British Organic Geochemistry Society 10th meeting 1998

An archive of oral presentations that took place 15–17 July 1998

Oral presentations

Lipid Biomarker Proxies for Submerged and Emergent Aquatic Macrophytes from Crater Lakes, Mount Kenya, East Africa

Kath J. Ficken (1), Baochai Li1, F. Alayne Street-Perrott (2), David Swain (2), Andrew D.Q. Agnew (3), Steve Mathai (4)
and Geoffrey Eglinton (1)

(1) Biogeochemistry Centre, Department of Geology, Wills Memorial Building,
Queens Road, Bristol BS8 1RJ, UK

(2) Tropical Palaeoenvironments Research Group, Department of Geography,
University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK

(3) Department of Biology, University of Wales Aberystwyth, Penglais, Aberystwyth, UK

(4) National Museums of Kenya, Nairobi, Kenya

Many of the lakes on Mt. Kenya, especially those below treeline such as L. Nkunga and Sacred Lake, contain abundant aquatic macrophytes. However, this may not have been the situation throughout the lakes' history. Therefore, if biomarkers or biomarker proxies can be found for these aquatic macrophytes, their contribution to the lake sediments can be plotted with time. In Lake Nkunga and Sacred Lake sediments the n-C23 and n-C25 alkanes were unusually extremely abundant (Huang et al., 1995; Ficken et al., in press). The abundance of these compounds appeared to coincide with high abundances of Nymphaea pollen and so it was initially proposed that these mid-chain length homologues may derive from this source. To test this hypothesis, lipids from 17 aquatic macrophytes: submerged (7 species), floating (1 species) and emergent (9 species) were examined along with 3 species of terrestrial vegetation. The mid-chain length homologues (C23 and C25 n-alkanes, C22 and C24 n-alkanols and n-alkanoic acids) were more abundant in the submerged and floating macrophytes. The emergent macrophytes n-alkyl lipid distributions were similar to the terrestrial vegetation i.e. the long-chain length homologues (C29 and C31 n-alkanes, C28 and C30 n-alkanols and n-alkanoic acids) were the most abundant. This suggests that the submerged and floating macrophytes can be distinguished from the emergent species on the basis of n-alkyl lipid chain length. However, as yet, the emergent species cannot be differentiated from the terrestrial vegetation.

Floating and emergent aquatic macrophytes use atmospheric CO2 whereas submerged macrophytes behave isotopically like algae in the fixation of carbon (Keeley and Sandquist, 1992). At normal lake water temperature HCO3- is 7-11 per cent heavier than CO2 (aq). Some submerged plants, such as Potamogeton, along with green and blue green algae and some diatoms, possess a CO2 concentrating mechanism involving HCO3- uptake, which would give them a selective advantage at times of lower CO2. Deployment of these mechanisms would cause an increase in the d13C values of aquatic organic matter. An example of the use of the proposed biomarker proxies and their d13C signatures in order to determine the input of submerged aquatic macrophytes to Lake Nkunga will be discussed.

References

  • Ficken, K.J. Street-Perrott, F.A., Perrott, R.A., Swain, D., Olago, D.O. and Eglinton, G. (in press) Glacial/interglacial variations in carbon cycling revealed by molecular and isotope stratigraphy of Lake Nkunga, Mt. Kenya, East Africa. Organic Geochemistry.
  • Huang, Y., Street-Perrott, F.A., Perrott, R.A., Harkness, D.D., Olago, D. and Eglinton, G. (1995) Molecular and carbon isotope stratigraphy of sediments from the last glacial/interglacial sequence of a tropical freshwater lake, Sacred Lake Mt. Kenya. In Organic Geochemistry: Developments and Applications to Energy Climate, Environment and Human History, eds. J.O. Grimalt and C. Dorronsoro pp. 826-829, Pergamon.
  • Keeley, J.E. and Sandquist, D.R. (1992) Carbon: freshwater plants. Plant, Cell and Environment 15, 1021-1035.


The Effects of Diagenesis on the UK37 Index

Jeremy R. Marlow, Paul Farrimond and Antoni Rosell-Melé

Fossil Fuels & Environmental Geochemistry, Drummond Building, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK.

The UK37 index is a climate proxy used for the reconstruction of palaeo-sea surface temperatures (SSTs). It is defined as a function of the relative concentrations of the di-, tri- and tetra-unsaturated methyl ketones ([37:2Me], [37:3Me] and [37:4Me] respectively) found in the lipid fraction of sediments, water column particulates or algal cultures. The alkenones are biosynthesised by selected species of marine algae from the class Prymnesiophyceae, notably the coccolithophorid Emiliania huxleyi. The tetra-unsaturated component is not always detected in sedimentary samples so an alternative algorithm (UK37') excludes 37:4Me.

The UK37 and/or UK37' values obtained for a series of samples have been correlated with the known growth temperatures to formulate calibration equations. Measured values of UK37 and/or UK37' from down-core sediment samples can then be used to estimate palaeo-SSTs (see Brassell, 1993 for a review).

The model relationship between SST and sedimentary UK37' values assumes no significant preferential alteration in the relative abundance of either of the unsaturated alkenones. Initial investigations of the preservation potential of alkenones showed that the absolute abundance of alkenones decreases during down water-column flux and early sedimentary diagenesis in similar or greater magnitude as total organic carbon. However, the relative proportions of the alkenones were shown to remain sufficiently constant so as to have an insignificant bias on the resulting UK37' value (e.g. Conte et al., 1992; Prahl et al., 1989).

More recent research suggests that 37:4Me can be more labile to sedimentary diagenesis than the less unsaturated alkenones (Flügge, 1996), and that under oxic sedimentary conditions there is evidence for preferential degradation of 37:3Me compared to 37:2Me (Hoefs et al., 1998). In the latter study the authors concluded that application of UK37' derived absolute SSTs may not be justified. Such a categorical conclusion should not be accepted without further corroborative studies.

The work presented describes the methods adopted for preliminary investigations into the effects of diagenesis on alkenones by studying the ‘free’ and ‘bound’ lipid constituents of water-column and sedimentary material from well-constrained environments. These methods have been used to compare contrasting anoxic and oxic basins of the Baltic Sea and the highly productive upwelling region of the Benguela Current in the South Atlantic Ocean off the west coast of Africa (ODP Hole 1084A). The resulting data for the relative abundance of the alkenones in the free and bound fractions was examined for significant preferential degradation of individual alkenones by developing degradation ratios. These ratios express the differences in concentration of an individual alkenone between the degraded and less degraded states. Ratio differences become significant when the corresponding bias in UK37' is equivalent to > ±0.5ºC of the interpolated SST. In most instances, detectable quantities of alkenones were released upon alkaline hydrolysis of the solvent-extracted sediment residues. The degradation ratios in the free extract were compared with those calculated for the bound fraction and differences in the preservation potential between the two types of sedimentary matrix were indicated. Although the alkenones cannot be directly linked to the ester-bound fraction of the sediments it is likely that the proto-kerogen/humin fraction consisting of ester cross-linkages incorporates a proportion of the alkenones within the macro-molecular matrix and consequently gives protection from diagenetic alterations.

The results obtained from these and further planned experiments should allow conclusions to be made regarding the effects of early sedimentary diagenesis on UK37' in various diagenetic regimes of the global marine environment. These conclusions can then be used either to support the assumptions presently made in interpreting UK37' data or reinforce the calls for a more cautious approach when using UK37' in areas prone to significant sedimentary organic matter diagenesis. In addition, potential biases other than diagenesis (e.g. deposition of ice-rafted debris) will also be investigated to further evaluate the accuracy of UK37' as a palaeo-SST proxy.

