Herbicide sprayers, cohort

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. 

Cohort studies of herbicide sprayers are presented in Table V. An excess of mortality from stomach cancer was statistically significant in one small Swedish study (27). No specific malignancies were found in excess in the other studies. All had low statistical power and limited exposure assessments. The researchers had insufficient information about the types of phenoxy herbicides to which the workers were exposed and limited data about the intensity and duration of the exposures. Some phenoxy herbicides do not contain 2,3,7,8-TCDD. Corroborating results from other studies and additional observations obtained through further vital status follow-up of the cohorts may reduce the ambiguity of the results. 

SOLVING HAZARDOUS WASTE PROBLEMS TABLE V, Cohort Mortality Studies of Herbicide Sprayers... 

Vena J, Boffetta P, Becher H, et al. 1998. Exposure to dioxin and nonneoplastic mortality in the expanded IARC international cohort study of phenoxy herbicide and chlorophenol production workers and sprayers. Environ Health Perspect 106(Suppl 2) 645-653. 

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