title: Chlorine-36 as a tracer of perchlorate origin.
abstract: Perchlorate (ClO4(-)) is ubiquitous in the environment. It is produced naturally by atmospheric photochemical reactions, and also is synthesized in large quantities for military, aerospace, and industrial applications. Nitrate-enriched salt deposits of the Atacama Desert (Chile) contain high concentrations of natural ClO4(-), and have been exported worldwide since the mid-1800s for use in agriculture. The widespread introduction of synthetic and agricultural ClO4(-) into the environment has contaminated numerous municipal water supplies. Stable isotope ratio measurements of Cl and O have been applied for discrimination of different ClO4(-) sources in the environment. This study explores the potential of 36Cl measurements for further improving the discrimination of ClO4(-) sources. Groundwater and desert soil samples from the southwestern United States (U.S.) contain ClO4(-) having high 36Cl abundances (36Cl/Cl = 3100 x 10(-15) to 28,800 x 10(-15)), compared with those from the Atacama Desert (36Cl/Cl = 0.9 x 10(-15) to 590 x 10(-15)) and synthetic ClO4(-) reagents and products (36Cl/Cl = 0.0 x 10(-15) to 40 x 10(-15)). In conjunction with stable Cl and O isotope ratios, 36Cl data provide a clear distinction among three principal ClO4(-) source types in the environment of the southwestern U.S.
authors.affiliation: University of Illinois at Chicago, Chicago, Illinois 60607, USA. sturchio@uic.edu
authors.forename: Neil C
authors.initials: NC
authors.lastname: Sturchio
authors.forename: Marc
authors.initials: M
authors.lastname: Caffee
authors.forename: Abelardo D
authors.initials: AD
authors.lastname: Beloso
authors.forename: Linnea J
authors.initials: LJ
authors.lastname: Heraty
authors.forename: John Karl
authors.initials: JK
authors.lastname: Böhlke
authors.forename: Paul B
authors.initials: PB
authors.lastname: Hatzinger
authors.forename: W Andrew
authors.initials: WA
authors.lastname: Jackson
authors.forename: Baohua
authors.initials: B
authors.lastname: Gu
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Heikoop
authors.forename: Michael
authors.initials: M
authors.lastname: Dale
mesh_terms: D002677:Chile; D002713:Chlorine / Q000737:chemistry*; D003889:Desert Climate; D009566:Nitrates / Q000737:chemistry; D010472:Perchlorates / Q000737:chemistry*; D011849:Radioactive Tracers; D011868:Radioisotopes / Q000737:chemistry*; D012987:Soil; D014316:Tritium; D014874:Water Pollutants, Chemical / Q000032:analysis; D014881:Water Supply
chemical_list: D009566:Nitrates; D010472:Perchlorates; D011849:Radioactive Tracers; D011868:Radioisotopes; D012987:Soil; D014874:Water Pollutants, Chemical; D014316:Tritium; D002713:Chlorine; C494474:perchlorate