Title: An investigation of the association between hazardous air pollutants and lymphohematopoietic cancer risk among residents of Harris County, Texas Authors: Kristina M. Walker, Ann L. Coker, Elaine Symanski, Philip J. Lupo Affiliation: University of Texas Health Science at Houston, School of Public Health Abstract While recent reports have commented on the elevated ambient levels of hazardous air pollutants (HAPs) in certain areas of Houston, relative to other cities, few studies have assessed the health effects of HAPs for Houstonians and none have evaluated the association between ambient levels of these pollutants and lymphohematopoietic cancer risk in this population. To begin to address this deficit in the literature, we conducted a population based analysis of ambient levels of HAPs and lymphohematopoietic cancer incidence in Harris County. Cancer cases were obtained from the Texas Cancer Registry (TCR), 1995-2003, and included adult and childhood cancers. We used existing monitoring data collected from 1992-2003 by the Texas Commission on Environmental Quality (TCEQ) to estimate ambient benzene and 1,3 butadiene levels for each census tract, which were then collapsed into 3 or 4 categories, respectively, in the analyses that were carried out. We also estimated risk of lymphohematopoietic cancer associated with residential proximity to the Houston Ship Channel (HSC) as another proxy (albeit a crude measure) of HAP exposure. Poisson regression was used to estimate rate ratios for increasing HAP levels and cancer rates, adjusting for gender, age, and a composite index for socioeconomic status and race / ethnicity. We observed an association among children living within two miles of the HSC and higher rates of acute lymphocytic leukemia (adjusted rate ratio [aRR] = 1.56; p=0.01) compared with those living greater than 10 miles from the HSC. Further, higher 1,3-butadiene levels (> 1.15 parts per billion [ppbV] relative to <0.266 ppbV) were associated with acute lymphocytic leukemia, acute myeloid leukemia and all leukemias in children. While we did not observe statistically significant associations for the other two categories (i.e., 0.266 - 0.381 ppbV or 0.382 - 1.15 pbbV) as compared to the referent group of <0.226 ppbV, a trend of increasing 1,3-butadiene levels and increasing leukemia rates was noted for these cancers. Higher benzene levels were not associated with lymphohematopoietic cancer by types in children. Among adults, neither proximity to the HSC, nor ambient levels of benzene or 1,3-butadiene levels were associated with lymphohematopoietic cancers in a dose dependent manner for either males or females. Additional analyses using more sophisticated methods to assess exposure are planned to confirm our findings. Additionally, future analyses will address many of the limitations of the current analysis. However, observing a specific health effect of HAPs in light of recently documented elevated levels of two known carcinogens, benzene and 1,3 butadiene, in Houston,(1) suggests a need to explore this issue further and to potentially take action to limit potential exposure to HAPs.