Mg Of Soil Research Articles

Tools used to estimate soil quality in coal combustion waste areas

Soil is a highly complex environmental compartment that has suffered with the contamination of substances of various origins. Among the main activities that affect soil quality are power generation activities that use fossil fuels, such as mineral coal. Environmental protection agencies encourage scientific investigations using tools described in legal devices or standard protocols to evaluate the potential of coal as a pollutant, especially in places that have large reserves of this mineral like the state of Rio Grande do Sul. The aim of this study was to characterize the leached extracts of different soils from an area influenced by coal waste, to classify them according to the guideline values for groundwater described in CONAMA's n. 420/2009, and to estimate the effects of the leachates ingestion in DNA mutation rates. The volume of soil needed to induce a 100% increase in the spontaneous mutation rate varied between 129.3 and 1544.1 mg of soil among the soils studied. Metals such as Mn, Pb, Cd and Ni surpassed the investigation limits for groundwater at least in one soil sample. The results showed that there can be transfer of soil contaminants to groundwater and soil intake in the area could contribute to the increased mutagenic risk.

Methods for Assessing the Effects of Land Use Changes on Carbon Stocks of Subtropical Oxisols

This paper examines a number of calculation methods of soil carbon stocks (CS) to best assess the effects of land use changes in Oxisols and to determine the CS in different agro-ecosystems. The methods were fixed depth (FD), original equivalent soil mass (ESMO), equivalent soil layer (ESL), equivalent soil mass (ESM), fixed mass of 2500 Mg of soil (FM2500), cumulative mass coordinate system (CMC), material coordinate system (SCM), and direct carbon concentrations (CC). The soil sampling was performed in Oxisols in Misiones (Argentina). A randomized complete block design was used with four blocks, and the treatments were subtropical forest (S), tobacco (Nicotiana tabacum L.) (T), satsuma (Citrus unshiu Marc.) (Ci), and yerba mate (Ilex paraguariensis St. Hil.) (Y). The soils were clayey, and the variables measured were soil bulk density (BD) and C concentrations. To assess the effect of BD changes on the CS calculated, one simulation was conducted based on averaged data for BD and original carbon situation without disturbance. When the calculation was performed per FD, CS overestimations were found in cultivated soils.Significant differences were observed among CS under different simulated BD situations when using the FD, ESMO, ESM, FM2500, and CMC methods. The ESL and SCM were the most appropriate methods for assessing CS because in the first case, CS are not influenced by changes in BD and in the second case, even if the CS has been slightly modified because of changes in the BD, it was more sensitive to changes in land use. Soils cultivation resulted in a 23 to 36% C loss as compared with the original CS, when the SCM was applied.

Investigating carbonate formation in urban soils as a method for capture and storage of atmospheric carbon

This paper investigates the potential for engineered urban soils to capture and store atmospheric carbon (C). Calcium (Ca) and magnesium (Mg) bearing waste silicate minerals within the soil environment can capture and store atmospheric C through the process of weathering and secondary carbonate mineral precipitation. Anthropogenic soils, known to contain substantial quantities of Ca and Mg-rich minerals derived from demolition activity (particularly cement and concrete), were systematically sampled at the surface across a 10ha brownfield site, Science Central, located in the urban centre of Newcastle upon Tyne, U.K. Subsequent analysis yielded average carbonate contents of 21.8±4.7% wt CaCO3. Isotopic analysis demonstrated δ18O values between −9.4‰ and −13.3‰ and δ13C values between −7.4‰ and −13.6‰ (relative to Pee Dee Belemnite), suggesting that up to 39.4±8.8% of the carbonate C has been captured from the atmosphere through hydroxylation of dissolved CO2 in high pH solutions. The remaining carbonate C is derived from lithogenic sources. 37.4kg of atmospheric CO2 has already been captured and stored as carbonate per Mg of soil across the site, representing a carbon dioxide (CO2) removal rate of 12.5kgCO2Mg−1yr−1. There is the potential for capture and storage of a further 27.3kgCO2Mg−1 in residual reactive materials, which may be exploited through increased residence time (additional in situ weathering). Overall, the Science Central site has the potential to capture and store a total of 64,800Mg CO2 as carbonate minerals. This study illustrates the potential for managing urban soils as tools of C capture and storage, an important ecosystem service, and demonstrates the importance of studying C storage in engineering urban anthropogenic soils.

