Measurement of activity concentrations of <Superscript>40</Superscript>K, <Superscript>226</Superscript>Ra and <Superscript>232</Superscript>Th for assessment of radiation hazards from soils of the southwestern region of Nigeria

Activity concentrations of the selected radionuclides ⁴⁰K, ²²⁶Ra and ²³²Th were measured in surface soil samples collected from 38 cities in the southwest region of Nigeria by means of gamma spectroscopy with a high-purity germanium detector. Measured activity concentration values of ⁴⁰K varied from 34.9 ± 4.4 to 1,358.6 ± 28.5 Bq kg⁻¹ (given on a dry mass (DM) basis) with a mean value of 286.5 ± 308.5 Bq kg⁻¹; that of ²²⁶Ra varied from 9.3 ± 3.7 to 198.1 ± 13.8 Bq kg⁻¹ with a mean value of 54.5 Bq kg⁻¹ and a standard deviation of 38.7 Bq kg⁻¹, while that of ²³²Th varied from 5.4 ± 1.1 to 502.0 ± 16.5 Bq kg⁻¹ with a mean value of 91.1 Bq kg⁻¹ and standard deviation of 100.9 Bq kg⁻¹. The mean activity concentration values obtained for ²²⁶Ra and ²³²Th are greater than the world average values reported by the United Nations Scientific Committee on Effects of Atomic Radiation for areas of normal background radiation. Radiological indices were estimated for the radiation/health hazards of the natural radioactivity of all soil samples. Estimated absorbed dose rates in air varied from 12.42 ± 2.25 to 451.33 ± 19.06 nGy h⁻¹, annual outdoor effective dose rates from 0.015 ± 0.003 to 0.554 ± 0.023 mSv year⁻¹, internal hazard index from 0.10 ± 0.03 to 3.02 ± 0.16, external hazard index from 0.07 ± 0.01 to 2.60 ± 0.11, representative level index from 0.19 ± 0.03 to 6.84 ± 0.29, activity index from 0.09 ± 0.02 to 3.42 ± 0.15, and radium equivalent activity from 26.95 ± 5.04 to 963.15 ± 41.87 Bq kg⁻¹. Only the mean value of the representative level index exceeds the limit for areas of normal background radiation. All other indices show mean values that are lower than the recommended limits.     

Radium-226 levels in the Cauvery river ecosystem, India

We studied the natural radioactivity distribution of an α-emitting radionuclide,²²⁶Ra in water, sediment and biota (plankton, weed, snail, bivalve, prawn and fish) of Cauvery river ecosystem extending a stretch of 95 km. The dissolved²²⁶Ra concentration in river water ranged from 0.82mBq.I^-1 to l 06mBq.l^-1 (mean: 0.93mBq.l^-1) and the activity in river sediments from 4.7Bq.kg^-1 to 6.9Bq.Kg^-1 (mean: 5.6Bq.kgg^-1 dry wt.). The²²⁶Ra activity levels in the biota were within a narrow range from below detection limit to 3.80 Bq.kg^-1 (wet wt). Generally higher²²⁶Ra concentrations are observed in the shells and bones of aquatic organisms than in their tissues and muscles. The concentration factors (CFs) of²²⁶Ra for the biotic components ranged from ∼10¹ to ∼10³. The significance of²²⁶Ra activity in the abiotic and biotic components of Cauvery river are discussed.     

Statistical analysis of natural radioactivity data of clay samples in Tiruvannamalai,Tamilnadu, India

The activity concentration of ²²⁶Ra, ²³²Th and ⁴⁰K were determined in clay samples collected from Tiruvannamalai district, Tamilnadu using gamma ray spectrometry. The determined activity concentration ranges from BDL to 16 Bq Kg⁻¹, 18 to 192 Bq Kg⁻¹, 288 to 901 Bq Kg⁻¹ for ²²⁶Ra, ²³²Th and ⁴⁰K respectively. The concentration of these radionuclides is compared with world average values. Radiological risk evaluation was done by calculating radium equivalent activity (Ra_eq), absorbed gamma dose rate (D_R), annual effective dose rate (H_R), annual gonadal dose equivalent (AGDE), criteria formula (CF), representative level index (RLI), activity utilization index (AUI), gamma index (Iγ), alpha index ((Iα), the external hazard (Hex) and internal hazard (Hin) due to internal exposure to radionuclides distributed in clay samples. Multivariate statistical techniques were used to study the relation between activity concentration and radiation hazards of clay samples.     

