Seasonal variation in natural abundance of δ13C and 15N in Salicornia brachiata Roxb. populations from a coastal area of India

High and fluctuating salinity is characteristic for coastal salt marshes, which strongly affect the physiology of halophytes consequently resulting in changes in stable isotope distribution. The natural abundance of stable isotopes (δ¹³C and δ¹⁵N) of the halophyte plant Salicornia brachiata and physico-chemical characteristics of soils were analysed in order to investigate the relationship of stable isotope distribution in different populations in a growing period in the coastal area of Gujarat, India. Aboveground and belowground biomass of S. brachiata was collected from six different populations at five times (September 2014, November 2014, January 2015, March 2015 and May 2015). The δ¹³C values in aboveground (?30.8 to ?23.6?‰, average: ?26.6?±?0.4?‰) and belowground biomass (?30.0 to ?23.1?‰, average: ?26.3?±?0.4?‰) were similar. The δ¹³C values were positively correlated with soil salinity and Na concentration, and negatively correlated with soil mineral nitrogen. The δ¹⁵N values of aboveground (6.7–16.1?‰, average: 9.6?±?0.4?‰) were comparatively higher than belowground biomass (5.4–13.2?‰, average: 7.8?±?0.3?‰). The δ¹⁵N values were negatively correlated with soil available P. We conclude that the variation in δ¹³C values of S. brachiata was possibly caused by soil salinity (associated Na content) and N limitation which demonstrates the potential of δ¹³C as an indicator of stress in plants.     

Oxygen and nitrogen isotopic composition of nitrate in commercial fertilizers,nitric acid,and reagent salts

Nitrate is a key component of synthetic fertilizers that can be beneficial to crop production in agro-ecosystems, but can also cause damage to natural ecosystems if it is exported in large amounts. Stable isotopes, both oxygen and nitrogen, have been used to trace the sources and fate of nitrate in various ecosystems. However, the oxygen isotope composition of synthetic and organic nitrates is poorly constrained. Here, we present a study on the N and O isotope composition of nitrate-based fertilizers. The δ¹⁵N values of synthetic and natural nitrates were 0?±?2?‰ similar to the air N₂ from which they are derived. The δ¹⁸O values of synthetic nitrates were 23?±?3?‰, similar to air O₂, and natural nitrate fertilizer δ¹⁸O values (55?±?5?‰) were similar to those observed in atmospheric nitrate. The Δ¹⁷O values of synthetic fertilizer nitrate were approximately zero following a mass-dependent isotope relationship, while natural nitrate fertilizers had Δ¹⁷O values of 18?±?2?‰ similar to nitrate produced photochemically in the atmosphere. These narrow ranges of values can be used to assess the amount of nitrate arising from fertilizers in mixed systems where more than one nitrate source exists (soil, rivers, and lakes) using simple isotope mixing models.     

Isotope (δ13C, δ15N, δ2H) diet–tissue discrimination in African grey parrot Psittacus erithacus: implications for forensic studies

Diet–tissue isotopic relationships established under controlled conditions are informative for determining the dietary sources and geographic provenance of organisms. We analysed δ¹³C, δ¹⁵N, and non-exchangeable δ²H values of captive African grey parrot Psittacus erithacus feathers grown on a fixed mixed-diet and borehole water. Diet–feather Δ¹³C and Δ¹⁵N discrimination values were +3.8?±?0.3?‰ and +6.3?±?0.7?‰ respectively; significantly greater than expected. Non-exchangeable δ²H feather values (?62.4?±?6.4?‰) were more negative than water (?26.1?±?2.5?‰) offered during feather growth. There was no positive relationship between the δ¹³C and δ¹⁵N values of the samples along each feather with the associated samples of food offered, or the feather non-exchangeable hydrogen isotope values with δ²H values of water, emphasising the complex processes involved in carbohydrate, protein, and income water routing to feather growth. Understanding the isotopic relationship between diet and feathers may provide greater clarity in the use of stable isotopes in feathers as a tool in determining origins of captive and wild-caught African grey parrots, a species that is widespread in aviculture and faces significant threats to wild populations. We suggest that these isotopic results, determined even in controlled laboratory conditions, be used with caution.     

