Graduate Thesis Or Dissertation

An evaluation of well-water nitrate exposure and related health risks in the Lower Umatilla Basin of Oregon

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  • Excessive nitrates in drinking water pose a human health threat, especially to infants. Methemoglobinemia, or blue-baby syndrome, is a potentially fatal condition that inhibits the ability of red blood cells to bind and transport oxygen. Nitrates/nitrites have also been linked to such conditions as cancer, birth defects, and behavioral and developmental abnormalities. Nitrates are frequently found in wells in rural farming areas because synthetic fertilizers (containing nitrates) leach from the soil into the groundwater. The Lower Umatilla Basin (LUB) in Morrow and Umatilla counties of Oregon represents an intensively farmed and irrigated area in which relatively high amounts of nitrates are present in the groundwater and domestic well water. This study investigated population demographics for the rural Lower Umatilla Basin, comparing these data to identified well-water nitrate levels for the purpose of estimating nitrate exposures and potential risk of adverse health effects in the survey area. Results of the investigation revealed that 25 percent of the domestic-use wells in the survey area had nitrate levels that were in excess of the 10 ppm nN MCL for drinking water, as established by the U.S. Environmental Protection Agency. From access to these wells, 23 percent of the surveyed population was exposed to nitrate concentrations in excess of the MCL standard. However, resident infants were neither exposed to well-water nitrates in excess of the standard, nor were they exposed to illness that could have increased the risk of methemoglobinemia. The LUB survey population was generally older than the populations from cities in the LUB or the combined populations of rural areas of Morrow and Umatilla counties. The population included few women of childbearing age, and it was not subject to an appreciable increase in the proportion of younger to older families. These factors reduced the likelihood of a significant increase in the infant population, which also minimized the risk of methemoglobinemia to this population. Even though the risk of methemoglobinemia to infants was low in the LUB area, it is recommended that exposures to well-water nitrates be prevented, if possible even for adults, to reduce the potential for chronic, adverse health effects from excess nitrate ingestion. Continued monitoring of private wells by state agencies is recommended, with attention directed at domesticuse wells with nitrate levels in excess of 10 ppm nN. This information should be shared with local health departments for follow-up, investigation, and educational efforts as needed. Future studies by the Oregon DEQ, or other agencies which seek to document the sources of well-water nitrate contamination in the LUB, should include an investigation of the influence of local sources of nitrate contamination.
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