Assessment of Natural Radioactivity Levels and Potential Radiological Risks of Common Building Materials Used in Bangladeshi Dwellings

The concentrations of primordial radionuclides (²²⁶Ra, ²³²Th and ⁴⁰K) in commonly used building materials (brick, cement and sand), the raw materials of cement and the by-products of coal-fired power plants (fly ash) collected from various manufacturers and suppliers in Bangladesh were determined via gamma-ray spectrometry using an HPGe detector. The results showed that the mean concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in all studied samples slightly exceeded the typical world average values of 50 Bq kg⁻¹, 50 Bq kg⁻¹ and 500 Bq kg⁻¹, respectively. The activity concentrations (especially ²²⁶Ra) of fly-ash-containing cement in this study were found to be higher than those of fly-ash-free cement. To evaluate the potential radiological risk to individuals associated with these building materials, various radiological hazard indicators were calculated. The radium equivalent activity values for all samples were found to be lower than the recommended limit for building materials of 370 Bq kg^-1, with the exception of the fly ash. For most samples, the values of the alpha index and the radiological hazard (external and internal) indices were found to be within the safe limit of 1. The mean indoor absorbed dose rate was observed to be higher than the population-weighted world average of 84 nGy h^–1, and the corresponding annual effective dose for most samples fell below the recommended upper dose limit of 1 mSv y^–1. For all investigated materials, the values of the gamma index were found to be greater than 0.5 but less than 1, indicating that the gamma dose contribution from the studied building materials exceeds the exemption dose criterion of 0.3 mSv y^-1 but complies with the upper dose principle of 1 mSv y⁻¹.     

Transfer of radionuclides to ants, mosses and lichens in semi-natural ecosystems

There is a scarcity of data on transfer of both natural and anthropogenic radionuclides to detritivorous invertebrates for use in the assessment of radiation exposure. Although mosses and lichens have been extensively used in biomonitoring programs, the data on transfer of radionuclides to these species are limited, particularly for natural radionuclides. To enhance the available data, activity concentrations of ¹³⁷Cs, ²²⁶Ra and ²²⁸Ra were measured in ants, mosses and lichens and corresponding undisturbed soil collected from semi-natural ecosystems in Serbia and Montenegro and biota/soil concentration ratios (CR) calculated. Since the majority of internal dose to biota is expected to come from ⁴⁰K, the activity concentrations of this radionuclide were also determined. The mean CR values for ¹³⁷Cs, ²²⁶Ra and ²²⁸Ra in ants analyzed in this study were found to be 0.02, 0.06 and 0.02, respectively. The mean CR values of radionuclides in mosses were found to be 2.84 for ¹³⁷Cs, 0.19 for ²²⁶Ra and 0.16 for ²²⁸Ra, while those in lichens were found to be 1.08 for ¹³⁷Cs, 0.15 for ²²⁶Ra and 0.13 for ²²⁸Ra. The CR values obtained in this study were compared with default CR values used in the ERICA Tool database and also with those reported in other studies.     

Radionuclide concentrations in the diet of residents in a high level natural radiation area in Iran

Concentrations of ¹³⁷Cs and ²²⁶Ra in the diet (foodstuffs and drinking water) of adult inhabitants in the high-level natural radiation area (HLNRA) of Ramsar, Iran have been determined. The annual intake of foodstuffs was estimated on the basis of their average annual consumption. Food samples collected from local markets were analyzed by means of a gamma spectrometer. The estimated annual dietary intakes of ¹³⁷Cs and ²²⁶Ra were 130Bq and 245Bq, respectively. The concentrations of natural radionuclides in food and drinking water of the residents are higher than the world average, and are correlated with the high concentration of these radionuclides in soil and water. Calculations were also made to determine the potential dose to an individual consuming such diets.     

