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PubMed2005

Uptake and elimination of perchlorate in eastern mosquitofish.

The purpose of this study was to investigate the uptake and elimination of perchlorate in eastern mosquitofish (Gambusia holbrooki). Fish were exposed to 0.1-1000 mg/l sodium perchlorate for 12h, 1, 2, 5, 10, and 30 days, and perchlorate was determined in whole body extracts. Perchlorate was not detected in mosquitofish exposed to the low concentrations of perchlorate (0, 0.1, and 1mg/l sodium perchlorate), regardless of the exposure time, whereas it was detected when fish were exposed to 10, 100, and 1000 mg/l. The tissue concentrations were approximately 10 times less than that in the water. There was no difference in the uptake of perchlorate depending upon the exposure time, however, a difference in perchlorate uptake depending upon the concentration of the exposure dose (P<0.001) was observed. Uptake (K(u)) and elimination (K(e)) rate constants were 0.09 l/mg day and 0.70 day(-1), respectively. The half-life (T1/2) of perchlorate was 0.99 day. Thus, it appears that perchlorate is rapidly taken up and eliminated in eastern mosquitofish. These results are critical and may be used to develop models of fate, effects, and transport of perchlorate in natural systems, as well as to assess ecological risk in affected ecosystems.

Animals↗
PubMed2005

Aluminum-based drinking-water treatment residuals: a novel sorbent for perchlorate removal.

Perchlorate contamination of aquifers and drinking-water supplies has led to stringent regulations in several states to reduce perchlorate concentrations in water at acceptable levels for human consumption. Several perchlorate treatment technologies exist, but there is significant cost associated with their use, and the majority of them are unable to degrade perchlorate to innocuous chloride. We propose the use of a novel sorbent for perchlorate, i.e. an aluminum-based drinking-water treatment residual (Al-WTR), which is a by-product of the drinking-water treatment process. Perchlorate sorption isotherms (23+/-1 degrees C) showed that the greatest amount (65%) of perchlorate removed by the Al-WTR was observed with the lowest initial perchlorate load (10 mg L(-1)) after only 2 h of contact time. Increasing the contact time to 24 h, perchlorate removal increased from 65 to 76%. A significant correlation was observed between the amounts of perchlorate removed with evolved chloride in solution, suggesting degradation of perchlorate to chloride.

Adsorption↗
PubMed2006

Kinetics of a hydrogen-oxidizing, perchlorate-reducing bacterium.

This paper provides the first kinetic parameters for a hydrogen-oxidizing perchlorate-reducing bacterium (PCRB), Dechloromonas sp. PC1. The qmax for perchlorate and chlorate were 3.1 and 6.3 mg/mgDW-day, respectively. The K for perchlorate was 0.14 mg/L, an order of magnitude lower than reported for other PCRB. The yields Y on perchlorate and chlorate were 0.23 and 0.22 mgDW/mg, respectively, and the decay constant b was 0.055/day. The growth-threshold, Smin, for perchlorate was 14 microg/L, suggesting that perchlorate cannot be reduced below this level when perchlorate is the primary electron-acceptor, although it may be possible when oxygen or nitrate is the primary acceptor. Chlorate accumulated at maximum concentrations of 0.6-4.3 mg/L in batch tests with initial perchlorate concentrations ranging from 100 to 600 mg/L. Furthermore, 50 mg/L chlorate inhibited perchlorate reduction with perchlorate at 100 mg/L. This is the first report of chlorate accumulation and inhibition for a pure culture of PCRB. These Chlorate effects are consistent with competitive inhibition between perchlorate and chlorate for the (per)chlorate reductase enzyme.

Bacteria↗
PubMed2002

Treatment of perchlorate- and nitrate-contaminated groundwater in an autotrophic, gas phase, packed-bed bioreactor.