The relative isotopic abundance (δ13C, δ15N) during composting of agricultural wastes in relation to compost quality and feedstock

Variations in the relative isotopic abundance of C and N (δ¹³C and δ¹⁵N) were measured during the composting of different agricultural wastes using bench-scale bioreactors. Different mixtures of agricultural wastes (horse bedding manure?+?legume residues; dairy manure?+?jatropha mill cake; dairy manure?+?sugarcane residues; dairy manure alone) were used for aerobic–thermophilic composting. No significant differences were found between the δ¹³C values of the feedstock and the final compost, except for dairy manure?+?sugarcane residues (from initial ratio of ?13.6?±?0.2?‰ to final ratio of ?14.4?±?0.2?‰). δ¹⁵N values increased significantly in composts of horse bedding manure?+?legumes residues (from initial ratio of +5.9?±?0.1?‰ to final ratio of +8.2?±?0.5?‰) and dairy manure?+?jatropha mill cake (from initial ratio of +9.5?±?0.2?‰ to final ratio of +12.8?±?0.7?‰) and was related to the total N loss (mass balance). δ¹³C can be used to differentiate composts from different feedstock (e.g. C₃ or C₄ sources). The quantitative relationship between N loss and δ¹⁵N variation should be determined.     

Field-deployable measurements of free-living individuals to determine energy balance: fuel substrate usage through δ13C in breath CO2 and diet through hair δ13C and δ15N values

Carbon isotopes of breath CO₂ vary depending on diet and fuel substrate used. This study examined if exercise-induced δ¹³C-CO₂ changes in substrate utilization were distinguishable from baseline δ¹³C-CO₂ variations in a population with uncontrolled diet, and compared hair isotope values and food logs to develop an isotope model of diet. Study participants included nine women with diverse Body Mass Index (BMI), age, ancestry, exercise history, and diet. Breath samples were collected prior to and up to 12?h after a 5- or 10?K walk/run. Indirect calorimetry was measured with a smartphone-enabled mobile colorimetric device, and a field-deployable isotope analyzer measured breath δ¹³C-CO₂ values. Diet was assessed by food logs and δ¹³C, δ¹⁵N of hair samples. Post-exercise δ¹³C-CO₂ values increased by 0.54?±?1.09‰ (1 sd, n?=?9), implying enhanced carbohydrate burning, while early morning δ¹³C-CO₂ values were lower than daily averages (p?=?0.0043), indicating lipid burning during overnight fasting. Although diurnal δ¹³C-CO₂ variation (1.90?±?0.77‰) and participant baseline range (3.06‰) exceeded exercise-induced variation, temporal patterns distinguished exercise from dietary isotope effects. Hair δ¹³C and δ¹⁵N values were consistent with a new dietary isotope model. Notwithstanding the small number of participants, this study introduces a novel combination of techniques to directly monitor energy balance in free-living individuals.     

Stable carbon and nitrogen isotope discrimination and turnover in a small-bodied insectivorous lizard

Laboratory experiments are useful for estimating the carbon and nitrogen isotope discrimination factors and turnover rates that are critical for drawing field-based inferences on consumer diets using stable isotopes. Although the utility of these discrimination factors is widely recognized, work in terrestrial systems has largely been limited to studies involving mammals and birds. In contrast, scant attention has been paid to the application of isotopic techniques to reptiles, despite their broad diversity in terms of numbers of species as well as their trophic roles. Here we estimate carbon and nitrogen isotope discrimination factors and turnover for the tree lizard (Urosaurus ornatus) using a diet-switch experiment. Lizards were collected from a C₄-dominated grassland and then switched to C₃-based diet (crickets) in the laboratory. We estimated discrimination by lizard claw tissue as Δ¹³C?=?1.2?±?0.1?‰ for carbon and Δ¹⁵N?=?0.7?±?0.1?‰ (mean?±?1 SE) for nitrogen, with 95?% turnover occurring after ～15.5 days. These estimates should be appropriate for use in trophic studies of U. ornatus, and possibly other related small-bodied insectivorous lizards.     