Natural variation in <Superscript>210</Superscript>Po and <Superscript>210</Superscript>Pb activity concentrations in the urine of Finnish population groups

A study to determine activity concentrations of ²¹⁰Pb and ²¹⁰Po in the urine of certain Finnish population groups was conducted, to investigate the variation in natural background level of urinary excretion. The study participants were divided into three groups mainly based on their diet. The first group comprised recreational fishermen and the second group represented people consuming more reindeer meat than an average Finn, while people using drinking water with very high activity concentrations of ²¹⁰Po were selected for the third group. The fourth group was a control group. The mean urinary excretion of ²¹⁰Po in groups 1 and 2 was 73 and 100 mBq d⁻¹, respectively. These values were higher than the value of the control group (20 mBq d⁻¹) and the mean values reported in the literature. The mean daily urinary excretion of ²¹⁰Pb in groups 1 and 2, 70 and 52 mBq d⁻¹, was also slightly higher than that in the control group (32 mBq d⁻¹). In contrast, the excretion rates of both ²¹⁰Po and ²¹⁰Pb for the members of group 3 were one to two orders of magnitude higher than those reported in the literature. This was clearly due to the elevated levels of natural radionuclides in their drinking water. The present study demonstrates the importance of possessing good knowledge of the background levels, in order to allow the determination of the additional exposure due, for example, to the malevolent use of radiation.     

Radionuclides content in grape molasses soil samples from Central Black Sea region of Turkey

The activity concentrations of radionuclides in grape molasses soil samples collected from Zile (Tokat) plain in the Central Black Sea region of Turkey were measured by using gamma spectrometer with a NaI(Tl) detector. Also, the concentrations of ²²²Rn in soil samples and air were estimated essentially taking the activity concentrations of ²²⁶Ra measured in soil samples. Grape molasses soil samples with calcium carbonate content are used for sedimentation for making molasses in this region. The average activity concentrations of ²³²Th, ²²⁶Ra, ⁴⁰K, and ¹³⁷Cs were found as 62 ± 2, 68 ± 3, 479 ± 35, and 8.0 ± 0.3 Bq kg^?1, respectively. The average concentrations of ²²²Rn in soil samples and air were estimated to be 50 kBq m^?3 and 144 Bq m^?3. From the activity concentrations, absorbed gamma dose rate in outdoor air (D), annual effective dose from external exposure (E_E), annual effective dose from inhalation of radon (E_I), and excess lifetime cancer risk (ELCR) were estimated in order to assess radiological risks. The average values of D, E_E, E_I, and ELCR were found to be 90 nGy h^?1, 110 μSv y^?1, 1360 μSv y^?1, and 4 × 10^?4, respectively.     

Internal dose assessment of <Superscript>210</Superscript>Po using biokinetic modeling and urinary excretion measurement

The mysterious death of Mr. Alexander Litvinenko who was most possibly poisoned by Polonium-210 (²¹⁰Po) in November 2006 in London attracted the attention of the public to the kinetics, dosimetry and the risk of this high radiotoxic isotope in the human body. In the present paper, the urinary excretion of seven persons who were possibly exposed to traces of ²¹⁰Po was monitored. The values measured in the GSF Radioanalytical Laboratory are in the range of natural background concentration. To assess the effective dose received by those persons, the time-dependence of the organ equivalent dose and the effective dose after acute ingestion and inhalation of ²¹⁰Po were calculated using the biokinetic model for polonium (Po) recommended by the International Commission on Radiological Protection (ICRP) and the one recently published by Leggett and Eckerman (L&E). The daily urinary excretion to effective dose conversion factors for ingestion and inhalation were evaluated based on the ICRP and L&E models for members of the public. The ingestion (inhalation) effective dose per unit intake integrated over one day is 1.7 × 10⁻⁸ (1.4 × 10⁻⁷) Sv Bq⁻¹, 2.0 × 10⁻⁷ (9.6 × 10⁻⁷) Sv Bq⁻¹ over 10 days, 5.2 × 10⁻⁷ (2.0 × 10⁻⁶) Sv Bq⁻¹ over 30 days and 1.0 × 10⁻⁶ (3.0 × 10⁻⁶) Sv Bq⁻¹ over 100 days. The daily urinary excretions after acute ingestion (inhalation) of 1 Bq of ²¹⁰Po are 1.1 × 10⁻³ (1.0 × 10⁻⁴) on day 1, 2.0 × 10⁻³ (1.9 × 10⁻⁴) on day 10, 1.3 × 10⁻³ (1.7 × 10⁻⁴) on day 30 and 3.6 × 10⁻⁴ (8.3 × 10⁻⁵) Bq d⁻¹ on day 100, respectively. The resulting committed effective doses range from 2.1 × 10⁻³ to 1.7 × 10⁻² mSv by an assumption of ingestion and from 5.5 × 10⁻² to 4.5 × 10⁻¹ mSv by inhalation. For the case of Mr. Litvinenko, the mean organ absorbed dose as a function of time was calculated using both the above stated models. The red bone marrow, the kidneys and the liver were considered as the critical organs. Assuming a value of lethal absorbed dose of 5 Gy to the bone marrow, 6 Gy to the kidneys and 8 Gy to the liver, the amount of ²¹⁰Po which Mr. Litvinenko might have ingested is therefore estimated to range from 27 to 1,408 MBq, i.e 0.2–8.5 μg, depending on the modality of intake and on different assumptions about blood absorption.     

