Perchlorate In Soil Research Articles

Determination of Trace Perchlorate in Soil using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

The international standard (IS) currently used for determining perchlorate in soil is not applicable to trace perchlorate. We developed a quantitative analysis method using liquid chromatography–tandem mass spectrometry (LC-MS/MS) for the trace perchlorate in soil. The perchlorate was extracted from air-dried soil (<150 μm) with distilled water. We proposed the optimum extraction method that included mechanical shaking followed by centrifugation. An internal standard material (Cl18O4-) was added to the extracts and standard solutions at concentration of 5 μg L-1. The samples were analyzed by LC-MS/MS equipped with a reversed phase C18 column packed with core-shell particles containing trimethylsilane functional groups. Samples that may be interfered with organic matter present in the soil should be purified with a C18 cartridge. The method detection limit and limit of quantitation for our method was 1.31 and 4.36 μg/kg, respectively. We verified the proposed method through interlaboratory comparison test; both coefficients of variation for repeatability (CVr) and reproducibility (CVR) were less than 5%. Therefore, we concluded that the proposed method may be used for precise quantitative analysis of trace amounts of perchlorate in soil.

Sources and sinks of perchlorate in soil in coastal ice-free areas of Antarctica

Perchlorate (ClO4−), a persistent inorganic compound, has harmful effects on human health. Natural ClO4− is formed in the atmosphere and enters into the surface environment through deposition. However, the knowledge on the occurrence, spatial variability and sinks of natural ClO4− in different environments remains limited, especially in the polar regions. Here, we investigate the sources and sinks of ClO4− in soil collected in three ice-free areas in coastal Antarctica, where the research stations and wildlife colonies are mainly distributed. No statistically significant difference in ClO4− concentrations between sites near and away from the stations suggests that local human presence is not a significant source of ClO4− in soil. Concentrations of ClO4− in soil from wildlife colonies are not significantly higher than those from sites with no intense wildlife activities, indicating that wildlife activities have no significant influences on ClO4− in soil. Thus, atmospherically formed ClO4− is the main source for soil in Antarctica. In general, ClO4− concentrations (0.1–5.1 μg kg−1) in soil in this study are much lower than those in the arid environments and comparable to those in the unsaturated zones. Leaching by snow meltwater may be the main sink for ClO4− in soil, and deeper depths for aqueous migration may contribute to the lower ClO4− concentrations in Antarctic surface soil compared to the values in the arid areas with low precipitation amount. Due to the biological origin of NO3−, no correlation between NO3− and ClO4− in soil is observed in this study, different from the observations in arid areas. In addition, no significant correlation is observed between organic matter contents and ClO4− concentrations in soil, suggesting that biological reduction is not an important sink for ClO4− in Antarctic soil.

Perchlorate and chlorate contamination associated with fireworks in Kerala, India

Firework displays are an integral part of festivals. Kerala is a host of innumerable firework displays. Perchlorate is used as an oxidizer in fireworks. Water samples and soil samples collected after firework display in selected sites of Kerala were analyzed using liquid chromatography–mass spectrometry (LC–MS). Both soil and water samples after the firework display were found to be contaminated with perchlorate. Average perchlorate in soil ranges from below detectable limits to 20451.14 ppb and in water from below detectable limits to 7.23 ppb. Perchlorate in soil was found to be maximum on the third day after the fireworks display. The present study gives an awareness of the perchlorate contamination resulting from the fireworks display in Kerala.

Ultrasensitive luminescent turn-on detection of perchlorate particulates by triggering supramolecular self-assembly of platinum(II) complex in hydrogel matrix

Onsite ultrasensitive identification of the airborne or deposited perchlorate particulates is crucial for homeland security, forensic analysis, and environment monitoring. However, few of the currently developed luminescent sensor focus on the direct and ultratrace detection of its solid particulates as the low level of analyte and the difficulty in exhaustive collection of the trace sample. Here, a general design strategy for the direct, ultrasensitive, and specific luminescent turn-on sensing of perchlorate particulates is proposed by triggering supramolecular self-assembly of cationic platinum(II) complex in a hydrogel matrix, in which the self-assembly of platinum(II) complex endows the luminescence turn-on response and the hydrogel matrix creates excellent confinement effect for terminating the diffusion of generated luminescent 1D aggregates. The proposed hydrogel-based sensor is capable to detect the airborne perchlorate particulate of 1.12 ng by naked eye and 0.11 fg by common optical microscope. Further practical sensing performances for real firecracker and buried perchlorate in soil demonstrates the excellent environmental adaptability, and the latent fingerprint visualization shows great potential for clue tracking. This study provides an inspirable strategy for designing ultrasensitive luminescent sensor for trace solid sample.