Temporal diet changes recorded by stable isotopes in Asiatic black bear (Ursus thibetanus) hair

Carbon and nitrogen stable isotope ratios were measured in hair samples of the Asiatic black bear (Ursus thibetanus) inhabiting the Northern Japanese Alps (NJA) (n?=?20) and the periphery of Nagano City (NC) (n?=?6), in Nagano Prefecture, Japan. The hair of NJA bears, which did not have access to anthropogenic foods, showed lower values of δ¹³C and δ¹⁵N than that of NC bears which had access to garbage and corn fields, especially during the summer. These results reflect somewhat differing diets between the NJA and NC bears. We attempted to assess the feeding history during the hair growth cycle using the growth section analysis method. Each hair sample had been cut into 3?mm lengths from root to tip, labeled, and analyzed along the hair growth. We measured the carbon and nitrogen stable isotope ratios of each 3?mm length of hair sample from one NC bear which had been killed while raiding a corn field. The sections showed wide ranges of isotope ratios, from ?23.2‰ to ?14.6‰ for δ¹³C, and from 0.3‰ to 4.6‰ for δ¹⁵N. It was shown that the diet of this bear shifted dramatically from principally C₃ plants to more C₄ plants and to foods of animal origin. An analysis of the whole hair reflects just the average feeding habit during hair growth, but the present method can trace its diet history. This method can contribute to obtain precise ecological information of wildlife.     

Estimation of microbial methane generation and oxidation rates in the municipal solid waste landfill of Kaluga city,Russia

Using a theoretical model and mass isotopic balance, biogas (methane and CO₂) released from buried products at their microbial degradation was analysed in the landfill of municipal and non-toxic industrial solid organic waste near Kaluga city, Russia. The landfill contains about 1.34×10⁶ tons of waste buried using a ‘sandwich technique’ (successive application of sand–clay and waste layers). The δ¹³C values of biogenic methane with respect to CO₂ were?56.8 (±2.5) ‰, whereas the δ¹³C of CO₂ peaked at+9.12‰ (+1.4±2.3‰ on average), reflecting a virtual fractionation of carbon isotopes in the course of bacterial CO₂ reduction at the landfill body. After passing through the aerated soil layers, methane was partially oxidised and characterised by δ¹³C in the range of?50.6 to?38.2‰, evidencing enrichment in ¹³C, while the released carbon dioxide had δ¹³C of?23.3 to?4.04‰, respectively. On the mass isotopic balance for the δ¹³C values, the methane production in the landfill anaerobic zone and the methane emitted through the aerated landfill surface to the atmosphere, the portion of methane oxidised by methanotrophic bacteria was calculated to be from 10 to 40% (averaged about 25%). According to the theoretical estimation and field measurements, the annual rate of methane production in the landfill reached about 2.9(±1.4)×10⁹ g C CH₄ yr^?1 or 5.3(±2.6)×10⁶ m³ CH₄ yr^?1. The average rates of methane production in the landfill and methane emission from landfill to the atmosphere are estimated as about 53 (±26) g C CH₄ m^?2 d^?1 (or 4 (±2) mol CH₄ m^?2 d^?1) and 33 (±12) g C CH₄ m^?2 d^?1 (or 2.7 (±1) mol CH₄ m^?2 d^?1), respectively. The calculated part of methane consumed by methanotrophic bacteria in the aerated part of the landfill was 13(±7) g C CH₄ m^?2 d^?1 (or 1.1(±0.6) mol CH₄ m^?2 d^?1) on average.     

Is the ‘canine surrogacy approach’ (CSA) still valid for dogs and humans in market-oriented and subsistence-oriented communities in Brazil?

