Solvent-extractable Lipids Research Articles

Particulate Organic Matter Mobilization and Transformation Along a Himalayan River Revealed by ESI‐FT‐ICR‐MS

AbstractTracing pathways and transformations of particulate organic carbon from landscape sources to oceanic sinks is commonly done using the isotopic composition or biomarker content of particulate organic matter (POM). However, similarity of source characteristics and complex mixing in rivers often preclude a robust deconvolution of individual contributions. Moreover, these approaches are limited in detecting organic matter transformations. This impedes understanding of carbon cycling. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT‐ICR‐MS) can simultaneously identify many molecular formulas from mixtures of organic matter, and provide direct information on its compositional variability. Here, we investigate how FT‐ICR‐MS can give insight into POM dynamics on a landscape scale, focusing on the trans‐Himalayan Kali Gandaki River, Nepal. Using molecular information, we identify source tracers in the solvent extractable lipid fraction of riverine POM, finding up to 102 indicative molecular formulas for individual sources. Further, we assess molecular transformations of the lipid fraction of POM during its transfer from litter into topsoil, and onwards into the river. A large number of shared mass formulas and a well‐preserved isoprenoidal patterns suggest efficient incorporation of litter into topsoil. In contrast, we observe a selective loss of mass formulas and a preferential export of formulas with low double bond equivalents and a low nominal oxidation state of carbon after organic matter entrainment in the river. Our results demonstrate the potential of FT‐ICR‐MS for source‐to‐sink studies, allowing detailed organic matter source characterization and discrimination, and tracking of molecular transformations along organic matter pathways spanning different spatial and temporal scales.

Organic matter biomarker and 13C NMR characteristics of soil and sediment standard reference materials from China.

Soil and sediment organic matter (OM) in terrestrial environments represent two critical organic carbon pools on Earth and are likely subject to distinct degrees of oxidation and modification. However, few studies have identified critical molecular-level characteristics that differentiate soil and sediment OM from various climate zones. Using biomarkers and solid-state 13C nuclear magnetic resonance (NMR) spectroscopy analyses, we studied the OM characteristics of 11 soil and 7 sediment standard reference materials (SRMs) originating from various geographical locations in China. Results showed significantly higher concentrations of lignin phenols in sediment OM than in soil OM, which may result from protection by higher contents of CaO and less microbial degradation in sediments. Nevertheless, the relative abundances of solvent-extractable lipids (alkanes, alkanols, and alkanoic acids) and ester-bound cutin and suberin biomarkers did not differ significantly between soil and sediment SRMs. The concentrations of lignin biomarkers decreased with increasing weathering degree of the soil, while cutin biomarkers increased with mean annual temperature and precipitation. This phenomenon was not observed in sediment SRMs. This study reveals the distinct OM characteristics between Chinese soil and sediment SRMs and provides fundamental data for future studies to link OM characteristics and functions.

Chemical characterization of mountain forest soils: impact of long-term atmospheric deposition loadings (Czech-Polish-German border region).

The composition of lipids in soil offers clues to soil degradation processes due their persistency and selectivity in soil, and close relation to long-term processes in the ecosystem, thanks to their role in cell membranes of organisms. Organic solvent-extractable compounds were recovered from soils collected at two sites differing in the degree of forest damage. Gas chromatography/mass spectroscopy and Fourier transform infrared spectroscopy were applied in order to characterize solvent-extractable lipids. Raman spectroscopy was also applied as it provides distinct advantages for determining the structural order of carbonaceous materials. The organic matter measurement techniques were combined with an established simultaneous multi-element measurement technique. Variations in individual soil horizons from the sites were reflected in the crystallinity of epicuticular waxes, presence of long-chain aliphatic hydrocarbons, concentrations of n-alkanes, saturated and unsaturated fatty acids, dicarboxylic acids, and in the content of aromatic structures, hydroxyl, ester, and carboxylic acid groups. The results are explained by differently transformed organic matter. The concentrations of elements in the soils were also affected by atmospheric depositions, including higher accumulations of arsenic and antimony, and lower contents of natural nutrients. These data have potential to be used as sensitive biogenic indicators of ecosystem damage by long-term atmospheric depositions.

