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PubMed2005

Benchmark calculations for perchlorate from three human cohorts.

The presence of low concentrations of perchlorate in some drinking water sources has led to concern regarding potential effects on the thyroid. In a recently published report, the National Academy of Sciences indicated that the perchlorate dose required to cause hypothyroidism in adults would probably be > 0.40 mg/kg-day for months or longer. In this study, we calculated benchmark doses for perchlorate from thyroid-stimulating hormone (TSH) and free thyroxine (T4) serum indicators from two occupational cohorts with long-term exposure to perchlorate, and from a clinical study of volunteers exposed to perchlorate for 2 weeks. The benchmark dose for a particular serum indicator was defined as the dose predicted to cause an additional 5 or 10% of persons to have a serum measurement outside of the normal range. Using the data from the clinical study, we estimated the half-life of perchlorate in serum at 7.5 hr and the volume of distribution at 0.34 L/kg. Using these estimates and measurements of perchlorate in serum or urine, doses in the occupational cohorts were estimated and used in benchmark calculations. Because none of the three studies found a significant effect of perchlorate on TSH or free T4, all of the benchmark dose estimates were indistinguishable from infinity. The lower 95% statistical confidence limits on benchmark doses estimated from a combined analysis of the two occupational studies ranged from 0.21 to 0.56 mg/kg-day for free T4 index and from 0.36 to 0.92 mg/kg-day for TSH. Corresponding estimates from the short-term clinical study were within these ranges.

Air Pollutants, Occupational↗
PubMed2006

Perchlorate versus other environmental sodium/iodide symporter inhibitors: potential thyroid-related health effects.

OBJECTIVE: Perchlorate is a known competitive inhibitor of the sodium/iodide symporter (NIS). Possible thyroid-related effects of environmental perchlorate have created great health concerns, especially in the US, resulting in a debated reference dose (RfD) of 0.0007 mg/kg per day in drinking water recommended by the National Academy of Sciences (NAS). However, the impact of other environmental NIS inhibitors and the role of iodine seem to have received little attention in the whole debate. METHODS: We performed a PubMed search for articles published up to February 2006, using the key terms perchlorate, nitrate, thiocyanate, iodine, NIS, RfD, thyroid (alone or in combinations), with particular attention for human studies. In parallel, we critically analysed the January 2005 NAS' report, entitled 'Health implications of perchlorate ingestion'. RESULTS: The relative potencies of prevalent environmental NIS inhibitors (nitrate, thiocyanate and perchlorate) to inhibit iodine uptake have been estimated repeatedly with robust results. Our calculations show that nitrate and thiocyanate, acquired through drinking water or food, account for a much larger proportion of iodine uptake inhibition than perchlorate. Furthermore, the iodine uptake inhibitory effects of nitrate and thiocyanate - as defined by their legally accepted maximal contaminant levels in drinking water - exceed the potential effect of the proposed RfD for perchlorate by far. CONCLUSIONS: Iodine uptake inhibition and any potential downstream effect by perchlorate are highly dependent on the presence of other environmental NIS inhibitors and iodine intake itself. These potential confounders should therefore be considered in future studies and calculations for risk assessment.

Animals↗
PubMed2005

Effects of perchlorate exposure on resting metabolism, peak metabolism, and thyroid function in the prairie vole (Microtus ochrogaster).

