Cohort studies chemical workers

Ward EM, Fajen JM, Ruder AM, et al Mortality study of workers in 1,3-butadiene production units identified from a chemical workers cohort. Environ Health Perspect 103(6) 598-603, 1995... 

When the data as a whole are reviewed for studies on humans exposed to ethylene oxide, no conclusion can be made that there is an increase in mortahty associated with those exposed to ethylene oxide. Two Swedish studies (247,248) indicated an increase in leukemia for workers exposed to multiple chemicals including ethylene oxide however, in a recent larger Swedish study (249) of workers exposed to only ethylene oxide, there was no association of any type of cancer increase for these workers. In a recent study sponsored by NIOSH, there was no significant increase in mortahty observed for cancer when all types are combined or for certain individual types of cancer, even for those people who worked the longest and were observed the longest. However, a statistically significant increase in mortahty from certain types of lymphoma was observed for male workers. This is contrary to the results observed for female workers. In addition, four other cohort studies of ethylene oxide-exposed workers have been pubhshed (250—253), but no unequivocal increase in the risk of cancer was observed. 

Studies of workers in the endrin manufacturing industry have not shown an association between occupational exposure to endrin and any type of human cancer. No excess cancers could be attributed to exposure to endrin in 52 chemical workers in an endrin manufacturing facility after exposures lasting 4-13 years (Versteeg and Jager 1973). Fifteen years later, the same worker cohort showed no evidence of increased cancer rates. The small size of the cohort gives the study a low statistical power (Ribbens 1985). 

Whorton MD, Amsel J, Mandel J Cohort mortality study of prostrate cancer among chemical workers. Am J Ind Med 33(3) 293-296, 1998... 

Cohort studies of agricultural chemical production workers found decreased mortality from all cancers among workers who had probable exposure to atrazine. Findings of an increased risk of non-Hodgkin lymphoma among farmers could not be attributed to atrazine exposure when adjustment was made for other pesticide exposure. ... 

Gardner MJ, Pannett B, Winter PD et al A cohort study of workers exposed to formaldehyde in the British chemical industry an update. BrJ Ind Med 50 827-834, 1993... 

In a cohort study of workers at a rubber chemicals plant, exposure to MBT did not seem to increase the risk of most cancers, including cancers of the lung and prostate. ... 

Sorahan, T. Pope, D. (1993) Mortality study of workers employed at a plant manufacturing chemicals for the rubber industry 1955-86. Br. J. ind. Med., 50, 998-1002 Sorahan, T., Hamilton, L. Jackson, J.R. (2000) A further cohort study of workers employed at a factory manufacturing chemicals for the rubber industry, with special reference to the chemicals 2-mercaptobenzothiazole (MBT), aniline, phenyl-beta-naphthylamine and o-toluidine. Occup. environ. Med., 57, 106-115... 

A nested case-control study of lung cancer in a cohort of chemical workers showed no association with exposure to carbon tetrachloride. 

Several studies have examined mortality or cancer incidence among chemical workers potentially exposed to 1,2-dichlorocthanc. Hogstedt et al. (1979) performed a cohort mortality study of 175 Swedish ethylene oxide production workers followed from 1961 through 1977. The workers had been employed for at least one year and were potentially exposed to... 

Bond et al. (1986) conducted a nested case-control study of lung cancer among a cohort of 19 608 male chemical workers in the United States (Bond et al., 1985). Further details of the study are reported in Section 2.2 of the monograph on carbon tetrachloride in this volume. Ever having been exposed to epichlorohydrin was associated with a decreased risk of lung cancer (odds ratio, 0.3 95% CI, 0.1-0.9 5 exposed cases). 

One cohort study of workers at three chemical manufacturing plants included a subgroup with potential exposure to methyl bromide, among whom there were two deaths from testicular cancer (0.11 expected). 