Organic matter protection by kaolinite over bio-decomposition as suggested by lignin and solvent-extractable lipid molecular markers

The formation of organo-mineral complexes is essential in organic matter (OM) stabilization. However, limited studies have been conducted to systematically examine the mineral influence on the decomposition of plant residuals at a molecular level. In this study, pine needles and chestnut leaves were mixed with kaolinite at the weight ratio of 5:1. The controls were plant tissues without kaolinite. All the samples were incubated in the laboratory for one year. Molecular markers, including lignin-derived phenols (e.g. Vanilly units, syringyl units and cinnamyl units) and solvent-extractable lipids (e.g. n-alkanoic acid, n-alkanols and n-alkanes), were analyzed. The concentrations of lignin-derived phenols and lipid compounds were higher in the presence of kaolinite than without kaolinite. Lower degradation indexes, such as (Ad/Al)V (ratio of vanillic acid to vanillin) and CPI (carbon preference index of n-alkanoic acid and n-alkanes), were found in the kaolinite system. These results indicate that kaolinite reduced the OM decomposition. The addition of kaolinite also stabilized some carbohydrates from plants. Furthermore, the degradation of OM led to the generation of persistent free radicals, indicated by electron paramagnetic resonance (EPR) signals. The EPR signals were higher with than without kaolinite. We hypothesize that the adsorption of semiquinone or quinone radicals on kaolinite may limit their reaction with other OM moieties and thus extended their lifetimes. In addition to embedding OM in soil aggregates, our results provide direct evidence of another mineral protective mechanism of soil OM.

Temporal Variability of Source-Specific Solvent-Extractable Organic Compounds in Coastal Aerosols over Xiamen, China

This study describes an analysis of ambient aerosols in a southeastern coastal city of China (Xiamen) in order to assess the temporal variability in the concentrations and sources of organic aerosols (OA). Molecular-level measurements based on a series of solvent extractable lipid compounds reveal inherent heterogeneity in OA, in which the concentration and relative contribution of at least three distinct components (terrestrial plant wax derived, marine/microbial and fossil fuel derived organic matter (OM)) exhibited distinct and systematic temporal variability. Plant wax lipids and associated terrestrial OM are influenced by seasonal variability in plant growth; marine/microbial lipids and associated marine OM are modulated by sea spill and temperature change, whereas fossil fuel derived OM reflects the anthropogenic utilization of fossil fuels originated from petroleum-derived sources and its temporal variation is strongly controlled by meteorological conditions (e.g., the thermal inversion layer), which is analogous to other air organic pollutions. A comparative study among different coastal cities was applied to estimate the supply of different sources of OM to ambient aerosols in different regions, where it was found that biogenic OM in aerosols over Xiamen was much lower than that of other cities; however, petroleum-derived OM exhibited a high level of contribution with a higher concentration of unresolved complex matters (UCM) and higher a ratio between UCM and resolved alkanes (UCM/R).

Plant leaves as indoor air passive samplers for volatile organic compounds (VOCs)

Volatile organic compounds (VOCs) enter indoor environments through internal and external sources. Indoor air concentrations of VOCs vary greatly but are generally higher than outdoors. Plants have been promoted as indoor air purifiers for decades, but reports of their effectiveness differ. However, while air-purifying applications may be questionable, the waxy cuticle coating on leaves may provide a simple, cost-effective approach to sampling indoor air for VOCs. To investigate the potential use of plants as indoor air VOC samplers, a static headspace approach was used to examine the relationship between leaf and air concentrations, leaf lipid contents and octanol-air partition coefficients (Koa) for six VOCs and four plant species. The relationship between leaf and air concentrations was further examined in an actual residence after the introduction of several chlorinated VOC emission sources. Leaf-air concentration factors (LACFs), calculated from linear regressions of the laboratory headspace data, were found to increase as the solvent extractable leaf lipid content and Koa value of the VOC increased. In the studies conducted in the residence, leaf concentrations paralleled the changing air concentrations, indicating a relatively rapid air to leaf VOC exchange. Overall, the data from the laboratory and residential studies illustrate the potential for plant leaves to be used as cost effective, real-time indoor air VOC samplers.