Sensitive Detection of Bacillus anthracis Spores by Immunocapture and Liquid Chromatography–Tandem Mass Spectrometry

Bacillus anthracis is one of the most dangerous agents of the bioterrorism threat. We present here a sensitive immuno-liquid chromatography-tandem mass spectrometry (immuno-LC-MS/MS) approach to spore detection in complex environmental samples. It is based on the combined specificity and sensitivity of two techniques: immunocapture and targeted mass spectrometry. The immunocapture step, realized directly on the intact spores, is essential for their selective isolation and concentration from complex environmental samples. After parallel trypsin and Glu-C digestions, proteotypic peptides corresponding to small acid-soluble spore protein-B (SASP-B) are specifically monitored in the multiple reaction monitoring (MRM) mass spectrometry mode. Peptide ratio is carefully monitored and provides an additional level of specificity, which is shown to be highly useful for distinguishing closely related samples and avoiding false-positive/negative results. Sensitivity at the level of the infectious dose is demonstrated, with limits of detection of 7 × 10(3) spores/mL of milk or 10 mg of soil. This mass spectrometry approach is thus complementary to polymerase chain reaction (PCR) techniques.

The Spatial Heterogeneity of Polycyclic Aromatic Hydrocarbons in Soil Depends on Their Physico-chemical Properties

The present study investigates the heterogenic distribution of nine polycyclic aromatic hydrocarbons (PAHs) in soil on a microscale. For this purpose, we developed a method allowing for the detailed analysis of PAHs in minute amounts of soil (5 to 25 mg). A certified reference soil with a known PAH content and a diffusely polluted Danish surface soil from central Copenhagen were used in the study. In order to separate soil heterogeneity from analytical variation, we attempted to establish the least amount of soil in which homogeneous and reproducible results could be obtained for the PAHs in question. The results demonstrated that for fluoranthene, analytical results in accordance with the certified reference values could be obtained in quantities of 10 mg of soil or more. For phenanthrene and pyrene, certified reference values could be obtained in quantities of 25 mg of soil or more. Similar results were obtained with the Nyboder soil, using the reference soil for quality and quantity assurance. For quantification of all nine PAHs, a minimum of 100 mg of soil was needed for both soils. In order to obtain an expression for the degree of heterogeneity of PAHs in the soils, a subsample variation was calculated based on overall sample variation and analytical measurements variation. The results demonstrate that the PAHs in the Nyboder soil are much more heterogeneously distributed than the PAHs in the reference soil due to much larger subsample variations. Furthermore, strong relationships between different physico-chemical properties and subsample variation were found. These included molecular weight, water solubility, log octanol/water partition coefficient, and soil–water distribution coefficient of the investigated PAHs, demonstrating that the heterogeneity of PAHs in the Nyboder soil is significantly influenced by such parameters.

PCR detection of Pseudoperonospora humuli in air samples from hop yards

Downy mildew of hop, caused by Pseudoperonospora humuli, is an important disease in most regions of hop production and is managed largely with regular fungicide applications. A PCR assay specific to P. humuli and the related organism P. cubensis was developed and used to monitor airborne inoculum in hop yards to initiate fungicide applications. The PCR amplified as little as 1 fg of genomic DNA of P. humuli, and yielded an amplicon in 70% of reactions when DNA was extracted from single sporangia. In the presence of 25 mg of soil, an amplicon was amplified in 90% of reactions when DNA was extracted from 10 or more sporangia. During nine location‐years of validation, PCR detection of the pathogen in air samples occurred no later than 8 days after the appearance of trace levels of disease signs and/or detection of airborne spores in a volumetric spore sampler. Inoculum was detected on average 4·5 days before (range −8 to 14 days) the first appearance of basal spikes in six commercial yards, or 1·3 days after (range −5 to 1 days) sporangia were detected in a volumetric spore sampler in experimental plots. In commercial yards, use of PCR to initiate the first fungicide application led to enhanced disease control or a reduction in fungicide use in four of six yards compared to growers’ standard practices. These results indicate that the efficiency and efficacy of hop downy mildew management can be improved when control measures are timed according to first detection of inoculum.