Based on the assumptions that human food is available for dogs and isotope diet–tissue differences are similar in dogs and humans, the ‘canine surrogacy approach’ (CSA) has been used to infer patterns of ancient populations. The goal of this study was to test the CSA in urban (Brasília and Piracicaba) and in rural (Ubatuba and Maraã) areas. The hair C and N isotope ratios of modern dogs were compared with those of human fingernails from different regions of Brazil. Our CSA results showed a correlation between dog and human isotopes values: in rural areas δ¹⁵N of humans and dogs was not statistically different; contrarily, in urban centres, δ¹⁵N of humans was approximately 1?‰ higher (p?<?0.01) than δ¹⁵N of dogs; humans had lower δ¹³C values (p?<?0.01) than dogs in Brasília, Piracicaba and Ubatuba. In Maraã, there was not any significant difference between dogs and humans. We concluded that CSA is still valid as a first approach in modern societies. However, isotopic differences found suggest that in modern societies processed dog food is increasingly disconnecting human and dog, jeopardising the use of CSA in the future if the trend of increasing processed dog food consumption continues to occur.     

Biological fractionation of stable Ca isotopes in Göttingen minipigs as a physiological model for Ca homeostasis in humans

In order to investigate fractionation of calcium (Ca) isotopes in vertebrates as a diagnostic tool to detect Ca metabolism dysfunction we analyzed the Ca isotopic composition (δ^44/40Ca?=?[(⁴⁴Ca/⁴⁰Ca)_sample/(⁴⁴Ca/⁴⁰Ca)_reference]?1) of diet, faeces, blood, bones and urine from Göttingen minipigs, an animal model for human physiology. Samples of three groups were investigated: 1. control group (Con), 2. group with glucocorticosteroid induced osteoporosis (GIO) and 3. group with Ca and vitamin D deficiency induced osteomalacia (?CaD). In contrast to Con and GIO whose average δ^44/40Ca_faeces values (0.39?±?0.13‰ and 0.28?±?0.08‰, respectively) tend to be lower than their diet (0.47?±?0.02‰), δ^44/40Ca_faeces of ?CaD (?0.27?±?0.21‰) was significantly lower than their δ^44/40Ca_diet (0.37?±?0.03‰), but also lower than δ^44/40Ca_faeces of Con and GIO. We suggest that the low δ^44/40Ca_faeces of ?CaD might be due to the contribution of isotopically light Ca from gastrointestinal fluids during gut passage. Assuming that this endogenous Ca source is a common physiologic feature, a fractionation during Ca absorption is also required for explaining δ^44/40Ca_faeces of Con and GIO. The δ^44/40Ca_urine of all groups are high (>2.0‰) reflecting preferential renal reabsorption of light Ca isotopes. In Göttingen minipigs we found a Ca isotope fractionation between blood and bones (Δ^44/40Ca_blood-bone) of 0.68?±?0.15‰.     

Carbon isotopic signature reveals the geographical trend in methane consumption and production pathways in alpine ecosystems over the Qinghai–Tibetan Plateau

On the Qinghai–Tibetan Plateau, isotopic signatures in soil–atmosphere CH₄ fluxes were investigated in nine grasslands and three wetlands. In the grasslands, the fractionation factor for soil CH₄ uptake, α_soil, was much smaller than the usually reported value of 0.9975–1.0095. Stepwise multiple variation analysis indicates that α_soil is higher for higher soil water contents but is lower for higher C/N ratios of soil surface biomass. In the three wetlands, the soil-emitted δ¹³C–CH₄ was similar (?55.3?±?5.5?‰ and ?53.0?±?5.5?‰) in two bogs separated by >1000?km but was lower (?63.4?±?6.3?‰) in a marsh. Environmental factors related to intrasite variations in soil-emitted δ¹³C–CH₄ include the soil C/N ratio, oxidation–reduction potential, soil C concentration and soil water contents. Geographical isotopic surveys revealed environmental constraints on the CH₄ consumption pathways in grasslands and the biome type-specific consistency in CH₄ production pathways in wetlands.     