Variation in solvent-extractable lipids and n-alkane compound-specific carbon isotopic compositions with depth in a southern China karst area soil

Because literatures about the lipid compositions of modern soils in karst areas are scarce, we have studied the soil horizons overlying the Heshang (和尚) Cave that has provided paleoclimate records from speleothem lipid contents. Our analysis reveals a series of n-alkanes, free fatty acids, n-alkanols and n-alkan-2-ones distribution and relative abundance changing with the depth, and in which the ratios of the lower molecular weight to higher molecular weight n-alkanes, free fatty acids, n-alkanols and n-alkan-2-ones have a peak at a subsurface depth of 5 to 10 cm. An accompanying peak in 17β(H), 21β(H)-hop-22(29)-ene (diploptene) and a shift to less negative n-alkane carbon isotopic values also identify this layer in the karst soil. This pattern indicates the existence of a subsurface soil layer in which the microorganisms that produce these compounds are especially abundant. The carbon isotopic values of individual plant wax n-alkanes are about 3‰ greater at the base of the 30- to 40-cm soil profile than in the surface layer, probably as a result of selective microbial degradation of n-alkanes from different primary sources. The lipids and carbon isotopic values of individual plant wax n-alkanes study of the overlying soil show a strong microbial activity in this karst soil and help in interpreting the lipid compositions and specific carbon isotopic value of n-alkanes of the stalagmites of the Heshang Cave for paleoenvironmental reconstructions.

Bound forms, compositional features, major sources and diagenesis of long chain, alkyl mid-chain diols in Lake Baikal sediments over the past 28,000 years

To elucidate the possibility of long chain, alkyl mid-chain diols (hereafter, mid-chain diols) in Lake Baikal sediments over the past 28 ka being paleoproxies, we studied their: (i) bound forms and compositional features, (ii) major sources and (iii) diagenesis during sedimentation. Of the seven bound forms investigated, i.e. free form (free type), three base-hydrolysable types (base-1, base-2, and base-3) and acid-hydrolysable type (acid-1 type) in solvent extractable lipids and base hydrolysable (NB) and acid hydrolysable (NA) types in non-solvent extractable (NONEX) lipids, only three, viz. free, NB, and base-3 types, were found. The relative compositions of the three types were 70–100%, 0–30% and 0–8%, respectively. The most abundant component of the free-type diols was the C 32 1,15-diol, whereas that of the base-3 and NB types was the C 30 1,13-diol. The average chain length, ratio of total amount of even chain lengths to that of odd chain lengths, the relative composition of positional isomers for each carbon number, and the diol index, obtained using the equation [C 30 1,15-diol]/([C 30 1,15-diol] + [C 32 1,15-diol]) × 100, hardly responded to reported major paleoenvironmental changes around the Lake Baikal region over the last 28 ka. Comparison of mid-chain diol compositions and their bound forms with those in possible sources suggested that the major biological source of all mid-chain diols in the sediments might be the Eustigmatophyceae class of algae. In the alga, the occurrence of mid-chain diols in the five bound forms, free, base-3, acid-1, NB and NA types, was suggested, while the acid-1 and NA types were not found in the sediments. Under the oxic depositional conditions of Lake Baikal, most of the acid-1 and NA type diols and part of the base-3 and NB type diols might be degraded and/or released free-type diols. In the anoxic sediments of the lake, the base-3 and NB diols seem to be resistant to diagenesis. All investigated parameters for the free, base-3 and NB diols in the sediments did not provide any information on paleoenvironments around the lake. On the other hand, among the fluxes of the three diol types, the base-3 type diol flux seems to have responded to the climatic events around the lake, especially over the last 15 ka. Hence, this flux might be a potential paleoproxy for the productivity of the biological source(s) and associated environmental factors.

