A historical cohort on the risk of death from cancer in forestry workers possibly exposed to dioxin from spraying weeds

2002 Fiscal Year Final Research Report Summary

• Project/Area Number: 12670326
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Hygiene
• Research Institution: Nara Medical University
• Principal Investigator: KURUMATANI Norio Department of Hygien, Nara Medical University, Professor, 医学部・医学科, 教授 (10124877)
• Co-Investigator(Kenkyū-buntansha): MORINAGA Kenji Osaka Prefectural Institute of Public Health, Professor, 調査部・参事
• Project Period (FY): 2000 – 2002
• Keywords: Herbicide / Forestry workers / Historical cohortstudy / Cause of death / Dioxins

Research Abstract

This study aimed to clarify the influence of dioxin on health, particularly the degree of risk of death from cancer, by tracking a group of national forestry workers who may have been exposed to dioxin.
Of 2266 national forestry workers identified from several name lists, 2091 workers whose addresses were also available were listed as members of the cohort. It was ascertained whether these workers were alive or dead. In the cases of death, permission from the Ministry of Justice was obtained to examine the death certificate or death registration certificate. After determining the primary cause of death according to the International Classification of Diseases (ICD), estimation of whether or not there were excessive deaths was made based on the Standardized Mortality Ratio (SMR) at the 95% confidence interval.
Of the 966 male workers assumed to have been exposed by spraying a weed killer containing 2, 4, 5 - T, 224 workers had died in the period from 1978 (when tracking was started) to 20 02. Analysis of the total deaths of these male workers produced an SMR of 0.69 (95% confidence interval: 0.6 1 -0.79), which was significantly lower than the national average. Death due to cardiac disease was 0.58 (0.39-0.85), and death due to cerebral vascular accident was 0.58 (0.37-0.85), with the SMR being significantly lower than 1 in both cases. Of the 192 female forestry workers, 16 had died. The SMR of total deaths in this group was 0.43 (0.26-0.69), which was significantly lower than the national average. Although the confidence interval was large, because few subjects died from cardiac disease or cerebral vascular accident, the point estimation value was less than 1. These results include those for 64 workers in seedling fields, which were the same as the results for the male workers. It was thought that these results suggested an effect of healthy workers.
The SMR for all malignant tumors as the cause of death for male forestry workers was 0.70 (0.56-0.86), for female forestry workers it was 0.78 (0.41-1.42) and for female workers in the seedling fields it was 1.42 (0.67-2.9 1 ). These values are lower than the national average. No significantly increased deaths of site-specific cancers were observed in both sexes.
The death rate for all subjects in the time period analyzed remained at around 20%. Therefore, we believe that it is necessary to follow the subjects for a longer period in order to obtain a definite conclusion.