A mortality, morbidity, and hematology study of petrochemical employees potentially exposed to 1,3-butadiene monomer.

This three-part study is an update of a previous report that examined the mortality, morbidity, and hematological data of employees from a petrochemical facility in Texas who had potential exposure to 1,3-butadiene monomer. The first part describes the updated cause-specific mortality of 614 workers. Vital status for each cohort member was ascertained through 1998, a 9-year extension of the previous study. The second part is an examination of the morbidity experience of cohort members who were still working during 1992-1998, including 289 of the 614 mortality cohort members. The third part is an evaluation of the hematological results from routine health surveillance and/or medical examinations. Approximately 430 of the 614 employees who had complete blood count (CBC) data as of December 1999 were included in the hematological evaluations. The most recent examination containing CBC data was used and compared with similar data for over 2600 other employees from this facility. Overall mortality during the follow-up period, 1948-1998, was significantly lower than for the local comparison population (standardized mortality ratio (SMR) of 0.55 with a 95% confidence interval (CI) of 0.42-0.70). Mortality for all cancer was also significantly lower (SMR, 0.57; 95% CI, 0.32-0.92). Mortality for all lymphohematopoietic cancer was about the same as the comparison population (SMR, 1.06; 95% CI, 0.22-3.11). None of the cause-specific morbidity was in excess compared with an internal comparison group. There were no differences in the distribution or mean values of hematological variables (e.g. white blood cells, red blood cells, hemoglobin, platelets, mean corpuscular volume) between the butadiene cohort and the comparison group, or between a subgroup of workers in jobs with the highest potential for butadiene exposure (i.e. shipping) and the rest of the butadiene cohort. The findings of this study suggest that the butadiene exposure at this facility in the last 20 years does not pose a health hazard to employees.

Medical surveillance for hematological disorders among active and retired oil refinery workers.

Ten-year (1985-1995) results of an expanded medical surveillance program of 2475 active employees and retirees of an oil refinery and petrochemical complex in Illinois are presented. At the end of the program, 116 participants with persistent abnormalities of complete blood cell count had been referred for hematologic evaluation, and most were found to have benign conditions. Fifteen of the 116 were referred for bone marrow and cytogenetic studies. All of the referred active employees (seven) were found to have completely normal bone marrows with no evidence of any myelopathic process. Among the eight retirees, two had normal bone marrows, one was diagnosed with Philadelphia chromosome-positive chronic myelogenous leukemia, one declined to participate, and four were diagnosed to have myelodysplastic syndrome (MDS) of various subtypes. A total of eight cases of MDS were identified, including six cases among program participants and two cases among nonparticipants. The MDS standardized incidence ratio of 1.26 (95% confidence interval = 0.54-2.47) was not statistically significant, and there was virtually no increase of MDS in persons less than 80 years of age (4 observed and 3.8 expected). This MDS increase was entirely from program participants, probably because of intensive follow-up and diagnostic screening. Routine surveillance of complete blood cell count information did not identify any new cases of leukemia or MDS in active employees. These findings suggest that the utility of expanded medical surveillance program in this population is very limited.

Long-term follow-up mortality study of petroleum refinery and chemical plant employees.

A previous report presented the 1948-1983 mortality patterns of the Shell Deer Park Manufacturing Complex employees who were employed for at least 3 months from 1948 through 1972. The present study updates the earlier investigation by extending the vital status follow-up through 1989 and by expanding the cohort to include employees hired after 1972. As in the previous study, the overall mortality and cancer mortality for both refinery and chemical employees were quite favorable compared to residents in the local population. Among refinery workers, cancers for which a suspicion of work-relatedness was raised in the previous study, i.e. leukemia and cancers of the central nervous system and biliary passage/liver, no supportive evidence was found in this update. For both refinery and chemical plant employees, the mortality rate due to cancers of all lymphopoietic tissue increased with increasing duration of employment; this finding was also noted by the original study. This was also evident for lymphoreticulosarcoma in refinery employees and for leukemia in chemical plant employees. However, elevations of cancers of all lymphatic and hematopoietic tissue are primarily confined to employees who started work at the complex before 1946. By contrast, deaths from cancer of all lymphatic and hematopoietic tissue for employees hired after 1945 were 22% lower than the comparison population. Seven deaths with mesothelioma mentioned on the death certificates were identified, with 3.2 deaths expected, resulting in a statistically nonsignificant SMR of 219.

