@article{1064e1f0e691457e83404a1f18471f56,
title = "Isotopic discrimination of natural and anthropogenic perchlorate sources in groundwater in a semi-arid region of northeastern Oregon (USA)",
abstract = "Perchlorate (ClO4−) has synthetic and natural sources. Synthetic ClO4− is released to the environment from its use as an oxidant in military and aerospace applications, and from its presence in a variety of common commercial products, such as safety flares, chlorate herbicides, and fireworks. Natural sources of ClO4− in the environment include imported nitrate fertilizers derived from salt deposits in the Atacama Desert of Chile and indigenous natural ClO4− that accumulates in unsaturated soils and groundwaters in other arid and semi-arid environments, largely from atmospheric deposition. The stable isotope ratios of chlorine (37Cl/35Cl) and oxygen (18O/16O, 17O/16O) and the isotopic abundance of radioactive 36Cl in ClO4− can be used to discriminate these different sources. Perchlorate was previously detected at relatively high concentrations (3.8–34.7 μg/L) in groundwater from many wells in the Boardman-Umatilla area near the Columbia River in northeastern Oregon, which is a semi-arid, highly agricultural, heavily irrigated area that includes several past and current military installations. Eight representative groundwater wells were sampled throughout this region and isotopic characteristics of ClO4− collected from each well were measured along with other chemical and isotopic parameters including tritium and other groundwater age indicators. Isotopic data indicate that indigenous natural ClO4− was present in groundwater from all sampled wells and was the predominant source in five of the wells. Synthetic ClO4− was present in the three remaining wells with natural ClO4−, and a minor fraction of Atacama-fertilizer-derived ClO4− was indicated in one of the wells. Data from this study expand the geographic area of the USA in which indigenous natural ClO4− has been detected to include the semi-arid northwest. This study also illustrates the role of irrigation recharge as a mechanism for producing relatively high concentrations of indigenous natural ClO4− in groundwater by flushing accumulated salts from the unsaturated zone.",
keywords = "Atacama, Chile, Fertilizer, Groundwater, Irrigation, Isotope, Nitrate, Oregon, Perchlorate, Umatilla",
author = "Hatzinger, {Paul B.} and B{\"o}hlke, {J. K.} and Jackson, {W. Andrew} and Baohua Gu and Mroczkowski, {Stanley J.} and Sturchio, {Neil C.}",
note = "Funding Information: We wish to thank Mr. Harry Craig from the USEPA and Mr. Phil Richerson from Oregon DEQ for assisting in all phases of well selection and sample collection. We gratefully acknowledge the financial and technical support provided for this project by the Environmental Security Technology Certification Program (ESTCP; Contract W912HQ-05-C-0022) and the Strategic Environmental Research and Development Program (SERDP; Contract W912HQ-08-0061) of the U.S. Department of Defense. Additional support was provided by the U.S. Geological Survey (USGS) Water Mission Area and Environmental Health Mission Area. We thank Dr. Andrea Leeson from ESTCP for her guidance. Other major contributors to this work included Linnea Heraty, Abe Beloso Jr., and Balaji Rao. Hank Johnson (USGS) and two anonymous reviewers provided many helpful suggestions for improving the manuscript. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Funding Information: Given the widespread irrigation in this region, the mobilization of indigenous natural ClO4− from vadose soils to groundwater is one possible explanation for its widespread occurrence. This scenario would be similar to that of the Southern High Plains (SHP) of West Texas and New Mexico, where widespread irrigation has been hypothesized to have flushed substantial quantities of indigenous natural ClO4− and other salts from the unsaturated zone to groundwater (Jackson et al., 2004, 2005; Dasgupta et al., 2006; Rajagopalan et al., 2006; Rao et al., 2007). This hypothesis was supported by stable isotopic analyses of ClO4− in the SHP regional aquifer (Jackson et al., 2010). However, the Boardman-Umatilla area also includes current and former military installations (Boardman Bombing Range, Cold Springs Bombing Range, Umatilla Chemical Depot) and a former Boeing rocket engine testing facility, in addition to intensive agricultural land use. Thus, the list of possible ClO4− sources includes indigenous natural salt deposits, Atacama nitrate fertilizer used for agriculture, synthetic ClO4− from past military and aerospace activities, and possibly ClO4− from bleach used to treat large-scale drip irrigation systems (Oregon DEQ, 2006). Road flares and fireworks also may be possible sources of synthetic ClO4−. Publisher Copyright: {\textcopyright} 2022 Elsevier Ltd",
year = "2022",
month = apr,
doi = "10.1016/j.apgeochem.2022.105232",
language = "English",
volume = "139",
journal = "Applied Geochemistry",
issn = "0883-2927",
}