References

  • Brassell, S.C. (1993) in Organic Geochemistry, Principles and Applications, 699-738, Plenum.
  • Conte, M.H., Eglinton, G., Madureira, L.A.S. (1992) Org. Geochem. 19, 287-298.
  • Flügge, A. (1996) PhD Thesis. Christian-Albechts-Universität zu Kiel, Germany.
  • Hoefs, M.J.L., Versteegh, G.J.M., Rijpstra, W.I.C., de Leeuw, J.W. and Sinninghe Damste, J.S. (1998) Paleoceanography 13, 42-49.
  • Prahl, F.G., de Lange, G.J., Lyle, M. and Sparrow, M.A. (1989) Nature 341, 434-437.


Hydroxy and Ketonic Androstanes: A New Class of Sterol Diagenetic Products in Peat

Luke A. Avsejs, Chris J. Nott, James R. Maxwell and Richard P. Evershed

Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK

Pre- and post-burial structural alterations of sterols have been investigated in many sedimentary environments and have been shown to involve a wide variety of transformations. In recent sediments the steroid components that have been reported include intact sterols and their saturated counterparts (e.g. McLean et al., 1958) and ketones and sterenes (e.g. Wakeham et al., 1980). Most reports of steroid derivatives relate to components in which the carbon skeleton of the C-17 side chain has remained intact, although hydrocarbons with the androstane skeleton have been reported in ancient sediments and are presumed to originate through side chain cleavage (Matveyeva and Petrov, 1992) or as partially and fully aromatised components (Chaffee and Johns, 1983).

In a study of the lipid fractions of peat taken from Bolton Fell Moss (Cumbria, U.K.), aimed at relating compounds found within the peat to those present in the specific peat-forming plants that grow on the surface of the bog, we observed a group of oxygenated compounds with the androstane skeleton. 3b-Hydroxy-5a-androstan-17-one (epiandrosterone), 5a-androstan-3,17-dione, 3a-hydroxy-5a-androstan-17-one (androsterone), 5a-androstan-3b,17b-diol and 5a-androstan-3a,17b-diol have been identified in the solvent soluble fractions of peat from 3-4 m depth.

It has been reported, based on laboratory biodegradation studies, that bacteria can degrade the side chains of common sterols such as cholesterol and sitosterol, to produce androstane-type products (Bhattacharyya et al., 1984). Since the bacteria used in the experiments were isolated from soil, similar microorganisms may be, or may have been, active in the peat. Hence, by analogy with the findings of Bhattacharyya et al. (1984) and by comparison of sterol and stanol distributions with those of androstanes in Bolton Fell Moss peat it appears that 24R-stigmast-5-en-3b-ol and other sterols and stanols are transformed in this environment to 3b-hydroxy-5a-androstan-17-one. Other androstane compounds found in the peat may be products from the microbial oxidation of other sterols within the peat or indeed other products from this transformation, such as 3a-hydroxy-5a-androstan-17-one.

The structures and d13C values of these androstane derivatives indicate a diagenetic origin in sterols also present in the peat and provide the first evidence that cleavage of the C-17 side-chain can occur during early diagenesis.

References

  • Bhattacharyya, P.K. et al., (1984) J. Indian Chem. Soc. 66, 1-15.
  • Chaffee, A.L. and Johns, R.B. (1983) Geochim. Cosmochim. Acta 47, 2141-2155.
  • Matveyeva, I.A. and Petrov, A.A. (1992) Pet. Chem. 32, 360-366.
  • McLean, J. et al., (1958) Chem. Ind. (London), 1515-1516.
  • Wakeham, S.G. et al., (1980) Nature. 286, 798-800.


Developments in Resonance Raman Spectroscopy for Structural Studies of Chlorophyll Derivatives

Brendan J. Keely

Department of Chemistry, University of York, Heslington, York YO1 5DD, UK

Vibrational spectroscopies are sensitive indicators of the nature of chemical bonds within molecules and also of the immediate chemical environment in which the molecules are located. Accordingly, infrared and Raman spectroscopies have many and varied applications. In attempts to achieve high levels of sensitivity Raman spectroscopists often exploit resonance excitation to enhance the intensity of Raman scattering. In addition, in non-polar solvents surface enhancement has been employed to improve signal strength. We have successfully combined these two strategies for enhancement of signal intensity through the use of a molecular spacer, obtaining unperturbed Raman spectra at high levels of sensitivity. The ability to derive structural information from the technique has been demonstrated using chlorophyll derivatives in which there are differences in functionality and conformation.


Characterisation of "Embalming Resins" from Ancient Egyptian Mummies

S.A. Buckley, A.W. Stott and R.P. Evershed

Organic Geochemistry Unit, School of Chemistry, University of Bristol,
Cantock’s Close, Bristol BS8 1TS, UK

There has long been a fascination with the mummies of ancient Egypt. Despite this however, surprisingly little is known about the so-called "art" of mummification. In fact very few analytical studies have been carried out to gain insight into the embalming process, specifically to identify the "embalming resins" employed. These resins played a crucial role in the mummification of the body. A number of preservatives have been proposed, including true resins, e.g. coniferous resins (diterpenoids) and non-coniferous Pistacia resins (triterpenoids), gum resins, e.g. frankincense and myrrh, bitumen, pitch, honey and beeswax.

The few studies carried out to date, on Egyptian mummies have used a number of analytical techniques to identify the nature and origin of "embalming resins" based on the presence of specific biological marker compounds. Techniques used include high performance liquid chromatography (HPLC) (Nissenbaum et al., 1992), gas chromatography-mass spectrometry (GC/MS) (Rullkotter et al., 1988; Gulaçar et al., 1989; Koller et al., 1998), pyrolysis-mass spectrometry (Py-MS) (Wright et al., 1987), and fast atom bombardment tandem mass spectrometry (FABMS) (Proefke et al., 1992). There remain however, many unanswered questions concerning the technology of mummification during the 3000 years in which embalming was practised in ancient Egypt.

We now have the opportunity in our laboratory to carry out a comprehensive analytical study on a relatively large number of ancient Egyptian mummy samples from a wide range of dates, status’, geographical locations and contexts. The "resins" present in the mummies are complex aged organic materials of uncertain origin. Their original composition is likely to have changed substantially over time as degradation processes such as oxidation, reduction, hydrolysis, aromatisation and polymerisation have taken place. The analytical approach must take account of these chemical transformations and the resulting modified molecules if an accurate assessment is to be achieved. We have therefore, employed a dual approach utilising: (i) solvent extraction followed by GC/MS, and (ii) a combined sequential TD-GC/MS (310°C/10s) and Py-GC/MS (610° C/10s) (Chemical Data Systems 1000 Pyroprobe) methodology to allow the convenient study of both "free" and "bound" biomarkers deriving from the "embalming resins" in these samples. A distinct advantage of employing sequential TD-GC/MS and Py-GC/MS is the small sample sizes (ca 0.1 mg) required allowing rapid screening of a larger number of samples and micro-scale analysis facilitating the essentially non-destructive analysis of the mummified bodies, thus ultimately aiding sampling from historically valuable museum specimens. However, solvent extraction also provides valuable information which is not obtained using TD alone. This demonstrates that more than one approach may be necessary if the "resins" are to be satisfactorily characterised.

References

  • Gülaçar F.O. et al., (1989) J. Chromatogr. 479, 61-72.
  • Koller et al., (1998) Nature 391, 343-344.
  • Nissenbaum A. (1992) J. Archaeological. Science 19, 1-6.
  • Proefke M.L. et al., (1992) Anal. Chem. 64, Vol. 2, 105A-111A.
  • Rullkotter J. & Nissenbaum A. (1988) Naturwissenshafen 75, 618-621.
  • Wright M.M.. & Wheals B.B. (1987) J. Anal. Appl. Pyrolysis 11, 195-211.