Mortality among maintenance employees potentially exposed to asbestos in a refinery and petrochemical plant.

This paper reports the mortality experience from 1948 to 1989 of 2,504 maintenance employees who had a minimum of one year of employment in jobs with potential exposure to asbestos at a Texas refinery and petrochemical plant. For the purposes of this study, "potential exposure" is equated with those jobs or crafts having the greatest direct potential proximity to, or which worked directly with, asbestos-containing materials, especially asbestos-containing thermal insulation. Approximately one-half of the study population had 10 years or longer potential exposure, and 80% had their first potential exposure before 1970. The total population exhibited significantly lower mortality for all causes, the standardized mortality ratio (SMR = 77); and for all cancer (SMR = 85), as compared to residents in the surrounding communities. Statistically significant deficits in mortality were also observed in a number of noncancerous diseases such as heart disease (SMR = 78; 95% CI = 69-88), nonmalignant respiratory disease (SMR = 70; 95% CI = 50-95), and cirrhosis of the liver (SMR = 44; 95% CI = 22-79). Mortality among employees who had 20 years or longer since their first potential exposure was also examined; the pattern of mortality was similar to that exhibited by the total cohort, with a slight increase in the SMR for most of the causes. The only statistically significant excess of mortality found was a fourfold increase in mesothelioma (5 observed and 1.2 expected deaths) the SMR was 428 (95% CI = 139-996) for the total cohort and was 469 (95% CI = 152-1093) for those who had 20 years or more since first potential exposure. In contrast to asbestos industry worker studies, mortality for lung cancer was substantially lower than the general population (SMR = 81; 95% CI = 63-103). The observed number of deaths for cancer of the larynx was virtually the same as expected (3 observed vs. 2.8 expected). This study also showed decreased mortality for cancers of gastrointestinal organs such as the esophagus (SMR = 78), stomach (SMR = 63), large intestine (SMR = 91), rectum (SMR = 55), or pancreas (SMR = 90)--cancers that have been reported to be elevated in studies of various industry workers directly exposed to asbestos.

A cohort mortality study of two California refinery and petrochemical plants.

This study examined the 1973 to 1989 mortality experience of Shell's two California manufacturing locations' employees who worked more than 6 months before December 31, 1989 and pensioners who were alive as of January 1, 1973. Vital status of each employee as of December 31, 1989 was determined from various sources including company records, the National Death Index, and the Social Security Administration's Master Beneficiary Record file. The study included many long-term employees, with more than half (57%) of the total population working 20 years or longer. The total population exhibited 11% lower all causes mortality and 20% lower cancer mortality, as compared with the California general population. There were no significant excesses of any cause-specific mortality including cancer. Among total employees, mortality for several cancer sites showed a statistically nonsignificant increase, for example, cancer of the kidney (8 observed deaths and 6.02 expected), cancer of the bladder (11 observed deaths and 9.17 expected), and Hodgkin's disease (2 observed deaths and 1.01 expected). A review of these work histories revealed no predominant work area or job assignment. In contrast to the ecologic studies based on local county rates, lung cancer mortality in this study was significantly lower (Standardized Mortality ratio [SMR] = 0.73). In addition, statistically significant deficits in mortality were found for cirrhosis of the liver (SMR = 0.63) and all external causes of death (SMR = 0.74). This study also failed to show an increased mortality rate for cancers of the brain, stomach, and prostate--causes which have been reported to be elevated in other refinery and petrochemical employee studies.

A prospective study of morbidity patterns in a petroleum refinery and chemical plant.

This study examined the morbidity experience from 1981 to 1988 of a prospective cohort of 3422 refinery and petrochemical plant employees from the Shell Deer Park manufacturing complex. The morbidity data for this study, which include all illness and absence records in excess of five days, were extracted from the morbidity section of the Shell health surveillance system. Standardised morbidity ratios (SMRs) of disease prevalence in this cohort were calculated using an internal comparison group of all manufacturing employees of the Shell Oil Company. Among production employees, the overall morbidity was statistically significantly higher (SMR = 109) than that of the comparison group. Illness due to hypertension (SMR = 144), haemorrhoids (SMR = 149), diseases of the nervous system (SMR = 120), respiratory system (SMR = 108), and digestive system (SMR = 117) were also raised for this group. The increased risk due to these medical conditions does not appear to be associated with occupational factors. Lymphatic and haematopoietic tissue neoplasms were raised (SMR = 124), but were based on only four cases.

