Defense Date

2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Epidemiology & Community Health

First Advisor

Resa Jones

Abstract

Abstract 1 – A Geographic Information System for Evaluating Residential Pesticide Exposure and Prostate Cancer Incidence Agricultural pesticide exposure is hypothesized to be a risk factor for prostate cancer, and such exposures are of particular concern for men living in farming communities where large-scale pesticide applications occur. Prostate cancer incidence data were obtained from the State Health Registry of Iowa for the years 1996 through 2006, and county and census tract level age-adjusted incidence rates were calculated. Historical crop-specific land use records and pesticide sales data for the state of Iowa during 1990 were integrated into a geographic information system (GIS), where estimates of predicted exposure to the four most commonly used pesticides in Iowa (atrazine, metolachlor, cyanazine, alachlor) were produced. Ecological correlation between pesticide exposure and prostate cancer incidence was evaluated using Spearman’s (rank) correlation coefficient and linear regression analysis. Statistically significant associations between prostate cancer incidence and percent of acres of corn and soybean crops were found at both the county (r=0.22, p=.031 and r=0.33, p=.001, respectively) and census tract (r=0.10, p=.007 and r=0.13, p<.001, respectively) level. The associations between percent of land exposed to the specific pesticides and prostate cancer were not statistically significant. Our findings suggest that residential proximity to corn and soybean fields, and by association the pesticides used on those crops, is correlated with increased prostate cancer risk, but that the increase in risk is not correlated with exposure to the four most commonly used pesticides in Iowa in 1990. Findings from this study underscore the need for continued investigation of the association between agricultural exposures and prostate cancer incidence. Abstract 2 – Spatial Analysis of Prostate Cancer Incidence and Residential Pesticide Exposure in Iowa A statistically significant positive association between prostate cancer incidence and residential proximity to corn and soybean fields in Iowa exists. Research suggests that exposure to pesticides used on these crops increases prostate cancer risk. The objective of this study was to investigate clustering of prostate cancer risk in the presence of potential exposure to pesticides in Iowa. Prostate cancer incidence data (1996-2006) were obtained from the State Health Registry of Iowa. Using SaTScan software, clusters of high and low prostate cancer risk were identified. Ecological correlation between exposure to the four most commonly used pesticides (atrazine, metolachlor, cyanazine, alachlor) in Iowa during 1990 and residence in a cluster of relatively high or low prostate cancer incidence was evaluated using Pearson’s chi-square test statistic and logistic regression analysis. Clusters of increased prostate cancer risk were associated with a greater percentage of land used for all crops of interest (i.e., corn and soybean farming (p <0.001), corn farming (p <0.001), soybean farming (p <0.001)) and low exposure to alachlor (p =0.032) than did clusters with decreased risk of prostate cancer. After adjustment for percent of land used for each crop type, no association between pesticide exposure and prostate cancer risk was observed. Residence in or near agricultural communities increases prostate cancer risk. Our findings suggest that residential proximity to exposures specific to corn and soybean farming increases prostate cancer risk. Evaluation of exposure to less commonly used pesticides and those used in lower quantities is needed.   Abstract 3 – Multilevel Analysis of Residential Pesticide Exposure and Prostate Cancer Incidence An association between residential exposure to factors specific to corn and soybean farms in Iowa exists. The objectives of this study were to statistically assess spatial autocorrelation in prostate cancer incidence in Iowa and to evaluate the effect of residential exposure to the most commonly used pesticides for corn and soybean farms in Iowa in 1990 on prostate cancer incidence. Prostate cancer incidence data were obtained from the State Health Registry of Iowa for the years 1996 through 2006. Spatial patterning of age-adjusted incidence rates was assessed via Moran’s I global index of spatial autocorrelation. A hierarchical regression modeling approach with an assumed Poisson distribution was used to characterize the relationship between census tract level prostate cancer incidence and exposure to pesticides. Statistically significant spatial patterning of prostate cancer incidence, corn and soybean fields and pesticide use (p<.001 for all variables) was observed. After adjustment for individual and area level characteristics, prostate cancer risk increased by approximately 25% for each percentage point increase in percent of land used for corn and soybean crops. Prostate cancer risk was approximately 25% higher for Black men exposed to corn and soybean fields compared to white men exposed to corn and soybean fields. Results from this study support the need for further evaluation of residential exposure to environmental hazards specific to corn and soybean farming.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

August 2010

Included in

Epidemiology Commons

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