Chlorine-36 as a Tracer of Perchlorate Origin

摘要

Perchlorate (ClO_4~-) 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 CIO_4~-, and have been exported worldwide since the mid-1800s for use in agriculture. The widespread introduction of synthetic and agricultural ClO_4~- into the environment has contaminated numerous municipal water supplies. Stable isotope ratio measurements of Cl and O have been applied for discrimination of different ClO_4~- sources in the environment This study explores the potential of ~(36)Cl measurements for further improving the discrimination of CIO_4~- sources. Groundwater and desert soil samples from the southwestern United States (U.S.) contain ClO_4~- having high ~(36)Cl abundances (~(36)Cl/Cl = 3100 × 10~(-15) to 28,800 × 10~(-15)), compared with those from the Atacama Desert (~(36)Cl/Cl = 0.9 × 10~(-15) to 590 × 10~(-15)) and synthetic CIO_4~- reagents and products (~(36)Cl/Cl = 0.0 × 10~(-15) to 40 × 10~(-15)). In conjunction with stable Cl and 0 isotope ratios, ~(36)Cl data provide a clear distinction among three principal ClO_4~- source types in the environment of the southwestern U.S.