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The corresponding lung cancer standardized mortality ratio (SMR) for 20 or more years after first
exposure was only 1.12 (90% confidence limits 0.56 and 2.02). Air levels of nickel were in the range
of 0.01-5.0 mg/m 3 .
The ICNCM (1990) reported a further five years of follow-up of this cohort up to 1982. Among
workers hired before 1947 and who had 15 or more years since first exposure in calcining, there were
eight lung cancer deaths yielding an SMR estimate of 1.15 (90% confidence limits 0.57 - 2.07). Two
nasal cancer deaths were reported with 0.9 expected.
The Ontario cohort involved refinery workers at Copper Hill, Ontario (Chovil et al., 1981; Roberts et
al., 1984; Muir et al., 1985). A subcohort with high exposure to nickel consisted of 495 workers with
five or more years’ work history at a sinter plant operated by the INCO between 1948 and 1963.
Workers were followed up from 1963 to the end of 1978, a minimum of 15 years. Eighty-five cohort
members died during the follow-up period, of which 37 were lung cancer deaths. The SMR for lung
cancer was 8.71, (90% confidence limits 6.49 and 11.45).
The ICNCM (1990) reported a further follow-up of this cohort up to 1984. There were a total of 63
lung cancer deaths and 6 nasal cancer deaths among the Copper Cliff sinter plant workers with 15 or
more years since first exposure. Of the 63 lung cancer deaths, 33 had five or more years of exposure
and yielded an SMR of 7.89 (90% confidence limits 5.78 - 10.56). For those who commenced work
prior to 1952, the SMR estimate was 8.55 (90% confidence limits 6.15 - 11.59). These estimates are
close to the SMR of 8.71 obtained from the earlier report by Chovil et al. presented above. Exposure
data were given by Roberts et al. (1984) who estimated a level of 400 mg/m 3 in 1950, falling to 100
mg/m 3 “toward the end of the plant’s productive life in 1958.” Calculations based on the data give an
average of 158 mg/m 3 for measurements made before 1952 and an average level of 73 mg/m 3 for
measurements made after 1952.
Studies of a Welsh nickel refinery cohort involved 967 refinery workers, some of whom started working
as early as 1910 at a nickel refinery in Clydach Wales, operated by INCO. Several publications
provide some form of dose-response data. These studies include: 1) Doll et al. (1977) in which lung
cancer mortality is presented by year of first employment; 2) Peto et al. (1984) study which categorized
the cohort members by duration of exposure in the calcining furnaces, and 3) analyses by various
exposure variables by Breslow and Day (1987) and Kaldor et al. (1986).
The Doll et al. (1977) study followed the employees up until the end of 1971 and calculated man-years
at risk from 1934-1971. There were 689 total deaths in the cohort, including 145 lung cancer deaths,
yielding a lung cancer SMR of 5.28 (90% CI: 4.58-6.03). The risk of lung cancer was increased in
workers exposed before 1930.
The Peto et al. (1984) study updated dates of first employment in cases where additional information
had come to light since the publication of the Doll et al. (1977) paper. Employees were classified into
low and high exposure groups based on the number of years each employee spent at the furnaces or in
the copper sulfate work areas. The lung cancer SMR for the low exposure group was 3.7 while that for
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