Spring response to precipitation events using δ18O and δ2H in the Tanour catchment,NW Jordan

The Tanour spring is one of the several karst springs located in the northern part of Jordan. Water samples from the Tanour spring and precipitation were collected in the area of Ajloun in NW Jordan for the analysis of stable oxygen and hydrogen isotopes to evaluate the spring response to precipitation events. Rainwater and snow samples were collected from different elevations during winters of 2013–2014 and 2014–2015. In addition, spring samples were collected between December 2014 and March 2015. δ¹⁸O values in rainwater vary from ?3.26 to ?17.34?‰ (average: ?7.84?±?3.23?‰), while δ²H values range between ?4.4 and ?110.4?‰ (average: ?35.7?±?25.0?‰). Deuterium excess ranges from 17.8 to 34.1?‰ (average: 27.1?±?4.0?‰). The Local Meteoric Water Line for the study area was calculated to be δ²H?=?7.66*δ¹⁸O?+?24.43 (R²?=?0.98). Pre-event spring discharge showed variation in δ¹⁸O (range ?6.29 to ?7.17?‰; average ?6.58?±?0.19?‰) and δ²H values (range ?28.8 to ?32.7?‰; average: ?30.5?±?1.0?‰). In contrast, δ¹⁸O and δ²H rapidly changed to more negative values during rainfall and snowmelt events and persisted for several days before returning to background values. Spring water temperature, spring discharge, and turbidity followed the trend in isotopic composition during and after the precipitation events. The rapid change in the isotopic composition, spring discharge, water temperature, and turbidity in response to recharge events is related to fast water travel times and low storage capacity in the conduit system of the karst aquifer. Based on the changes in the isotopic composition of spring water after the precipitation events, the water travel time in the aquifer is in the order of 5–11 days.     

Elastische Elektronenstreuung an14N,15N,16O und18O bei kleiner Impulsübertragung

Elastic electron scattering cross sections of¹⁴N and¹⁶O have been measured relative to the proton and of¹⁵N and¹⁸O relative to the lighter isotope (¹⁴N,¹⁶O resp.) using gas targets. The momentum transfer ranged from 0.22 to 0.48 fm^?1. The data were analyzed by phase shift calculations assuming harmonic oscillator shell model charge distributions. The following rms charge radii have been deduced: R_m(¹⁴N)=2.540±0.020 fm R_m(¹⁵N)=2.580±0.026 fm R_m(¹⁶O)=2.718±0.021 fm R_m(¹⁸O)=2.789±0.027 fm. The errors include statistical and systematic uncertainties and an estimate of effects due to the choice of the model. The radius differences of the isotopes are smaller than the values predicted by anA ^1/3 relation     

Time resolved simultaneous detection of 14NO and 15NO via mid-infrared cavity leak-out spectroscopy

We present a ring-down absorption spectrometer based on a continuous-wave CO laser in the mid-infrared spectral region near λ?=?5 μm. Using a linear ring-down cavity (length: 0.5 m) with high reflective mirrors (R?=?99.988 %), we observed a noise-equivalent absorption coefficient of 3?×?10^?10 cm^?1Hz^?1/2. This corresponds to a noise-equivalent concentration of 800 parts per trillion (ppt) for ¹⁴NO and 40 ppt for ¹⁵NO in 1 s averaging time. We achieve a time resolution of 1 s which allows time resolved simultaneous detection of the two N isotopes. The δ¹⁵N value was obtained with a precision of ±1.2‰ in a sample with a NO fraction of 11 ppm. The simultaneous detection enables the use of ¹⁵NO as a tracer molecule for endogenous biomedical processes.     

13C and 15N Abundances in the Sediment Core (VER 92/1-St-10-GC2) from Northern Lake Baikal

Abstract

Carbon and nitrogen stable isotope compositions of organic matter, TOC/TN ratio, and manganese concentration in a sediment core that was collected in northern part of Lake Baikal (VER92ST10-GC2, water depth at 922 m, about 3 m long) were investigated to elucidate the origin of the sedimentary organic matter and its associated environmental factors.

The sediment core was composed of mainly two parts: turbidite sections and other sections. Constant δ¹³C and δ¹⁵N values of the turbidite sections were observed (- 26.8 ±0.2 ‰ for δ¹³C and 3.2 ± 0.1 ‰ for δ¹⁵N) throughout the core. The higher δ¹³C in turbidite sections (about - 27 ‰) than that of the other sections (- 31 to - 29 ‰) was clearly observed, and δ¹⁵N was different between turbidite sections (about 3‰) and other sections (3 to 5 ‰). δ¹³C of other sections was close to that of pelagic phytoplankton, indicating that sediment other than turbidite sections is composed of autochthonous components. The variation of stable isotopes in other sections may be possibly caused by the changes in either phytoplankton growth rate or contribution ratios of terrestrial to aquatic plants for δ¹³C. Either denitrification or fluctuation of δ¹⁵N in pelagic phytoplankton can be the cause of variable δ¹⁵N in other sections.     