The Death of Countess Agusta in Portofino (Northern Italy) and the Soil from Two Mismatched Slippers

Accident, suicide, or homicide might have caused the death of Countess Agusta who fell from the 80-m tall cliff of her villa. Two mismatched slippers were recovered along the cliff. Use was made of microscope, X-ray diffractometry, scanning electron microscopy, and microprobe techniques to compare 40 mg of soil collected from the slipper soles with samples from the villa garden. Structural details of the slipper soles were consistent with the lady wearing them during the fall. Analysis of the soil residues confirmed that they originated from the garden only. The features of a few, minute glass chips adhering to the slipper soles reasonably matched those of other fragments that were found on a small ledge on the cliff beyond the garden parapet. Based on this and other evidence, the case was closed with a verdict of accidental fall.

Thermally evolved gas analysis (TEGA) of hyperarid soils doped with microorganisms from the Atacama Desert in southern Peru: Implications for the Phoenix mission

TEGA, one of several instruments on board of the Phoenix Lander, performed differential scanning calorimetry and evolved gas analysis of soil samples and ice, collected from the surface and subsurface at a northern landing site on Mars. TEGA is a combination of a high temperature furnace and a mass spectrometer (MS) that was used to analyze samples delivered to the instrument via a robotic arm. The samples were heated at a programmed ramp rate up to 1000 °C. The power required for heating can be carefully and continuously monitored (scanning calorimetry). The evolved gases generated during the process can be analyzed with the evolved gas analyzer (a magnetic sector mass spectrometer) in order to determine the composition of gases released as a function of temperature. Our laboratory has developed a sample characterization method using a pyrolyzer integrated to a quadrupole mass spectrometer to support the interpretations of TEGA data. Here we examine the evolved gas properties of six types of hyperarid soils from the Pampas de La Joya in southern Peru (a possible analog to Mars), to which we have added with microorganisms ( Salmonella typhimurium, Micrococcus luteus, and Candida albicans) in order to investigate the effect of the soil matrix on the TEGA response. Between 20 and 40 mg of soil, with or without ∼5 mg of lyophilized microorganism biomass (dry weight), were placed in the pyrolyzer and heated from room temperature to 1200 °C in 1 h at a heating rate of 20 °C/min. The volatiles released were transferred to a MS using helium as a carrier gas. The quadrupole MS was ran in scan mode from 10 to 200 m/z. In addition, ∼20 mg of each microorganism without a soil matrix were analyzed. As expected, there were significant differences in the gases released from microorganism samples with or without a soil matrix, under similar heating conditions. Furthermore, samples from the most arid environments had significant differences compared with less arid soils. Organic carbon released in the form of CO 2 (ion 44 m/z) from microorganisms evolved at temperatures of ∼326.0 ± 19.5 °C, showing characteristic patterns for each one. Others ions such as 41, 78 and 91 m/z were also found. Interestingly, during the thermal process, the release of CO 2 increased and ions previously found disappeared, demonstrating a high-oxidant activity in the soil matrix when it was subjected to high temperature. Finally, samples of soil show CO 2 evolved up to 650 °C consistent with thermal decomposition of carbonates. These results indicate that organics mixed with these hyperarid soils are oxidized to CO 2. Our results suggest the existence of at least two types of oxidants in these soils, a thermolabile oxidant which is highly oxidative and other thermostable oxidant which has a minor oxidative activity and that survives the heat-treatment. Furthermore, we find that the interaction of biomass added to soil samples gives a different set of breakdown gases than organics resident in the soil. The nature of oxidant(s) present in the soils from Pampas de La Joya is still unknown.

