Effects of anticoagulants time storage on stable isotope values of crocodilians' blood tissues.

Rapid coagulation of reptile blood often hinders its use in studies in remote and difficult-to-access areas, necessitating chemical preservation. Therefore, understanding the potential effects of anticoagulants on the isotopic compositions of blood is essential to avoid issues in interpreting the results for ecological studies. In this study we aimed to verify whether the storage time of the blood tissue in anticoagulants can influence its isotopic compositions of the broad-snouted caiman (Caiman latirostris), an ectothermic top predator from eastern South America. Blood samples were obtained from ten adult females of C. latirostris from a commercial breeding facility in 2015. Samples were stored in vials containing ethylenediaminetetraacetic acid (EDTA) and sodium heparin (SH) and centrifuged after 2 and 8 h to separate red blood cells and plasma. No effect of time was found on the δ13C and δ15N of whole blood, plasma, and red blood cells in contact with the two types of anticoagulants, EDTA and SH. The findings have practical implications for researchers in this field, as they suggest that anticoagulants can be used effectively for at least eight hours under refrigeration.

Measurement Uncertainty and Risk of False Compliance Assessment Applied to Carbon Isotopic Analyses in Natural Gas Exploratory Evaluation.

The concept of uncertainty in an isotopic analysis is not uniform in the scientific community worldwide and can compromise the risk of false compliance assessment applied to carbon isotopic analyses in natural gas exploratory evaluation. In this work, we demonstrated a way to calculate one of the main sources of this uncertainty, which is underestimated in most studies focusing on gas analysis: the δ13C calculation itself is primarily based on the raw analytical data. The carbon isotopic composition of methane, ethane, propane, and CO2 was measured. After a detailed mathematical treatment, the corresponding expanded uncertainties for each analyte were calculated. Next, for the systematic isotopic characterization of the two gas standards, we calculated the standard uncertainty, intermediary precision, combined standard uncertainty, and finally, the expanded uncertainty for methane, ethane, propane, and CO2. We have found an expanded uncertainty value of 1.8‰ for all compounds, except for propane, where a value of 1.6‰ was obtained. The expanded uncertainty values calculated with the approach shown in this study reveal that the error arising from the application of delta calculation algorithms cannot be neglected, and the obtained values are higher than 0.5‰, usually considered as the accepted uncertainty associated with the GC-IRMS analyses. Finally, based on the use of uncertainty information to evaluate the risk of false compliance, the lower and upper acceptance limits for the carbon isotopic analysis of methane in natural gas are calculated, considering the exploratory limits between -55‰ and -50‰: (i) for the underestimated current uncertainty of 0.5‰, the lower and upper acceptance limits, respectively, are -54.6‰ and -50.4‰; and (ii) for the proposed realistic uncertainty of 1.8‰, the lower and upper acceptance limits would be more restrictive; i.e., -53.5‰ and -51.5‰, respectively.

Sources and processes affecting the abundances of atmospheric NHx using δ15N over northwestern Indo-Gangetic plain.

Ammonia (NH3) is the major constituent among all the reactive nitrogen species present in the atmosphere, and the most essential species for secondary inorganic aerosol formation. Recent satellite-based observations have identified the Indo-Gangetic Plain (IGP) as a major hotspot of global NH3 emission; however, the major sources and atmospheric processes affecting its abundance are poorly understood. The present study aims to understand the wintertime sources of NH3 over a semi-urban site (Patiala, 30.3°N, 76.4°E, 249 m amsl) located in the IGP using species specific δ15N in PM2.5. A distinct diurnal variation in the stable isotopic signature of total nitrogen (δ15N-TN) and ammonium (δ15N-NH4+) were observed; although, average day and night time concentrations of TN and NH4+ were similar. Mixing model results using δ15N-NH3 reveal the dominance of non-agricultural emissions (NH3 slip: 47 ± 24%) over agricultural emissions (24 ± 11%), combustion sources (19 ± 14 %), and biomass burning (10 ± 8%) for atmospheric NH3. Diurnal variability in source contributions to NH3 was insignificant. Further, significantly negative correlations of δ15N-NH4+ with ambient relative humidity (RH) and daytime NO3--N concentration were observed, and attributed to the possibility of NH4NO3 volatilization during day-time owing to lower RH and higher temperature, resulting in isotopic enrichment of the remaining NH4+ in aerosol phase. This study, a first of its type from India, highlights the importance of non-agricultural NH3 emissions over the agriculture dominated IGP region, and the role of local meteorology on the isotopic fractionation of δ15N in aerosol NH4+.