The biological degradation of perchlorate was examined using a laboratory-scale, autotrophic, packed-bed biofilm reactor. The reactor was operated in unsaturated-flow mode and continuously fed water containing perchlorate (ClO4-) (as an electron acceptor), and a gas mixture of hydrogen (5%) and carbon dioxide at a retention time of 1.5 min. In the absence of nitrate, perchlorate removal rate (rp, ppb/min) in the reactor was found to be first order with respect to perchlorate concentration (c, ppb) according to rp = 0.16 +/- 0.06c(0.97+/-0.12) (n = 11, R2 = 0.97, p < 10(-5)). Perchlorate removal rates in the hydrogen feed were found to be comparable to rates found by others for fixed film bioreactors using either hydrogen gas or organic electron donors such as acetate, although the rate coefficient was reduced to slightly less than unity (r(p) = 0.22 +/- 0.08c(0.91+/-0.08); n = 19, R2 = 0.89, p < 10(-5)). When nitrate was present in the water, similar perchlorate removals were achieved despite nitrate concentrations three orders of magnitude higher than perchlorate concentrations. Perchlorate was removed by an average of 25 +/- 5% from a perchlorate-contaminated groundwater containing 73 +/- 2 ppb of perchlorate and 21 +/- 2 ppm of nitrate. This removal was slightly higher than the removal of 17 +/- 3% measured for a synthetic groundwater containing 79 +/- 3 ppb of perchlorate and 22 +/- 2 ppm of nitrate. In both cases, there was an average of 10% nitrate removal.

Biodegradation, Environmental↗
PubMed2005

Perchlorate accumulation in forage and edible vegetation.

The accumulation of perchlorate in vegetation is becoming a concern, with increasing numbers of sites reporting the presence of perchlorate in groundwater and surface water. This study investigated potential perchlorate uptake and distribution by a variety of forage and edible crops in both the laboratory and the field. Perchlorate concentrations in soybean leaves grown in the greenhouse were significantly higher than perchlorate concentrations in soybean seeds and pods. Perchlorate concentrations in alfalfa grown in sand were significantly lower than those in alfalfa grown in soil. The concentration of perchlorate in tomato was lower in the fruit than the leaves. Commercially grown wheat and alfalfa samples all contained perchlorate, 0.72-8.6 mg/kg of fresh weight (FW) in the wheat stems, 0.71-4.4 mg/kg of FW in the wheat heads, and 2.9 mg/kg of FW in alfalfa. All field garden samples tested (including cucumber, cantaloupe, and tomato) that were irrigated with perchlorate-tainted water contained perchlorate at various concentrations ranging from 0.040 to 1.65 mg/kg of FW. Bioconcentration factors (BCF), ratios of plant fresh weight concentrations to estimated or measured groundwater concentrations [(microg/kg of FW)/microg/L], were all in the same order of magnitude ranging from 215 +/- 126 for wheat stems to 233 +/- 264 for wheat heads and to 380 +/- 89 for alfalfa. BCF for garden fruit samples were much lower (0.5-20). Results from this study highlight the potential for perchlorate exposure by routes other than drinking water.

Animal Feed↗
PubMed2001

Preliminary assessment of perchlorate in ecological receptors at the Longhorn Army Ammunition Plant (LHAAP), Karnack, Texas.

There have been increasing human health and ecological concerns about ionic perchlorate (ClO4-) since it was detected in drinking water sources in 1997. Perchlorate is known to affect thyroid function, causing subsequent hormone disruption and potential perturbations of metabolic activities. According to current estimates, perchlorate is found in the surface of groundwater of 14 states, including Texas. Longhorn Army Ammunition Plant, located in east central Texas, was a facility historically associated with perchlorate-containing propellants and rocket motors. Subsequently, perchlorate contamination in ground and surface waters at the facility has been reported. Soil, sediment, water, vegetation, and animal tissue samples were collected from several locations within the plant for a preliminary site assessment of perchlorate contamination. Perchlorate concentrations ranged from 555-5,557,000 ppb in vegetation, 811-2038 ppb in aquatic insects, below detection limits (ND) to 207 ppb in fish, ND-580 ppb in frogs, and ND-2328 ppb in mammals. Consistent with our hypothesis, aquatic organisms inhabiting perchlorate-contaminated surface water bodies contained detectable concentrations of perchlorate. Additionally, terrestrial organisms were exposed through pathways not necessarily related to contaminated surface waters. Therefore, these data demonstrate that aquatic and terrestrial species are exposed to perchlorate in the environment. To our knowledge, this represents the first incidence of perchlorate exposure among wild animals reported in the scientific literature.