Dishing the Dirt on the Vikings - Phosphatised Crab Apple Pips from a Tenth Century Cess Pit at Coppergate, York

Lucy M.E. McCobb (1,2), Derek E.G. Briggs (1) and Richard P. Evershed (2)

(1) Biogeochemistry Research Centre, Department of Earth Sciences,
University of Bristol, Queens Road, Bristol BS8 1RJ, UK

(2) Organic Geochemistry Unit, School of Chemistry, University of Bristol,
Cantock's Close, Bristol BS8 1TS, UK

The fossils studied by environmental archaeologists are a valuable (and until now unexploited) source of data on the effects of early diagenetic processes in terrestrial environments. The plant and arthropod cuticles, wood, seeds and bone fragments preserved represent a taphonomic stage intermediate between initial decay and eventual fossilisation. Two broad depositional categories can be recognised, each with considerable associated taphonomic bias. Waterlogged deposits are typically dominated by the thick cuticles of plants and arthropods. In dry deposits, above the water table, organics are usually oxidised and only organisms which have undergone authigenic mineralisation survive.

A preliminary study has been carried out on a sub-fossil plant assemblage recovered from a tenth century cess pit at Coppergate in York, which is dominated by the waterlogged remains of edible plants. Among these, crab apple seeds are unique in combining mineralised embryos with organic seed coats. SEM reveals replacement of the endosperm and cotyledon tissues by calcium phosphate, a process that in some cases has extended to include the seed coat. Elemental concentrations in the calcium phosphate give an insight into the likely conditions and processes of early diagenesis in the cess pit.

Py-GC/MS (flash pyrolysis-gas chromatography/mass spectrometry) was used to establish the composition of the organic Coppergate seed coats, with modern crab apple seed coats analysed for comparison. The pyrolysates of the modern and sub-fossil specimens are very similar, indicating that the Coppergate pips retain well preserved seed coats. Typical lignin markers [e.g. guaiacol (2-methoxyphenol) and syringol (2,6-dimethoxyphenol)] make only a minor contribution, with the pyrolysate being dominated by cellulose markers [2-furaldehyde, 1-acetoxypropan-2-one and anhydroglucopyranose (levoglucosan)] and compounds of uncertain affinity [phenol, 4-methylphenol and catechol (1,2-benzenediol)] which are tentatively attributed to tannins based on previous studies (Galletti, 1991; Stankiewicz et al., 1997; van Bergen et al., 1996). Future work in this area will have implications not only for the environmental reconstruction of our recent history but also for interpretation of the ancient terrestrial fossil record.

References

  • van Bergen, P.F., Hatcher, P.G., Boon, J.J., Collinson, M.E. and de Leeuw, J.W. (1996) Macromolecular composition of the propagule wall of Nelumbo nucifera. Phytochemistry 45, 601-610.
  • Galletti, G.C. (1991) Py-GC-ion trap detection of sorghum grain polyphenols (syn. vegetable tannins): preliminary results. American Chemical Society - Division Fuel Chemistry Preprints 36, 691-697.
  • Stankiewicz, B.A., Mastalerz, M., Kruge, M.A., van Bergen, P.F. and Sadowska, A. (1997) A comparative study of modern and fossil cone scales and seeds of conifers: a geochemical approach. New Phytologist 135, 375-393.


Bitumen vs. Kerogen-Bound Biomarkers: The Generation Game

Jane C. Barnard (1), Andrew N. Bishop (2), Nils Telnæs (3) and Paul Farrimond (1)

(1) Fossil Fuels & Environmental Geochemistry, Drummond Building,
University of Newcastle, Newcastle upon Tyne NE1 7RU, UK

(2) Texaco EPTD, 3901 Briarpark, Houston, TX 77042, USA 

(3) Norsk Hydro AS, Forskningssenter, 5020 Bergen, Norway

Biological markers are molecules analysed in the solvent-extracts of source rocks and oils, the molecular structures of which suggest an unambiguous link with natural products found in the biosphere. Biomarkers are routinely analysed by petroleum geochemists to assess the source, depositional environment, and maturity of organic matter in source rocks and are especially useful in investigating the origin and nature of oils, where other information is limited. This study centres around the hopanoids, a group of biomarkers originating from bacterial precursors which have a C27-C35 pentacyclic ring system with an extended side chain.

Organic matter within source rocks is divided into two operational fractions: the bitumen is solvent-soluble and is routinely analysed for biomarkers in petroleum geochemistry, while the dominant, insoluble macromolecular fraction (kerogen) is usually disregarded in biomarker studies due to analytical difficulties. Hopanoids are known to be bound into the kerogen structure during early diagenesis via the side chain, causing a high proportion of the hopanoids to be removed from the bitumen fraction. As maturation progresses, increased thermal stress causes breakdown of bonds within the kerogen, and hopanes (and other biomarkers) are subsequently released back into the bitumen. The nature of the bonds between the hopanoids and the kerogen will determine the maturity at which these molecules are generated, as stronger bonds will break at an increased level of thermal stress than weaker links. If hopanoid molecules are bound predominantly by weak bonds, these will break easily, releasing a high proportion of intact (C35) hopanoid skeletons into the bitumen. If bound by stronger bonds, side chains are more likely to be broken during the generation process, giving smaller hopanoid molecules. These released hopanes will progressively overprint the original biomarker composition of the bitumen as generation proceeds.

An investigation of the hopane distributions of bitumens from a North Sea well has shown a significant enrichment of the C35 hopanes relative to lower homologues. By comparison with modelled homohopane distributions we will demonstrate that this unusual composition may be due to extensive binding of the C35 hopane precursors to the kerogen by weak sulphur linkages, and subsequent preferential release of the intact C35 carbon skeleton into the bitumen. Production Index (PI) data support this hypothesis: the interval of enhanced C35 hopane content is coincident with much higher PIs, indicating the onset of significant hydrocarbon generation. Organic sulphur measurements of the kerogen proved inconclusive in showing that the C35 hopanes were previously bound via sulphur-bonds, as the sulphur may have been lost from the kerogen during the generation process.

The hopane distributions from this sample suite are dominated by hopanes that were previously bound into the kerogen and have been subsequently generated at an early stage due to weak C-S linkages in the kerogen, thus modifying the bitumen biomarker signal. This process has major implications for the interpretation of biomarker data in petroleum exploration.


Comparison of Covalently-Bound Aliphatic Biomarkers Released via Hydropyrolysis with their Solvent-Extractable Counterparts for a Suite of Kimmeridge Clays

Ian P. Murray (1), Gordon D. Love (1),†, Colin E. Snape (1) and Nigel J.L. Bailey (2)

(1) Department of Pure & Applied Chemistry, University of Strathclyde, Thomas Graham Building, Glasgow GI 1XL, UK

(2) Geochem Group Ltd., Chester Street, Chester CH4 8RD, UK

† Present address: Fossil Fuels and Environmental Geochemistry, Drummond Building, University of Newcastle, Newcastle upon Tyne NE1 7RU, UK

Fixed-bed hydropyrolysis at pressures greater than 10 MPa has the unique ability to maximise the yields of covalently-bound alkanes without adversely affecting their stereochemistries. In order to compare the yields and compositions of the solvent-extractable and kerogen-bound hopanes and steranes for source rocks of varying maturity, six Kimmeridge clay samples (Jurassic. type 11 kerogen) have been subjected to successive dichloromethane extraction and hydropyrolysis. The ratios of free to kerogen-bound aliphatic biomarkers increase markedly at relatively low vitrinite reflectance (ca 0.45-0.50%) with large reductions occurring in the concentrations of bound hopanes and steranes. However, the fact that the total concentrations of observable hopanes and steranes (i.e. free plus kerogen-bound) do not decrease until the vitrinite reflectance is greater than ca 0.50% provides evidence that neither oil migration nor aromatisation has begun to occur to a significant extent below this maturity level. To the authors' knowledge, this represents the first study to observe a systematic change in epimer ratios with increasing maturity for hopanes and steranes covalently bound in kerogens. Indeed, the kerogen-bound hopanes and steranes undergo the same epimerization reaction pathways as their free counterparts in the bitumen, but they are generally less mature in terms of isomerisation at both ring and side-chain chiral centres. Indeed, the range of the moretane/hopane index for the hydropyrolysis oils is much larger than that for the bitumens (ca 5 times), indicating a much greater sensitivity to relatively small changes in maturity. The covalently-bound hopanes and steranes released via hydropyrolysis have enabled the maturity of a contaminated core from the North Sea (Central Graben) to be assessed and have showed that it is compatible with the Kimmeridge formation.