Using the RESRAD Code to Assess Human Exposure Risk to 226Ra, 232Th,and 40K in Soil

This article evaluates the health risk raised by exposure to naturally occurring radionuclides in soil around Khak-Sefid, Ramsar, Iran, which is an area of high natural background radiation. A high purity germanium detector was used to determine levels of radionuclides in soil samples and the cancer morbidity risk for a hypothetical resident farmer was evaluated using the RESidual RADioactivity (RESRAD) code. The average activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were found to be 13,201 ± 391, 27.9 ± 2.4, and 415.5 ± 16 Bq/kg, respectively. The maximum assessed cancer morbidity risks were calculated from external and internal exposure pathways as 4.73 × 10^?2 and 3.40 × 10^?2 for ²²⁶Ra, 1.41 × 10^?4 and 7.88 × 10^?5 for ²³²Th, and 1.3 × 10^?4 and 4.233 × 10^?4 for ⁴⁰K. The RESRAD calculations also showed total cancer morbidity risks from external gamma and plant ingestion pathways were more important than from other exposure pathways. A sensitivity analysis was also performed to determine the input parameter values in the risk assessment process. In general, due to the high calculated risk of ²²⁶Ra compared with ²³²Th and ⁴⁰K it can be the major source of concern for human heath in the study area.     

<Superscript>137</Superscript>Cs, <Superscript>40</Superscript>K, <Superscript>238</Superscript>Pu, <Superscript>239+240</Superscript>Pu and <Superscript>90</Superscript>Sr in biological samples from King George Island (Southern Shetlands) in Antarctica

There are few data reported on radionuclide contamination in Antarctica. The aim of this paper is to report ¹³⁷Cs, ⁹⁰Sr and ^238,239+240Pu and ⁴⁰K activity concentrations measured in biological samples collected from King George Island (Southern Shetlands, Antarctica), mostly during 2001–2002. The samples included: bones, eggshells and feathers of penguin Pygoscelis papua, bones and feathers of petrel Daption capense, bones and fur of seal Mirounga leonina, algae Himantothallus grandifolius, Desmarestia anceps and Cystosphaera jacquinotii, fish Notothenia corriceps, sea invertebrates Amphipoda, shells of limpet Nacella concina, lichen Usnea aurantiaco-atra, vascular plants Deschampsia antarctica and Colobanthus quitensis, fungi Omphalina pyxidata, moss Sanionia uncinata and soil. The results show a large variation in some activity concentrations. Samples from the marine environment had lower contamination levels than those from terrestrial ecosystems. The highest activity concentrations for all radionuclides were found in lichen and, to a lesser extent, in mosses, probably because lichens take up atmospheric pollutants and retain them. The only significant correlation (except for that expected between ²³⁸Pu and ^239+240Pu) was noted for moss and lichen samples between plutonium and ⁹⁰Sr. A tendency to a slow decrease with time seems to be occurring. Analyses of the activity ratios show varying fractionation between various radionuclides in different organisms. Algae were relatively more highly contaminated with plutonium and radiostrontium, and depleted with radiocesium. Feathers had the lowest plutonium concentrations. Radiostrontium and, to a lesser extent, Pu accumulated in bones. The present low intensity of fallout in Antarctic has a lower ²³⁸Pu/^239+240Pu activity ratio than that expected for global fallout.     