Amphibians↗
PubMed2006

Perchlorate exposure of the US Population, 2001-2002.

Perchlorate is commonly found in the environment and can impair thyroid function at pharmacological doses. As a result of the potential for widespread human exposure to this biologically active chemical, we assessed perchlorate exposure in a nationally representative population of 2,820 US residents, ages 6 years and older, during 2001 and 2002 as part of the National Health and Nutrition Examination Survey (NHANES). We found detectable levels of perchlorate (>0.05 microg/l) in all 2,820 urine samples tested, indicating widespread human exposure to perchlorate. Urinary perchlorate levels were distributed in a log normal fashion with a median of 3.6 microg/l (3.38 microg/g creatinine) and a 95th percentile of 14 microg/l (12.7 microg/g creatinine). When geometric means of urinary perchlorate levels were adjusted for age, fasting, sex and race-ethnicity, we found significantly higher levels of urinary perchlorate in children compared with adolescents and adults. We estimated total daily perchlorate dose for each adult (ages 20 years and older), based on urinary perchlorate, urinary creatinine concentration and physiological parameters predictive of creatinine excretion rate. The 95th percentile of the distribution of estimated daily perchlorate doses in the adult population was 0.234 microg/kg-day [CI 0.202-0.268 microg/kg-day] and is below the EPA reference dose (0.7 microg/kg-day), a dose estimated to be without appreciable risk of adverse effects during a lifetime of exposure. These data provide the first population-based assessment of the magnitude and prevalence of perchlorate exposure in the US.

Adolescent↗
PubMed2001

Perchlorate clinical pharmacology and human health: a review.

Potassium perchlorate has been used at various times during the last 50 years to treat hyperthyroidism. Since World War II ammonium perchlorate has been used as a propellant for rockets. In 1997, the assay sensitivity for perchlorate in water was improved from 0.4 mg/L (ppm) to 4 microg/L (ppb). As a result, public water supplies in Southern California were found to contain perchlorate ions in the range of 5 to 8 ppb, and those in Southern Nevada were found to contain 5 to 24 ppb. Research programs have been developed to assess the safety or risk from these exposures and to assist state and regulatory agencies in setting a reasonable safe level for perchlorate in drinking water. This report reviews the evidence on the human health effects of perchlorate exposure. Perchlorate is a competitive inhibitor of iodine uptake. All of its pharmacologic effects at current therapeutic levels or lower are associated with inhibition of the sodium-iodide symporter (NIS) on the thyroid follicular cell membrane. A review of the medical and occupational studies has been undertaken to identify perchlorate exposure levels at which thyroid hormone levels may be reduced or thyrotropin levels increased. This exposure level may begin in the 35 to 100 mg/d range. Volunteer studies have been designed to determine the exposure levels at which perchlorate begins to affect iodine uptake in humans. Such effects may begin at levels of approximately 1 mg/d. Environmental studies have assessed the thyroidal health of newborns and adults at current environmental exposures to perchlorate and have concluded that the present levels appear to be safe. Whereas additional studies are underway both in laboratory animals and in the field, it appears that a safe level can be established for perchlorate in water and that regulatory agencies and others are now trying to determine that level.

Carrier Proteins↗
PubMed2003

Pediatric neurobehavioral diseases in Nevada counties with respect to perchlorate in drinking water: an ecological inquiry.