Perchlorate, the oxidizer component in most solid rocket propellant formulations, is known to inhibit the uptake of iodide into the thyroid gland, thereby reducing production of the thyroid hormones, triiodothyronine and thyroxine (T4). Thyroid hormones regulate metabolism in endothermic organisms and are responsible for maintenance of homeothermic body temperatures. Little is known about the effects of perchlorate on metabolic capacity. The objectives of the present study were to determine if subchronic (51 d; 0, 1, and 10 mg/kg/d) and chronic (180 d; 0.75 mg/kg/d) perchlorate exposure in adult male prairie voles (Microtus ochrogaster) would alter resting metabolic rates as a result of decreased circulating thyroid hormone concentrations and to determine if perchlorate exposure disrupts thermogenesis in mammals exposed to cold stress. Voles exposed to perchlorate for 51 or 180 d experienced no significant alterations in resting metabolic rates at any point during the exposure period. Additionally, the treatment had no effect on peak metabolic rates or plasma thyroid hormone concentrations. However, thyroid gland T4 concentrations were significantly lower in perchlorate-exposed voles than in controls, indicating that thyroid gland T4 content may be a more sensitive endpoint than other thyroid variables for assessing perchlorate exposure. Overall, the present study did not provide evidence for energetic alterations associated with perchlorate exposure at concentrations that are higher than those typically found in groundwater or surface water in the environment.

Animals↗
PubMed2002

Environmentally relevant concentrations of ammonium perchlorate inhibit development and metamorphosis in Xenopus laevis.

We determined whether environmentally relevant concentrations of ammonium perchlorate alter development and metamorphosis in Xenopus laevis. Eggs and larvae were exposed to varying concentrations of ammonium perchlorate or control medium for 70 d. Most treatment-related mortality was observed within 5 d after exposure and was due in large part to reduced hatching success. The 5- and 70-d median lethal concentrations (LC50s) were 510 +/- 36 mg ammonium perchlorate/L and 223 +/- 13 mg ammonium perchlorate/L, respectively. Ammonium perchlorate did not cause any concentration-related developmental abnormalities at concentrations below the 70-d LC50. Ammonium perchlorate inhibited metamorphosis in a concentration-dependent manner as evident from effects on forelimb emergence, tail resorption, and hindlimb growth. These effects were observed after exposure to ammonium perchlorate concentrations in the parts-per-billion range, at or below concentrations reported in surface waters contaminated with ammonium perchlorate. Ammonium perchlorate significantly inhibited tail resorption after a 14-d exposure in the U.S. Environmental Protection Agency (U.S. EPA) Endocrine Disruptor Screening and Testing Committee (EDSTAC) Tier I frog metamorphosis assay for thyroid disruption in amphibians. We believe that ammonium perchlorate may pose a threat to normal development and growth in natural amphibian populations.

Animals↗
PubMed1999

35Cl and (37)Cl Magic-Angle Spinning NMR Spectroscopy in the Characterization of Inorganic Perchlorates.

35Cl quadrupole coupling constants (C(Q)), asymmetry parameters (eta(Q)), and isotropic chemical shifts (delta(iso)) have been determined for a series of inorganic perchlorates from (35)Cl magic-angle spinning (MAS) NMR spectra at 14.1 T. Illustrative (37)Cl MAS NMR spectra are obtained and analyzed for some of the samples. For perchlorate anions with quadrupolar couplings less than about 1 MHz, the (35)Cl/(37)Cl NMR parameters are most precisely determined from the full manifold of spinning sidebands observed for the satellite transitions while line-shape analysis of the central transition is employed for the somewhat larger quadrupolar couplings. The environments for the individual perchlorate anions are best characterized by the quadrupole coupling parameters (e.g., C(Q) ranges from 0.3 to 3.0 MHz), while the dispersion in the isotropic (35)Cl chemical shifts is small (1029 ppm < delta(iso) < 1049 ppm) for the perchlorates studied. Due to the variation in quadrupole coupling parameters, (35)Cl MAS NMR may conveniently be employed for identification of anhydrous and hydrated phases of perchlorates, in studies of phase transitions, hydration reactions, and the composition of mixed phases. The perchlorates studied include anhydrous KClO(4), RbClO(4), CsClO(4), (CH(3))(4)NClO(4), and the anhydrous and/or hydrated forms of LiClO(4), NaClO(4), Mg(ClO(4))(2), Ba(ClO(4))(2), and Cd(ClO(4))(2). The (35)Cl MAS NMR spectra of LiClO(4), Mg(ClO(4))(2), and Ba(ClO(4))(2), for which the crystal structures are unknown, reveal that each of these salts possesses a single perchlorate site in the asymmetric unit. The (35)Cl NMR data for Mg(ClO(4))(2) and Ba(ClO(4))(2) suggest that these two samples are isostructural. Relationships between the (35)Cl NMR parameters and crystal symmetries are discussed for the other perchlorates where crystal structure data have been reported.