Sorptive Behavior of Sorgoleone in Ultisol in Two Solvent Systems and Determination of Its Lipophilicity

Sorgoleone (SGL) exuded by sorghum roots inhibits the development of some weeds. Due to its high hydrophobicity, it is expected that SGL presents low soil mobility and limited allelopathic activity in the field. This work aims to evaluate the sorptivity of sorgoleone in octanol-water and in soil under two solvent systems. The two solvent systems were methanol:water (60:40) (MeOH:H2O) and pure methanol (MeOH). These two solvent systems promote different conditions for SGL solubility. Treatments were arranged in a 2 × 6 factorial (solvent systems × equilibrium concentrations in the solution (EC)). For each solvent, the sorption was achieved by shaking 500 mg of soil with 10 ml of 0, 5, 10, 15, 25, 40, and 60 mg L−1 of SGL solution, during 24 h. After centrifugation, the supernatant was filtered and the SGL concentration was determined by high performance liquid chromatography (HPLC). Data of sorbed amount of SGL were submitted to variance analysis, using a hierarchic factorial model. The data of sorbed amount (x/m) and equilibrium concentration (C) were fitted to the linear (x/m = a + K d C) and to the Freundlich (x/m = K f C 1/n ) models. The isotherm obtained for the MeOH:H2O system presented linear shape, whereas for the MeOH system a two subsequent linear isotherm was fitted. Sorgoleone is a highly hydrophobic compound, presenting a log K ow of 6.1. The sorption of sorgoleone to the soil was very high. The organic environment stimulated the sorgoleone sorption to the soil.

Predicting Soil Erosion for Alternative Land Uses

The APEX (Agricultural Policy-Environmental eXtender) model developed in the United States was calibrated for northwestern China's conditions. The model was then used to investigate soil erosion effects associated with alternative land uses at the ZFG (Zi-Fang-Gully) watershed in northwestern China. The results indicated that the APEX model could be calibrated reasonably well (+/-15% errors) to fit those areas with >50% slope within the watershed. Factors being considered during calibration include runoff, RUSLE (Revised Universal Soil Loss Equation) slope length and steepness factor, channel capacity flow rate, floodplain saturated hydraulic conductivity, and RUSLE C factor coefficient. No changes were made in the APEX computer code. Predictions suggest that reforestation is the best practice among the eight alternative land uses (the status quo, all grass, all grain, all grazing, all forest, half tree and half grass, 70% tree and 30% grain, and construction of a reservoir) for control of water runoff and soil erosion. Construction of a reservoir is the most effective strategy for controlling sediment yield although it does nothing to control upland erosion. For every 1 Mg of crop yield, 11 Mg of soil were lost during the 30-yr simulation period, suggesting that expanding land use for food production should not be encouraged on the ZFG watershed. Grass species are less effective than trees in controlling runoff and erosion on steep slopes because trees generally have deeper and more stable root systems.

Microbial Assemblages in Soil Microbial Succession After Glacial Retreat in Svalbard (High Arctic)