In a cohort study of workers in two Danish chemical plants (Lynge, 1985), potential exposure to 2,4,5-trichlorophenol occurred between 1951 and 1959, when small amounts were produced or purchased to make 2,4,5-T. No overall increase in cancer incidence rate was observed, but there were significantly increased risks of soft-tissue sarcoma and lung cancer in certain subcohorts. [The Working Group noted that 2,4-dichlorophenol is an intermediate in the production of 2,4-D, which was produced by the larger of the two plants.]... 

The carcinogenicity of 2,3,7,8-TCDD in humans has been assessed in numerous case-control and mortality cohort studies of chemical manufacturing and processing workers and phenoxy herbicide and chlorophenols applicators, Vietnam veterans exposed to Agent Orange, and residents of Seveso, Italy. A major weakness in many of these studies is the lack of adequate exposure data. Exposure levels or... 

Ott MG, Olson RA, Cook RR. 1987. Cohort mortality study of chemical workers with potential exposure to the higher chlorinated dioxins. J Occup Med 29 422-429. 

Virtually all of the information regarding health effects in humans comes from studies of workers exposed to benzene-containing solvents and/or adhesives. Exposures to benzene occurred at rotogravure printing shops at shoe, rubber, and raincoat manufacturing plants and during chemical manufacturing processes. Case reports and cohort studies describe both acute and chronic health effects. The predominant route of exposure in these studies is inhalation. Dermal contact is also suspected as a possible route of exposure in these studies. 

Epidemiology studies have shown no increase in cancer in workers exposed to phosgene compared to controls. Polednak (1980) and Polednak and Hollis (1985) examined a cohort of chemical workers exposed to chronic low levels of phosgene as well as daily exposures above 1 ppm. Approximately 35 years after exposure to phosgene, no increase in overall mortality or mortality from cancer or respiratory disease was noted. 

Several epidemiological studies on the effects of PPOA in humans have been conducted on workers. These studies did not examine developmental outcomes. A retrospective cohort mortality study demonstrated a statistically significant association between prostate cancer mortality and employment duration in the chemical facility of a plant that manufactures PPOA. However, this result was not observed in an update to the study in which more specific exposure measures were used. 

Morgenstein H, Ritz B. Effects of radiation and chemical exposures on cancer mortality among Rocketdyne workers A review of three cohort studies. Occup Med 2001 16(2) 219 37. 

Wong O. 1983. An epidemiologic mortality study of a cohort of chemical workers potentially exposed to formaldehyde, with a discussion on SMR and PMR. In Gibson JE, ed. Formaldehyde toxicity. Washington, DC Hemisphere Publishing Corporation, 256-272. 

Elevated risk of death from cancer and from lung cancer was reported in a retrospective cohort study of 6,635 male workers employed for more than 15 years during the period 1970-1985 in seven factories in China (Liu et al. 1997). The main chemical exposure was to coal tar pitch volatiles. Significantly... 

In evaluating the results of an epidemiologic study, it is important to examine the extent of exposure of the subjects. "Exposure" is defined by the researchers and is specific only to that study. For example, in some cohort studies of chemical workers the exposure has been defined as assignment to the TCP or 2,4,5-T production processes. In other studies, the definition of exposure has been less specific for example, in some cohort studies of herbicide sprayers, all sprayers have been considered "exposed" even though the authors have no knowledge whether the various herbicides sprayed by a particular individual included 2,4,5-T. 

Cohort Studies. To date, a number of cohort studies have been conducted of chemical workers from the U.S. and Europe and of herbicide sprayers from Sweden and Finland (20-28). In general, the studies have not demonstrated a definitive relationship between mortality from any malignant or nonmalignant condition and exposure to chlorophenols or phenoxy herbicides. All of the studies lacked sufficient statistical power due to the small number of individuals in each cohort. 

Table IV presents the cohort studies of chemical workers. In two cohort studies of U.S. chemical workers, statistically nonsignificant excesses in mortality were observed for the ICD categories describing cancers of the lung, soft tissue sarcoma, stomach, male genital organs and for non-Hodgkins lymphoma (21,23). One soft tissue sarcoma death was observed in the Zack study (21), but the meaning of one death is difficult to interpret. The Cook study (23) updated two earlier studies, so those are not shown here (22,29).

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