Growth and physiological activity in <Emphasis Type="Italic">Larix kaempferi</Emphasis> seedlings inoculated with ectomycorrhizae as affected by soil acidification

To evaluate the effect of ectomycorrhizal colonization on growth and physiological activity of Larix kaempferi seedlings grown under soil acidification, we grew L. kaempferi seedlings with three types of ectomycorrhizae for 180 days in acidified brown forest soil derived from granite. The soil had been treated with an acid solution (0 (control), 10, 30, 60, and 90 mmol H⁺ kg⁻¹). The water-soluble concentrations of Ca, Mg, K, Al, and Mn increased with increasing amounts of H⁺ added to the soil. Ectomycorrhizal development significantly increased in soil treated with 10 and 30 mmol H⁺ kg⁻¹ but was significantly reduced in soil treated with 60 and 90 mmol H⁺ kg⁻¹. The concentrations of Al and Mn in needles or roots increased with increasing H⁺ added to the soil. The total N in seedlings significantly increased with increasing H⁺ in soil and colonization with ectomycorrhiza. The maximum net photosynthetic rate at light and CO₂ saturation (P _max) was greater in soil treated with 10 mmol H⁺ kg⁻¹ than in controls, and was less is soils treated with greater than with 30 mmol H⁺ kg⁻¹, especially with 60 and 90 mmol H⁺ kg⁻¹. However, colonization with ectomycorrhiza significantly reduced the concentration of Al and Mn in needles or roots and increased the values of P _max and total dry mass (TDM). The relative TDM of L. kaempferi seedlings was approximately 40% at a (BC, base cation)/Al ratio of 1.0. However, ectomycorrhizal seedlings had a 100–120% greater TDM at a BC/Al ratio of 1.0 than non-ectomycorrhizal seedlings, even though the acid treatment reduced their overall growth.     

Metagenome Cloning and Functional Analysis of Na<Superscript>+</Superscript>/H<Superscript>+</Superscript> Antiporter Genes from Keke Salt Lake in China

Na⁺/H⁺ antiporters are ubiquitous membrane proteins and play a central role in cell homeostasis including pH regulation, osmoregulation, and Na⁺/Li⁺ tolerance in bacteria. The microbial communities in extremely hypersaline soil are an important resource for isolating Na⁺/H⁺ antiporter genes. A metagenomic library containing 35,700 clones was constructed by using genomic DNA obtained from the hypersaline soil samples of Keke Salt Lake in Northwest of China. Two Na⁺/H⁺ antiporters, K1-NhaD, and K2-NhaD belonging to NhaD family, were screened and cloned from this metagenome by complementing the triple mutant Escherichia coli strain KNabc (nhaA ⁻ , nhaB ⁻ , chaA ⁻) in medium containing 0.2 M NaCl. K1-NhaD and K2-NhaD have 75.5% identity at the predicted amino acid sequence. K1-NhaD has 78% identity with Na⁺/H⁺ antiporter NhaD from Halomonas elongate at the predicted amino acid sequence. The predicted K1-NhaD is a 53.5 kDa protein (487 amino acids) with 13 transmembrane helices. K2-NhaD has 73% identity with Alkalimonas amylolytica NhaD. The predicted K2-NhaD is a 55 kDa protein (495 amino acids) with 12 transmembrane helices. Both K1-NhaD and K2-NhaD could make the triple mutant E. coli KNabc (nhaA ⁻ , nhaB ⁻ , chaA⁻) grow in the LBK medium containing 0.2–0.6 M Na⁺ or with 0.05–0.4 M Li⁺. Everted membrane vesicles prepared from E. coli KNabc cells carrying K1-NhaD or K2-NhaD exhibited Na⁺/H⁺ and Li⁺/H⁺ antiporter activities which were pH-dependent with the highest activity at pH 9.5. Little K⁺/H⁺ antiporter activity was also detected in vesicles form E. coli KNabc carrying K1-NhaD or K2-NhaD.     

Enhanced anti-tumor activity of interferon-alpha in SOCS1-deficient mice is mediated by CD4<Superscript>+</Superscript> and CD8<Superscript>+</Superscript> T cells