BACKGROUND: Contamination of drinking water with perchlorate, a known thyrotropic agent, has been demonstrated in areas in the western United States. The health consequences of that exposure have been studied, particularly in the State of Nevada. Previous studies in Nevada, comparing the area with perchlorate in the drinking water and the areas without perchlorate in the drinking water, have found no difference in neonatal thyroxine (T(4)) or thyrotropin (TSH) levels, or in the prevalences of thyroid diseases and thyroid cancer. This same study design has now been applied to the major neurobehavioral diseases of childhood (i.e., attention deficit-hyperactivity disorder (ADHD) and autism) and to school performance in order to determine whether those conditions are more frequent in the area with perchlorate-contaminated water. METHODS: Medical services data on ADHD and autism were obtained from the Nevada Medicaid system for the period of January 1, 1996, to December 31, 2000, with county of residence used as the basis for residential information. Analyses of fourth-grade school performance results for two recent time periods came from the state government. Perchlorate concentrations in drinking water had been determined by local water authorities. ADHD and autism rates for the area with perchlorate in the drinking water (Clark County) were calculated and compared with the rates for the other areas in the state, as were fourth-grade school performances. RESULTS: Analysis of the data from the Nevada Medicaid program shows that the rates for ADHD and for autism in the area where perchlorate was in the drinking water did not exceed the rates in those areas where there was no perchlorate contamination in the drinking water. Fourth-grade standardized test results for students in Clark County were not different from those of the remainder of the state. CONCLUSIONS: This ecological study of children in the exposure area did not find evidence of an increased risk of either ADHD or of autism caused by perchlorate contamination in the drinking water. Furthermore, no difference in overall fourth-grade school performance was observed. No evidence was found that children from the area with perchlorate in the drinking water (up to 24 microg/liter) had either an increase in pediatric neurobehavioral disease (ADHD and autism) or a decrease in fourth-grade academic performance. The limitations of this ecological study relate to diagnostic criteria and ascertainment of geographic and demographic differences and to data on individual residence and water consumption during pregnancy.

Attention Deficit Disorder with Hyperactivity↗
PubMed2006

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 50mM 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.

Chemical Fractionation↗
PubMed2006

Effects of larval-juvenile treatment with perchlorate and co-treatment with thyroxine on zebrafish sex ratios.

The objective of this study was to determine the effect of larval-juvenile exposure to perchlorate, a thyroid hormone synthesis inhibitor, on the establishment of gonadal sex ratios in zebrafish. Zebrafish were exposed to untreated water or water containing perchlorate at 100 or 250 ppm for a period of 30 days starting at 3 days postfertilization (dpf). Recovery treatments consisted of a combination of perchlorate and exogenous thyroxine (T4; 10 nM). Thyroid histology was assessed at the end of the treatment period (33 dpf), and gonadal histology and sex ratios were determined in fish that were allowed an additional 10-day period of growth in untreated water. As expected, exposure to perchlorate caused changes in thyroid histology consistent with hypothyroidism and these effects were reversed by co-treatment with exogenous T4. Perchlorate did not affect fish survival but co-treatment with T4 induced higher mortality. However, relative to the corresponding perchlorate concentration, co-treatment with T4 caused increased mortality only at a perchlorate concentration of 100 ppm. Perchlorate alone or in the presence of T4 suppressed body length at 43 dpf relative to control values. Perchlorate exposure skewed the sex ratio toward female in a concentration-dependent manner, and co-treatment with T4 not only blocked the feminizing effect of perchlorate but also overcompensated by skewing the sex ratio towards male. Moreover, co-treatment with T4 advanced the onset of spermatogenesis in males. There was no clear association between sex ratios and larval survival or growth. We conclude that endogenous thyroid hormone plays a role in the establishment of gonadal sex phenotype during early development in zebrafish.

Age Factors↗
PubMed2001

Microbial reduction of perchlorate in pure and mixed culture packed-bed bioreactors.

