Rapid Communication Biological Perchlorate Reduction in High-salinity Solutions

Perchlorate (ClO4 ) has been detected in numerous ground and surface waters, and has recently been added to the drinking water Candidate Contaminant List in the United States. Perchlorate can be removed from drinking water using ion exchange, but this results in the production of highly saline (7–12%) perchlorate-contaminated brines. Perchlorate-degrading microbial enrichments capable of growth in highly saline water were obtained by screening six salt water environments including marine and lake surface waters, salt marshes, subtidal sediments, and a biofilm/sludge from a seawater filter. Perchlorate reduction was obtained in three of these samples (seawater, saline lake water, and biofilm/ sludge) at a salinity of 3%. The salinity range of two of these cultures was extended through serial transfers into media having higher salt concentrations (3–7%). Growth rates were measured over a salinity range of 1–15%. The maximum growth rate measured for the saline lake-water enrichment was 0.060 0.003 d 1 (doubling time of 11.6 0.8 d) at a salinity of 5%. Growth rates decreased to 0.037 0.002 d 1 at a salinity of 11%, and no growth was observed at salinities of 13 or 15%. These results demonstrate for the first time that biological perchlorate reduction is possible in solutions having a salinity typical of ion exchange brines. # 2001 Elsevier Science Ltd. All rights reserved Key words}ammonium perchlorate, biodegradation, brine, chlorate, drinking water, ion exchange, munitions, perchlorate, rocket propellant INTRODUCTION intermediates accumulate in solution (Attaway and Perchlorate (ClO4 Smith, 1993; Logan, 1998; Herman and Franken­ ) has recently been added to the US Environmental Protection Agency’s drinking berger, 1998). Chlorite disproportionation to chlor­ water Candidate Contaminant List due to its ide and oxygen is a non-energy yielding step interference with hormone production by the thyroid catalyzed by chlorite dismutase, but both chlorate gland, and additional toxicity studies are underway and oxygen are used as electron acceptors by (Urbansky and Schock, 1999). A survey of surface perchlorate-respiring microbes (Rikken et al., 1996; and ground waters in the US has indicated that Coates et al., 1999). perchlorate contamination is extensive in many Several ion exchange systems have been developed locations, particularly in the arid southwestern states to remove perchlorate from contaminated waters (Urbansky, 1998). Perchlorate is used as an oxidizer (Kawaski et al., 1993; Batista et al., 2000; Gu et al., in solid rocket propellant, but it exists naturally in 2000; Tripp and Clifford, 2000; Venkatesh et al., fertilizers derived from Chilean caliche (Schilt, 1979; 2000). Due to the high affinity of perchlorate for Attaway and Smith, 1993; Susarla et al., 1999, 2000; these resins, very high salt concentrations (7–12%) Nzengung et al., 1999; Urbansky et al., 2000). are needed to regenerate the column (Venkatesh Perchlorate is used as a terminal electron acceptor et al., 2000; Batista et al., 2000). The perchlorate in by pure and mixed cultures of microorganisms these brines can be treated through a high-tempera­ during the oxidation of many different substrates ture, rare earth metal process (Venkatesh et al., 2000) (Logan, 1998; Herman and Frankenberger, 1998). but costs could be reduced if treatment could be The reduction sequence of perchlorate is conducted at lower temperatures without expensive ClO4 ! ClO2 catalysts. ! ClO3 ! Cl +O2, and none of the Microbiological treatment of perchlorate-contain­ ing solutions has not been reported thus far to occur *Author to whom all correspondence should be addressed. at the high salinities typical of perchlorate-contamiTel.: +1-814-863-7908; fax: +1-814-863-7304; e-mail: nated ion exchange brines. A perchlorate-degrading [email protected] isolate obtained by Bruce et al. (1999) had an optimal