Microbial community composition (cyanobacteria and eukaryotic microalgae abundance and diversity, bacterial abundance, and soil respiration) was studied in subglacial and periglacial habitats on five glaciers near Ny-Alesund, Svalbard (79 degrees N). Soil microbial communities from nonvegetated sites (subglacial, recently deglaciated, and cryoconite sediments) and sites with plant cover (deglaciated some hundreds of years ago) were analyzed. Physicochemical analyses (pH, texture, water content, organic matter, total C and N content) were also performed on the samples. In total, 57 taxa of 23 genera of cyanobacteriaand algae were identified. Algae from the class Chlorophyceae (25 species) and cyanobacteria (23 species) were richest in biodiversity. The numbers of identified species in single habitat types were 23 in subglacial, 39 inbarren, 22 in cryoconite, and 24 in vegetated soils. The highest cyanobacterial and algal biovolume and cell numbers, respectively, were present in cryoconite (13x10(4) microm3 mg-1 soil and 508 cells per mg of soil), followed by barren (5.7x10(4) and 188), vegetated (2.6x10(4) and 120), and subglacial (0.1x10(4) and 5) soils. Cyanobacteria prevailed in all soil samples. Algae (mainly green algae) were present only as accessory organisms. The density of bacteria showed a slightly different trend to that of the cyanobacterial and algal assemblages. The highest number of bacteria was present in vegetated (mean: 13,722x10(8) cells per mg of soil dry wt.), followed by cryoconite (3802x10(8)), barren (654x10(8)), and subglacial (78x10(8)) soils. Response of cyanobacteria and algae to physical parameters showed that soil texture and water content are important for biomass development. In addition, it is shown that nitrogen and water content are the main factors affecting bacterial abundance and overall soil respiration. Redundancy analysis (RDA) with forward selection was used to create a model explaining variability in cyanobacterial, algal, and bacterial abundance. Cryoconites accounted for most of the variation in cyanobacteria and algae biovolume, followed by barren soils. Oscillatoriales, desmids, and green coccoid algae preferred cryoconites, whereas Nostocales and Chroococcales occurred mostly in barren soils. From the data obtained, it is evident that of the studied habitats cryoconite sediments are the most suitable ones for the development of microbial assemblages. Although subglacial sediments do not provide as good conditions as cryoconites, they support the survival of microbial communities. Both mentioned habitats are potential sources for the microbial recolonization of freshly deglaciated soil after the glacier retreat.

History, origin and extent of soil erosion on Easter Island (Rapa Nui)

The isolated Easter Island (Rapa Nui) is an outstanding example of land degradation caused by land use in a sensitive ecosystem. The focus of the investigation was placed on Poike peninsula, the most eastern part of Rapa Nui. While Poike peninsula was once supplied with fertile soils, in large areas desertification takes place today. Detailed analysis of soil profiles allowed the reconstruction of the history and of causes and effects of soil erosion and gullying in the context of land use history and cultural evolution. The results of the stratigraphic analysis prove that from the beginning of human settlement around AD 300/600 until AD 1280 the agriculture on Poike peninsula was characterised by sustainable land use and a traditional type of agro-forestry. Soil erosion was not significant. At around AD 1280 the woodland on Poike, dominated by the endemic palm Jubaea sp., was cleared by slashing and burning. Intensive farming on the upper slopes of the volcanic peninsula resulted in sheet erosion lasting until the 20th century. Settlements and ceremonial places which were built around AD 1300 on downslope areas were buried soon by sediments. Agriculture ceased around AD 1400 on downslope areas as the fertile soils were completely eroded. From AD 1400 until the late 19th century sheet erosion and the accumulation of fine-layered sediments migrated upslope. On average 8.6 Mg of soil per hectare and per year were reworked by erosion (eroded and accumulated within the catchment). Gullying began on Rapa Nui with the sudden increase in the number of sheep during the early 20th century. Gullies are still developing on the island and their ongoing enlargement created extended badlands on Poike which pose a significant problem for ecological and archaeological conservation strategies. Gullying rates exceed 190 Mg ha − 1 y − 1 .

Lipase assay in soils by copper soap colorimetry

A simple and sensitive method for the estimation of lipase activity in soils is reported. In this method, 50 mg of soil is incubated with emulsified substrate, the fatty acids liberated are treated with cupric acetate–pyridine reagent, and the color developed is measured at 715 nm. Use of olive oil in this protocol leads to an estimation of true lipase activity in soils. The problem of released fatty acids getting adsorbed onto the soil colloids is obviated by the use of isooctane, and separate standards for different soils need not be developed. Among the various surfactants used for emulsification, polyvinyl alcohol is found to be the most effective. Incubation time of 20 min, soil concentration of 50 mg, pH 6.5, and incubation temperature of 37 °C were found to be the most suitable conditions for this assay. During the process of enrichment of the soils with oil, interference by the added oil is avoided by the maintenance of a suitable control, wherein 50 mg of soil is added after stopping the reaction. This assay is sensitive and it could be adopted to screen for lipase producers from enriched soils and oil-contaminated soils before resorting to isolation of the microbes by classical screening methods.