Use of stable carbon isotope ratios to determine the source of cypermethrin in so-called natural plant extract formulations used for organic farming

Some natural plant extract formulations (NPEFs, also referred to as essential oils) used in organic farming have been shown to contain synthetic pesticides. We obtained samples of four NPEFs (Muso, Hekiro, Kensogen-Ten, and Nurse Green) that were contaminated with the synthetic pyrethroid cypermethrin, and we used gas chromatography coupled with combustion, cryofocusing, and isotope ratio mass spectrometry to determine the stable carbon isotope ratios (δ¹³C) for the cypermethrin in the four NPEF samples, as well as in ten cypermethrin reagents and two commercial pesticide formulations (Agrothrin emulsion and Agrothrin water-dispersible powder). Our goal was to identify the source of the cypermethrin in the NPEFs. Cryofocusing markedly sharpened the cypermethrin peak and thus improved the accuracy and precision of the determined δ¹³C values. The δ¹³C values (±?SD) of the 16 cypermethrin samples ranged from ?28.3?±?0.2 to ?24.5?±?0.2?‰. Surprisingly, the four NPEFs showed similar δ¹³C values (?26.8 to ?27.3?‰), suggesting that the cypermethrin in all the samples came from the same source (either the same chemical reaction or the same primary material). This possibility was supported by previously published results. In addition, the δ¹³C values of the two commercial pesticides were similar to the values for the NPEFs, suggesting that the commercial pesticides had been diluted and sold as NPEFs.     

Studies of the protein and the energy metabolism in man during a wintering in Antarctica

During the 29th Soviet Antarctic Expedition in Novolazarevskaya from March 1984 to March 1985, the protein and energy metabolisms were studied in six expeditioners from the German Democratic Republic. The investigations were carried out at the beginning of the expedition (May), during the polar night (July) and during the polar day (December). The effect of a special stress situation (sledge trek in April 1984) was investigated in one subject. The stable nitrogen isotope ¹⁵N was used to study the protein metabolism. The assessment of the energy metabolism was based on the oxygen consumption, which was determined by means of a spirograph. In addition, the vital capacity, the breath minute volume, the blood pressure, etc. were measured. The following results were obtained: During the polar night, the utilisation of the dietary proteins and the whole body protein synthesis calculated by means of the ¹⁵N excretion of the total nitrogen in urine were greater (73.6±0.9 % and 3.48±0.17 g protein d^?1 kg^?1, n=3) than the respective values during the polar day (69.7±1.2, p<0.05, n=3 and 3.05±0.07, p<0.05, n=3) and at the beginning of the expedition (69.6±1.4, p<0.02, n=5 and 2.81±0.09, p<0.01, n=5). The lowest values (58.0 % and 2.43 g protein d^?1 kg^?1) were obtained in the subject after the trek. The resting metabolic rate (in kJ d^?1 m^?2) was decreased during the polar night (45.6±5.0, n=4) in comparison with the polar day (61.5±11.3, n=3) and the beginning of the expedition (52.3±9.6, n=4) with p<0.01 in both cases.     