The potential of plant biomarker evidence derived from rock hyrax middens as an indicator of palaeoenvironmental change

Hyrax middens are unique environmental archives with the potential to provide unprecedented high-resolution palaeoenvironmental records, particularly in the arid regions of southern Africa. This study provides the first detailed characterisation of the organic matter composition of hyraceum and aims to identify biomarker evidence capable of providing new or supplementary palaeoenvironmental data from these novel archives. Pyrolysis gas chromatography mass spectrometry reveals hyraceum to be dominated by nitrogen-containing aromatic compounds, notably benzamide. This is almost certainly derived directly from the hyrax urine and is probably the main source of nitrogen as measured in bulk δ 15N measurements. Solvent-extractable lipids comprise homologous suites of long-chain n-alkanes (C 24–C 34) and n-alkanols (C 16–C 26), characteristic of higher plant leaf waxes, along with an abundance of animal-derived sterols, higher plant sterols and terpenoids; as well as the ubiquitous benzamide. n-alkane distributions and compound specific δ 13C clearly differentiate samples from the C 3 vegetation dominated Cape Floristic Region, and the more arid, C 4 grass-rich savannas of central Namibia (Klein Spitzkoppe). Distinct changes in n-alkane distribution and δ 13C are observed within the Spitzkoppe midden; most notably the mid to late Holocene period (c. 6000–2000 cal yr BP), which records a progressive reduction in grass-derived organic matter inputs. Based on the animal's feeding behaviour and contemporary site ecology, a phase of increasing aridity is inferred, which is consistent with other proxy data from this site (e.g. bulk δ 15N). The excellent preservation of plant and animal biomarkers suggests that there is significant potential for midden-derived biomarkers to provide long-term palaeoenvironmental proxies.

Biomolecular characteristics of an extensive tar layer generated during eruption of the Soufrière Hills volcano, Montserrat, West Indies

On December 26th, 1997, a violent pyroclastic density current (PDC), resulting from an eruption of the Soufriere Hills volcano, occurred on the island of Montserrat. About 4 km 2 of the area devastated by the PDC was covered partially by a blackened tar layer, of about 1–4 mm depth. Organic geochemical evidence strongly supports the hypothesis that the tar layer was created from soil and associated vegetation, probably in the form of a combustion cloud generated by the PDC. Vegetation, soil and tar were investigated using solid state 13C nuclear magnetic resonance spectroscopy (NMR), reflectance microscopy and scanning electron microscopy (SEM) to provide a general overview of the organic matter (OM) composition and morphology. Parallel investigations of the lipid, carbohydrate and lignin contents using gas chromatography (GC) and GC–mass spectrometry (GC/MS) were also undertaken. Solid state 13C NMR revealed that the majority of the OM in both vegetation (∼70%) and soil (∼40%) was cellulose and hemicellulose, with the remainder comprising predominantly aromatic, N-alkyl/methoxyl and alkyl structures. Contrastingly, the two tar layers were shown to be composed of 44% and 52.5% aromatic moieties, attesting to their thermogenic origin. Analysis of solvent extractable lipids revealed an n-alkane distribution in the tar layer that correlated with those observed for the vegetation and soil, maximising at C 33. Moreover, a higher relative abundance of the C 22 and C 32 n-alkanols was observed in the same tar layer compared with that obtained from the soil. This indicated that both vegetation and soil were major contributors of OM to the tar layer. Overall, the two tar layers were shown to contain lipids in differing states of preservation, indicating a higher temperature of formation for one of the layers, resulting from large, local temperature variation within the PDC. Analysis of total hydrolysable carbohydrates confirmed the large loss of these components in the tar layers, corroborating the information obtained from 13C NMR. This almost total loss of carbohydrates and concomitant increase in aromatised components in the tar layers is indicative of a PDC temperature >325 °C. CuO oxidation afforded lignin derived products for each sample, the relative distributions of which revealed that significant oxidation had occurred in the tar layers. Further information obtained from the tar layers using reflectance spectroscopy enabled the minimum temperature of the PDC to be constrained to 325–370 °C, possibly rising as high as 425 °C.