13CH4/12CH4 sensing using Raman spectroscopy.

The paper presents a technique for measuring the concentration of 13CH4 in natural methane using Raman spectroscopy. The peak positions and the relative scattering cross-sections of the Q-branches for the most intense vibrational bands of 13CH4 are determined. Features of the 13CH4/12CH4 ratio measurement methods using Q-branches of the ν1 and ν3 bands were considered. It was shown that the 13CH4/12CH4 ratio can be determined by simulation of the ν3 bands of these molecules without the use of experimental spectra. In our experiments the measurement error of δ13C value was 10 ‰ using the 100-s exposure spectrum at a gas pressure close to 1 atm recorded on the developed Raman spectrometer. In addition, the Raman spectra of alkanes (up to n-hexane) in the range of 2850-3050 cm-1 at a resolution of 0.4 cm-1 are presented, and their integrated intensities in the ranges of the characteristic bands of 13CH4 and 12CH4 are provided. The data obtained make it possible to expand the capabilities of Raman gas analyzers in the mud gas logging industry.

Mitigated N2O emissions from submerged-plant-covered aquatic ecosystems on the Changjiang River Delta.

Submerged plants affect nitrogen cycling in aquatic ecosystems. However, whether and how submerged plants change nitrous oxide (N2O) production mechanism and emissions flux remains controversial. Current research primarily focuses on the feedback from N2O release to variation of substrate level and microbial communities. It is deficient in connecting the relative contribution of individual N2O production processes (i.e., the N2O partition). Here, we attempted to offer a comprehensive understanding of the N2O mitigation mechanism in aquatic ecosystems on the Changjiang River Delta according to stable isotopic techniques, metagenome-assembly genome analysis, and statistical analysis. We found that the submerged plant reduced 45 % of N2O emissions by slowing down the dissolved inorganic nitrogen conversion velocity to N2O in sediment (Vf-[DIN]sed). It was attributed to changing the N2O partition and suppressing the potential capacity of net N2O production (i.e., nor/nosZ). The dominated production processes showed a shift with increasing excess N2O. Meanwhile, distinct shift thresholds of planted and unplanted habitats reflected different mechanisms of stimulated N2O production. The hotspot zone of N2O production corresponded to high nor/nosZ and unsaturated oxygen (O2) in unplanted habitat. In contrast, planted habitat hotspot has lower nor/nosZ and supersaturated O2. O2 from photosynthesis critically impacted the activities of N2O producers and consumers. In summary, the presence of submerged plants is beneficial to mitigate N2O emissions from aquatic ecosystems.

Rapid quantification of biological nitrogen fixation using optical spectroscopy.

Biological nitrogen fixation (BNF) provides a globally important input of nitrogen (N); its quantification is critical but technically challenging. Leaf reflectance spectroscopy offers a more rapid approach than traditional techniques to measure plant N concentration ([N]) and isotopes (δ15N). Here we present a novel method for rapidly and inexpensively quantifying BNF using optical spectroscopy. We measured plant [N], δ15N, and the amount of N derived from atmospheric fixation (Ndfa) following the standard traditional methodology using isotope ratio mass spectrometry (IRMS) from tissues grown under controlled conditions and taken from field experiments. Using the same tissues, we predicted the same three parameters using optical spectroscopy. By comparing the optical spectroscopy-derived results with traditional measurements (i.e. IRMS), the amount of Ndfa predicted by optical spectroscopy was highly comparable to IRMS-based quantification, with R2 being 0.90 (slope=0.90) and 0.94 (slope=1.02) (root mean square error for predicting legume δ15N was 0.38 and 0.43) for legumes grown in glasshouse and field, respectively. This novel application of optical spectroscopy facilitates BNF studies because it is rapid, scalable, low cost, and complementary to existing technologies. Moreover, the proposed method successfully captures the dynamic response of BNF to climate changes such as warming and drought.

Tracing sources of atmospheric methane using clumped isotopes.