Occurrence, distribution and dynamics of perchlorate in soil, water, fertilizers, vegetables and fruits and associated human exposure in Chile.

Perchlorate (ClO4-) has been identified as a persistent environmental contaminant of concern. Perchlorate exposure is a potential health concern because it interferes with hormone production by thyroid gland. Food (fruits and vegetables) and drinking water are an important source of human exposure to perchlorate. However, little is known about the occurrence of perchlorate in Chile. The purpose of this study was to determine the occurrence of perchlorate in 145 samples (soil, drinking water, surface water, groundwater, fertilizers, fruits and vegetables) collected across Chile and estimate associated exposure to consumers. Our results show that perchlorate was detected in soil (median: 22.2ngg-1), drinking water (median: 3.0ngmL-1), fruits (median: 0.91ngg-1 fresh weight [FW]), lettuce (median: 5.0ngg-1 FW) and chard (median: 4.15ngg-1 FW). Interestingly, perchlorate concentrations detected in drinking water from three regions (Serena, Copiapo and Illapel) exceeded the USEPA interim drinking water health advisory level of 15ngmL-1. Median concentrations of perchlorate in non-nitrogenous fertilizers (3.1mgkg-1) were higher than those in nitrogenous fertilizers (1.3mgkg-1). Estimated daily intake (EDI) of perchlorate via drinking water was lower than the USEPA's reference dose (7000ngkg-1 bw day-1). The EDI of perchlorate via vegetables (chard and lettuce) produced in northern Chile was three times higher than those produced in other regions. The results of this study provide information about perchlorate sources in Chile, which will be helpful in modifying current regulations.

Sources and fates of perchlorate in soils in Chile: A case study of perchlorate dynamics in soil-crop systems using lettuce (Lactuca sativa) fields.

Perchlorate occurs naturally in the environment in deposits of nitrate and can be formed in the atmosphere and precipitate into soil. However, little is known about the occurrence and levels of perchlorate in soils and fertilizers in Chile and its impacts on agricultural systems and food safety. In this study, concentrations of perchlorate were determined in 101 surface soils and 17 fertilizers [nitrogenous (n = 8), nitrogen-phosphorous-potassium (NPK; n = 3), phosphate (n = 2) and non-nitrogenous (n = 4)] collected across Chile from 2017 to 2018. Our results show that perchlorate was detected mainly in agricultural soils (mean: 0.32 ng g−1), grassland rotation sites (0.41 ngg−1) and urban locations (0.38 ng g−1). Interestingly, elevated concentrations of perchlorate (9.66 and 54.0 ng g−1) were found in agricultural soils. All fertilizers contained perchlorate: nitrogenous fertilizers (mean: 32.6 mg kg−1), NPK (mean: 12.6 mg kg−1), non-nitrogenous fertilizers (mean: 10.2 mg kg−1) and phosphates (mean: 11.5 mg kg−1). Only one type of nitrogenous fertilizer (KNO3: 95.3 mg kg−1) exceeded the international regulation limit (50 mg kg−1). For two agronomic practices, the content of perchlorate in lettuce increased as the fertilizer application rate increased, with fertigation promoting a more significant accumulation. However, the concentrations generally remained below regulatory values. Our results suggest that fertilizers constitute an important source of perchlorate in soils.

Seasonal Variation and Exposure Risks of Perchlorate in Soil, Indoor Dust, and Outdoor Dust in China.

A total of 97 paired soil, outdoor dust, and indoor dust samples were collected in the national scale of China in summer, and the perchlorate levels were compared with those in soil and outdoor dust samples collected in winter in our previous study. The median perchlorate concentrations in the outdoor dust, indoor dust, and soil samples were 8.10, 11.4, and 0.05mg/kg, respectively, which were significantly lower than those in the winter samples due to the natural factors and human activities. No significant differences in perchlorate concentrations were found between Northern and Southern China in the dust samples, whereas the difference was obtained in the soil samples. In the terms of possible source, the perchlorate levels in the outdoor dust exhibited strong correlation with SO42- (r2 = 0.458**) and NO3- (r2 = 0.389**), indicating part of perchlorate in outdoor environment was likely from atmospheric oxidative process in summer. The perchlorate, SO42-, and Cl- levels in the indoor dust were significantly related to those in the outdoor dust, suggesting that outdoor contaminants might be an important source for indoor environment. Furthermore, the human exposure to perchlorate was under relatively safe state in China except for special sites or periods with high perchlorate levels. Dust made an unexpected contribution of 41.3% to the total daily perchlorate intake for children, whereas 2.46% for adults in China based on biomonitoring, which deserves more attention.

