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EC number: 235-727-4
CAS number: 12626-81-2
Significant mortality results for selected causes by duration of
exposure for entire cohort
*Significantly elevated at the .05 level (two-tailed).
The previously observed excess deaths due to accidents and nonmalignant
respiratory disease continued to be significantly elevated in this
cohort. However, a review of death certificates and employment
applications indicated that these excesses were probably due to work in
the mining industry rather than lead exposure.
Lung cancer and bladder cancer deaths showed nonsignificant elevations
(standardized mortality ratios = 1.18 and 1.93, respectively). However,
neither cancer was particularly elevated in the subcohort with high lead
exposure. Neither cancer has been implicated in animals studies, and,
with the exception of a single study with a lung cancer excess, there is
little epidemiologic evidence implicating these cancers. Both cancers
are related to smoking, and excess smoking in the cohort may have
contributed to their elevation.
Regarding a priori outcomes, the most important findings from this
update are the persistence of kidney cancer excess and the lowering of
the nonmalignant renal disease excess. Cerebrovascular disease mortality
was elevated only slightly overall. However, there was an increasing
trend in standardized mortality ratios with increasing duration of
exposure (P = .07).
The kidney cancer excess (standardized mortality ratio = 1.93), while
based on small numbers (nine observed), is supported by the increase in
the standardized mortality ratio in the subcohort with high lead exposre
(standardized mortality ratio = 2.39). The kidney cancer excess was not
clearly related to duration of exposure, but duration of exposure fails
to account for intensity; thus, duration may not be a good indication of
cumulative dose. The fact that animal studies show that lead causes
kidney cancer lends strength to these findings. Kidney cancer is only
weakly related to smoking, and excess smoking by this cohort would not
be expected to lead to an appreciable excess.
That a kidney cancer excess was not observed in other studies may be
partly attributable to a lack of power in those studies due to small
sample size. On the other hand, the study by Cooper et al (1985) did
have high exposure and substantial sample size, yet the kidney cancer
standardized mortality ratio was only 0.50 (10 observed). There is no
obvious explanation for this discrepancy with these findings.
The excess of nonmalignant renal disease observed in this data was
concentrated in earlier calendar periods and among those with logest
duration. Studies of other lead cohorts have also found that
nonmalignant renal disease excesses were confined to earlier calendar
periods, among those exposed to presumably high historical levels.
Objective: Mortality studies of lead workers have shown excesses of
nonmalignant renal disease and cerebrovascular disease. Animal studies
and one human study have shown excess of kidney cancer. This is an
updated mortality study of male lead smelter workers (n = 1990).
Methods: An analysis was conducted using standard life table techniques.
The updated analysis added 11 years of follow-up and 363 new deaths.
Results: The original study had found elevated but nonsignificant risks
for kidney cancer, stroke, and nonmalignant renal disease, probably
attributable to lead exposure. Deaths from accidents and nonmalignant
respiratory disease were significantly elevated, but probably not as a
result of lead exposure. In the updated study, no new deaths from
nonmalignant renal disease occurred (9 observed, standardized mortality
ratio = 1.21). Three more deaths from kidney cancer were observed,
yielding a standardized mortality ratio of 1.93 ( 9 observed, 95% CI =
0.88, 3.67), which increased for those who had worked in areas with the
highest lead exposure ( 8 observed, standardized mortality ratio = 2.39,
95% CI = 1.03, 4.71). Cerebrovascular disease remained elevated for
those with more than 20 years of exposure (26 observed, standardized
mortality ratio = 1.41, 95% CI = 0.92, 2.07)..
Conclusions: This cohort with high lead exposure showed a diminishing
excess of death from nonmalignant renal disease, a continued excess of
cerebrovascular disease only in those with longest exposure to lead (Am
J Public Health. 1992;82: 1641 -1644).
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