We apply a recently developed measurement technique for methane (CH4) isotopologues* (isotopic variants of CH4-13CH4, 12CH3D, 13CH3D, and 12CH2D2) to identify contributions to the atmospheric burden from fossil fuel and microbial sources. The aim of this study is to constrain factors that ultimately control the concentration of this potent greenhouse gas on global, regional, and local levels. While predictions of atmospheric methane isotopologues have been modeled, we present direct measurements that point to a different atmospheric methane composition and to a microbial flux with less clumping (greater deficits relative to stochastic) in both 13CH3D and 12CH2D2 than had been previously assigned. These differences make atmospheric isotopologue data sufficiently sensitive to variations in microbial to fossil fuel fluxes to distinguish between emissions scenarios such as those generated by different versions of EDGAR (the Emissions Database for Global Atmospheric Research), even when existing constraints on the atmospheric CH4 concentration profile as well as traditional isotopes are kept constant.

Oral Cavity Cancer Tissues Differ in Isotopic Composition Depending on Location and Staging.

The aim of this paper was to characterise the isotopic composition of oral squamous cell carcinoma (OSCC) specimens of different areas of the oral cavity. Secondly, we assessed whether there was a correlation between clinical stages of OSCC and isotopic abundance. The IRMS procedure was performed on 124 samples derived from 31 patients with OSCC of 15 N and 13 C to assess the isotopic composition. From each individual, four samples from the tumour, two from the margins, and two samples of healthy oral mucous membranes were derived. The two samples from the tumour and two samples from the margin were additionally subjected to histopathological assessment. Then, statistical analysis was conducted. Tumour infiltration tissues of the lower lip were characterised by higher mean δ13C values compared to samples derived from cancers of the other oral cavity regions (-23.82 ± 1.21 vs. -22.67 ± 1.35); (p = 0.04). The mean percentage of nitrogen content in tumour tissues was statistically higher in patients with the most advanced cancers (11.89 ± 0.03%) versus the group of patients with II and III stage cancers (11.12 ± 0.02%); (p = 0.04). In patients at stage IV, the mean δ13C value in the cancer samples equalled -22.69 ± 1.42 and was lower than that in patients at less severe clinical stages (p = 0.04). Lower lip cancer tissues differed in the isotopic abundance of carbon in comparison with tissues derived from the group of combined samples from other locations. Values of δ13C observed in specimens derived from lower lip cancers were similar to those observed in healthy oral mucous membranes. Cancer tissues obtained from patients in the last stage of OSCC had a different isotopic composition in comparison with those obtained from earlier stages. To confirm these observations, further research on larger groups of patients is needed.

Impact of forest fire on the mercury stable isotope composition in litter and soil in the Amazon.

Mercury (Hg) emissions from forest fires, especially tropical forests such as the Amazonian forest, were shown to contribute significantly to the atmospheric mercury budget, but new methods are still necessary to improve the traceability and to reduce the great uncertainties related to this emission source. Recent studies have shown that the combustion process can result in Hg stable isotope fractionation that allows tracking coal combustion Hg emissions, as influenced by different factors such as combustion temperature. The main goal of the present study was, therefore, to investigate for the first time the potential of Hg stable isotopes to trace forest fire Hg emissions and pathways. More specifically, small-scale and a large scale prescribed forest fire experiments were conducted in the Brazilian Amazonian forest to study the impact of fire severity on Hg isotopic composition of litter, soil, and ash samples and associated Hg isotope fractionation pathways. In the small-scale experiment, no difference was found in the mercury isotopic composition of the samples collected before and after burning. In contrast, the larger-scale experiment resulted in significant mass dependent fractionation (MDF δ202Hg) in soils and ash suggesting that higher combustion temperature influence Hg isotopic fractionation with the emission of lighter Hg isotopes to the atmosphere and enrichment with heavier Hg in ashes. As for coal combustion, mass independent fractionation was not observed. To our knowledge, these results are the first to highlight the potential of forest fires to cause Hg isotopic fractionation, depending on the fire severity. The results also allowed to establish an isotopic fingerprint for tropical forest fire Hg emissions that corresponds to a mixture of litter and soil Hg isotopic composition (resulting atmospheric δ202Hg, Δ200Hg and Δ199Hg were -1.79 ± 0.24‰, -0.05 ± 0.04‰ and -0.45 ± 0.12‰, respectively).

Near-infrared reflectance spectroscopy accurately predicted isotope and elemental compositions for origin traceability of coffee.