Sorption and fate of perchlorate in arid soils

ABSTRACTThe mobility of perchlorate in soils depends on several factors, including soil mineralogy and the presence of other oxyanions that compete with perchlorate for the retention sites. Currently, there are no studies that evaluate the mobility of perchlorate in arid soils. The present study evaluated the mobility of ClO4– in three arid soils, Canchones, Humberstone and Pica, exposed to two ClO4– concentration ranges and different ionic strengths. In Humberstone (non-agricultural) and Pica (agricultural) soils, the sorption processes were not important for both concentration ranges, while Canchones soil (agricultural) showed a decrease in perchlorate concentration associated with microbial degradation processes. The increase of medium ionic strength by addition of Ca(NO3)2 only had an important effect on Humberstone soil, associated with the presence of kaolinite and muscovite (variable charge). A competition effect was observed between perchlorate, nitrate and other anions presents in solution by absorption sites generated from variable charge mineral and calcium. Considering the quite low sorption capacity of the soils and the high solubility, perchlorate can be absorbed by fruit and vegetables of export in concentrations over the healthy levels established by international organization.

이온크로마토그래피를 이용한 토양 중 퍼클로레이트 정량에 관한 국제표준(안) 연구

ABSTRACT Based on the literature study for the determination of perchlorate in soil we chose the ion chromatography as ameasurement method and decided to use 70 mM KOH as an eluent to avoid the interference derived from the co-elutionof pyrophosphate (P 2 O 74− ), tripolyphosphate (P 3 O 105− ). Also we proposed to use air dried soil through 0.15 mm sieve anddistilled water as an extractant. Under the these basic concepts, we carried out the experiments to set up the detailprocedure like solid to liquid ratio (S/L ratio), extraction time, device for extraction and indicating factors for qualitycontrol (e.g. precision, accuracy, MDL, LOQ). In case of time and device for extraction, 5 hours of mechanical shaking or1 hour of centrifugation showed better precision and accuracy than that of sonication for 1 hour According to these results,we proposed the extraction method combining 5 hours of mechanical shaking with 1 hour of centrifugation. From theaspect of S/L ratio, the ratio of 1/2 or 1/3 showed resonable precision and accuracy. In case of the ratio of 1/2, there wouldbe some problems in the separation process when the proportion of fine particle is high. Therefore, we proposed theextraction ratio of solid to liquid as 1/3 instead of 1/2. With the consideration of cost effectiveness and soil salinity, weproposed the use of cartridge for removing the interfering anions like chloride, sulfate and carbonate in specific samplesuch as saline soil.Key words : Perchlorate, Soil analysis, International standard, S/L ratio

Perchlorate Uptake and its Effect on Physiological, Biochemical and Growth Parameters of Eucalyptusplant under Ammonium Perchlorate Stress

Perchlorate is a significant environmental pollutant affecting public health. When entered in ecosystem it is highly toxic. Present investigation focused on the influence of perchlorate on physiological and biochemical parameters of Eucalyptus citriodora and also its accumulation in plant tissue and depletion from soil. Eucalyptus plants were treated with varying concentration of ammonium perchlorate from 1000ppm, 2000ppm, 5000ppm and 10000 ppm. Perchlorate inside the plant tissue and in soil was quantified at regular intervals. Amount of perchlorate inside plant tissue observed to increase with number of days after treatment and is proportional to concentration of perchlorate in soil. Morphological characters like shoot length, root length, number of leaf were observed to decrease with increasing concentration of perchlorate. The present study revealed decrease in chlorophyll and reducing sugar content in leaf tissue under varying concentration of perchlorate and is indirectly proportional to amount of perchlorate. While total protein, proline, and phenol content showed a gradual increase with increase in concentration of perchlorate and in different experimental set up, suggesting increase in non-enzymatic stress parameters with increased level of toxicity. An increased activity of peroxidase enzyme was observed with increased dose of ammonium perchlorate. It can be concluded that perchlorate related influence on plant are both qualitative and quantitative and depends upon its concentration and duration of exposure.