Combined application of non-discriminated conventional pyrolysis and tetramethylammonium hydroxide-induced thermochemolysis for the characterization of the molecular structure of humic acid isolated from polluted sediments from the Ravenna Lagoon

Humic acid (HA) isolated from highly polluted sediment from the Ravenna Lagoon (Italy) was subjected to pyrolysis/tetramethylammonium hydroxide (TMAH)-induced thermochemolysis to reveal the impact of industrial activities on humification. Special effort was made to distinguish between analytes originating from the polymeric humic organic matter network along with sequestered compounds (which cannot be released by solvent extraction), and the solvent-extractable lipid fraction sorbed onto the organic matrix. Exhaustive solvent extraction of the isolated HA proved mandatory to avoid biased results when identifying the origin of the pyrolyzates of untreated samples. Conventional pyrolysis at 750 °C of the “degreased” HA revealed a characteristic polycyclic aromatic hydrocarbon (PAH) pattern, which was significantly different than patterns obtained from the pyrolysis of natural humic acids. TMAH-induced thermochemolysis at 500 °C provided information on carboxylic acids covalently bound inside the HA network via ester bonds. Thermochemolysis of the “degreased” matrix at 750 °C, resulting in the cleavage of C–O and C–C bonds, revealed a significant PAH pattern very similar to that obtained by conventional pyrolysis. The uncommon PAH pattern points to the formation of bound residues as the humification/detoxification pathway. Recalcitrant hopane hydrocarbons showed very similar patterns for both the untreated and exhaustively solvent-extracted samples, which points to hopanes being linked inside the humic network via C–C bonds. The technique of non-discriminating flash pyrolysis used in this study, based on extremely rapid capacitive discharge heating in a Silcosteel capillary, proved to be an excellent method to obtain high-boiling pyrolyzates (PAHs beyond 252 Da molecular weight, C 29–C 31-hopanes).

Lipid geochemistry of lake sediments from semi-arid Spain: Relationships with source inputs and environmental factors

The lipid geochemistry of lake sediments can provide information on past environmental change. Detailed interpretation is, however, often hampered by a limited understanding of the provenance of many compounds and the multiple factors influencing their distributions in modern lake sediments. We have quantified the solvent extractable lipid compositions of modern surface sediments from fifty four Spanish lakes covering a range of hydrochemical (fresh to hypersaline) and hydrological (shallow ephemeral to deep permanent) conditions. Lipid compositions across the dataset are dominated by carboxylic acids (up to 86% total solvent extractable lipids), alkanols (up to 63%) and sterols (up to 58%), with smaller relative proportions of alkanes, alkenes, ketones (including long chain alkenones) and hopanols. Here we employ the distributions of these dominant compounds to explore relationships between lipid composition, source inputs and lake type. Source input is the major factor influencing the lipid composition, but there are also some indicators of early stages of lipid diagenesis in these surface sediments. Multivariate data analysis (non-metric multidimensional scaling ordination and cluster analysis) of normalised lipid concentrations shows a distinction between compounds originating primarily from algal, bacterial, macrophyte or terrestrial plant sources. This statistical technique enables sites to be grouped according to their dominant lipid compositional characteristics as well as enabling us to identify broad trends in groups of sites in terms of their environmental features (e.g. shallow or deep lakes). This modern training set study provides insight into patterns of contemporary lipid distributions and lipid source and site relationships across diverse lacustrine environments, which can then be useful in environmental monitoring and palaeoenvironmental studies using sediment cores.

Characterization and quantification of biomarkers from biomass burning at a recent wildfire site in Northern Alberta, Canada

The composition of organic matter (OM) in pine vegetation and soil samples from a pine forest which was charred by a wildfire was analyzed using solid-state nuclear magnetic resonance ( 13C NMR) and gas chromatography–mass spectrometry (GC–MS) of solvent extracts to study the effects of thermal alteration on soil organic matter (SOM). The NMR data revealed the presence of unaltered biomolecules (cellulose, proteins) and low contents of aromatic C (15%) in the charred pine wood and cones while the charred soil samples exhibited higher contents of aromatic C (39–56%). The solvent extraction of charred and uncharred plant and soil samples yielded diterpenoids, triterpenoids, steroids, a series of aliphatic lipids, phenols and carbohydrates indicating the predominant input of higher plant OM and minor contributions from microorganisms and/or fauna. The lower yield of solvent extractable aliphatic lipids in the charred samples versus the uncharred samples suggests that these compounds are thermally degraded during a wildfire. Molecular markers for the burning of cellulose (levoglucosan, mannosan, galactosan) were detected in all charred samples. The comparison of charred and uncharred samples allowed the identification of unaltered pine derived biomolecules and their thermal alteration products in the charred samples. Terpenoid and steroid biomolecules were in part altered during incomplete combustion to aromatic, unsaturated and polar derivatives (“pyromolecules”) that still retained the characteristic skeleton of their precursors. Since some of the polar degradation products found in the charred soils can be generated either from thermal or microbial degradation, the aromatic and unsaturated hydrocarbon products are preferred as molecular markers for SOM burning. Ratios of biological precursors to aromatic (diterpenoids) or unsaturated products (steroids) indicate that the cyclic lipids in the pine wood and the soil surface horizon were highly altered. In conclusion, the solvent extractable lipids and carbohydrates in charred SOM are valuable, source-specific molecular markers for the burning of plant biomass and for tracing the biogeochemistry of charred residues in soils.