Stable isotope ratios and trace elements are well-established tools that act as signatures of the product's environmental conditions and agricultural processes; but they involve time, money, and environmentally destructive chemicals. In this study, we tested for the first time the potential of near-infrared reflectance spectroscopy (NIR) to estimate/predict isotope and elemental compositions for the origin verification of coffee. Green coffee samples from two continents, 4 countries, and 10 regions were analysed for five isotope ratios (δ13C, δ15N, δ18O, δ2H, and δ34S) and 41 trace elements. NIR (1100-2400 nm) calibrations were developed using pre-processing with extended multiplicative scatter correction (EMSC) and mean centering and partial-least squares regression (PLS-R). Five elements (Mn, Mo, Rb, B, La) and three isotope ratios (δ13C, δ18O, δ2H) were moderately to well predicted by NIR (R2: 0.69 to 0.93). NIR indirectly measured these parameters by association with organic compounds in coffee. These parameters were related to altitude, temperature and rainfall differences across countries and regions and were previously found to be origin discriminators for coffee.

Leaf cell wall properties and stomatal density influence oxygen isotope enrichment of leaf water.

Measurements of oxygen isotope enrichment of leaf water above source water (Δ18 OLW ) can improve our understanding of the interaction between leaf anatomy and physiology on leaf water transport. Models have been developed to predict Δ18 OLW such as the string-of-lakes model, which describes the mixing of leaf water pools, and the Péclet effect model, which incorporates transpiration rate and the mixing length between unenriched xylem and enriched mesophyll water in the mesophyll (Lm ) or veins (Lv ). Here we compare measurements and models of Δ18 OLW on two cell wall composition mutants grown under two light intensities and relative humidities to evaluate cell wall properties on leaf water transport. In maize (Zea mays), the compromised ultrastructure of the suberin lamellae in the bundle sheath of the ALIPHATIC SUBERIN FERULOYL TRANSFERASE mutant (Zmasft) reduced barriers to apoplastic water movement, resulting in higher E and, potentially, Lv and, consequently, lower Δ18 OLW . The difference in Δ18 OLW in cellulose synthase-like F6 (CslF6) mutants and wild-type of rice (Oryza sativa) grown under two light intensities co-varied with stomatal density. These results show that cell wall composition and stomatal density influence Δ18 OLW and that stable isotopes can facilitate the development of a physiologically and anatomically explicit water transport model.

Hydrogeochemical evaluation, groundwater contamination and associated health risk in southern Tangail, Bangladesh.

Water pollution is a worldwide concern that has growing severe in developed and developing nations. Increasing groundwater pollution threatening both the physical and environmental health of billions of people as well as economic progress. Consequently, hydrogeochemistry, water quality and potential health risk assessment is crucial for water resource management. The study area comprises Jamuna Floodplain (Holocene deposit) area in the west and the Madhupur tract (Pleistocene deposit) area in the eastern part. Total 39 groundwater samples were collected from the study area and were analyzed for physicochemical parameters, hydrogeochemical, trace metals, and isotopic composition. The water types are mainly Ca-HCO3- to Na-HCO3- types. The isotopic compositions (δ18O‰ and δ2H‰) analysis traces the recent recharge in Floodplain area from rainwater and no recent recharge in Madhupur tract. The concentration of NO3-, As, Cr, Ni, Pb, Fe, and Mn in shallow and intermediate aquifer at the Floodplain area exceed the WHO-2011 permissible limit and is lower at deep Holocene and Madhupur tract aquifer. The integrated weighted water quality index (IWQI) exposed groundwater from shallow and intermediate aquifer are unsuitable for drinking and deep Holocene aquifer and Madhupur tract are suitable for drinking purposes. PCA analysis confirmed that anthropogenic activity is dominant in shallow and intermediate aquifers. The non-carcinogenic and carcinogenic risk for adults and children is due to oral and dermal exposure. The non-carcinogenic risk evaluation revealed that the mean hazard index (HI) values range from 0.009742 to 16.37 for adults and 0.0124-20.83 for children, respectively, and most groundwater samples from shallow and intermediate aquifers exceed the permissible limit (HI>1). The carcinogenic risk ranges from 2.71 × 10-6-0.014 for adults and 3.44 × 10-6-0.017 for children via oral consumption and 7.09 × 10-11-1.18 × 10-6 for adults and 1.25 × 10-10-2.09 × 10-6 for children via dermal exposure. Spatial distribution shows the presence of trace metal and associated health risk is high in shallow and intermediate aquifer (Holocene) than in the deep (Holocene) Madhupur tract (Pleistocene). The study implies that effective water management will ensure safe drinking water for the future generation of people.