Journal Article↗
PubMed1990

Effect of perchlorate on calcium release in skinned fibres stimulated by ionic substitution and caffeine.

We have determined the effects of the perchlorate ion on the contracture of skinned (sarcolemma removed) skeletal muscle fibres, stimulated either by ionic substitution or caffeine. Calcium release was monitored in single cells by measuring the peak height of tension transients. Perchlorate significantly sensitizes fibres to activation by ionic substitution, a manipulation that is thought to trigger calcium release via the normal physiological pathway. Adding 0.8 mM perchlorate to the solutions shifted the curve relating the magnitude of ionic substitution to the level of activation leftward, such that smaller stimuli were needed to produce a contracture of a given height. Perchlorate could also trigger a contracture directly. Exposing fibres to 1.0 mM perchlorate caused contractures averaging 60% of bracketing controls. In contrast to contractures stimulated by ionic substitution, those triggered by caffeine were unaffected by perchlorate. Since caffeine is thought to act directly on the sarcoplasmic reticulum to cause calcium release, these results suggest that perchlorate enhances activation in skinned fibres by interacting with transverse tubular membranes.

Animals↗
PubMed2002

Perchlorate as an environmental contaminant.

Perchlorate anion (ClO4-) has been found in drinking water supplies throughout the southwestern United States. It is primarily associated with releases of ammonium perchlorate by defense contractors, military operations, and aerospace programs. Ammonium perchlorate is used as a solid oxidant in missile and rocket propulsion systems. Traces of perchlorate are found in Chile saltpeter, but the use of such fertilizer has not been associated with large scale contamination. Although it is a strong oxidant, perchlorate anion is very persistent in the environment due to the high activation energy associated with its reduction. At high enough concentrations, perchlorate can affect thyroid gland functions, where it is mistakenly taken up in place of iodide. A safe daily exposure has not yet been set, but is expected to be released in 2002. Perchlorate is measured in environmental samples primarily by ion chromatography. It can be removed by anion exchange or membrane filtration. It is destroyed by some biological and chemical processes. The environmental occurrence, toxicity, analytical chemistry, and remediative approaches are discussed.

Biodegradation, Environmental↗
PubMed2005

Bioremediation potential of a perchlorate-enriched sewage sludge consortium.

The purpose of this work was to explore the reductive bioremediation potential of a perchlorate-enriched facultative anaerobic consortium. Rapid perchlorate reduction and bacterial growth were observed up to 1.84 g l(-1) of perchlorate, but not at 3.82 g l(-1) due to the toxicity. The specific growth rate of the mixed consortium was 0.1 h(-1). The consortium co-reduced perchlorate and nitrate with acetate as e- donor and carbon source. The presence of nitrate slowed down the perchlorate reduction rate. The other e- acceptors utilized include oxygen, chlorate, Cr(VI), and selenate. Over 95% of the 16 mg l(-1) of added Cr(VI) was reduced within 24 h of incubation with a high-density perchlorate-grown consortium. However, the consortium failed to couple growth with reduction of nitrite, sulfate, thiosulfate, and sulfite. During the search for autotrophic perchlorate reduction, many consortia from very diverse natural sources could not use sulfur compounds such as thiosulfate as e- donor.

Bacteria, Anaerobic↗
PubMed2004

Perchlorate in water, soil, vegetation, and rodents collected from the Las Vegas Wash, Nevada, USA.

Water, soil, vegetation, and rodents were collected from three areas along the Las Vegas Wash, a watershed heavily contaminated with perchlorate. Perchlorate was detected at elevated concentrations in water, soil, and vegetation, but was not frequently detected in rodent liver or kidney tissues. Broadleaf weeds contained the highest concentrations of perchlorate among all plant types examined. Perchlorate in rodent tissues and vegetation was correlated with perchlorate concentrations in soil as expected, however rodent residues were not highly correlated with plant perchlorate concentrations. This indicates that soil may be a greater source, or a more constant source of perchlorate exposure in rodents than vegetation.