Interferon-alpha (IFN-α) is an immunomodulatory cytokine that is used clinically for the treatment of melanoma in the adjuvant setting. The cellular actions of IFN-α are regulated by the suppressors of cytokine signaling (SOCS) family of proteins. We hypothesized that the anti-tumor activity of exogenous IFN-α would be enhanced in SOCS1-deficient mice. SOCS1-deficient (SOCS1^−/−) or control (SOCS1^+/+) mice on an IFN-γ^−/− C57BL/6 background bearing intraperitoneal (i.p.) JB/MS murine melanoma cells were treated for 30 days with i.p. injections of IFN-A/D or PBS (vehicle). Log-rank Kaplan-Meier survival curves were used to evaluate survival. Tumor-bearing control SOCS1^+/+ mice receiving IFN-A/D had significantly enhanced survival versus PBS–treated mice (P = 0.0048). The anti-tumor effects of IFN-A/D therapy were significantly enhanced in tumor-bearing SOCS1^−/− mice; 75% of these mice survived tumor challenge, whereas PBS-treated SOCS1^−/− mice all died at 13-16 days (P = 0.00038). Antibody (Ab) depletion of CD8⁺ T cells abrogated the anti-tumor effects of IFN-A/D in SOCS1^−/− mice as compared with mice receiving a control antibody (P = 0.0021). CD4⁺ T-cell depletion from SOCS1^−/− mice also inhibited the effects of IFN-A/D (P = 0.0003). IFN-A/D did not alter expression of CD80 or CD86 on splenocytes of SOCS1^+/+ or SOCS1^−/− mice, or the proportion of T regulatory cells or myeloid-derived suppressor cells in SOCS1^+/+ or SOCS1^−/− mice. An analysis of T-cell function did reveal increased proliferation of SOCS1-deficient splenocytes at baseline and in response to mitogenic stimuli. These data suggest that modulation of SOCS1 function in T-cell subsets could enhance the anti-tumor effects of IFN-α in the setting of melanoma.     

Oxygen consumption rate and Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase activity in early developmental stages of the sea urchin <Emphasis Type="Italic">Paracentrotus lividus</Emphasis> Lam.

Changes in oxygen consumption rate and Na⁺/K⁺-ATPase activity during early development were studied in the sea urchin Paracentrotus lividus Lam. The oxygen consumption rate increased from 0.12 μmol O₂ mg protein⁻¹ h⁻¹ in unfertilized eggs to 0.38 μmol O₂ mg protein⁻¹ h⁻¹ 25 min after fertilization. Specific activity of the Na⁺/K⁺-ATPase was significantly stimulated after fertilization, ranging up to 1.07 μmol P_i h⁻¹ mg protein⁻¹ in the late blastula stage and slightly lower values in the early and late pluteus stages.     

Effects of Zn<Superscript>2+</Superscript> on nodulation and growth of a South American actinorhizal plant, <Emphasis Type="Italic">Discaria americana</Emphasis> (Rhamnaceae)

Discaria americana is a xerophytic shrub which lives in symbiosis with an actinomycete of the genus Frankia. The objective of this paper was to investigate the effects of high soil Zn²⁺ concentrations on growth and nodulation on the association Discaria americana–Frankia with the aim of determining if this association is suitable for improving contaminated soils. Two experiments were performed in 1 dm³ pots containing soil and different Zn additions, from 0 to 2,000 mg Zn²⁺ kg⁻¹ dry soil, with or without N fertilization. Zn additions strongly delayed shoot and root growth, but once growth was initiated, the biomass production of the plants supplied with moderate Zn amounts did not differ from the control plants. Zn reduced the final nodule number, but not the total nodule biomass. At the end of the experiment only the highest Zn treatments showed a lower nodule weight than the control plants, while N addition completely inhibited nodulation. It is concluded than Zn reduces the number of Frankia infections, but once the actinomycete is inside the roots, nodules can continue growing according to plant demand for N, compensating the reduced nodule number with more biomass. On the other hand, there is a toxic effect of Zn itself on plants when present in very high concentrations.     

The saturation of N cycling in Central Plains streams: <Superscript>15</Superscript>N experiments across a broad gradient of nitrate concentrations