Perchlorate (ClO4-) has been detected in a large number of surface and ground waters in the US. Due to health concerns of perchlorate in drinking water, the California Department of Health Services has established a provisional action level of 18 microg/L. Several microbial isolates have been obtained capable of microbiological perchlorate reduction through cell respiration, but few of these have been tested for perchlorate removals to these low levels. The feasibility of using one isolate (KJ) for water treatment was tested in a packed-bed bioreactor by comparing minimum detention times necessary to achieve complete removal of perchlorate. Perchlorate was reduced approximately from 20 mg/L to non-detectable (< 4 microg/L) levels in acetate-fed columns inoculated with KJ or mixed cultures. The complete conversion of perchlorate to chloride was demonstrated by a stoichiometric ratio of perchlorate to chloride of 1.0 +/- 0.14. Perchlorate removal to non-detectable levels required a minimum empty bed contact time (EBCT) of only 2.1 min for the column inoculated with KJ, vs. 31 min for the mixed culture column. Acetate was used at a molar ratio of C2H3O2-/ClO4- of 2.9 (n = 6) for the mixed culture, while more than twice as much acetate was consumed on average (6.6 +/- 2.0, n = 156) by the pure culture. These results demonstrate that detention times of packed-bed bioreactors can be substantially reduced using isolate KJ, but that larger concentrations of acetate will be necessary to reduce perchlorate to low levels necessary for drinking water.

Absorption↗
PubMed2000

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 cedar (Tamarix ramosissima) growing in the Las Vegas Wash. Perchlorate is an oxidant, but its reduction is kinetically hindered. Concern over thyroid effects caused the Environmental Protection Agency (EPA) to add perchlorate to the drinking water Contaminant Candidate List (CCL). Beginning in 2001, utilities will look for perchlorate under the Unregulated Contaminants Monitoring Rule (UCMR). In wood samples acquired from the same plant growing in a contaminated stream, perchlorate concentrations were found as follows: 5-6 microg g(-1) in dry twigs extending above the water and 300 microg g(-1) in stalks immersed in the stream. Perchlorate was leached from samples of wood, and the resulting solutions were analyzed by ion chromatography after clean-up. The identification was confirmed by electrospray ionization mass spectrometry after complexation of perchlorate with decyltrimethylammonium cation. Because salt cedar is regarded as an invasive species, there are large scale programs aimed at eliminating it. However, this work suggests that salt 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 effects that eradication might have on perchlorate-tainted riparian ecosystems, such as the Las Vegas Wash. This is especially important since water from the wash enters Lake Mead and the Colorado River and has the potential to affect the potable water source of tens of millions of people as well as irrigation water used on a variety of crops, including much of the lettuce produced in the USA.

Chromatography, Ion Exchange↗
PubMed2005

The origin of naturally occurring perchlorate: the role of atmospheric processes.

Perchlorate, an iodide uptake inhibitor, is increasingly being detected in new places and new matrices. Perchlorate contamination has been attributed largelyto the manufacture and use of ammonium perchlorate (the oxidizer in solid fuel rockets) and/or the earlier use of Chilean nitrate as fertilizer (approximately 0.1% perchlorate). However, there are regions such as the southern high plains (Texas Panhandle) where there is no clear historical or current evidence of the extensive presence of rocket fuel or Chilean fertilizer sources. The occurrence of easily measurable concentrations of perchlorate in such places is difficult to understand. In the southern high plains groundwater, perchlorate is better correlated with iodate, known to be of atmospheric origin, compared to any other species. We show that perchlorate is readily formed by a variety of simulated atmospheric processes. For example, it is formed from chloride aerosol by electrical discharge and by exposing aqueous chloride to high concentrations of ozone. We report that perchlorate is present in many rain and snow samples. This strongly suggests that some perchlorate is formed in the atmosphere and a natural perchlorate background of atmospheric origin should exist.

Atmosphere↗
PubMed2006

Perchlorate reduction by autotrophic bacteria in the presence of zero-valent iron.

