Leukemia incidence and benzene air pollution in Portland Oregon: An ecologic investigation

Benzene is a widespread urban pollutant emitted by industrial sources and transportation vehicles. Nationally and in Oregon, benzene is the largest contributor to total cancer risk from air pollutants. This study sought to determine if the incidence of acute myeloid leukemia in Portland, Oregon during the period 1995-2004, varied with ambient airborne benzene. We used modeled ambient benzene exposure and leukemia incidence data at the census tract level to examine the correlation of benzene with three leukemia types. Modeled benzene values were averaged to census tracts using GIS methods. We performed Poisson regression on data for all census tracts and also aggregated data to quartiles of benzene modeled exposure to determine incidence rate ratios (IRR). We mapped the distribution of benzene, and age-standardized leukemia rates to examine spatial distribution patterns. Results showed no overall statistically significant association between benzene and leukemia at the census tract level. Acute myeloid leukemia (AML) was slightly elevated for females at the second quartile of benzene modeled exposure. We did not observe an increasing trend of higher cancer incidence with higher modeled benzene exposure; however, we did see increased cancer incidence near some point sources for adult AML and near roads for total myeloid leukemia in those under age 19. Proximity to traffic may be a better approximation of exposure risk for leukemia than modeled benzene exposure at the census tract level. Available census tract level data may not represent mobile source pollution accurately enough to always be useful in ecologic studies of leukemia.