PLANTS AS BIOACCUMULATORS OF PERCHLORATE

Perchlorate can have both natural and anthropogenic origins. Our knowledge of the extent and origin of perchlorate in the environment is incomplete. Early studies conducted for the United States Air Force (USAF) by the United States Environmental Protection Agency (USEPA) and the University of Georgia-Athens showed that a number of different plants under a variety of lab and field conditions can accumulate perchlorate. To test the efficacy of plants as bioindicators of perchlorate, the United States Geological Survey (USGS), USAF, and Texas Tech University obtained leaves and other biomass in remote locations in the southwestern United States and western North Atlantic. Water extraction of this biomass was performed and analyses of the extracts were conducted by IC-MS. Results to date have shown that perchlorate can be detected in several different marine plants from the western North Atlantic, in one specimen from off the coast of Chile, and in dominant xerophytes from the southwestern US. Testing of commercially available species specific kelp meal reveal that Chondrus crispus, Ascophyllum nodosoum, Laminria sp. around New Brunswick and Nova Scotia typically contain 20-80 ppb and Gigartina from the Pacific Ocean off Chile contained less than 10 ppb perchlorate on a dry weight basis. Dominant desert scrub, non-succulent xerophytes from remote locations in the four major deserts of the southwestern US (Chihuahuan, Great Basin, Mojave, and Sonoran) reveal that perchlorate can be found in concentrations ranging from less than 10 parts per billion (ppb) to almost 600 ppb. Limited testing of succulents of the genus Opuntia revealed levels of perchlorate greater than 1 part per million (ppm). Results from long-lived xerophytes such as Larrea tridentate (creosote bush) suggest that xerophytes may be sinks for atmospherically-derived perchlorate. Additional studies are in progress to investigate this possibility.