Seasonal heavy metal speciation in sediment and source tracking via Cu isotopic composition in Huangpu River, Shanghai, China.

The present study systematically analyzed and evaluated the variations in chemical speciation, pollution assessment, and source identification of heavy metals in sediments of Huangpu River. The methods employed included heavy metal concentration, chemical speciation and Cu isotopic compositions analysis. Results showed that the chemical speciation of sediment-bound heavy metals, characterized by significant seasonal variation, shifted from non-residual fractions dominating in spring and summer to residual fractions dominating in autumn and winter. Precipitation was identified as an important factor influencing the chemical speciation of sediment-bound heavy metals. Furthermore, ratio of the secondary phase to the primary phase, RSP (=Cnon-residual/Cresidual) values in Huangpu River sediments were higher than 1 in spring and summer, indicating that sediment-bound heavy metals in Huangpu River were mainly composed of non-residual fractions and could potentially be released into the river water. Principal component analysis (PCA) revealed that navigation, traffic, agricultural, and industrial activities could be the potential sources of heavy metal pollution. Notably, the δ65Cu values in Huangpu River sediments were observed to be isotopically lighter (from -0.37 to +0.18 ‰), suggesting that navigation might be the primary pollution source. These results will not only provide guidance in reducing heavy metal concentrations, but also serve as a crucial basis for policy making regarding heavy metal control.

Quantitative discrimination of algae multi-impacts on N2O emissions in eutrophic lakes: Implications for N2O budgets and mitigation.

It is generally accepted that eutrophic lakes significantly contribute to nitrous oxide (N2O) emissions. However, how these emissions are affected by the formation, disappearance, and mechanisms of algal blooms in these lakes has not been systematically investigated. This study examined and determined the relative contribution of spatiotemporal N2O production pathways in hypereutrophic Lake Taihu. Synchronously, the multi-impacts of algae on N2O production and release potential were measured in the field and in microcosms using isotope ratios of oxygen (δ18O) and bulk nitrogen (δ15N) to N2O and to intramolecular 15N site preference (SP). Results showed that N2O production in Lake Taihu was derived from microbial effects (nitrification and incomplete denitrification) and water air exchanges. N2O production was also affected by the N2O reduction process. The mean dissolved N2O concentrations in the water column during the pre-outbreak, outbreak, and decay stages of algae accumulation were almost the same (0.05 µmol·L-1), which was 2-10 times higher than in lake areas algae was not accumulating. However, except for the central lake area, all surveyed areas (with and without accumulated algae) displayed strong release potential and acted as the emission source because of dissolved N2O supersaturation in the water column. The mean N2O release fluxes during the pre-outbreak, outbreak, and decay stages of algae accumulation areas were 17.95, 26.36, and 79.32 µmol·m-2·d-1, respectively, which were 2.0-7.5 times higher than the values in the non-algae accumulation areas. In addition, the decay and decomposition of algae released large amounts of nutrients and changed the physiochemical properties of the water column. Additionally, the increased algae biomass promoted N2O release and improved the proportion of N2O produced via denitrification process to being 9.8-20.4% microbial-derived N2O. This proportion became higher when the N2O consumption during denitrification was considered as evidenced by isotopic data. However, when the algae biomass was excessive in hypereutrophic state, the algae decomposition also consumed a large amount of oxygen, thus limiting the N2O production due to complete denitrification as well as due to the limited substrate supply of nitrate by nitrification in hypoxic or anoxic conditions. Further, the excessive algae accumulation on the water surface reduced N2O release fluxes via hindering the migration of the dissolved N2O into the atmosphere. These findings provide a new perspective and understanding for accurately evaluating N2O release fluxes driven by algae processes in eutrophic lakes.

Isotopic composition of serum zinc and copper in healthy children and children with autism spectrum disorder in North America.