Desenvolvimento do tomateiro e modificações nas propriedades químicas do solo em função da aplicação de resíduos orgânicos, sob cultivo protegido

O experimento foi conduzido de fevereiro a agosto de 1997 no município de Piracicaba (SP), a fim de avaliar os efeitos de doses e resíduos orgânicos no desenvolvimento do tomateiro (Lycopersicon esculentum Mill) cultivado em estufa e nos atributos químicos de um solo Podzólico vermelho-amarelo abrupto, A moderado, textura arenosa/média. O delineamento experimental foi de blocos casualizados em esquema fatorial 3 x 4, sendo usados três resíduos orgânicos [composto de lodo de cervejaria e cavaco de eucalipto (CLC), composto de lixo (CL) e cama de frango (CF)] e quatro doses equivalentes a 0; 100; 150 e 200 kg ha-1 de N, com quatro repetições. A produção de frutos de tomate não aumentou com a adição dos materiais orgânicos. A aplicação de CF reduziu o pH e o teor de Mg no solo. As doses do CLC elevaram o conteúdo de matéria orgânica, o teor de cálcio trocável e a capacidade de troca de cátions do solo. O CL, por sua vez, não alterou as propriedades químicas do solo.

Rainfall and crop residue effects on soil dispersion and Beauveria bassiana spread to corn

The entomopathogenic fungus Beauveria bassiana infects a wide range of insects and survives as a soil saprophyte and a plant endophyte. The objective of our study was to determine the role of rainfall in dispersing B. bassiana (Balsamo) Vuillemin to the surface of corn ( Zea mays) from soil with different levels of crop residue. Laboratory studies which simulated field tillage systems, had levels of crop residue which covered 0.53 (control), 34, 59 and 84% of the soil surface. Simulated rainfall in a raindrop tower at an intensity of 73 mm/h caused a significant increase in the mean number of B. bassiana colony forming units (CFU) isolated from the surface of corn plants. Plants receiving rain had a mean (±S.E.M.) of 8.8±2.8 CFU per plant; controls had a mean of 0.03±0.01 CFU per plant. The mg of soil collected from the surface of plants also was significantly influenced by rainfall. Plants receiving rain had a mean of 15.7±1.7 mg of soil per plant while controls had a mean of 3.4±0.4 mg of soil per plant. Linear regression revealed highly significant negative relationships between the mean mg of soil and the mean number of CFU per plant, over the four levels of crop residue. The amount of soil and number of CFU per plant decreased significantly with increasing levels of crop residue. In field studies with conservation- and no-till systems, results were similar to those recorded in the raindrop tower. The mean number of CFU and mg of soil per plant were both higher in conservation-till plots than in no-till plots, where surface residue averaged 45 and 95%, respectively. Rainfall plays an active role in the dispersal of B. bassiana from the soil environment to the surface of whorl-stage corn. Increased levels of crop residue reduce the amount of soil and fungal transfer to the surface of young corn.

Detection of 2-chloroethylethyl sulfide on soil particles using ion trap-secondary ion mass spectrometry

2-Chloroethylethyl sulfide (CEES) is used as a simulant for mustard (HD) in a study to develop secondary ion mass spectrometry (SIMS) for rapid, semi-quantitative detection of mustard on soil. Selectivity and sensitivity are markedly improved employing multiple-stage mass spectrometry (MS n ) using an ion trap SIMS. C 2H 5SC 2H 4 + from CEES eliminates C 2H 4 and H 2S, which are highly diagnostic. CEES was detectable at 0.0012 monolayer on soil. This corresponds to approximately 15 ppm (mass/mass) for a soil having a surface area of 12 m 2 g −1. A single analysis could be conducted using only 2 mg of soil in under 5 min.