Perchlorate Levels in Soil and Waters from the Atacama Desert

Perchlorate is an anion that originates as a contaminant in ground and surface waters. The presence of perchlorate in soil and water samples from northern Chile (Atacama Desert) was investigated by ion chromatography-electrospray mass spectrometry. Results indicated that perchlorate was found in five of seven soils (cultivated and uncultivated) ranging from 290 ± 1 to 2,565 ± 2 μg/kg. The greatest concentration of perchlorate was detected in Humberstone soil (2,565 ± 2 μg/kg) associated with nitrate deposits. Perchlorate levels in Chilean soils are greater than those reported for uncultivated soils in the United States. Perchlorate was also found in superficial running water ranging from 744 ± 0.01 to 1,480 ± 0.02 μg/L. Perchlorate water concentration is 30-60 times greater than levels established by the United States Environmental Protection Agency (24.5 μg/L) for drinking.

Use of Dissolved Organic Carbon to Biostimulate Rapid Rhizodegradation of Perchlorate in Soil

The main limitation to biodegradation of perchlorate in most soils and groundwater tends to be the availability of an adequate supply of organic carbon or electron donors. This study investigated the use of electron sources provided as Dissolved Organic Carbon (DOC) from chicken litter extract and acetate to enhance and sustain rhizodegradation of perchlorate in contaminated soils. This approach should reduce the residence time of perchlorate in vegetated soils and minimize the well-documented plant uptake of perchlorate at contaminated field sites and by food crops. Willow trees (Salix nigra) planted in 20 L soil bioreactors were dosed with perchlorate-contaminated water multiple times. The rate of biodegradation of perchlorate in willow-planted soil bioreactors provided with electron sources as 300 mg L-1 DOC was very rapid and described by zero-order kinetics with a maximum rate constant of 24 mg L-1 day-1. For planted control experiments in which DOC was limiting, the removal of perchlorate primarily by biodegradation was described by pseudo-first-order kinetics with a maximum rate constant of 0.35 day-1. The fraction of perchlorate phytoaccumulated in the control plants was an order of magnitude higher than in plants grown in the DOC-dosed bioreactors. The results of this study confirms that the slow buildup of DOC in the rhizosphere by root exudation and organic matter decomposition is insufficient to sustain a high rate of biodegradation and/or rhizodegradation of perchlorate and perhaps other degradable contaminants in vegetated contaminated soils. It is recommended that an optimum design of phytoremediation of perchlorate should include enhancement of rhizodegradation by providing an optimum and sustained supply of carbon source.

Discovery of Natural Perchlorate in the Antarctic Dry Valleys and Its Global Implications

In the past few years, it has become increasingly apparent that perchlorate (ClO(4)(-)) is present on all continents, except the polar regions where it had not yet been assessed, and that it may have a significant natural source. Here, we report on the discovery of perchlorate in soil and ice from several Antarctic Dry Valleys (ADVs) where concentrations reach up to 1100 microg/kg. In the driest ADV, perchlorate correlates with atmospherically deposited nitrate. Far from anthropogenic activity, ADV perchlorate provides unambiguous evidence that natural perchlorate is ubiquitous on Earth. The discovery has significant implications for the origin of perchlorate, its global biogeochemical interactions, and possible interactions with the polar ice sheets. The results support the hypotheses that perchlorate is produced globally and continuously in the Earth's atmosphere, that it typically accumulates in hyperarid areas, and that it does not build up in oceans or other wet environments most likely because of microbial reduction on a global scale.

Rapid full‐scale bioremediation of perchlorate in soil at a large brownfields site

AbstractThe former Bermite site north of Los Angeles, California, was used to manufacture various explosives and related products containing energetic compounds, including perchlorate. Remediation of perchlorate in site soil and groundwater is being conducted to meet regulatory requirements and allow planned redevelopment activities to proceed. The general approach to perchlorate remediation of shallow soil at the site includes excavation of affected soils followed by ex situ bioremediation. Glycerin was chosen for use as an electron donor because of its stability, safety, low cost, and regulatory acceptance. However, full‐scale bioremediation operation with glycerin initially resulted in inconsistent results despite consistent perchlorate biodegradation observed in treatability study microcosms. To eliminate the inconsistency and optimize the biotreatment process, additional studies were performed in the field on parallel tracks to determine crucial factor(s) that influenced inconsistent breakdown of perchlorate in site soils. Total Kjeldahl nitrogen (TKN) was determined to be a significant factor limiting perchlorate biodegradation. The addition of di‐ammonium phosphate (DAP) resulted in the consistent and complete perchlorate removal, generally within two weeks of incubation with a median destruction rate of about 200 μg/kg/day. Soil processing rates were gradually increased over the year, and, by the summer, approximately 2,000 to 2,500 tons of soil were being processed per day with a total of approximately 160,000 tons processed by the end of July. The total unit treatment cost for the process is about approximately $35/ton. The glycerin‐DAP process is playing a major role in the remediation of this 1,000‐acre former industrial site. © 2008 Wiley Periodicals, Inc.