N2O emissions and source processes in snow-covered soils in the Swiss Alps

Nitrous oxide (N₂O) emissions from snow-covered soils represent a significant fraction of the annual flux from alpine, subalpine or cold-temperate regions. In winter 2010–2011, we investigated the temporal variability of N₂O emissions and source processes from a subalpine valley in the Swiss Alps. The study included regular measurements of N₂O snow profiles at a fixed location and an intensive sampling campaign along a transversal cut through the valley with grassland at the bottom and coniferous forest at the slopes. During the intensive campaign, recently developed laser spectroscopy was employed for high-precision N₂O isotopomer analysis. Maximum N₂O fluxes (0.77±0.64 nmol m^?2 h^?1) were found for periods with elevated air temperature and, in contrast to our expectations, were higher from forest than from grassland in mid-February. At maximum snow height (63 cm) the main N₂O source processes were heterotrophic denitrification and nitrifier denitrification. The reduction of N₂O by heterotrophic denitrifiers was much more pronounced for the grassland compared with the forest soil, as indicated by the ¹⁵N site preferences of 16.4±11.5 ‰ (grassland) and?1.6±2.1 ‰ (forest). This illustrates the potential of laser spectroscopic N₂O isotopomer analysis for the identification of source processes even at low emission rates in nutrient poor ecosystems.     

Degradation pathways of dissolved carbon in landfill leachate traced with compound-specific 13C analysis of DOC

The isotopic compositions of carbon compounds in landfill leachate provide insights into the biodegradation pathways that dominate the different stages of waste decomposition. In this study, the carbon geochemistry of different carbon pools, environmental stable isotopes and compound-specific isotope analysis (CSIA) of leachate dissolved organic carbon (DOC) fractions and gases show distinctions in leachate biogeochemistry and methane production between the young area of active waste emplacement and the old area of historical emplacement at the Trail Road Landfill (TRL).

The active area leachate has low DOC concentrations (<200 mg l^?1) dominated by fulvic acid (FA=160 mg l^?1), and produces CH₄ dominantly by CO₂ reduction (D? excess=20.6‰). Leachate generated in the area of older waste has high DOC (>4770 mg l^?1) dominated by FA (4482 mg l^?1) and simple fatty acids (acetic=1008 mg l^?1 and propionic=608 mg l^?1), and produces CH₄ by the acetate fermentation pathway (D? excess=9.8‰). CSIA shows an advanced degradation and a progressive accumulation of ¹³C of fatty acids in leachate from the older area. The enriched ¹³C value of FA (?20 and?26‰ for the older and active parts, respectively,) and of low molecular weight DOC (?8 and?27‰) as well as of the bulk DOC (?21 and?25‰) shows more advanced degradation in the older part of the landfill, which is consistent with the shift in the humic/FA ratios (0.05 and 0.18). The ¹³C enrichment of acetate (?12‰) above the ¹³C of DOC (?21‰) and of propionic acid (?19‰), in older leachate, suggests that this acetate has not evolved from the simple degradation of larger organic molecules, but by homoacetogenesis from the enriched dissolved inorganic carbon (DIC) pool (8‰) and H_2, which produce a more enriched ¹³C of acetate. In contrast, the ¹³C of the minor acetate in the active area (?17‰) indicates that CO₂-reducing bacteria must be the primary consumers of H₂, which has resulted in enriched ¹³C_DIC (10‰) and depleted ¹³C_CH4 (?58‰).     

Simultaneous measurements of indoor radon and thoron and inhalation dose assessment in Douala City,Cameroon

ABSTRACT

Radon, thoron and associated progeny measurements have been carried out in 71 dwellings of Douala city, Cameroon. The radon–thoron discriminative detectors (RADUET) were used to estimate the radon and thoron concentration, while thoron progeny monitors measured equilibrium equivalent thoron concentration (EETC). Radon, thoron and thoron progeny concentrations vary from 31?±?1 to 436?±?12 Bq?m^–3, 4?±?7 to 246?±?5 Bq?m^–3, and 1.5?±?0.9 to 13.1?±?9.4 Bq?m^–3. The mean value of the equilibrium factor for thoron is estimated at 0.11?±?0.16. The annual effective dose due to exposure to indoor radon and progeny ranges from 0.6 to 9?mSv?a^–1 with an average value of 2.6?±?0.1?mSv?a^–1. The effective dose due to the exposure to thoron and progeny vary from 0.3 to 2.9?mSv?a^–1 with an average value of 1.0?±?0.4?mSv?a^–1. The contribution of thoron and its progeny to the total inhalation dose ranges from 7 to 60?% with an average value of 26?%; thus their contributions should not be neglected in the inhalation dose assessment.