Degradation and Preservation of Vascular Plant-derived Biomarkers in Grassland and Forest Soils from Western Canada

The total solvent extracts (TSE) of mineral and organic horizons of selected soils and overlying vegetation were analyzed using gas chromatography–mass spectrometry (GC–MS) to determine the composition of solvent-extractable (‘free’) lipids in soils and to study the degradation and possible preservation of vascular plant-derived molecular markers (biomarkers) in soils. Major compound classes in the TSE of soils and vegetation included a homologous series of aliphatic lipids (alkanoic acids, alkanols, alkanes), steroids, and terpenoids. Characteristic patterns of aliphatic and cyclic biomarkers derived from the overlying, native vegetation were recognized in the associated soil samples indicating the preservation of lipids from the external waxes of vascular plants in the soil organic matter (SOM). The observed biomarker patterns in the grassland soils (Brown Chernozems) were similar to the compounds identified in their major source vegetation, Western Wheatgrass. A similar composition of biomarkers was observed in Aspen leaves and the soil horizons of the forest–grassland transition soil (Dark Gray Chernozem). The Lodgepole Pine needles yielded a characteristic pattern of diterpenoids that was also detected in leaf litter and the O horizon of the associated forest soil (Brunisol). The results demonstrate that solvent extractable biomarkers derived from vascular plants maintain their characteristic pattern of aliphatic and cyclic lipids despite ongoing degradation processes and are thus valuable molecular markers for the determination of the sources of SOM. Furthermore, the abundance of aliphatic wax lipids in plant material and soils decreased at higher rates than the steroids and terpenoids indicating the preferential degradation of aliphatic over cyclic biomarkers. Most of the plant-derived steroids and terpenoids identified in the soils were unaltered, preserved biomolecules as observed in the source vegetation, but minor amounts of their degradation products were also present. Oxidation products of plant sterols are reported here for the first time in soils. The detected alteration products of steroids and diterpenoids are consistent with the oxidative degradation of free cyclic biomarkers in decomposing plant material and soils.

Pyrolysis–GC–MS to trace terrigenous organic matter in marine sediments: a comparison between pyrolytic and lipid markers in the Adriatic Sea

The effectiveness of semiquantitative pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS) as a rapid analytical technique for sourcing continental organic matter (OM) in marine sediments was examined by comparison with classical GC–MS analyses of solvent extractable lipid markers. Py–GC–MS was directly applied to HCl/HF de-ashed surface sediment samples collected in five stations located in north western Adriatic Sea. The resulting pyrolysates were characterised by compounds indicative of different biological precursors (e.g. proteins, carbohydrates, chlorophylls), including lignin methoxyphenols diagnostic for continental inputs. The relative abundance of pyrolytic markers was compared to the distribution of n-alkanes, n-alkanols and sterols extracted from the same sediments and determined by GC–MS analyses. For each class of molecular indicators, the terrigenous to aquatic ratio (TAR) was determined as follows: relative abundance of methoxyphenol/protein markers (TAR PY), concentration ratios of (C27 + C29 + C31)/(C15 + C17 + C19) n-alkanes (TAR HC), (C26 + C28+ C30)/(C14 + C16) n-alkanols (TAR AL) and sitosterol/cholesterol (TAR ST). A positive correlation was found between TAR PY and both TAR HC and TAR AL indicating a decreasing contribution of land-plant-derived materials seaward in two investigated transects. TAR ST values displayed a different trend suggesting a mixed origin for sitosterol. The distribution of TAR PY values was also in good agreement with that of atomic C/N ratios. Considering the complexity of environmental systems (diagenetic alteration, different fractions of OM analysed) the obtained results indicate that the pyrolytic marker approach by Py–GC–MS is valuable for sourcing marine OM on a semiquantitative base, providing data consistent with GC–MS determinations of lipid markers and elemental bulk analyses.