The Variability of PCBs in UK Sediments

Jacquie Reed

CEFAS, Burnham Laboratory, Burnham-on-Crouch, Essex CM0 8HA, UK

The economic development of many countries has led to the increased use of both natural and man-made chemicals in the environment. Organic compounds are of particular concern because certain classes of compounds are persistent pollutants that can cause toxicological effects in organisms. One class of persistent organic compounds are PCBs. Commercial mixtures of PCBs have been used extensively throughout the world and as a consequence, are widely distributed in the environment. The measurement of PCB concentrations in marine sediments and dredge spoil material have been assessed to determine their spatial distributions in the UK.

PCBs levels in sediments in coastal environments have been measured between 1990-1997. The magnitude, variability and spatial distribution of PCBs have been investigated to determine whether levels in the environment are declining as a consequence of their ban in the UK in the 1980s. The levels of contamination have been divided into four categories; "contamination not detectable" (<0.2 mg kg-1), "slightly contaminated" (0.2-20 mg kg-1), "contaminated" (21-100 mg kg-1) and "heavily contaminated" (> 100 mg kg-1) (Wells et al., 1989).

The highest levels of total PCBs were measured in; Blyth, Swansea, Tees, Tyne, Mersey, Orwell, Humber, Avonmouth, Barry, Cardiff and Newport. There were a large number of sites with total PCB levels in the "heavily contaminated" category. Since 1990, there has been an increasing percentage of dredge spoil sites in the "heavily contaminated" category. The range of total PCB levels found are 0-3500 mg kg-1. A comparison with other coastal areas has shown that the levels in the UK are more elevated than some of the other estuaries in Europe.

The measurement of total PCB concentrations in offshore sediments are lower than the dredge spoil material and the majority of sediments are categorised as "slightly contaminated". The concentration of total PCBs in marine sediments are representative of background levels expected in the UK (~30 mg kg-1). The level of total PCBs in dredge spoil material are two orders of magnitude higher than offshore sediments.

The results from the preliminary data analyses provide evidence that PCBs are elevated in a number of UK coastal areas especially in harbours and dockyards. An unbalanced hierarchical nested sampling scheme was employed to determine the variability and estimation of PCB levels in sediments in Swansea Docks using variograms and kriging techniques. The extreme levels found in dock and harbour sediments are regarded as "hotspots" and the sampling undertaken at Swansea uses geostatistics as a tool to establish local spatial distributions.


The Role of Surfactants on the Sorption of Hydrophobic Organic Micropollutants in Estuaries

Tracey L. Hyde, Andrew Turner and Geoffrey E. Millward

Department of Environmental Sciences, University of Plymouth, Plymouth, PL4 8AA, UK

The extensive use of surfactants in domestic and industrial applications has generated considerable interest towards their influence on the properties of co-existing contaminants such as hydrophobic organic micropollutants (HOMs). Surfactants exhibit both hydrophobic and hydrophilic properties which, depending on charge and concentration, allow them to enhance or reduce both solubilisation and adsorption of HOMs to sediment. Estuaries frequently receive both surfactants and HOMs from various waste streams, and here lies the concern, since HOMs are by nature lipophilic and may induce a toxic or carcinogenic response in aquatic organisms. Therefore, from an ecological and remediation point of view, there is a need to define the impact of surfactant behaviour on HOM partitioning between water and sediment. The experimental method employed in this study involves tracing the solubility and sorption of a selection of 14C-labelled polycyclic aromatic hydrocarbons (PAHs) in the presence of surfactants (principally sodium dodecyl sulphate or SDS) under simulated estuarine conditions. The radiolabelled PAH is added, at concentrations typically found in the environment, to fresh and saline waters containing sediment particles of less than 63 µm. Results are presented for phenanthrene, a moderately hydrophobic PAH, and SDS, an anionic surfactant. The adsorption of both compounds may be defined by the Freundlich isotherm, which reveals minimal sensitivity to salinity for both SDS and phenanthrene at environmental concentrations. The most important controlling variable is the particle concentration, whereby the partition coefficient is reduced from approximately 2000 to 200 ml g-1 for SDS and 11000 to 2000 ml g-1 for phenanthrene, with an increasing particle concentration from 20 to 1000 mg L-1. These results are discussed in the context of the likely estuarine behaviour of surfactants and HOMs. The next stage of the research will be to determine how the solubility and sorption of phenanthrene and SDS interact with each other.


Poster presentations

Laboratory Decay Experiments of Milk, Olive Oil and Pure Triacylglycerols Absorbed in Potsherds

S. Aillaud, S.N. Dudd, M. Régert† and R.P. Evershed

Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK

†Present address: Laboratoire de Recherche des musées de France, 6 rue des Pyramides, 75041 Paris, cedex 01, France

The walls of unglazed archaeological pottery vessels have been shown frequently to contain appreciable quantities of lipid absorbed during the processing of food and other commodities (Charters et al., 1993). Analyses have shown that lipids are always affected by the various processes of degradation occurring during vessel use and burial. It has also been shown that it is possible to simulate the decay of lipids absorbed in potsherds in the laboratory and that such experiments can help to identify degradation pathways and assist in archaeological interpretations based on lipid residues (Charters, 1996; Dudd et al., in press). As degradation must be to a large extent microbiologically mediated it has been suggested that archaeological residues will be an admixture of bacterial components and the original lipid substrate. An overrepresentation of bacterial components amongst the lipid extracts may have important consequences for the level of information that can be obtained from such residues. It is also likely that the pathways and extent of lipid degradation will depend upon the local burial conditions, e.g. geology, pH, degree of waterlogging, etc. A better understanding of the factors affecting degradation will lend confidence to interpretations based on residues from different sites and different contexts within a single site.

We present here the results of laboratory decay experiments which have been carried out using milk, olive oil and pure triacylglycerols (tristearin and triolein) as substrates absorbed in a fired clay matrix. The influences of temperature and water content of the burial environment on the degradation of lipids have been investigated. The analytical approach involved solvent extraction of powdered fragments of potsherds yielding a lipid extract which was then analysed by gas chromatography (GC) and GC-mass spectrometry. The hydrolytic decay of triacylglycerols was found to be rapid in all experiments. As anticipated the degradation rate of lipids depended on the burial conditions, e.g. degradation being slower under colder and dryer conditions. Significantly, trace amounts of bacterial and fungal markers appeared in the degraded residues originating from the incubation all substrates although quantitative analyses showed these compounds made little significant contribution to the overall lipid distribution of the residues.

References

  • Charters, S. (1996) Chemical investigation of absorbed lipids and laboratory simulation experiments to interpret archaeological pottery vessel content and use. Ph.D. Thesis, University of Bristol.
  • Charters, S., Evershed, R.P., Goad, L.J., Blinkhorn, P.W. and Denham, V. (1993) Quantification and distribution of lipid in archaeological ceramics: implications for sampling potsherds for organic residue analysis. Archaeometry 35, 211-223.
  • Dudd, S.N. Régert, M. and Evershed, R.P. (in press) Assessing microbial distributions to acyl lipids during laboratory degradation of fats and oils absorbed into ceramic potsherds. Org. Geochem. conference proceedings.


Archaeological Ceramics: Evidence for and Origin of Oxidised Lipids

Helen A. Bland, Martine Regert and Richard P. Evershed

School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK

Solvent extractable lipids preserved in ancient ceramic vessels are proving to be a valuable source of information in establishing palaeodietary influences in ancient civilisations (Evershed et al., 1997). Assessments on the origins of these components rely on a detailed knowledge of chemical alterations occurring in constituent molecules during vessel use and burial. In order to provide new information on lipid degradation in archaeological pottery, chemical investigations (gas chromatography, GC, GC/mass spectrometry, GC/MS, and isotope ratio GC/MS) have been performed on ceramic vessels recovered from both arid and water-logged burial environments: Qasr Ibrîm, Upper Egypt, ca 6th century AD and Chalain lake dwellings in Jura (France), Final Neolithic, ca 3000 BC, respectively.

