Groundwater arsenic concentrations and cancer incidence rates : a regional comparison in Oregon Public Deposited


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  • Arsenic contamination of groundwater is a global issue with national and local implications. Chronic exposure to arsenic in drinking water has been linked to both carcinogenic and non-carcinogenic health outcomes. The primary exposure route of inorganic arsenic is ingestion from drinking water due to natural contamination in groundwater from dissolution of natural mineral deposits and anthropogenic sources. The purpose of this study was to determine if there is a spatial relationship between groundwater arsenic concentrations and cancer incidences within two regions of Oregon. The objectives of this study were to: (1) determine if there is a spatial relationship between arsenic concentrations in the Willamette Valley and Southeast Oregon and incidence rates of bladder, kidney, liver and lung cancers; (2) contribute to the Centers for Disease Control and Prevention’s development of the Environmental Public Health Tracking network by using secondary data to investigate linkages of arsenic in groundwater and associated health effects; and (3) serve as an exploratory tool for identifying a public health concern that can be followed up with comprehensive analytical studies of the region. The study used four secondary data sets: Cancer data from the Oregon State Cancer Registry; community water system arsenic data from the Oregon Department of Human Services Drinking Water Program; groundwater arsenic data from the U.S. Geological Survey National Water Inventory System; and population data from the U.S. Census Bureau. Data set were combined and then analyzed with statistical and spatial analysis methods. This study did incur challenges of data compatibility and required extensive data preparation activities of several of the data sets. One such data manipulation was the integration of two independent sources of water quality data which had not been done before in Oregon and may not have accurately defined the exposure risk of sub-populations. Another limitation was that missing cases due to geocoding were more likely to be in rural census tracts due to the P.O. Box and Rural Route addresses, thus possibly contributing to an underestimation of the number of cancer cases used in the study analyses. Results indicate several significant differences of risk between demographic and arsenic concentration intervals. However, the inherent limitations of secondary data have produced some unexpected results. Using the arsenic Quintile 1 (0 - 0.9 μg/L) as a reference point, the results showed that arsenic concentration levels in groundwater do not impact the incidence rates of bladder, kidney, liver or lung cancer in populations over the age of 40 in regions with arsenic concentrations above 1 μg/L. Further, although cancer incidence rates might be expected to increase with increasing groundwater arsenic concentrations in Quintiles 3, 4 and 5, the results in this study show otherwise. Maps of the study regions depicting arsenic concentration levels in groundwater show that arsenic is widely distributed but concentration levels can vary greatly between census tracts located in close proximity. The distribution of arsenic in the region may be affected by geological formations that are known to be associated with higher arsenic levels. Follow-up studies are recommended for regions of the state that were found to have arsenic concentration at or above the current MCL regulated by the Safe Drinking Water Act. Rural regions of the state that rely on private groundwater wells not regulated by the federal standard would also be appropriate. Results of this study will be shared with the Oregon Environmental Public Health Tracking network, their research partners and other interested state and local agencies.
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