Graduate Thesis Or Dissertation
 

Childhood cancer and spatial analyses of benzene exposure in Texas

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/zk51vn23b

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  • Childhood cancers are rare diseases that affect 188 children in Texas for every million born. Leukemia is the most common childhood cancer and accounts for roughly one third of childhood cancer cases. However, it is estimated that only 10% of childhood cancer cases can be explained by known risk factors. Although environmental pollutants (e.g., pesticides, groundwater, air pollutants) have been suspected as causes of childhood cancers their relationship with childhood leukemia have not been clearly established. Previous epidemiological studies that examined benzene and childhood cancers have used a variety of exposure metrics to estimate benzene exposure, including proximity to major roads, road density, proximity to industrial facilities and natural gas wells, and estimates from emission models. Despite the number of studies, no single metric of exposure to benzene has been consistently linked to childhood cancers. We performed three analyses using spatially-derived metrics to assess the relationship between benzene exposure and childhood cancers, including acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML), and central nervous system tumors (CNS) among a study population of 24,164 children in Texas born 1996 to 2009. First, we conducted an exploratory analysis to assess agreement among six spatially-derived metrics as a basis for determining exposure to benzene. Second, we conducted a case-control study to calculate the risk of childhood cancers based on exposure to benzene in utero. Finally, we used a spatial scanning method to identify clustering among children with ALL in five metropolitan areas in Texas. Results indicate that aside from proximity to major road and major road density, few metrics of exposure to benzene agree, because the distribution and density of benzene-producing sources such as roads, industrial facilities, and gas wells differ among the major metropolitan areas in Texas. Childhood ALL was most consistently associated with natural gas wells, road density, and National Air Toxics Assessment benzene estimates (NATA), with an upper range of estimated effect at 1.30, a 30% increased risk. AML was less clearly associated with metrics of exposure to benzene. Central nervous system tumors showed a similar magnitude of risk as ALL with the NATA estimates of benzene exposure. The cluster analysis using spatial scan statistics identified four statistically significant clusters in the Houston metropolitan area and one space-time cluster in the Dallas-Ft. Worth metropolitan area. These findings indicate that spatial scan statistical methods can be used to detect and infer significance of clustering of higher than expected levels of adverse health outcomes. Collectively, the results of this research highlight the need for future studies to use multiple metrics to assess exposure to carcinogenic chemicals such as benzene, and to utilize novel methods to identify locations with elevated cancer rates. Further spatial epidemiological research and analysis using a variety of exposure sources and innovative methods will help pinpoint the causes of childhood cancers and potential measures to counteract this disease.
  • Keywords: spatial analysis, acute myeloid leukemia, benzene, childhood cancer, Texas, leukemia, central nervous system, acute lymphocytic leukemia, spatial epidemiology
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