Lipid constituents of peat humic acids and humin. Distinction from directly extractable bitumen components using TMAH and TEAAc thermochemolysis

Humic acids and humin from an acidic peat were investigated using solid state 13C NMR and pyrolysis with tetramethylammonium hydroxide (TMAH) and tetraethylammonium acetate (TEAAc). The degradation products were compared with the solvent extractable lipids. The latter appeared to originate mostly from plant material, whereas the products derived from the humic fractions showed a more complex structure, partly inherited from natural insoluble material. The major products of TMAH thermochemolysis were aromatic compounds derived from lignin moieties, hydrocarbons and fatty acid methyl esters (FAMEs) partly incorporated via ester or ether bonds. Aliphatic hydrocarbons were present as n-alkene/ n-alkane doublets with a Gaussian distribution in the C 17–C 35 range. These unsaturated and saturated hydrocarbons arose from resistant biopolymers. Bifunctional aliphatic compounds were also incorporated into the humic structure, contributing to alkyl bridges. Thermochemolysis of humin produced more aliphatic structures than did humic acids. The application of TEAAc thermochemolysis allowed identification of a wide range of products initially retained in the humic macromolecules via non-covalent bonds, thereby indicating that weak bonds such as hydrogen bonds play a key role in the structure of humic substances. The association of thermochemolysis using TMAH and TEAAc thus allows covalently-bound fatty acids, trapped fatty acids and trapped fatty acid methyl esters present in the structure of humic acids or humin to be distinguished.

Solvent-extractable lipids in an acid andic forest soil; variations with depth and season

Total lipid extracts from an acid andic soil profile located on Madeira Island (Portugal) were analysed using gas chromatography (GC) and GC–mass spectrometry (GC/MS). The profile was covered mainly by grass. Bulk soil characteristics determined included soil pH (H 2O) ranging from 4.5 to 4.0 and TOC, ranging from 84 to 30 g kg −1. A decrease of the contribution of lipids per TOC with depth was observed. The absence of typical bacterial markers might be an indication for reduced bacterial activity, most likely related to the low soil pH and the presence of Al and Fe (oxides). The distribution observed in the top layer with a dominant C 26 n-alkanol, steroids and triterpenoids, reflected mainly an input by grass leaves. A strong decrease in both relative and absolute concentration of these leaf-derived compounds was observed when comparing the litter layer with the mineral soil. The presence of C 22–C 32 n-alkanoic acids, C 22–C 26 ω-hydroxy acids, C 31 n-alkane and C 22–C 32 n-alkanols observed in the sub-soil is indicative of an important contribution by (grass) roots. In summer, a signal most likely reflecting the leaching of microbially derived products from the litter and/or aerial vegetation at the surface was observed.

Composition, age, and provenance of organic matter in NW African dust over the Atlantic Ocean