GC profiles of total lipid extracts (TLE) of the Qasr Ibrîm vessels revealed the presence of a series of dicarboxylic acids, with azaleic acid (C9) being the most dominant component; along with the more typical components of C16 and C18 carboxylic acids. The TLEs of the Chalain samples were free from oxidised lipids, however, the insoluble solvent extracted residue was saponified in order to investigate compounds chemically bound to the pot matrix. GC/MS analysis showed that the distribution of components obtained were dominated by dicarboxylic acids and mono- and dihydroxy fatty acids. Further analysis of the solvent extracted residue of lamps from Qasr Ibrîm revealed similar distributions of acids. These components result from oxidation and/or hydroxylation of the double bonds of unsaturated fatty acids (Gillan and Johns, 1982). Carbon isotope values of methyl ester derivatives of lipid profiles from Qasr Ibrîm sherds have provided evidence for the source of their original lipid components. These results will, therefore, have potentially important consequences for the assignment of natural sources of commodities processed in ceramic vessels.

References

  • Evershed, R.P., Mottram, H.R., Dudd, S.N., Charters, S., Stott, A.W., Lawrence, G.J., Gibson, A.M., Conner, A., Blinkhorn, P.W. and Reeves, V. (1997) New criteria for the identification of animal fats preserved in archaeological pottery. Natturwissenschaften 84, 402-405.
  • Gillan, F.T. and Johns, R.B. (1982) Oxic diagenetic products as indicators of past algal populations and diversity. Nature 298, 744-746.


A Stable Carbon Isotopic Study of Carbon Assimilation in the Soil Collembolan Folsomia candida

Paul M. Chamberlain (1), Ian D. Bull1, Philip Ineson (2), Helaina Black (2) and Richard P. Evershed (1)

(1) Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK

(2) Merlewood Research Station, Institute of Terrestrial Ecology, Grange-over-Sands, Cumbria LA11 6JU, UK

A recent Royal Commission report on environmental pollution has highlighted the inadequacy of our knowledge of soil biodiversity and emphasised the need for more basic information on the role of soil biota in dynamic soil processes (RCEP, 1995). An important first step in trying to understand the inherently complex structure of the soil biological community is to classify species of soil fauna into feeding types, since broad groups may have very different functional roles in soil. Collembola are a class of ubiquitous soil arthropoda, existing in numbers of many thousands of insects per square meter of top soil. They are major decomposer organisms, subsisting on fungi, plant detritus and nematodes, the exact proportion of which varies between collembolan species. This study aims to elucidate soil collembolan trophic preferences by using stable carbon isotopic measurements (d13C) to investigate the assimilation of isotopically distinct food sources into the body tissues of various species of collembola.

Bulk stable carbon isotopic measurements of bakers yeast and collembola grown from birth consuming only this yeast were analysed. As expected, when moving up one trophic level, a 1 per cent increase in bulk d13C value is observed between yeast and insect (DeNiro and Epstein, 1978). The individual fatty acid isotope ratios of yeast and collembola are, however, significantly different due to fractionations occurring during the synthesis of collembolan lipids (DeNiro and Epstein, 1977). Sugars derived from plants possessing C3 and C4 photosynthetic pathways were used to isotopically label yeast, which in turn was fed to populations of Folsomia candida, thereby also isotopically labeling the insects. A time-course diet switching experiment was performed, where ‘C4’ yeast was introduced to groups of ‘C3’ collembola. The assimilation of the ‘C4’ yeast components into collembolan tissue was monitored over the course of three weeks through compound specific stable carbon isotopic analysis of fatty acids and other molecular components, e.g. N-acetylglucosamine derived from chitin. An overview of results obtained to date will be presented.

References

  • DeNiro M. J. and Epstein S. (1977) Mechanism of carbon isotope fractionation associated with lipid synthesis. Science 197, 261-263.
  • DeNiro M. J. and Epstein S. (1978) Influence of diet on the distribution of carbon isotopes in animals. Geochimica Cosmochimica Acta 42, 495-506.
  • RCEP (1995) Sustainable use of soils. Royal Commission on Environmental Pollution Report. HMSO, London.


Chemical Investigations of Pottery and Bone from the Arid Nubian Site of Qasr Ibrim, Egypt

M.S. Copley (1), R.P. Evershed (1), and M.C. Horton (2)

(1) Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK

(2) Department of Archaeology, University of Bristol, 11 Woodland Road, Bristol BS8 1TB, UK

Qasr Ibrim, southern Egypt was occupied from approximately 1000 BC to AD 1812, and lies within Lower Nubia, close to what was the border with Ancient Egypt. The site comprised a fortified citadel which gained religious, administrative, commercial and strategic importance (Horton, 1991). Previous chemical investigations of material from the site have shown that the naturally arid environment has led to the exceptional survival of organic materials - particularly ancient biomolecules (O’Donoghue et al., 1996; Evershed et al., 1997; Regert et al., in prep.).

From the Meroitic period (c. 100 BC - AD 350) to the post-Meroitic and X-group period (c. AD 350 - 550), there is evidence for political and economic change in Nubia, with the decline of the Kushite Kingdom. Associated with this are variations in the ceramic wares in use, the introduction of the saqia which allowed irrigation and botanical changes. Through large scale chemical analysis of Meroitic and X-group pottery vessels (n = 400) excavated during the 1998 season (organised by the Egypt Exploration Society), coupled with a study of animal bones, the following are being investigated: (i) Whether there was a change in the use of ceramic vessels over time. (ii) If so, then how this is linked with the archaeological evidence. (iii) Whether different pottery vessel wares were used for different purposes and how this fits in with the established evolution of pottery wares.

In order to establish the survival of organic molecules in different pottery vessel ware types, previously excavated vessels and animal bones are being analysed. Trimethylsilyl (TMS) esters/ethers of the total lipid extracts were analysed via high temperature gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). In addition, after saponification, the acid and neutral fractions are also examined, by GC and GC-MS, as fatty acid methyl esters (FAMES) and TMS derivatives respectively.

The results not only show the high concentrations of recovered lipid (typically 1-5 mg g-1 of pot sherd), but also the detection of less commonly ocurring classes of lipid. The presence of a,w-dicarboxylic acids (in the range of C4-C14, with C9 being predominant) indicates the survival of oxidised lipids (Regert et al., in prep.). The plant sterols b-sitosterol and stigmasterol, 1- and 2-alkanols, and odd chain n-alkanes (C25-C33) point to plant sources for some of the lipids. The complex suite of lipids detected is not only indicative of the high level of preservation of biomolecules from the site, but also of the continued reuse of the vessels.

References

  • Evershed, R.P., Bland, H.A., van Bergen, P.F., Carter, J.F., Horton, M.C. and Rowley-Conwy, P.A. (1997) Volatile compounds in archaeological plant remains and the maillard reaction during decay of organic matter. Science 278, 432-433.
  • Horton, M. (1991) Africa in Egypt: new evidence from Qasr Ibrim’, pp. 264-277 in W.V. Davies (ed.) Egypt and Africa - Nubia from prehistory to Islam British Museum Press: London.
  • O’Donoghue, K., Clapham, A., Evershed, R.P. and Brown, T.A. (1996) Remarkable preservation of biomolecules in ancient radish seeds, Proceedings of the Royal Society London B 263, 541-547.
  • Regert, M., Bland, H.A., Dudd, S.N., van Bergen, P.F. and Evershed, R.P. Free and bound fatty acid oxidation products in archaeological ceramic vessels, submitted.


