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EC number: 204-424-9
CAS number: 120-78-5
MBT workers have expected rates of lung and prostate cancer. There was
an excess of bladder cancer among MBT worker who had definite exposure
to PAB and MBT workers with potential exposure to PAB. However, there
were no deaths from bladder cancer among workers with no exposure to PAB.
The authors concluded that the potential confounding of exposure to an
unknown portion of PAB in the MBT workers makes it impossible to
evaluate risk of bladder cancer in this population at this time.
However, exposure to MBT doses not seem to increase the risk of most
cancers including cancers of the lung and prostate.
In a follow up study, the mortalities of workers at the Nitro plant
(West Virginia) with exposure to 2-mercaptobenzothiazole were evaluated
(Collins 1999). In this study the mortalities of 1059 full time white
male production workers employed at the plant from 1955 to 1977 were
analyses. A detailed exposure assessment was done on the 600 workers
with exposure to MBT. Nine years of additional follow up to the previous
study (Strauss 1993) were added. In the follow-up study the standardised
mortality ratios of the production workers for all causes of death and
all cancers was at expected levels, which was different from the
findings of the original study (Strauss 1993). For the entire follow up
period lung cancer, prostate cancer, and the other cancer sites examined
were at expected levels. Among the cancers, only rates of bladder cancer
were greater than expected for the entire follow up period. The
standardised mortality ratios for total cancer of workers exposed to MBT
and potential exposure to PAB were similar to the entire study group and
to the local population. Rates for lung cancer and prostate cancer were
at expected levels. The standardised mortality ratio for bladder cancer
was greater than expected when compared with the external reference
group. The number of total cancers was greater than expected for MBT
workers with one or more jobs with exposure to PAB. The number of lung
cancers and bladder cancers for this group of workers were greater than
expected. The MBT workers without a job definite exposure to PAB during
their careers had an observed total cancer rate which was lower than
expected. Observed deaths from bladder cancer, however, were greater
than expected in this group based on five deaths. The five workers who
died of bladder cancer held jobs with plant-wide responsibilities. These
five workers had job titles of maintenance worker, yard labourer, or
general production worker and thus the authors suggested that a possible
risk of exposure to PAB. Workers with no potential exposure to PAB, or
those workers hired after 1955, have a lower observed than expected risk
of total cancer and there were no deaths from bladder cancer. The
authors concluded that MBT workers had bladder cancer rates which were
greater than expected, but an unknown portion of these workers had
exposure to PAB. The potential confounding exposure to PAB, a potent
bladder carcinogen, in an unknown portion of the MBT workers makes it
impossible to evaluate risk of bladder cancer in this population.
Although the lack of bladder cancers among workers hired after PAB
manufacture ended would argue against a relation with exposure to MBT,
the number of expected deaths in this group of workers is too small to
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