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.
- 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.
- 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.
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- 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.
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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.
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- Koller et al., (1998) Nature 391, 343-344.
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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.
- 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
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.