Animals↗
PubMed2005

Perchlorate in fish from a contaminated site in east-central Texas.

Perchlorate, a known thyroid endocrine disruptor, contaminates surface waters near military instillations where solid fuel rocket motors are manufactured or assembled. To assess potential perchlorate exposure to fish and the human population which may feed on them, fish were collected around the Naval Weapons Industrial Reserve Plant in McLennan County, TX, and analyzed for the presence of the perchlorate anion. The sampling sites included Lake Waco and Belton Lake, and several streams and rivers within their watersheds. The general tendency was that perchlorate was only found in a few species sampled, and perchlorate was not detected in every individual within these species. When detected in the fish, perchlorate tissue concentrations were greater than that in the water. This may be due to highly variable perchlorate concentrations in the water coupled with individual-level variation in elimination from the body, or to routes of exposure other than water.

Animals↗
PubMed2006

Evaluation of ammonium perchlorate in the endocrine disruptor screening and testing program's male pubertal protocol: ability to detect effects on thyroid endpoints.

The U.S. EPA Endocrine Disruptor Screening Program (EDSP) Tier 1 male pubertal protocol was designed as a screen to detect endocrine-disrupting chemicals which may alter reproductive development or thyroid function. One purpose of this in vivo screening protocol is to detect thyrotoxicants via a number of different mechanisms of action, such as thyroid hormone synthesis or clearance. Here we evaluate the ability of this EDSP male pubertal protocol to detect the known thyrotoxicant ammonium perchlorate as an endocrine disruptor. Ammonium perchlorate is a primary ingredient in rocket fuel, fertilizers, paints, and lubricants. Over the past 50 years, potassium perchlorate has been used to treat hyperthyroidism in humans. Perchlorate alters thyroid hormone secretion by competitively inhibiting iodide uptake by the thyroid gland. In this study, ammonium perchlorate was administered at 62.5, 125, 250, and 500 mg/kg to male Wistar rats based on a pilot study of oral dosing. Doses of 125-500 mg/kg perchlorate decreased T4 in a dose-dependent manner. TSH was significantly increased in a dose-responsive manner at the same doses, while T3 was unchanged at any dose. Thyroid histology was significantly altered at all doses, even at the 62.5 mg/kg, with a clear dose-dependent decrease in colloid area and increase in follicular cell height. No effects on preputial separation, a marker of pubertal progression, or reproductive tract development were observed at any dose. These results demonstrate that the male pubertal protocol is useful for detecting thyrotoxicants which target the thyroid axis by this mechanism (altered uptake of iodide). This study also found that perchlorate exposure during this period did not alter any of the reproductive developmental endpoints.

Administration, Oral↗
PubMed2006

Microbial reduction of perchlorate with zero-valent iron.

Microbial reduction of perchlorate in the presence of zero-valent iron was examined in both batch and column reactors to assess the potential of iron as the electron donor for biological perchlorate reduction process. Iron-supported mixed cultures completely removed 65 mg/L of perchlorate in batch reactors in 8 days. The removal rate was similar to that observed with hydrogen gas (5%) and acetate (173 mg/L) as electron donors. Repeated spiking of perchlorate to batch reactors containing iron granules and microorganisms showed that complete perchlorate reduction by the iron-supported culture was sustained over a long period. Complete removal of perchlorate by iron-supported anaerobic culture was also achieved in a bench-scale iron column with a hydraulic residence time of 2 days. This study demonstrated the potential applicability of zero-valent iron as a source of electrons for biological perchlorate reduction. Use of zero-valent iron may eliminate the need to continually supply electron donors such as organic substrates or explosive hydrogen gas. In addition, iron is inexpensive, safe to handle, and does not leave organic residuals in the treated water.