A series of batch experiments were performed to study the combination of zero-valent iron (ZVI) with perchlorate-reducing microorganisms (PRMs) to remove perchlorate from groundwater. In this method, H2 produced during the process of iron corrosion by water is used by PRMs as an electron donor to reduce perchlorate to chloride. Perchlorate degradation rates followed Monod kinetics, with a normalized maximum utilization rate (rmax) of 9200 microg g(-1) (dry wt) h(-1) and a half-velocity constant (Ks) of 8900 microg L(-1). The overall rate of perchlorate reduction was affected by the biomass density within the system. An increase in the OD600 from 0.025 to 0.08 led to a corresponding 4-fold increase of perchlorate reduction rate. PRM adaptation to the local environment and initiation of perchlorate reduction was rapid under neutral pH conditions. At the initial OD600 of 0.015, perchlorate reduction followed pseudo-first-order reaction rates with constants of 0.059 and 0.033 h(-1) at initial pH 7 and 8, respectively. Once perchlorate reduction was established, the bioreductive process was insensitive to the increases of pH from near neutral to 9.0. In the presence of nitrate, perchlorate reduction rate was reduced, but not inhibited completely.

Hydrogen↗
PubMed2006

Modelling salinity inhibition effects during biodegradation of perchlorate.

AIMS: To determine the mathematical kinetic rates and mechanisms of acclimated perchlorate (ClO)-reducing microbial cultures by incorporating a term to relate the inhibitory effect of high salinity during biological reduction of concentrated perchlorate solutions. METHODS AND RESULTS: Salt toxicity associated with the biodegradation of concentrated perchlorate (200, 500, 1100, 1700 and 2400 mg l(-1) as ClO) was investigated using two microbial cultures isolated from a domestic wastewater treatment plant [return activated sludge (RAS) and anaerobic digester sludge (ADS)]. Experiments were performed in wastewaters containing various sodium chloride concentrations, ranging from 0% to 4.0% (w/v) NaCl (ionic strength: 0.14-0.82 mol l(-1), total dissolved solids: 5.3-42.6 g l(-1)) at near-neutral values of pH (6.7-7.8). Perchlorate biodegradation was stimulated through stepwise acclimation to high salinity. The ADS culture was capable of reducing perchlorate at salinities up to 4% NaCl, while the RAS culture exhibited complete inhibition of perchlorate degradation at 4% NaCl, probably resulting from either a toxic effect or enzyme inactivation of the perchlorate-reducing microbes. Further, a kinetic growth model was developed based on experimental data in order to express an inhibition function to relate specific growth rate and salinity. CONCLUSIONS: Biological reduction of concentrated perchlorate wastewaters using either acclimated RAS or ADS cultures is feasible up to 3% or 4% NaCl, respectively. In addition, the kinetic model including a salinity inhibition term should be effective in many practical applications such as improving reactor design and management, furthering the understanding of high salinity inhibition, and enhancing bioremediation under high salinity loading conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: Applications of these findings in water treatment practice where ion exchange or membrane technologies are used to remove perchlorate from water can have the potential to increase the overall attractiveness of these processes by eliminating the need to dispose of a concentrated perchlorate solution.

Bacteria↗
PubMed1998

The influence of perchlorate ions on complex charging transients in amphibian striated muscle.