The Use of d13C Measurements of Individual n-Alkanoic Acids in the Detection of Dairy Fats in Archaeological Ceramics

Stephanie N. Dudd and Richard P. Evershed

Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK

While the domestication of animals by early farmers is relatively easy to deduce, the origins of dairying remains one of the most perplexing questions in archaeology. Our recent work has shown that a range of chemical criteria (fatty acid structures and distributions, triacylglycerol distributions and stable isotope data) can be used to distinguish between the most important categories of domesticated animals exploited in the UK in prehistory, based on remnant fats preserved in pottery vessels (Evershed et al., 1997). Most significant are the compound specific d13C values of individual fatty acids, providing a highly robust criteria, which appear unaffected by prolonged burial, even when compound distributions are altered by microbial or chemical degradation (Dudd et al., in press).

More recent work has shown that compound specific d13C values of fatty acids preserved in pottery from Late Saxon/early medieval and Iron Age/Romano-British sites allow dairy fats to be readily recognised. The recognition of dairy fats relies upon the phenomenon that during lactation ruminant animals route isotopically light fatty acids directly from the forage vegetation to milk, after biohydrogenation (conversion of C18:1, C18:2 and C18:3 à C18:0) in the rumen. This mechanism results in an isotopically distinct signature for milk compared with adipose fat for animals raised on similar pastures. This phenomenon establishes the basis of a new method for detecting the exploitation of animals for dairy products in prehistory through the identification of dairy fats preserved in ancient pottery vessels.

References

  • Evershed, R.P., Dudd, S.N., Mottram, H.R., Charters, S., Stott, A.W., Lawrence, G.J., Gibson, A.M., Conner, A., Blinkhorn, P.W. and Reeves, V. (1997) New criteria for the identification of animal fats preserved in archaeological pottery. Naturwissenschaften 84, 1-6.
  • Dudd, S.N., Regert, M. and Evershed, R.P. (in press) Assessing microbial contributions to absorbed acyl lipids during laboratory degradations of fats and oils and pure triacylglycerols absorbed into ceramic potsherds. Advances in Organic Geochemistry 1997.


The Quantification and Identification of Tar Balls in the South-West of England

Catherine E. Hutchinson

Institute of Marine Studies, University of Plymouth, Plymouth, Devon PL4 8AA, UK

Although the south-west of England is not renowned for oil pollution on its beaches compared to other parts of the world, there is substantial evidence that a considerable amount of oil, in the form of tar balls, is washed ashore in the region. The origin and amount of this background oil contamination is the basis of my current Masters project.

The quantification will be completed by weight of tar per metre of beach front. The oil will be extracted from the rest of the debris by dissolution in dichloromethane and then separated into different fractions by column chromatography. The aliphatic and aromatic hydrocarbon fractions will be initially analysed by GC-FID, followed by GC-MS using selected ion monitoring for biological markers (e.g. steranes and triterpanes). Further analysis will include the determination of aromatic steroids and other aromatic hydrocarbons (e.g. naphthalenes and phenanthrenes).

The probable origin the tar balls will be investigated by fingerprinting the biological marker distributions and comparison with data from reference oils and the literature. By using the biological marker data it may be possible to identify a particular region that is responsible for the majority of the tar balls. If so, links may be proposed between background pollution and the movement of oil tankers around the South-West of England.


Stable Isotope Analysis of Bone Cholesterol and Collagen for Palaeodietary Reconstruction

Susan Jim (1), Andrew W. Stott (1), Stanley H. Ambrose (2), Juliet M. Rogers (3) and Richard P. Evershed (1)

(1) Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK

(2) Department of Anthropology, University of Illinois, Urbana-Champaign, Urbana, IL 61801, USA 

(3) Rheumatology Unit, University Division of Medicine, Bristol Royal Infirmary, Bristol BS2 8HW, UK

The introduction of stable isotope analysis using carbon (13C/12C) and nitrogen (15N/14N) revolutionised palaeodietary research in the 1970s. This technique has been used to analyse both the collagen and apatite preserved in ancient skeletal remains and has been successful in assessing the consumption of protein vs. carbohydrates, C3 vs. C4 terrestrial resources and marine vs. terrestrial resources of ancient populations. The discovery that cholesterol is preserved in archaeological remains raised questions as to whether dietary information could also be derived from its isotopic signature (Evershed et al., 1995). Preliminary research has shown that the dietary signal derived from cholesterol is different from that derived from collagen and apatite, and so its use in conjunction with these existing methods should give a fuller insight into palaeodiet. Cholesterol can be separated, characterised and its d13C value measured by using gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and isotope ratio monitoring-gas chromatography mass spectrometry (irm-GCMS) (Stott and Evershed, 1996; Stott et al., 1997). Studies to date have demonstrated that the d13C value of cholesterol is almost homogenous within one skeletal type and highly consistent between different skeletal members. It has also been used successfully to distinguish subtle dietary differences between an English inland (Medieval, Abingdon Vineyard, Oxfordshire) and a coastal population (Saxon-Medieval, Barton-on-Humber, N. Lincolnshire; Stott et al., in prep.).

Current research in our laboratory is concentrating on determining the effects of differing nutritional inputs, metabolism and turnover rate on the isotopic composition of bone cholesterol. Holtzmann albino rats were raised on a variety of isotopically controlled diets consisting of differing combinations and proportions of C3, C4 and marine protein, and C3 and C4 energy components. Bulk d13C values of the diet, bone collagen, apatite, hair and flesh of these samples have already been measured in a previous study (Ambrose and Norr, 1993). The aim of this work is to measure the d13C content of the rats tissue cholesterol and individual fatty acids as a function of each different diet with a view to determining how and which specific biochemical fraction (protein and/or energy) present in their formulated diets most influences their lipid isotopic composition. Comparisons of the cholesterol d13C values obtained from studies of this type with those measured on cholesterol recovered from ancient human bone should allow us to make more accurate interpretations as to the dietary preferences of past populations.

References

  • Ambrose, S.H. and Norr, L. (1993) Experimental evidence for the relationship of the carbon isotope ratios of whole diet and dietary protein to those of bone collagen and carbonate, in Prehistoric human bone-archaeology at molecular level. (eds. J. Lambert and G. Grupe), 1-37, Springer Verlag.
  • Evershed, R.P., Turner-Walker, G., Hedges, R.E.M., Tuross, N.L. and Leyden, A. (1995) Preliminary results for the analysis of lipids in ancient bone. J. Archaeol. Sci., 22, 277-290.
  • Stott, A.W. and Evershed, R.P. (1996) d13C analysis of cholesterol preserved in archaeological bones and teeth. Anal. Chem. 68, 4402-4408.
  • Stott, A.W., Davies, E., Tuross, N. and Evershed, R.P. (1997) Monitoring the routing of dietary and biosynthesised lipids through compound-specific stable isotope (d13C) measurements at natural abundance. Naturwissenschaften, 84, 82-86.


Determination of the Possible Estrogenic Degradation Products of Cholesterol in Sewage Treatment Works

S.J. Niven (1), S. Rowland (1), J. McEvoy (2), M. Depledge (1), J. Snape (3), M. Evans (3) and M. Hetheridge (3)

(1) Plymouth Environmental Research Centre, University of Plymouth, Plymouth PL4 8AA, UK

(2) Environment Agency, Kings Meadow House, Kings Meadow Road, Reading, Berkshire RG1 8DQ, UK

(3) Zeneca Environmental Laboratory, Freshwater Quarry, Brixham, Devon TQ5 8BA, UK

Concentrations of cholesterol entering sewage treatment works (STW) are often in the order of mg/L influent yet comaparatively little is known about the production and fate of steroidal metabolites of cholesterol during sewage treatment. Given present concerns over the estrogenicity of several steroids found in sewage effluent, the present study was designed to examine the fate of isotopically-labelled cholesterol in a simulated sewage treartment system. Of particular interest was the possibility of a link between cholesterol and known estrogenic steroids including estrone, estradiol and a putative intermediate, 19-norcholest-1,3,5(10)-trien-3-ol (NCT) in STW. The simulated STW consisted of a 1 L Semi Continuous Activated Sludge (SCAS) system. Both aerobic and anaerobic incubation with radiolabelled 4-14C-cholesterol was carried out. The aerobic experiment was run over a 24 hour period prior to sampling of liquid and suspended solids. The anaerobic experiment was much slower and ran over a 9 week period. The solids from both experiments were extracted three times in methanol and liquid samples were extracted by solid phase extraction and elution with methanol. The resulting extracts were fractionated by reverse phase HPLC with radiodetection. The radioactive fractions were subsequently analysed by GC-FID coupled with a radiodetector. Preliminary results indicate that ~25 per cent of radiolabel added in the aerobic experiment were mineralised to CO2 within 24 hours.