Morbidity patterns among employees at a petroleum refinery.

This study examined the morbidity experience of a prospective cohort of 2132 male employees who worked at a petroleum refinery from 1981 through 1988. The morbidity data included all illness-absence episodes in excess of 5 days during the study period. Standardized morbidity ratios (SMRs) of disease prevalence were calculated using data from all manufacturing employees of the Shell Oil Company as an internal comparison group. As such, there is no potential bias associated with the "healthy worker effect" in this type of study design. Morbidity for all causes combined was virtually the same as that for the comparison group with 2,311 observed and 2,318 expected disease prevalence events. However, there were statistically increased prevalence of musculoskeletal system disorders (SMR = 136) and injuries (SMR = 125) among staff employees and skin and subcutaneous tissue disorders (SMR = 138) among production employees. A review of the original morbidity reports for these skin conditions revealed that none were due to exposure to chemical products or solvents. The SMR for neoplasms of the lymphatic and hematopoietic tissue among production employees was slightly elevated but was based on only three cases (2.4 expected). Of the three cases, none was due to leukemia.

Prospective morbidity surveillance of Shell refinery and petrochemical employees.

Results for a prospective morbidity study of 14,170 refinery and chemical workers from 1981 through 1988 are presented. Illness/absence data for this study were extracted from the morbidity section of the Shell Health Surveillance System which includes records of all illness/absences in excess of five days. Age adjusted annual morbidity frequency rates and annual durations of absence are presented by age, sex, job, and work status. Generally, rates and durations of absence were highest for older age groups, women, and production workers. Increased risk was associated with the presence of known disease risk factors. Overall, 48% of the employees had at least one illness/absence in excess of five days during the eight year period. Twelve per cent of the employees had four or more absences, which accounted for 54% of the total number of absences and 52% of the total work days lost. Among men, the five most common conditions accounted for 72% of all illness/absences. In descending order they were injuries (25%), respiratory illnesses (17%), musculoskeletal disorders (14%), digestive illnesses (9%), and heart disease (7%). Similar patterns were noted among women. These findings may be useful in setting priorities and directing efforts such as health education programmes and other strategies for the prevention of disease.

Long-term mortality study of oil refinery workers: V. Comparison of workers hired before, during, and after World War II (1940-1945) with a discussion of the impact of study designs on cohort results.

The mortality experience of a large refinery cohort (1937-1978) was examined by dividing it into three subcohorts according to hire dates: those hired before 1940, those hired during the period 1940-1945, and those hired after 1945. These three periods are approximately equivalent to before, during, and after World War II and span a total hiring period of more than 75 years. The results showed that a substantial portion of the cohort (3,330 or 27%) had been recruited during 1940-1945, and they contributed 980 or 28% of the total deaths. However, their mortality experience was quite different from the rest. A series of significant increases were seen among the external causes for accidents, suicide, and homicide. In terms of overall mortality and in contrast to the rest of the cohort, no "healthy worker effect" was seen (SMR = 1.00). They also showed increases in several types of cancer including cancers of the pancreas and prostate and leukemia. These unusual experiences cannot be explained either on the basis of their war-related deaths or on their period of employment (one-half were terminated within 1 year from date of hire), and data is insufficient to separate the role of hiring practices or their socioeconomic status. However, their life-styles were probably quite different judged from the fact that alcoholism-related deaths were increased as much as fivefold. Almost two-thirds of the total deaths occurred among 4,080 workers in the before 1940 subcohort. Further, the 5,117 workers of the after-1945 subcohort contributed only 5% of the total deaths. Thus, the results of the original refinery cohort (1937-1978) primarily reflect the experience of those employees hired before 1940. Given the same cohort method (historical prospective), cohort results vary widely according to different study designs, and this has implications for "generalizable" risk assessment or risk projections. A prospective study of new hires with 30 years of follow-up is rather inefficient because it would yield only a small number of deaths, with a strong healthy worker effect. The same is true for studies based on active workers with a short period of follow-up. Studies based on time of hire, however, provide a means for controlling time-related occupational exposures.