1. The effects of perchlorate ions on intramembrane charge movements were examined under different conditions of ryanodine receptor (RyR) modification in intact voltage-clamped amphibian skeletal muscle fibres studied in the gluconate-containing solutions previously reported to emphasize the features of q gamma at the expense of those of the q beta charge. 2. The introduction of graded increases in perchlorate concentration to the experimental solutions selectively shifted the threshold of appearance of the q gamma 'hump' currents to more negative test potentials at which they actually appeared in the absence of prior q beta transients at perchlorate concentrations of 4.0-8.0 mM. Such findings suggested that the delayed (q gamma) transitions can take place independently of any previous exponential (q beta) decay. 3. These kinetic effects were accompanied by hyperpolarizing shifts in the transition potentials (V*) of the steady-state voltage dependences of either the overall or the isolated q gamma charge. These shifts were graded with concentration and reached their maximum effects at 4.0-8.0 mM perchlorate. However, both the total charge (Qmax) and the steepness factor (k) remained conserved at values consistent with a system that included significant contributions from the steeply voltage-sensitive q gamma component (overall charge: Qmax approximately 19-21 nC microF-1, k approximately 7-9 mV; q gamma component alone: Qmax approximately 10-12 nC microF-1, k approximately 4-6 mV). This contrasts with earlier reports on the effects of perchlorate in fibres that were studied in sulphate- or methanesulphonate-containing extracellular solutions. 4. Perchlorate (8.0 mM) restored the 'hump' waveform associated with q gamma charge movements that had previously been obliterated by the prior application of fully effective (0.1 mM) concentrations of either ryanodine or daunorubicin. 5. Perchlorate similarly reversed the positive shift in the transition potential of the q gamma component that was brought about by such RyR modification (from V* approximately -40 mV back to V* approximately -60 mV). In contrast, the values of either Qmax (overall charge, 19-21 nC microF-1; q gamma component, 10-13 nC microF-1) or k (overall charge, 7-9 mV; q gamma component, 4-6 mV) remained conserved through all these experimental manoeuvres. 6. The inclusion of perchlorate also reversed the action of 2 mM tetracaine and restored delayed q gamma transients to an extent that was graded with concentration (0.5-8.0 mM perchlorate). There was an accompanying recovery of the steeply voltage-dependent steady-state (q gamma) component consistent with a competitive interaction between these agents upon the q gamma intramembrane charge. 7. The present findings suggest that perchlorate exerts a specific action upon the q gamma charge in independent transitions that are driven by the tubular membrane field. Its interactions with the known RyR inhibitors that nevertheless conserve both the charge and its voltage sensitivity suggest a primary action upon the RyR that in turn exerts reciprocal actions upon the voltage sensor.

Anesthetics, Local↗
PubMed2001

Kinetics of perchlorate- and chlorate-respiring bacteria.

Ten chlorate-respiring bacteria were isolated from wastewater and a perchlorate-degrading bioreactor. Eight of the isolates were able to degrade perchlorate, and all isolates used oxygen and chlorate as terminal electron acceptors. The growth kinetics of two perchlorate-degrading isolates, designated "Dechlorosoma" sp. strains KJ and PDX, were examined with acetate as the electron donor in batch tests. The maximum observed aerobic growth rates of KJ and PDX (0.27 and 0.28 h(-1), respectively) were only slightly higher than the anoxic growth rates obtained by these isolates during growth with chlorate (0.26 and 0.21 h(-1), respectively). The maximum observed growth rates of the two non-perchlorate-utilizing isolates (PDA and PDB) were much higher under aerobic conditions (0.64 and 0.41 h(-1), respectively) than under anoxic (chlorate-reducing) conditions (0.18 and 0.21 h(-1), respectively). The maximum growth rates of PDX on perchlorate and chlorate were identical (0.21 h(-1)) and exceeded that of strain KJ on perchlorate (0.14 h(-1)). Growth of one isolate (PDX) was more rapid on acetate than on lactate. There were substantial differences in the half-saturation constants measured for anoxic growth of isolates on acetate with excess perchlorate (470 mg/liter for KJ and 45 mg/liter for PDX). Biomass yields (grams of cells per gram of acetate) for strain KJ were not statistically different in the presence of the electron acceptors oxygen (0.46 +/- 0.07 [n = 7]), chlorate (0.44 +/- 0.05 [n = 7]), and perchlorate (0.50 +/- 0.08 [n = 7]). These studies provide evidence that facultative microorganisms with the capability for perchlorate and chlorate respiration exist, that not all chlorate-respiring microorganisms are capable of anoxic growth on perchlorate, and that isolates have dissimilar growth kinetics using different electron donors and acceptors.

Betaproteobacteria↗