A Preliminary Study Concerning the Effect of Soil pH on the Degradation of Soil Organic Matter

Chris J. Nott (1), Ian D. Bull (1), Pim F. van Bergen (1),†, Paul R. Poulton (2) and Richard P. Evershed (1)

(1) Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK

(2) Soil Science Department, IACR-Rothamsted, Harpenden, Herts. AL5 2JQ, UK

† Present address: Organic Geochemistry Group, Geochemistry, Faculty of Earth Sciences, Utrecht University, P.O. Box 80021, 3508 TA Utrecht, The Netherlands

Soil organic matter is composed of plant, animal and microbial residues, at varying stages of decomposition, and amorphous humic substances. These latter components are believed to be formed concomitantly during the microbial decomposition of the aforementioned residues. Humification and mineralisation processes are responsible for the chemical alteration of soil organic matter and are of great importance to the terrestrial carbon cycle (e.g. Oades, 1988; Jenkinson et al., 1992; Paul and Clark, 1996; Kögel-Knabner, 1992 and references cited therein). The magnitude of the soil organic matter reservoir depends upon plant production and the mineralization of plant residues entering the soil (Coûteaux et al., 1995). This, in turn, is dependent upon several factors including soil type, climate, chemical composition of the plant residue, and the nature and abundance of decomposing organisms. Soil pH also has a profound effect on soil organic matter preservation and decomposition, although its precise mode of influence has yet to be fully established (Motavalli et al., 1995).

Total lipid extracts and solvent insoluble organic matter in soils from the Park Grass Experiment at Rothamsted Experimental Station, Harpenden, UK were studied to determine the effect of pH on the preservation/degradation of plant derived biomolecules in soil organic matter. The plots selected for study have pH values ranging from 3.7 to 7.3, with acid soils being composed of two distinct horizons (i.e. humic rich top layer and mineral layer).

The total lipid extracts of the soil samples with low pH exhibit a higher relative abundance of long-chain (>C20) organic acids believed to be derived largely from oxidation of plant derived lipids. Characteristic components of overlying vegetation in the low molecular weight fraction are only retained in the humic rich top layer whilst the signal in the mineral layer is believed to derive primarily from previous vegetation. Compound specific stable carbon isotopic measurements of long-chain n-alkanols are considered demonstrative of differences in the rate of incorporation of vegetation lipids into the humic top layer of the acidic soils. Furthermore, in the soil samples exhibiting low pH lignin contributes to the high molecular weight fraction of the humic top soil layer, however, in contrast the mineral layer of the same soil shows little evidence of intact lignin and is instead dominated by amino acid derived products, which may be present as polypeptides. The pyrolysates of the mineral soils of high pH yield a distribution of products similar to that found in the bottom layer of the low pH samples but with evidence of lignin derived moieties. Overall soil pH was quite clearly found to have a significant effect on the preservation of higher plant derived biomolecules including ligno-cellulose.

References

  • Coûteaux M.-M., Bottner P. and Berg B. (1995) Litter decomposition climate and litter quality. Trends in Evolution and Ecologie 10, 63-66.
  • Jenkinson, D.S., Harkness, D.D., Vance, E.D., Adams, D.E. and Harrison, A.F. (1992) Calculating net primary production and annual input to soil from the amount and radiocarbon content of soil organic matter. Soil Biology and Biochemistry 24, 295-308.
  • Kögel-Knabner I. (1992) Forest soil organic matter: structure and formation. Bayreuther Bodenkundliche Berichte. 24. 103p.
  • Motavalli P.P., Palm C.A., Parton C.A., Elliott E.T. and Frey S.D. (1995) Soil pH and organic C dynamics in tropical forest soils: Evidence from laboratory and simulation studies. Soil Biology and Biochemistry 27, 1589-1599.
  • Oades J.M. (1988) The retention of organic matter in soils. Biogeochemistry 5, 35-70.
  • Paul, E.A. and Clark, F.E. (1996). Soil Microbiology and Biochemistry. Academic Press, San Diego.


Onocerane, an Unusual Triterpane in Middle Cretaceous Shales of the Upper Benue Trough, Nigeria

Mike Pearson (1) and Nuhu G. Obaje (2)

(1) Organic & Petroleum Geochemistry Group, Department of Geology & Petroleum Geology, University of Aberdeen, Aberdeen AB24 3UE, UK

(2) Chevron Nigeria Ltd., Geological Laboratory, PMB 12825, Lagos, Nigeria

The structures of three synthesized isomers (I - III) of onocerane were first reported together with corresponding mass spectra and retention indices by Kimble (1972). The first recorded geological occurrence of these compounds was from the Tertiary Clarkia beds of Idaho (Giannasi and Niklas, 1981) where onocerane I was associated with Miocene leaf fossils of the Pseudofagus taxon, a broad-leaved tree considered to have thrived in a warm-temperate, humid climate. Onocerane I has been subsequently reported in fluvial and lacustrine Oligocene shales from an intermontane basin in Montana (Curiale, 1988) and from a similar palaeo-environmental setting in a Chinese Palaeogene mudstone (Fu Jiamo et al., 1988) and an Oligocene oil (Wang Tieguan et al., 1988). Onocerane I has not previously been recorded in pre-Tertiary sediments although Wang Tieguan et al. (1988) reportedly found onoceranes III and II in Chinese lacustrine mudstones of varying salinity as old as mid- and late Carboniferous respectively.

We report here a Cretaceous occurrence of onocerane I (Fig. 1) as the dominant triterpane and a major component of the saturated hydrocarbon fraction in immature shales from the Pindiga formation of probable Turonian to Santonian age from the Gongola arm of the Upper Benue rift basin, Nigeria. The beds are lithologically unremarkable, being medium grey shales devoid of obvious macroflora or fauna. Geochemically, TOCs are around 2%, and soluble extracts (around 100 ppm) are largely aliphatic and dominated by triterpanes which outweigh n-alkanes by a ratio of about 3:1. Onocerane I is the single most abundant compound in some samples and co-occurring triterpenoids are mainly the C29-32 bb-hopane series and C29-30 hop-(17,21)-enes.

References

  • Curiale, J.A. (1988) Molecular genetic markers and maturity indicators in intermontane lacustrine facies: Kishenehn Formation, Montana. Advances in Organic Geochemistry 1987, Org. Geochem. 13, 633-638.
  • Fu Jiamo, Sheng Guoying and Liu Dehan (1988) Organic geochemical characteristics of major types of terrestrial petroleum source rocks in China. In: Fleet, A.J., Kelts, K. & Talbot, M.R. (eds) Lacustrine Petroleum Source Rocks. Geol. Soc. Spec. Publ. 40, 279-289.
  • Giannasi, D.E. and Niklas, K.L. (1981) Comparative palaeobiochemistry of some fossil and extant Fagaceae. Am. J. Botany. 68, 762-770.
  • Kimble, B. (1972) The geochemistry of triterpenoid hydrocarbons. PhD Thesis. University of Bristol.
  • Wang Tieguan, Fan Pu and Swain, F.M. (1988) Geochemical characteristics of crude oils and source beds in different continental facies of four oil-bearing basins, China. In: Fleet, A.J., Kelts, K. & Talbot, M.R. (eds) Lacustrine Petroleum Source Rocks. Geol. Soc. Spec. Publ. 40, 309-325.