To better understand zinc and copper regulation and their involvement in various biochemical pathways as it relates to autism spectrum disorder (ASD), isotopic composition of serum zinc and copper were evaluated in both healthy children and children with ASD in North America. No significant difference in isotopic composition of serum zinc or copper with respect to healthy controls and ASD children were identified. However, the isotopic composition of serum copper in boys was found to be enriched in 65Cu in comparison to previously published healthy adult copper isotopic composition. Furthermore, in both boys and girls, the average isotopic composition of serum zinc is heavier than previously published healthy adult isotopic zinc composition. There was also a negative association between total zinc concentrations in serum and the zinc isotopic composition of serum in boys. Finally, children with heavier isotopic composition of copper also showed a high degree of variability in their zinc isotopic composition. While numerous studies have measured the isotopic composition of serum zinc and copper in adults, this is one of the first studies which measured the isotopic composition of serum copper and zinc in children, specifically those diagnosed with ASD. The results of this study showed that age and gender specific normal ranges of isotopic composition must be established to effectively use isotopic composition analysis in studying various diseases including ASD.

Decline of anthropogenic lead in South Atlantic Ocean surface waters from 1990 to 2011: New constraints from concentration and isotope data.

Anthropogenic emissions have severely perturbed the marine biogeochemical cycle of lead (Pb). Here, we present new Pb concentration and isotope data for surface seawater from GEOTRACES section GA02, sampled in the western South Atlantic in 2011. The South Atlantic is divided into three hydrographic zones: equatorial (0-20°S), subtropical (20-40°S), and subantarctic (40-60°S). The equatorial zone is dominated by previously deposited Pb transported by surface currents. The subtropical zone largely reflects anthropogenic Pb emissions from South America, whilst the subantarctic zone presents a mixture of South American anthropogenic Pb and natural Pb from Patagonian dust. The mean Pb concentration of 16.7 ± 3.8 pmol/kg is 34 % lower than in the 1990s, mostly driven by changes in the subtropical zone, with the fraction of natural Pb increasing from 24 % to 36 % between 1996 and 2011. Although anthropogenic Pb remains predominant, these findings demonstrate the effectiveness of policies that banned leaded gasoline.

Land-use changes in Amazon and Atlantic rainforests modify organic matter and black carbon compositions transported from land to the coastal ocean.

This study assessed black carbon (BC) dynamics, concentrations, and the organic matter (OM) isotopic carbon composition in northeastern South America drainage basin coastal sediments. Paraíba do Sul (PSR; Atlantic Rainforest, Brazil) coastal sediments displayed more 13C-enriched values (-22.6 ± 1.3 ‰ [n = 13]) than Amazon and Sinnamary (Amazon Rainforest in French Guiana and Brazil) sediments (-25.0 ± 3.1 ‰ [n = 14] and - 26.1 ± 1.0 ‰ [n = 6], respectively), indicating that local land-use basin changes have altered the OM composition, i.e., from natural C3 plant to C4 plants contributions. BC contents normalized to total organic carbon (TOC) content were 0.32 ± 0.24 (n = 8), 0.73 ± 0.67 (n = 6), and 0.95 ± 0.74 (n = 13) mg g-1 TOC for Amazon, Sinnamary and PSR samples, respectively, with BC sources appearing to differ according to different drainage basin vegetation covers. With increasing distance from the river mouths, BC contents exhibited different trends between the coastal zones, with values increasing for the PSR and decreasing values for the Amazon samples. BC distribution in Sinnamary coastal sediments did not display specific patterns. Regarding the Amazon coastal zone, BC contents decreased while the B6CA:B5CA ratios did not show a pattern, which could indicate that BC in the area originates from river transport (aged BC) and that the hydrophobic component of dissolved BC is removed. The BC content mostly increased in the PSR coastal zone, while the B6CA:B5CA ratios were not altered for the entire gradient, indicating the BC stability and possible atmospheric deposition of soot. Our findings indicate that different sources, transformation processes, and hydrological conditions affect BC contents within coastal zones. Continuous land cover changes in both the Amazon and Atlantic Rainforests may result in large-scale marine carbon cycling impacts.

Source apportionment and transfer characteristics of Pb in a soil-rice-human system, Jiulong River Basin, southeast China.