Soil Ingestion in Adults—Results of a Second Pilot Study

Soil ingestion was evaluated in 10 adults as part of a larger study to evaluate soil ingestion in children. Each adult was followed for 4 weeks in a mass-balance study that was designed to evaluate the detection limit for soil ingestion in a similarly designed, concurrent children's study. After a baseline week, during Weeks 2 through 4, adults received daily soil capsules containing 20, 100, and 500 mg of soil, respectively. A 1-week period separated each study week. Based on the first 3 weeks of observation after subtracting the capsule ingestion amounts, the median, 75th percentile, and 95th percentile soil ingestion estimates were 1, 49, and 331 mg/day, with estimates calculated as the median of the three trace elements Al, Si, and Y. The average estimate of soil ingestion was 10 mg/day (SD = 94 mg/day). These findings augment sparse empirical data on adult soil ingestion, and suggest lower levels of soil ingestion in adults than previous studies.

Determination of Total Iodine in Soils by Inductively Coupled Plasma Mass Spectrometry

Abstract A method for the determination of the total amount of iodine in soil by inductively coupled plasma mass spectrometry was developed. Iodine in soil was completely extracted by heating a mixture of 5 mL of 5% tetramethylammonium hydroxide solution and 100 mg of soil for 3 h in an oven at 70°C. Indium as an internal standard was added and the extract was diluted at least more than 10-fold. Iodine amount in the solution was determined by measuring the signal intensity of 127I against that of 113In. When the method was tested by analyzing four reference soil samples (GSS-1, 4, 5, and 7), the iodine contents obtained were in good agreement with the certified values for the samples.

Use of radiolabelled thymidine and leucine to estimate bacterial production in soils from continental antarctica

Tritiated thymidine incorporation (TTI) into DNA was used to examine bacterial production in two soil types from the Robertskollen group of nunataks in northwestern Dronning Maud Land, providing the first estimates of bacterial production in soil habitats on the Antarctic continent. Although estimates of bacterial productivity in soils near to bird nests (344 (plusmn) 422 ng of C g [dry weight](sup-1) h(sup-1)) were higher than those for soils from beneath mosses (175 (plusmn) 90 ng of C g [dry weight](sup-1) h(sup-1); measured by TTI at 10(deg)C), these differences were not significant because of patchiness of bacterial activity (P > 0.05). TTI- and [(sup14)C]leucine ([(sup14)C]Leu)-derived estimates of bacterial production were similar when incubations of 3 h were used, although incubations as short as 1 h were sufficient for measurable uptake of radiolabel. Dual-label incorporation of [(sup3)H]thymidine ([(sup3)H]TdR) into DNA and [(sup14)C]Leu into protein indicated that TTI did not reflect bacterial production of in situ assemblages when incubations were longer than 3 h. Isotope dilution analysis indicated that dilution of the specific activity of exogenously supplied [(sup3)H]TdR by de novo synthesis of TdR precursor could be limited by additions of [(sup3)H]TdR at a concentration of 1 nmol per ca. 115 mg of soil. TTI exhibited a psychrotrophic response to variation in temperature, with a temperature optimum of ca. 15(deg)C and a Q(inf10) value for 0 to 10(deg)C of 2.41.

Supercritical fluid extraction/gas chromatography with thermal desorption modulator interface and nitro‐specific detection for the analysis of explosives

AbstractSupercritical fluid extraction (SFE) can greatly reduce the sample preparation time of analytes in solid matrices. The on‐line coupling of SFE with high‐speed gas chromatography (GC) can further reduce the total analysis time. SFE has been coupled to GC with a thermal desorption modulator (TDM) interface. A thermal energy analyzer (TEA), a chemiluminescence detector which is specific for nitro and nitroso compounds, has been coupled to the system to analyze explosives in soil samples.The use of organic modifiers to increase the solvation power of carbon dioxide was necessary for the extraction of various explosives, and did not adversely affect the performance of the system. Thermally labile compounds, however, such as the nitrate esters, were shown to decompose in the modulator before the chromatographic separation.This method allows for the rapid analysis of relatively volatile and thermally stable nitro compounds from solid matrices. The system can be used for screening small samples in short periods of time. Total analysis can be completed in less than 10 minutes and requires only 200 mg of soil. The minimum detectable quantity for the analysis of 2,4‐DNT was found to be 2.6 ppb in an actual soil sample.