Influence of soil type and extraction conditions on perchlorate analysis by ion chromatography

Perchlorate is a stable anion that has been introduced into the environment through activities related to its production and use as a solid rocket propellant. Perchlorate is thought to transport through soils without being adsorbed; thus, for determination of perchlorate in soil, samples are typically extracted with water prior to analysis. The completeness of extraction depends on perchlorate existing as a free ion within the soil matrix. In this study, perchlorate extraction efficiency was evaluated with five soil types under two different oxygen states. For each soil, 30% (w/w) slurries were prepared and equilibrated under either oxic or anoxic conditions prior to spiking with a stock solution of sodium perchlorate, and the slurries were then maintained for 1-week or 1-month. At the end of the exposure, slurries were centrifuged and separated into aqueous and soil phases. After phase separation, the soil was washed first with deionized water and then with 50 mM NaOH, producing second and third aqueous phases, respectively. Perchlorate concentrations in the three aqueous phases were determined using ion chromatography. The results obtained from this study suggest that matrix interference and signal suppression due to high conductivity have greater effects upon observed perchlorate concentrations by ion chromatography than does perchlorate interaction with soil. Thus, a single water extraction is sufficient for quantitative determination of perchlorate in soil.

Development of an extraction method for perchlorate in soils

Perchlorate originates as a contaminant in the environment from its use in solid rocket fuels and munitions. The current US EPA methods for perchlorate determination via ion chromatography using conductivity detection do not include recommendations for the extraction of perchlorate from soil. This study evaluated and identified appropriate conditions for the extraction of perchlorate from clay loam, loamy sand, and sandy soils. Based on the results of this evaluation, soils should be extracted in a dry, ground (mortar and pestle) state with Milli-Q water in a 1 ratio 1 soil ratio water ratio and diluted no more than 5-fold before analysis. When sandy soils were extracted in this manner, the calculated method detection limit was 3.5 microg kg(-1). The findings of this study have aided in the establishment of a standardized extraction method for perchlorate in soil.

Forensic Identification of Anthropogenic and Naturally Occurring Sources of Perchlorate

Perchlorate (ClO4 −) is an emerging contaminant whose presence and origin is of considerable environmental interest. This article discusses known sources of perchlorate and available forensic techniques to distinguish between naturally occurring and anthropogenic origins. Forensic techniques presented include stable isotopic analysis (37Cl/35Cl, 87Sr/86Sr, 16O/17O), surrogates analysis (nitrates, sodium, chlorides, phosphate, nitroglycerins, metals, strontium), historical information assessment (aerial photography, propellant use and chemistry, firing range usage), geologic analysis (limestone, caliche, playa crusts, hanksite [Na22K(SO4)9 (CO3)2Cl], potash, phosphate ore, etc.), x-ray diffraction (XRD), and scanning electron microscopy (SEM). In this article, the detection of a source of naturally occurring perchlorate in soil and groundwater associated with the Mission Valley Formation in San Diego California is presented. Modification of existing agricultural soil sampling techniques USDA 60-6(26) and USDA 60-6(27a) were used for sample preparation along with EPA Standard Method 314 for extract analysis. X-ray diffraction (XRD), polarized light microscopy (PLM), scanning electron microscopy (SEM), surrogates analysis, geologic evaluation, and aerial photography were used in this investigation. The results of this analysis indicated a naturally occurring source of perchlorate is associated with the Mission Valley Formation. No statistical relationship between major ions (sulfate, total nitrate, chloride) and perchlorate was identified.

