Exposure too-Toluidine, Aniline, and Nitrobenzene in a Rubber Chemical Manufacturing Plant: A Retrospective Exposure Assessment Update

Abstract

The National Institute for Occupational Safety and Health previously conducted a retrospective cancer incidence and mortality study of workers employed at a rubber chemical manufacturing plant. Compared with New York State incidence, the bladder cancer risk was 6.5 times higher for workers considered to have definite exposure to ortho-toluidine and aniline, and 4 times higher for workers with possible exposure. Exposure characterization in the original study utilized a surrogate measure based only on departments in which each worker was ever employed. As part of an update of that study, some departments in the three original exposure groups were reclassified based on a follow-up site visit; interviews with employees, management, and union representatives; and review of records including exposure data. An additional evaluation of department-job combinations, rather than only departments, was used to stratify exposure into four categories. An approximate rank of "relative" exposure level for each department-job-year combination was also assigned using a ranking scale of 0 to 10. The ranks were supported by quantitative exposure levels and by professional judgment. The numerical ranking scale was applied to each worker by multiplying the exposure rank by duration for each job held based on comprehensive individual work histories. The cumulative rank scores for this cohort ranged from 0 to 300 unit-years. The medians of the cumulative rank scores for the exposure categories showed very good agreement with increasing exposure classifications (e.g., 0.72, 4.6, 11, 14 unit-years for the four exposure categories). Workers' breathing zone air sampling data collected at this plant from 1976-2004 were well below published occupational exposure limits for these chemicals, but additional cases of bladder cancer have been reported. The exposure assessment revisions and rank estimates will be used to analyze the updated bladder cancer incidence data.

Bladder cancer incidence among workers exposed too-toluidine, aniline and nitrobenzene at a rubber chemical manufacturing plant

“…In 1990, NIOSH measured breathing zone air levels of o -toluidine (and aniline and nitrobenzene) in different processes throughout the Rubber Chemicals department; individual personal breathing zone o -toluidine concentrations ranged from 0.02 to 0.37 ppm, and geometric means ranged from 0.051 to 0.096 ppm. These measurements concur with those provided by the company for 1976–2004, and show a decrease in exposure concentrations over time 6. They also confirmed that exposure levels of o -toluidine were generally higher than those of aniline and nitrobenzene.…”

“…Likewise, increased bladder cancer incidence was observed even at the lower cumulative rank level. Air monitoring data showed that exposure concentrations even among the highest exposed workers were very low relative to existing occupational exposure limits 6. Currently, the Occupational Safety and Health Administration Permissible Exposure Limit (PEL) for o -toluidine is 5 ppm as an 8-h time-weighted average.…”

“…Previous exposure categories were based on department only, and did not differentiate between short-term and long-term exposure durations. By assigning exposure rank estimates based on department, job and year, and multiplying them by duration of exposure, we developed a cumulative exposure score for each worker's duration of employment 6. Industrial hygienists (KWH and SMV) blinded to the case status of the workers assigned exposure ranks to 225 department-job combinations, reducing the potential for differential misclassification of exposure.…”

“…Nevertheless, exposures to o -toluidine, aniline and nitrobenzene were concurrent 6. The antioxidant and accelerator manufacturing processes where these agents were used, were adjacent operations in the same buildings.…”

“…We have described in detail6 operations at the plant, our development of exposure categories based on department-job combinations and relative exposure ranks based on department-job-year combinations. Briefly, detailed work history records including begin/end dates, department and job title were available for all workers from 1946 to 2006.…”