Eolian dust deposited on a meteorology buoy over the boreal winter and spring of 1992/1993 in the Northeast Atlantic off Northwest Africa (18°N, 22°W) afforded sufficient material for detailed assessment of its biogeochemical characteristics and provenance. The sample was subjected to microscopic examination and bulk, elemental, isotopic, black carbon, and molecular (lignin, lipid) analyses. The bulk elemental composition and organic carbon (OC) content (1.02% dry weight) establishes the dust's origin as continental upper crust and is typical of dusts that emanate from West Africa. These data are in accord with the extensive satellite imagery documenting the transit of dust clouds from the Sahara and Sahel regions (e.g., NASA TOMS aerosol index). Microscopic examination reveals that charcoal‐like particles from vegetation fires (“black carbon” (BC)) are the most abundant morphologically distinct organic components. Accelerator mass spectrometry (AMS) 14C analysis yields conventional 14C ages for bulk OC of 1260 ± 40 years and BC of 2070 ± 35 years. Taken together with corresponding stable carbon isotopic compositions (δ13C, −18.9 and −15.1‰, respectively), these results suggest the presence of biomass and burning residues derived from predominantly C4 vegetation that accumulated in soils over the late Holocene. Molecular‐level measurements are also consistent with this scenario. For example, lignin‐derived phenols in the dustfall sample indicate a significant contribution of angiosperm grass‐type tissue. The altered nature of the lignin suggests storage as residues in soils. Solvent extractable (lipid) constituents include a marked leaf wax type component with a molecular and stable carbon isotopic composition similar to those observed in surface marine sediments in this region. The hydrocarbon fraction contained some diesel‐type contamination but the n‐alkanes (C23–C33) retained a prominent odd/even distribution, with δ13C ranging from −26.7 to −28.5‰. The suite of even carbon numbered n‐alkanols (C22–C32) is 14C dated at 647 ± 150 years, with δ13C values ranging from −23.9 to −30.4‰. The long‐chain n‐alkanoic acids (C22–C32) exhibited δ13C values ranging from −22.6 to −27.4‰. These waxes are evidently a mixed signal derived from contemporary C3 and C4 vegetation and from ablated soils and desiccated lake sediments of middle to late Holocene age. This molecular approach shows promise as a tool for continental paleoenvironmental assessment, particularly with respect to past vegetation cover, regional aridity, and wind systems.

Evidence for Varying Patterns of Exploitation of Animal Products in Different Prehistoric Pottery Traditions Based on Lipids Preserved in Surface and Absorbed Residues

The excavation of a barrow at Upper Ninepence, Walton in the Welsh Borderlands, U.K., revealed two phases of occupation associated with two different ceramic traditions, namely Grooved Ware (2500bc) and Peterborough Ware (3000bc). The Grooved Ware and Peterborough Ware pits seem to have a mutually exclusive distribution on the site. Screening of the sherds for lipid residues has revealed the presence of remnant fats in a remarkably well-preserved state considering the age of the finds. Investigations of various chemical characteristics of the remnant fats from absorbed and carbonized residues have enabled distinctions to be drawn between fats from non-ruminant (e.g. porcine) and ruminant (e.g. ovine or bovine) origins. Significantly, both ruminant and non-ruminant fats are found associated with the Grooved Ware whereas only ruminant fats are found associated with the Peterborough Ware. The assignments are based upon the distributions of solvent-extractable lipid components and the compound-specific stable carbon isotope values of the major n -alkanoic acids. The results reveal differences in vessel use and indicate possible changes in patterns of animal exploitation or dietary preferences between the two phases of occupation. The results illustrate the importance of residue analysis in archaeological investigations, particularly at prehistoric sites where evidence from faunal remains is limited or absent.

Partial Release of Covalently Bound 18-Methyleicosanoic Acid from Wool Cuticle with Primary Alcohols

The stability of the bond of 18-methyleicosanoic acid (18-MEA) from untreated and chlorinated wool towards transesterification by alcohols was investigated. The extraction of untreated wool top with methanol not only dissolves the readily solvent-extractable lipids, but also the methyl esters of palmitic acid and 18-MEA from the cuticle proteolipids. About 10% of the total amount of 18-MEA is released by a 100 h Soxhlet-extraction with methanol from untreated top. With methanol replaced by ethanol, the ethyl esters of 18-MEA were detected. Transesterification of the 18-MEA proteolipids with the secondary alcohol 2-propanol was not observed. The treatment of wool with formic acid resulted in the removal of the soluble cell membrane lipids from the fibre but not in the release of 18-MEA. However, the removal of cell membrane compounds by solvents was shown to increase the accessibility of the 18-MEA-proteolipid regions for transesterification, and the influence of industrial chlorination is even more pronounced. These findings support the view that a significant part of the 18-MEA is bound to membrane domains of cuticular membrane proteins. The major portion of 18-MEA-containing proteolipids, however, is localized in areas of the fibre which are not accessible after modification of the cell membrane complex with solvents or by industrial chlorination.