Biodegradation, Environmental↗
PubMed2000

Improved method for the determination of trace perchlorate in ground and drinking waters by ion chromatography.

Ammonium perchlorate, a key ingredient in solid rocket propellants, has been found in ground and surface waters in a number of U.S. states, and perchlorate contamination of public drinking water wells is now a serious problem in California. Perchlorate poses a health risk and preliminary data from the U.S. EPA reports that exposure to less than 4-18 microg/l provides adequate human health protection. An improved ion chromatographic method was developed for the determination of low microg/l levels of perchlorate in ground and drinking waters based on a Dionex IonPac AS16 column, an hydroxide eluent generated using an EG40 automated eluent generator, large loop (1000 microl) injection, and suppressed conductivity detection. The method is free of interferences from common inorganic anions, linear over the range of 2-100 microg/l perchlorate, and quantitative recoveries are obtained for low microg/l levels of perchlorate in spiked ground and drinking water samples. The MDL of 150 ng/l permits quantification of perchlorate below the levels that ensure adequate health protection.

Chromatography, Liquid↗
PubMed1998

Adhesive bonding to dentin with iron (II) perchlorate primers and a tri-n-butylborane-initiated luting agent.

OBJECTIVES: This study was conducted to measure the tensile bond strength of a resin to dentin when the dentin was primed with iron (II) perchlorate modified aqueous 2-hydroxyethyl methacrylate (HEMA) or an iron (II) perchlorate modified commercial self-etching primer (ED primer, Kuraray Co.). METHODS: Bovine dentin surfaces were ground flat and each specimen underwent one of the following two treatments: (1) priming with 2.0 x 10(-6) to 5.0 x 10(-4) mol/g iron (II) perchlorate in aqueous HEMA solutions after etching with 10 wt% phosphoric acid; (2) priming with self-etching primers containing 4.0 x 10(-7) to 2.0 x 10(-4) mol/g iron (II) perchlorate. Each specimen was then bonded to a stainless-steel rod with a luting agent (MMA-TBB resin) consisting of methyl methacrylate (MMA), poly(methyl methacrylate) (PMMA), and tri-n-butylborane (TBB) initiator. Tensile strengths of the bonded tooth specimens were then determined after 1 day immersion in water. Results were analyzed using ANOVA and Duncan's new multiple range test (p < 0.05). RESULTS: Tensile testing revealed the maximum mean bond strengths (22.5 MPa) when the dentin was primed with 2.0 x 10(-4) mol/g iron (II) perchlorate after etching with 10 wt% phosphoric acid aqueous solution. The highest level of bond strength with self-etching primer (19.6 MPa) was achieved using 1.0 x 10(-4) mol/g iron (II) perchlorate. SIGNIFICANCE: These bonding techniques, combining the use of iron (II) perchlorate modified HEMA primers with MMA-TBB resin, are potentially applicable for seating resin-bonded restorations.

Adhesiveness↗
PubMed2002

Reduction of perchlorate and nitrate by salt tolerant bacteria.

Spent regenerant brine from ion-exchange technology for the removal of perchlorate and nitrate produces a high salt waste stream, which requires remediation before disposal. Bioremediation is an attractive treatment option. In this study, we enriched for salt tolerant bacteria from sediments from Cargill salt evaporation facility (California, USA), the Salton Sea (California, USA), and a high density hydrocarbon oxidizing bacterial cocktail. The bacterial cocktail enrichment culture reduced ClO4- from 500 to 260 mg 1 in 4 weeks. Salt tolerant bacterial isolates from the enrichment cultures and two denitrifying salt tolerant bacteria, Haloferax denitrificans and Parococcus halodenitricans, substantially reduced perchlorate. The highest rate of perchlorate removal was recorded with the isolate, Citrobacter sp.: 32% reduction in 1 week. This bacterium substantially reduced perchlorate in 0-5% NaCl solutions and maximally at 30 degrees C and at an initial pH 7.5. In simulated brines containing 7.5% total solids, the Citrobacter sp. significantly reduced both perchlorate and nitrate with 34.9 and 15.6% reduction, respectively, in 1 week. Coculture of a potent perchlorate reducing, non-salt tolerant (non-saline) bacterium, perclace and the Citrobacter sp. proved most effective for perchlorate removal in the brine (46.4% in 1 week). This study demonstrates that both anions can be reduced in treatment of brines from ion exchange systems.

