Date of Degree
PhD (Doctor of Philosophy)
First Committee Member
Lynch, Charles F.
Second Committee Member
Third Committee Member
Kelly, Kevin M.
Fourth Committee Member
Robertson, Larry W.
Fifth Committee Member
Weyer, Peter J.
Arsenic and atrazine are two water contaminants of high public health concern in Iowa. Arsenic is released into drinking water from soil and atrazine is the most heavily used herbicide. My hypothesis was that people in Iowa have high risks of certain cancers from exposure to arsenic and atrazine via drinking water. This study was performed to examine this hypothesis with three study aims: 1) to quantify the contamination of arsenic and atrazine in Iowa drinking water, 2) to analyze patterns of major cancers in Iowa and the US, and 3) to evaluate the association between arsenic exposure from drinking water and prostate cancer.
First, I investigated the occurrence of arsenic and atrazine in drinking water from Iowa private wells and public water systems over several decades. Percentages of detection and violation of regulations were compared over region, season, and water source. Factors affecting detection and concentration of arsenic and atrazine, and correlations among atrazine and its degradation products, were analyzed using a mixed effects model. I found that detection and concentration of atrazine in drinking water decreased over time (all samples were below the drinking water standard of 3 ppb). However, the percentage of arsenic detections and concentrations higher than the drinking water standard (10 ppb) increased over time in the public water systems. Therefore, I focused on arsenic as a water contaminants of concern for the further study.
Second, the patterns of trends in cancers related to arsenic and atrazine in Iowa were analyzed and compared to the US. Cancer is the second leading cause of death in the USA. However, cancer rates vary by different regions. In this study, the cancer trends in Iowa were investigated and compared to 8 other states for white individuals aged over 20. Temporal trends in age-standardized cancer rates were evaluated using joinpoint regression analysis by gender. Results of analysis indicate that overall cancer incidence and mortality were lower in Iowa than the US, and different trends of major cancers were found between Iowa and the US. However, prostate cancer was the most frequent type of cancer in men in both Iowa and the US and I focused on prostate cancer for further study.
Lastly, based on what I found from previous studies, I conducted an ecologic study to evaluate the association of prostate cancer and arsenic in drinking water in Iowa, where exposure levels are low, but duration of exposure can be long. Spatial Poisson regressions were conducted to estimate the risk ratios of prostate cancer by tertiles of arsenic level at a county level, adjusted for demographic and risk factors. The county averages of water arsenic levels varied from 1.08 to 18.59 ppb across the counties, with three counties above the 10 ppb limit. Based on the tertiles of their arsenic levels, counties were divided into three groups: low (1.08-2.06 ppb), medium (2.07-2.98 ppb), and high (2.99-18.59 ppb). Spatial Poisson regression model analysis showed that the risk ratios of prostate cancer were 1.16 (95% CI, 1.10-1.23) and 1.28 (95% CI, 1.21-1.34) in the medium and high groups (p-trend < 0.001), compared to the low group after adjusting for risk factors. The results were similar when analyses were restricted to aggressive prostate cancers. These data show a significant dose-dependent association between low-level arsenic exposure and prostate cancer. These findings need to be confirmed from more in-depth individual studies.
Overall, the results showed that 1) the detections of arsenic increased in Iowa drinking water in the last decade, 2) there were disparities of trends in major cancers between Iowa and the rest of US, and 3) the risk of prostate cancer increased with arsenic exposure via drinking water. This study approach allows for the identification of possible health issues caused by water contaminants.
Arsenic and atrazine are two water contaminants of high public health concern in Iowa. Arsenic is found in soil from glacier deposits and atrazine is a commonly used herbicide. My questions were whether Iowans are exposed to higher levels of arsenic and atrazine from drinking water, whether Iowans have the same rates of cancers as the rest of the US, and whether higher levels of arsenic is some Iowa counties could lead to a higher risk for prostate cancer.
I investigated the occurrence of arsenic and atrazine in drinking water from Iowa private wells and public water systems. I found that detection and concentration of atrazine in drinking water decreased over time. However, the percentage of arsenic detections and concentrations higher than the current regulatory level increased over time in the public water systems. Therefore, arsenic was selected as a water contaminant for further study.
Cancer is the second leading cause of death in the US. However, cancer rates vary by different regions over time. In this study, the trends in cancers related to arsenic and atrazine exposures in Iowa were investigated and compared to 8 other states for white adults. I observed that the number of new overall cancer cases and death from them was lower in Iowa than the US, but different trends in major cancers were found between Iowa and the US. Importantly, prostate cancer was the most frequent type of cancer in men in both Iowa and the US and it was selected as a health outcome for further study.
Based on what I found in those previous studies, I conducted a county-level study comparing prostate cancer and arsenic in drinking water in Iowa. I estimated the risk of prostate cancer by the three range of arsenic level at a county level. The results of analysis showed that the risk of prostate cancer increased by 16 % and 28 % in the groups of counties with the medium and high arsenic level, compared to the group of counties with low arsenic level.
Together, these results indicate that the analysis of contaminants and regional occurrence of human diseases like cancer may be able to identify factors, like water contaminants, that have a negative effect on health. This knowledge can then be used to design methods to reduce or remove exposure to these contaminants.
viii, 118 pages
Includes bibliographical references (pages 98-118).
Copyright © 2016 Taehyun Roh
Roh, Taehyun. "Exposure to arsenic and atrazine from drinking water and risk of cancer." PhD (Doctor of Philosophy) thesis, University of Iowa, 2016.