Bioremediation and Biodegradation Transport and Biodegradation of Perchlorate in Soils

ing water (Giblin et al., 2000a,b; Herman and Frankenberger, 1999; Miller and Logan, 2000; Wallace et al., Perchlorate (ClO 4 ) contamination of ground water and surface 1998; Kim and Logan, 2000, 2001). Factors that affect the water is a widespread problem, particularly in the western United States. This study examined the effect of biodegradation on perchlofate and transport of perchlorate in the environment rate fate and transport in soils. Solute transport experiments were have received less attention. Several strains of perchloconducted on two surface soils. Pulses of solution containing perchlorate-reducing bacteria, all facultative anaerobes, have rate and Br were applied to saturated soil columns at steady state been isolated from environmental samples (Coates et water flow. Perchlorate behaved like a nonreactive tracer in Columbia al., 1999) and significant numbers of perchlorate-reducloam (coarse-loamy, mixed, superactive, nonacid, thermic Oxyaquic ing bacteria have been found in water and soil samples Xerofluvent) but was degraded in Yolo loam (fine-silty, mixed, super(Coates et al., 1999; Wu et al., 2001). Perchlorate has active, nonacid, thermic Mollic Xerofluvent). Batch experiments dembeen observed to adsorb slightly to variable charge soils onstrated that perchlorate removal from solution in Yolo loam was in low pH environments (Ji and Kong, 1992). The capaccaused by biodegradation. Other batch experiments with Yolo loam ity of biodegradation or adsorption to affect the fate surface and subsurface soils, Columbia loam surface soil, and dredge tailings demonstrated that perchlorate biodegradation required anaerand transport of perchlorate in soils, however, has not obic conditions, an adequate carbon source, and an active perchloratebeen studied extensively. Such information is essential degrading microbial population. The sequential reduction of perchloto assess the risk of human exposure to perchlorate and rate and NO 3 by an indigenous soil microbial community in Yolo predict the potential for contamination of water supplies loam batch systems was also studied. Nitrate reduction occurred much and irrigated crops. sooner than perchlorate reduction in soils that had not been previously The purpose of this research was to determine if bioexposed to perchlorate, but NO 3 and perchlorate were simultaneously degradation and/or sorption affects the fate and transreduced in soils previously exposed to perchlorate. The results of port of perchlorate in soils and to investigate the condithis study have implications for in situ remediation schemes and for tions under which these processes may occur. Because agricultural soils that have been contaminated by perchlorate-tainted of the potential for agricultural soils to be contaminated irrigation water. by perchlorate through irrigation, agricultural soils were used in this study. First, solute displacement experiments were conducted in saturated soil columns to deT large-scale disposal of explosives containing termine if biodegradation and/or sorption could affect ammonium perchlorate salts has resulted in perperchlorate fate and transport in two surface soils. Then, chlorate contamination of both ground water and sura series of batch experiments were conducted in surface face water, particularly in the western United States. and subsurface soils to measure the potential of native Perchlorate has been found in water supplies of more microbial communities to transform perchlorate under than 15 million people in California, Nevada, and Aridifferent conditions. zona (USEPA, 1999). It is also known to contaminate the Colorado River, a major source of irrigation water in the southwestern United States, which could result MATERIALS AND METHODS in the absorption of perchlorate into crops (Urbansky Solute Transport Experiments et al., 2000). The potential health concern associated with perchlorate is that it interferes with the uptake of Columbia loam and Yolo silt loam surface soils were coliodide by the pituitary gland, inhibiting the production lected in 1997 and 1993, respectively, from agricultural fields in Yolo County, California. Soils were air-dried, crushed, and of thyroid hormones required for normal metabolism stored at room temperature. Both soils were sieved through (Urbansky, 1998). a 1-mm sieve. Characteristics of both soils are given in Table 1. Perchlorate is very soluble and extremely slow to react A cylindrical column (15-cm length, 7.5-cm i.d.) was packed with other chemicals (Urbansky, 1998). These characwith soil to a uniform bulk density of approximately 1.45 g teristics make perchlorate-contaminated water very difcm . Porous plates were attached to either end of the column ficult to remediate with standard methods of water treatwith silicone sealant. The column was saturated from the botment (Urbansky, 1998; Logan, 2001). Because of this, tom slowly with a 1 g L 1 calcium sulfate solution. When the most research on perchlorate to date has focused on column was fully saturated, the inlet was attached to a peristaldeveloping methods to remove perchlorate from drinktic pump. The outlet was attached to short spaghetti tubing that led to a fraction collector containing test tubes. At the beginning of each experiment, valves in the tubing below the University of California Davis, Department of Land, Air, and Water inlet were turned so that a solution containing 660 mg L 1 Resources, Davis, CA 95616. Received 31 July 2001. *Corresponding Br and 10 mg L 1 perchlorate was pumped into the column. author ([email protected]). After the pulse had been applied to the column, the inlet solution was switched back to calcium sulfate in a similar manner. Published in J. Environ. Qual. 32:40–46 (2003).