Childhood leukemia mortality and farming exposure in South Korea: A national population-based birth cohort study

Abstract

Objectives: The aim of this study was to evaluate the relationship between leukemia mortality and exposure to farming among children in South Korea. Methods: A retrospective cohort study of South Korean children was conducted using data collected by the national birth register between 1995 and 2006; these data were then individually linked to death data. A cohort of 6,479,406 children was followed from birth until either their death or until December 31, 2006. For surrogate measures of pesticide exposure, we used residence at birth, paternal occupation, and month of conception from the birth certificate. Farming and pesticide exposure indexes by county were calculated using information derived from the 2000 agricultural census. Poisson regression analyses were used to calculate rate ratios (RRs) of childhood leukemia deaths according to indices of exposure to agricultural pesticides after adjustment for potential confounders. Results: In total 585 leukemia deaths were observed during the study period. Childhood leukemia mortality was significantly elevated in children born in rural areas (RR = 1.43, 95%CI 1.09-1.86) compared to those in metropolises, and in counties with both the highest farming index (RR = 1.33, 95%CI 1.04-1.69) and pesticide exposure index (RR = 1.30, 95%CI 1.02-1.66) compared to those in the reference group. However, exposure-response associations were significant only in relation to the farming index. When the analyses were limited to rural areas, the risk of death from leukemia among boys conceived between spring and fall increased over those conceived in winter. Conclusions: Our results show an increase in mortality from childhood leukemia in rural areas; however, further studies are warranted to investigate the environmental factors contributing to the excess mortality from childhood leukemia in rural areas. (C) 2014 Elsevier Ltd. All rights reserved.