We conducted ¹⁵NO₃⁻ stable isotope tracer releases in nine streams with varied intensities and types of human impacts in the upstream watershed to measure nitrate (NO₃⁻) cycling dynamics. Mean ambient NO₃⁻ concentrations of the streams ranged from 0.9 to 21,000 μg l⁻¹ NO₃⁻–N. Major N-transforming processes, including uptake, nitrification, and denitrification, all increased approximately two to three orders of magnitude along the same gradient. Despite increases in transformation rates, the efficiency with which stream biota utilized available NO₃⁻-decreased along the gradient of increasing NO₃⁻. Observed functional relationships of biological N transformations (uptake and nitrification) with NO₃⁻ concentration did not support a 1st order model and did not show signs of Michaelis–Menten type saturation. The empirical relationship was best described by a Efficiency Loss model, in which log-transformed rates (uptake and nitrification) increase with log-transformed nitrate concentration with a slope less than one. Denitrification increased linearly across the gradient of NO₃⁻ concentrations, but only accounted for ∼1% of total NO₃⁻ uptake. On average, 20% of stream water NO₃⁻ was lost to denitrification per km, but the percentage removed in most streams was <5% km⁻¹. Although the rate of cycling was greater in streams with larger NO₃⁻ concentrations, the relative proportion of NO₃⁻ retained per unit length of stream decreased as NO₃⁻ concentration increased. Due to the rapid rate of NO₃⁻ turnover, these streams have a great potential for short-term retention of N from the landscape, but the ability to remove N through denitrification is highly variable.     

Central ventilatory control in the South American lungfish, <Emphasis Type="Italic">Lepidosiren paradoxa:</Emphasis> contributions of pH and CO<Subscript>2</Subscript>

Lungfish represent a probable sister group to the land vertebrates. Lungfish and tetrapods share features of respiratory control, including central, peripheral and intrapulmonary CO₂ receptors. We investigated whether or not central chemoreceptors in the lungfish, L. paradoxa, are stimulated by CO₂ and/or pH. Ventilation was measured by pneumotachography for diving animals. The fourth cerebral ventricle was equipped with two catheters for superfusion. Initially, two control groups were compared: (1) catheterized animals with no superfusion and (2) animals superfused with mock CSF solutions at pH = 7.45; PCO₂ = 21 mmHg. The two groups had virtually the same ventilation of about 40 ml BTPS kg⁻¹ h⁻¹ (P > 0.05). Next, PCO₂ was increased from 21 to 42 mmHg, while pH_CSF was kept at 7.45, which increased ventilation from 40 to 75 ml BTPS kg⁻¹ h⁻¹. Conversely, a decrease of pH_CSF from 7.45 to 7.20 (PCO₂ = 21 mmHg) increased ventilation to 111 ml BTPS kg⁻¹ h⁻¹. Further decreases of pH_CSF had little effect on ventilation, and the combination of pH_CSF = 7.10 and PCO₂ = 42 mmHg reduced ventilation to 63 ml BTPS kg⁻¹ h⁻¹.     

CD133<Superscript>+</Superscript>CD44<Superscript>+</Superscript> subgroups may be human small intestinal stem cells

The identification and separation of small intestinal epithelial stem cells are still on the preliminary stage. In this study, we planned to utilize immunohistochemistry, fluorescence-activated cell sorting (FACS) and RT-PCR to investigate the possibility of CD133 and CD44 as markers of human small intestinal epithelial stem cells. The expressions of CD133, CD44 and Lgr5 were studied by immunohistochemistry. Four subgroups of CD133⁺CD44⁺, CD133⁺CD44⁻, CD133⁻CD44⁺, CD133⁻CD44⁻ were sorted out through FACS and the expression level of Lgr5 gene was measured by RT-PCR and polyacrylamide gel electropheresis (PAGE) with sliver stained. Ten cases of samples were available for analyzing. By immunohistochemical staining, few cells with positive expressions of CD133, CD44 and Lgr5 were distributed in the bottom of crypts with the expression locations somewhat overlapped. The average percentage of CD133⁺CD44⁺ cells was 0.0580 ± 0.0403%, while the corresponding contents of CD133⁺CD44⁻ cells, CD133⁻CD44⁺ cells and CD133⁻CD44⁻ cells were 0.4000 ± 0.1225%, 0.7000 ± 0.2646% and 76.5600 ± 3.5529% respectively. Ten times of positive expressions of Lgr5 were detected in the CD133⁺CD44⁺ groups, while 9/10, 8/10 and 4/10 times for CD133⁺CD44⁻, CD133⁻CD44⁺ and CD133⁻CD44⁻ subgroups respectively. With the help of Quantityone 4.62 software, the densities of corresponding place to Lgr5 and reference gene were obtained. The density ratios of corresponding place to Lgr5 to reference gene were significant difference between subgroups (P < 0.001). By means of LSD method, the density ratios in CD133⁺CD44⁺ subgroups had statistical differences from the other subgroups (P < 0.05). We concluded CD133⁺CD44⁺ cells may be human small intestinal epithelial stem cells, which need further researches to confirm.