Biodegradation, Environmental↗
PubMed2000

Determination of perchlorate at trace levels in drinking water by ion-pair extraction with electrospray ionization mass spectrometry.

Perchlorate has been added to the U.S. Environmental Protection Agency's Drinking Water Contaminant Candidate List (CCL). The present work describes the analysis of perchlorate in water by liquid-liquid extraction followed by flow injection electrospray mass spectrometry (ESI/MS). Cationic surfactants, mostly alkyltrimethyl-ammonium salts, are used to ion-pair aqueous perchlorate, forming extractable ion pairs. The cationic surfactant associates with the perchlorate ion to form a complex detectable by ESI/MS. The selectivity of the extraction and the mass spectrometric detection increases confidence in the identification of perchlorate. The method detection limit for perchlorate based on 3.14 sigma n-1 of seven replicate injections was 100 ng L-1 (parts per trillion). Standard addition was used to quantitate perchlorate in a drinking water sample from a contaminated source, and the concentration determined agreed within experimental error with the concentration determined by ion chromatography.

Flow Injection Analysis↗
PubMed2001

Determination of perchlorate in tobacco plants and tobacco products.

Previous field and laboratory studies with vascular plants have shown that perchlorate is transported from perchlorate fortified soils and is accumulated in the plant tissues and organs. This paper contains results of preliminary investigations on the occurrence of perchlorate in tobacco plants grown in soils amended with a fertilizer whose nitrogen content is derived from naturally occurring sodium nitrate (Chile saltpeter). Ion chromatography (IC) and capillary electrophoresis (CE) were used for quantitative analysis, while nuclear magnetic resonance (NMR) spectroscopy was used for qualitative analysis of perchlorate. Results show that perchlorate is accumulated by tobacco plants into the leaves from soils amended with fertilizers that contain perchlorate. Also, perchlorate can persist over an extended period of time and under a variety of industrial processes as shown by its presence in off-the-shelf tobacco products including cigarettes, cigars, and pouch and plug chewing tobaccos in concentrations ranging from nd to 60.4 +/- 0.8 mg/kg on a wet weight basis.

Chromatography, Ion Exchange↗
PubMed2003

Rate and extent of aqueous perchlorate removal by iron surfaces.

The rate and extent of perchlorate reduction on several types of iron metal was studied in batch and column reactors. Mass balances performed on the batch experiments indicate that perchlorate is initially sorbed to the iron surface, followed by a reduction to chloride. Perchlorate removal was proportional to the iron dosage in the batch reactors, with up to 66% removal in 336 h in the highest dosage system (1.25 g mL(-1)). Surface-normalized reaction rates among three commercial sources of iron filings were similar for acid-washed samples. The most significant perchlorate removal occurred in solutions with slightly acidic or near-neutral initial pH values. Surface mediation of the reaction is supported by the absence of reduction in batch experiments with soluble Fe2+ and also by the similarity in specific reaction rate constants (kSA) determined for three different iron types. Elevated soluble chloride concentrations significantly inhibited perchlorate reduction, and lower removal rates were observed for iron samples with higher amounts of background chloride contamination. Perchlorate reduction was not observed on electrolytic sources of iron or on a mixed-phase oxide (Fe3O4), suggesting that the reactive iron phase is neither pure zerovalent iron nor the mixed oxide alone. A mixed valence iron hydr(oxide) coating or a sorbed Fe2+ surface complex represent the most likely sites for the reaction. The observed reaction rates are too slow for immediate use in remediation system design, but the findings may provide a basis for future development of cost-effective abiotic perchlorate removal techniques.

Cost-Benefit Analysis↗