The source apportionment and transfer of Pb in a paddy soil-rice-human system within the Jiulong River Basin in southeast China was investigated by analyzing (1) the chemical fractionation of Pb in paddy soils using a modified BCR four-step sequential extraction procedure, and (2) the bioaccessibility of Pb in both paddy soils and rice grains using a Simple Bioaccessibility Extraction Test method. In addition, a qualitative Pb isotopic model was used in combination with IsoSource software to quantify the contribution of potential Pb sources. The results show the enrichment of Pb in agro-ecosystems in the Jiulong River Basin. Contaminant Pb in paddy soils was mainly present in the reducible (42.9%) and the residual fractions (27.1%). The average bioaccessibility of Pb in rice grains was significantly higher than that in paddy soil, with values of 77.85% and 37.44%, respectively. Lead in paddy soils was primarily derived from agricultural (35.3%), natural (25.5%), industrial (24.5%) and coal combustion sources (14.7%), while Pb in rice grains was primarily derived from coal combustion (54.1%), agricultural (35.1%), industrial (6.0%) and natural sources (4.8%). The bioaccessible Pb was mainly derived from anthropogenic sources [agricultural (42.3% for soil and 25.3% for grain) and coal combustion sources (25.3% for soil and 59.3% for grain)]. Lead isotopic ratios are an effective tracer of Pb transfer from potential sources to rice plants and within the rice plants. Rice plants absorb Pb from the soil and the atmosphere through the roots and leaves, respectively. Most of the Pb was accumulated in roots. The integrated use of chemical fractionation, bioaccessibility and Pb isotopic data provides an effective method to study the source apportionment and transfer characteristics of Pb in paddy soil-rice-human systems.

Application of amino acids nitrogen stable isotopic analysis in bioaccumulation studies of pollutants: A review.

Accurately quantifying trophic positions (TP) to describe food web structure is an important element in studying pollutant bioaccumulation. In recent years, compound-specific nitrogen isotopic analysis of amino acids (AAs-N-CSIA) has been progressively applied as a potentially reliable tool for quantifying TP, facilitating a better understanding of pollutant food web transfer. Therefore, this review provides an overview of the analytical procedures, applications, and limitations of AAs-N-CSIA in pollutant (halogenated organic pollutants (HOPs) and heavy metals) bioaccumulation studies. We first summarize studies on the analytical techniques of AAs-N-CSIA, including derivatization, instrumental analysis, and data processing methods. The N-pivaloyl-i-propyl-amino acid ester method is a more suitable AAs derivatization method for quantifying TP. The AAs-N-CSIA application in pollutant bioaccumulation studies (e.g., Hg, MeHg, and HOPs) is discussed, and its application in conjunction with various techniques (e.g., spatial analysis, food source analysis, and compound tracking techniques, etc.) to research the influence of pollutant levels on organisms is summarized. Finally, the limitations of AAs-N-CSIA in pollutant bioaccumulation studies are discussed, including the use of single empirical values of ßglu/phe and TDFglu/phe that result in large errors in TP quantification. The weighted ßglu/phe and the multi-TDFglu/phe models are still challenging to solve for accurate TP quantification of omnivores; however, factors affecting the variation of ßglu/phe and TDFglu/phe are unclear, especially the effect of pollutant bioaccumulation in organisms on internal AA metabolic processes.

Application of cavity ring-down spectroscopy and a novel near surface Gaussian plume estimation approach to inverse model landfill methane emissions.

Fugitive methane emissions from municipal solid waste landfills impact global climate change and reliable emissions quantification is of increasing importance. Ground-based cavity ring-down spectrometer (CRDS) measurements were used to determine methane concentrations and isotopic compositions of carbon in CH4. Then, CH4 oxidation through various cover materials was assessed using the Keeling plot method. A novel inverse modeling approach using Gaussian dispersion analysis, termed near-surface Gaussian plume estimation (NSGPE), was developed to predict whole-site landfill methane emissions. The concentration data obtained around the landfill perimeter with the mobile ground-based CRDS were used. Methane concentration data were integrated to parameterize discretized point source emissions from a Gaussian dispersion model. Post-processing algorithms were applied to refine modeling predictions to account for the influence of topographical and meteorological conditions on methane transport. Results indicate spatially resolved and consistent emissions estimates among multiple optimization simulations, with refinements increasing the resolution and spatial trends of emissions. Post-processing algorithms resolve consistent overestimation of emissions commonly observed using conventional Gaussian dispersion models.•Ground-based CRDS used to obtain methane concentration and oxidation data.•Novel inverse Gaussian dispersion modeling approach developed to predict methane emissions from landfills accounting for site-specific topography and meteorology.•Post-processing algorithms refine emissions estimates.