The Effect of Driving Conditions on the Emissions of Naphthalene from a Direct Injection Diesel Engine

Robin Pemberton, Paul Tancell, Michael Rhead and James Braven

Department of Environmental Sciences, University of Plymouth, Plymouth PL4 8AA, UK

This study reports on the sources of naphthalene (pyrosynthesised and survived) in diesel exhaust at different driving conditions. The effect of engine speed and load on the recovery of naphthalene and the contribution of pyrosynthesised and survived naphthalene to this recovered naphthalene were established using [14C]naphthalene. The most effective combustion conditions, i.e. with regard to overall recovery of naphthalene (survived and pyrosynthesised), were shown to be those at mid speed and load (2500 rpm and 50 Nm). At all the speeds and loads investigated the pyrosynthesised fraction of the recovered naphthalene was shown to be dominant. When sampling at constant speed, an increase in load resulted in an increase in the levels of both the survived and pyrosynthesised naphthalene in the emissions.


14 C Dating of Archaeological Pottery: A Compound Specific Approach using Individual Lipids

Andrew W. Stott (1), Richard P. Evershed (1), Robert E.M. Hedges (2), and Chris B. Ramsey (2)

(1) Organic Geochemistry Unit, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK

(2) Research Laboratory for Archaeology and the History of Art, University of Oxford, 6 Keble Road, Oxford OX1 3QJ, UK

Extensive studies of pottery recovered from archaeological sites have resulted in empirically derived sequences representing changes in pottery types or characteristics through time. Termed seriation, this process is widely used as a system of relative dating. Absolute dates, used to fix points in chronologies, are often derived from radiocarbon dating of associated finds at the excavation (e.g. bone, carbonised seeds) or by dendrochronology. Accelerator mass spectrometry (AMS) 14C dating is regarded as a routine technique in archaeology and is applicable to a wide range of biogenic materials e.g. wood, shell, teeth, bone, seeds, charred organics, etc. One of the major problems in radiocarbon dating arises from contamination of samples during burial by absorption of exogenous carbon containing components from the burial environment. The problem of contamination may be overcome by purification of the organics into components that can be directly linked to the sample itself, e.g. cellulose from wood, or collagen from bone. Accurate 14C dating of archaeological pottery remains an ongoing area of research to the archaeologist; the ideal method would be to date carbon deposits directly associated with or incorporated within the pottery itself.

It is well established that a wide range of lipids are detectable in appreciable concentrations in unglazed archaeological ceramics. These derive largely from the processing, procurement and storage of foodstuffs during vessel usage. The porous nature of the ceramic allows entrapment and affords considerable protection to otherwise readily degradable compounds (Evershed, 1993). Recently, AMS has been successfully applied to the dating of individual lipids from sedimentary organic matter (Eglinton et al., 1996). We are currently applying a similar approach to date individual lipids preserved in archaeological pottery. Lipids possess several important properties that make them favourable candidates for radiocarbon analysis: 1) their structures, distributions and 13C content are can be well characterised; 2) contaminants can be readily detected using gas chromatography mass spectrometry (GC/MS); 3) their hydrophobicity makes them relatively immobile in the burial environment, and 4) they possess young ages at the time of deposition. Using automated preparative gas chromatography (PCGC), individual lipids can be isolated from extracts in high purity and in sufficient concentrations (>200 mg) for high precision AMS dating. In this paper we will discuss the methodology of compound specific radiocarbon analysis and present results obtained from studies undertaken towards confirming relative chronologies and establishing secure sequences for selected British pottery using the single compound approach.

References

  • Evershed, R.P. (1993) World Archaeology 25, 75-93.
  • Eglinton T.I., Aluwihare L.I., Bauer J., Druffel E.R.M and McNichol A.P. (1996) Anal. Chem. 68, 904-912.


The Partitioning Behaviour of Chemicals in Oilfield Produced Water

E.D. Stutt

Petroleum & Environmental Geochemistry Group, Department of Environmental Sciences, University of Plymouth, Plymouth, Devon PL4 8AA, UK

Water associated with oil is brought to the surface at the same time during drilling and separated on the production platform before being discharged overboard into the sea. The average yearly input into the North Sea is in the region of 150 x 106 tons. Concern exists about the environmental impact of the more polar, water soluble petrogenic compounds present in the water and the speciality production chemicals which are added on the platform. The primary experimental objectives of this work are to measure time-dependent and equilibrium particle-water partition coefficients (Kd) for representative petrogenic compounds to assess their transport mechanisms and fate.

The compounds being considered will experience very different conditions in the formation reservoir, oil platform and sea. Partitioning experiments are carried out using 14C-radiolabelled chemicals and the master variables being considered for their effect on sorption processes are temperature, particle type and concentration, salinity, pH and oxygen concentration. The effects of different production chemicals, which are usually surfactants, are also being investigated.


Solving the Insoluble?

P. A. Sutton, C. A. Lewis and S. J. Rowland

Petroleum & Environmental Geochemistry Group, Department of Environmental Sciences, University of Plymouth, Plymouth, Devon PL4 8AA, UK

Despite its geochemical significance, sedimentary macromolecular organic matter, including biomolecular material, which is insoluble in non-oxidising acids, bases and normal organic solvents (insoluble organic matter, IOM), and which is termed kerogen when it occurs in Ancient sediments, has only been characterised in a limited number of elegant chemolytic studies. In the present, preliminary, study we report our attempts to dissolve IOM in order to make it more readily analysed by conventional methods. IOM was isolated by sequential digestion of soluble matter from the methanogens, Methanobacterium thermoautotrophicum, (0.1 per cent dry weight IOM) and Methanococcus jannaschii, (2.8 ± 0.3 per cent dry weight IOM) and from a Recent lacustrine sediment (Rostherne Mere, UK, 11-15 per cent dry weight IOM). Sequential removal was monitored by examination of the insoluble residues by pyrolysis-gas chromatography-mass spectrometry (py-GCMS) and solid state nuclear magnetic resonance spectroscopy (ss-NMR). IOM samples were then treated with an ionic liquid (1-ethyl-3-methyl imidazolium chloride/aluminium (III) chloride). A synthetic dendrimer was also treated with ionic liquid. Ionic liquid-sample mixtures were microwave heated, hydrolysed, filtered and both non-aqueous soluble retentates and aqueous filtrates collected. Aqueous filtrates and retentates were then extracted with organic solvents. The insoluble matter in the retentates was examined by py-GCMS. The organic solvent extracts of the retentates and of the aqueous filtrates were investigated using solution NMR.

The largest portion of solvent extractable organic matter was found in the aqueous filtrates, much of which remains to be identified by interpretation of the spectroscopic data. However, some preliminary observations can be made. Interestingly, the proton NMR spectrum of the dendrimer filtrate extract showed that ionic liquid treatment had substantially changed the dendrimer structure. Over 30 new alkyl resonances appear in the aliphatic region of the spectrum (d /ppm 0.5-4.0), and the pattern of aromatic resonances (d /ppm 6.3-8.2) was also changed. It is suggested that Freidel-Crafts-type alkylations could have been promoted by the aluminium (III) chloride moiety of the ionic liquid. When applied to unknown IOM from bacteria and sediments it appears that the addition of ionic liquid, heating and hydrolysis also chemically alters these substrates, since some previously solvent-insoluble organic matter became soluble. The proton NMR spectrum of the IOM filtrate extract of M. jannaschii contained predominantly aliphatic resonances with only one aromatic and two alkenic resonances. Proton NMR spectra of the sedimentary IOM filtrate extracts were also dominated by aliphatic signals, in contrast to solid state NMR analyses of the IOM before treatment, again suggesting alkylation of the original matter. If the mode of action of ionic liquid treatment is reproducible and can be better understood, this procedure may play a part in the further characterisation of IOM, but simple dissolution of IOM appears not to occur, judging from these preliminary experiments.