Long-term mortality study of oil refinery workers. IV. Exposure to the lubricating-dewaxing process.

A retrospective cohort mortality study of 1,008 male oil refinery workers who ever worked on the lubricating-dewaxing process of the lube oil department and who have been followed for a period of 43 years is presented. These workers were exposed to a number of solvents, primarily methyl ethyl ketone [(MEK) CAS: 78-93-3] and toluene (CAS: 108-88-3), but at levels far below the current Occupational Safety and Health Administration's standard. The standardized mortality ratio (SMR) for all causes (0.70) and the SMR for cancer (0.86) are much lower than unity when they are compared to the mortality experience of the U.S. population. Also observed in this study were 8 prostate cancer deaths (4.4 expected) with an SMR of 1.82, which was not statistically significant (P = .16). Seven of these 8 prostate cancer deaths occurred among nonwhite males, who showed an SMR of 2.47 (P = 0.53). However, only 1 prostate cancer death was seen among workers specifically assigned to the MEK units. The remaining deaths occurred among maintenance workers who had lube oil department-wide assignments. This cancer risk increased with increasing duration of employment in the lube oil department. A latency of 20 years or more was also observed for these prostate cancer deaths. In this study the processing of lubricating oils was found to be at least as important as the MEK solvents, and department-wide maintenance workers were as much at risk as the MEK unit workers. In view of this finding and findings obtained by others, it seems prudent to continue to study lubricating-dewaxing process workers, including the medical monitoring of all such workers for prostate cancer.

Long-term mortality of oil refinery workers. II. Comparison of the experience of active, terminated and retired workers.

In occupational epidemiology a retrospective cohort study normally includes active, terminated, and retired employees and the mortality results may vary considerably if any of the three groups is excluded from the study. From a large refinery cohort of 12,526 white male workers followed between January, 1937 and January, 1978, the mortality experience of three groups (the active, terminated and retired) has been examined; detailed results, along with the merits and problems of studying these groups separately, are presented. The standardized mortality ratios (SMRs) for all causes are 0.68, 1.04 and 0.89 for the active, the terminated and the retired, respectively, and for all cancer, 0.85, 0.98 and 1.05. Significantly decreased SMRs are seen for most of the causes among the active and may be attributed to the "healthy worker effect." Exclusive study of active workers, although it may yield certain useful information, particularly on diseases of the young and those with short latency periods, is primarily a study of the healthy worker effect. Many favorable effects of the active worker will be encountered. The retirees as a whole experienced no significant excess mortality for any causes, although examination of a subgroup, the early retirees, did reveal a significant excess of deaths from diseases of the nervous system and sense organs. The retired may appear to be an ideal group for study because they usually have worked for an extended period of time, they may have experienced long-term occupational exposure and they have lived long enough to develop diseases with long latency periods; however, serious problems arise from studying only the retirees and these are discussed. The terminated group contributed 41% of the person-years, 49% of the total number of individuals and 38% of the deaths and is far too important to be omitted. Contrary to previous reports, the terminated did not demonstrate a significantly adverse mortality experience when compared with the general population, although they did not show the healthy worker effect that was seen among the active.

Long-term mortality study of oil refinery workers. I. Mortality of hourly and salaried workers.

This longitudinal study examined the mortality and cancer experience of workers at the Gulf Oil refinery located in Port Arthur, Texas. The cohort was studied over a period of 41 years, from 1937 to 1978, and consisted of 16,880 employees, with an accumulation of 406,198 person-years; 4361 deaths were observed. Emphasis of this study was placed on the experience of the hourly and salaried male workers employed one day or more and those with a minimum of one year employment. The standardized mortality ratio analysis revealed generally favorable mortality experience of the refinery workers, including that of overall cancer. Statistically significant deficits in mortality were found for several cancer sites including bladder, liver, and esophageal cancer. Many of the increased cancer risks suggested in the literature were not confirmed in this study. Although bone cancer was found to be increased significantly, review of those death certificates raises questions as to the accuracy of the recording and coding of this cancer. Sample size of this study is capable of providing sufficient statistical power for the detection of a twofold increase in mortality risk for many cancers, if such risk exists.