Perchlorate uptake by salt cedar (Tamarix ramosissima) in the Las Vegas Wash riparian ecosystem

Perchlorate ion (ClO4-) has been identified in samples of dormant salt ceda r (Tamarix ramosissima) growing in the Las Vegas Wash. Perchlorate is an ox idant, but its reduction is kinetically hindered. Concern over thyroid effe cts caused the Environmental Protection Agency (EPA) to add perchlorate to the drinking water Contaminant Candidate List (CCL). Beginning in 2001, uti lities will look for perchlorate under the Unregulated Contaminants Monitor ing Rule (UCMR). In wood samples acquired from the same plant growing in a contaminated stream, perchlorate concentrations were found as follows: 5-6 mu g g(-1) in dry twigs extending above the water and 300 mu g g(-1) in sta lks immersed in the stream. Perchlorate was leached from samples of wood, a nd the resulting solutions were analyzed by ion chromatography after clean- up. The identification was confirmed by electrospray ionization mass spectr ometry after complexation of perchlorate with decyltrimethylammonium cation . Because salt cedar is regarded as an invasive species, there: are large s cale programs aimed at eliminating it. However, this work suggests that sal t cedar might play a role in the ecological distribution of perchlorate as an environmental contaminant. Consequently, a thorough investigation of the fate and transport of perchlorate in tamarisks is required to assess the e ffects that eradication might have on perchlorate-tainted riparian ecosyste ms, such as the Las Vegas Wash. This is especially important since water fr om the wash enters Lake Mead and the Colorado River and has the potential t o affect the potable water source of tells of millions of people as well as irrigation water used on a variety of crops, including much of the lettuce produced in the USA. (C) 2000 Elsevier Science B.V. All rights reserved.