble nickel and copper salts (sulphates) from aqueous solutions (6); and (iii) those involved in the electrolytic extraction of pure nickel or copper from electrolytes with a high level of nickel sulphate or nickel chloride (12).The discussion of which forms of nickel lead to respiratory cancer was addressed in a comprehensive epidemiological study by the International Committee on Nickel Carcinogenesis in Man (ICNCM), headed by Sir Richard Doll. In 1990, the Committee concluded that more than one form of nickel increased the risk (13), with the strongest evidence found for soluble nickel compounds (water-soluble salts) and particles containing nickel oxides and nickel sulphides. …