A study of treatment options to remediate explosives and perchlorate in soils and groundwater at Camp Edwards, Massachusetts

AbstractThe Army National Guard initiated an Innovative Technology Evaluation (ITE) Program in March 2000 to study potential remedial technologies for the cleanup of explosives‐contaminated soil and groundwater at the Camp Edwards site on the Massachusetts Military Reservation. The soil technologies chosen for the ITE program were: soil washing, chemical oxidation, chemical reduction, thermal desorption/destruction (LTTD), bioslurry, composting, and solid phase bioremediation. The technologies were evaluated based on their ability to treat both washed and untreated soil. A major factor considered was the ability to degrade explosives, such as RDX, found in particulate form in the soils. The heterogeneous nature of explosives in soils dictates that the preferred technology must be able to treat explosives in all forms, including the particulate form. Groundwater remediation technologies considered include: in situ cometabolic reduction, two forms of in situ chemical oxidation, Fenton‐like oxidation and potassium permanganate. This article presents the results of each of the remedial technologies evaluated and discusses which technologies met the established ITE performance goals. © 2003 Wiley Periodicals, Inc.

Perchlorate retention and mobility in soils.

Adsorption and release of perchlorate in a variety of soils, minerals, and other media were studied when the solid media were exposed to low and high aqueous solutions of perchlorate salts. Low level ClO4- exposure was investigated by subjecting triplicate 5.0 g portions of a solid medium (38 different soils, minerals, or dusts) to 25 mL of an aqueous ammonium perchlorate (NH4ClO4) solution containing 670 ng mL(-1) (6.8 microM) perchlorate. This corresponds to a perchlorate-to-soil ratio of 3.4 microg g(-1) (34 nmol g(-1)). At this level of exposure, more than 90% of the perchlorate was recovered in the aqueous phase, as determined by ion chromatography. In some cases, more than 99% of the perchlorate remained in the aqueous phase. In some cases, the apparent loss of aqueous perchlorate was not clearly distinguishable from the variation due to experimental error. The forced perchlorate anion exchange capacities (PAECs) were studied by soaking triplicate 5.0 g portions of the solid media in 250 mL of 0.20 M sodium perchlorate (NaClO4) followed by repeated deionized water rinses (overnight soaks with mixing) until perchlorate concentrations fell below 20 ng mL(-1) in the rinse solutions. The dried residua were leached with 15.0 mL of 0.10 M sodium hydroxide. The leachates were analyzed by ion chromatography and the perchlorate concentrations thus found were subsequently used to calculate the PAECs. The measurable PAECs of the insoluble and settleable residua ranged from 4 to 150 nmol g(-1) (micromol kg(-1)), with most in the 20-50 nmol g(-1) range. In some soils or minerals, no sorption was detectable. The mineral bentonite was problematic, however. Overall, the findings support the widely accepted idea that perchlorate does not appreciably sorb to soils and that its mobility and fate are largely influenced by hydrologic and biologic factors. They also generally support the idea that intrasoil perchlorate content is depositional rather than sorptive. On the other hand, sorption (anion replacement) of perchlorate appears to occur in some soils. Therefore, the measurement of perchlorate in soils requires accounting for ion exchange phenomena; leaching with water alone may give inaccurate results. If perchlorate anion exchange is confirmed to be negligible, then leaching procedures may be simplified accordingly.

Transport and biodegradation of perchlorate in soils.

Perchlorate (ClO4-) contamination of ground water and surface water is a widespread problem, particularly in the western United States. This study examined the effect of biodegradation on perchlorate fate and transport in soils. Solute transport experiments were conducted on two surface soils. Pulses of solution containing perchlorate and Br- were applied to saturated soil columns at steady state water flow. Perchlorate behaved like a nonreactive tracer in Columbia loam (coarse-loamy, mixed, superactive, nonacid, thermic Oxyaquic Xerofluvent) but was degraded in Yolo loam (fine-silty, mixed, superactive, nonacid, thermic Mollic Xerofluvent). Batch experiments demonstrated that perchlorate removal from solution in Yolo loam was caused by biodegradation. Other batch experiments with Yolo loam surface and subsurface soils, Columbia loam surface soil, and dredge tailings demonstrated that perchlorate biodegradation required anaerobic conditions, an adequate carbon source, and an active perchlorate-degrading microbial population. The sequential reduction of perchlorate and NO3- by an indigenous soil microbial community in Yolo loam batch systems was also studied. Nitrate reduction occurred much sooner than perchlorate reduction in soils that had not been previously exposed to perchlorate, but NO3- and perchlorate were simultaneously reduced in soils previously exposed to perchlorate. The results of this study have implications for in situ remediation schemes and for agricultural soils that have been contaminated by perchlorate-tainted irrigation water.