Loch Ness Project

By GORDON SANDERS
Institute of Environmental and Biological Sciences,
University of Lancaster

KEVIN C. JONES
Institute of Environmental and Biological Sciences,
University of Lancaster 

ADRIAN J. SHINE
Loch Ness and Morar Project

Introduction
The activities of man in the developed world, since the inception of the Industrial Revolution in the 1760s, has resulted in widespread global contamination from a variety of elements and compounds.  As environmental impact, toxicological awareness and analytical techniques have developed, so too has environmental consciousness.  Following the publicity given to several pollution disasters, followed by public lobbying and governmental legislative action, programmes were initiated to improve environmental quality.  Most noteworthy was the implementation of the Clean Air Act of 1956, directed at limiting toxic emissions to the atmosphere.  Unfortunately much environmental and ecotoxicological damage had already been perpetrated.  Heavy metal contamination was the first to receive attention, with mercury poisoning and emissions of lead from automobiles initially becoming popular avenues for research.  The impact from organic compounds (i.e. those containing carbon in their structure) was not fully recognised until the late 1960s, and remained somewhat under-investigated until quite recently.  Of the vast array of organic pollutants present within the environment, from natural and anthropogenic sources, few if any have been researched in as much detail as the polychlorinated biphenyls (PCBs) and polynuclear aromatic hydrocarbons (PAHs).

 PCBs and PAHs are examples of ubiquitous pollutants, generally found at elevated concentrations in urban/industrialised regions, and also distributed to

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remote locations by wet and dry atmospheric deposition processes and hydrospheric transport mechanisms.  They have been detected at varying magnitudes in a variety of terrestrial, aquatic, and marine biotic and abiotic matrices throughout the world, which demonstrate differences in compound uptake mechanism and composition.  PCBs are anthropogenic compounds, which were first produced in 1929 and found use as heat transfer fluids in electrical transformers and capacitors, and pneumatic systems.  PAHs, on the other hand, although produced naturally from the incomplete combustion of fossil fuels, are indicators of anthropogenic activity, in particular heavy industrial processes.  Combustion/emission controls (1950s), and usage and production bans (1970s), have been nationally and internationally imposed in an attempt to reduce releases of PAHs and PCBs, respectively, to the natural environment.

As concern relating to the environmental impact and burdens of these groups of compounds has grown, techniques have been developed to construct retrospective historical input profiles, and, in addition, to ascertain the long-term environmental response of contaminants following implementation of legislation to restrict their production and use. 

Many techniques have been introduced to assess temporal changes in levels of unaltered recalcitrant pollutants, including the utilisation of peat-cores and ice-cores (M.A.R.C., 1985), and the analysis of archived materials (Jones, Grimmer, Jacob and Johnston, 1989; Jones, 1991; Jones, Sanders, Wild, Burnett and Johnston, 1992).  Undisturbed dated sediment cores have also been widely used for constructing chronological pollutant trends, since lakes and oceans are ultimate deposition sites (Hites, Laflamme and Farrington, 1977; Eisenreich, Capel, Robbins and Bourbonniere, 1989; Sanders, Jones, Hamilton-Taylor and Dorr, 1992).

Historical inputs of twenty-nine individual PCB congeners and twelve unsubstituted PAHs, as determined from an undisturbed Loch Ness sediment core, are presented in this paper.  Contaminant flux trends are discussed in relation to potential source and use functions, and water column losses/chemical alteration.  Despite the breadth and scope of publications now available on these groups of compounds, there still remains a dearth of knowledge regarding their fate, behaviour and diagenesis in the natural environment.  In addition, little knowledge regarding British and European loadings of PCBs and PAHs is presently available.  As such, it is hoped that this current work will make a valuable contribution to our further understanding of the distribution and loadings of hydrophobic organic contaminants in rural British locations.

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Brief Background to PCBs and PAHs
Both groups of compounds have characteristic non-polar, semi-volatile properties, ubiquitous distribution throughout the globe, and are environmentally persistent.

PCBs.
Polychlorinated biphenyls, as the name indicates, consist of a biphenyl backbone, upon which are 10 available positions for chlorine (Cl) substitution (see Figure 1, 3K), giving rise to a sum of 209 different possible substitution patterns, referred to as congeners.  These extend from mono-Cl compounds right through to a totally Cl substituted deca-Cl congener.  Congener solubility and vapour pressure generally decrease with increasing levels of Cl substitution.  Of the 209 theoretical congeners produced, it is believed that only 140 to 150 separate congeners may exist within the environment at detectable levels (Schulz, Petrick and Duinker, 1989).  Ballschmitter and Zell (1980) developed a numbering system which relates a unique number (between 1 and 209) to a specific PCB congener/structure.  This nomenclature system has been internationally adopted.

PCBs were first commercially produced in 1929 by the straightforward chlorination of biphenyl in the presence of a ferric chloride catalyst.  The reaction mixtures produced were marketed on the basis of their average level of chlorination under the Aroclor, Askarel and Clophen trade names.  The bulk of PCBs produced between 1930 and 1980 were incorporated into electrical transformers and capacitors as heat transfer fluids, because of their chemical inertness.  PCBs also found use as additives in plasticising agents and carbonless copying paper.  In the environment, PCBs are best known for their bioaccumulatory properties.  Their apparent resistance to excretive loss, and affinity for fatty tissue, means that body burdens within lving organisms can be high, particularly in those close to the top of the food-chain with a staple diet of fish.  Biomagnification factors are particularly high for seals Phoca sp. and Polar Bears Thalarctos maritimus, despite their main habitats being remote from industrial conurbations (Norstrom, Simon, Muir and Schweinsburg, 1988; Morris, Law, Allchin, Kelly and Fileman, 1989).

Chronic exposure to PCBs may lead to chloracne, a pigmentation of the skin, and possible reproductive dysfunctions have also been reported.  Toxicological effects at subtle levels (i.e. those concentrations to which the vast majority of living organisms are subjected) are not clearly understood at present, and require further epidemiological investigation;  however, carcinogenic and mutagenic properties have been reported (Kimbrough, 1987).

PAHs.
Polynuclear aromatic hydrocarbons are emitted as by-products of the incomplete combustion of fossil fuels, and have therefore been present within the

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natural environment since at least the advent of fire.  The main building block is an arrangement of fused benzene rings linked within a conjugated system.  Figure 2 (11K) illustrates the structures of the twelve unsubstituted PAHs analysed for during this study.  These range from the 3-ringed structure of phenanthrene (molecular weight 178) to the 6-ringed coronene (molecular weight 300).  As for PCBs, solubility and volatility of PAHs tends to be inversely related to compound molecular weight.  All PAHs are known or suspected carcinogens, and as such are important from a toxicological point of view.  The compounds demonstrating the greatest carcinogenicity reported herein include benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[a]pyrene, dibenz[ah]anthracene and benzo[ghi]-perylene (Tuominen, 1990). 

Materials and Methods
Sampling
A 1.0 m long sediment core (10.3 cm internal diameter) was obtained from the North Basin of Loch Ness, using a modified Cullenberg gravity coring device (at 57°20'N, 4°24'W; water depth 210 m) during April 1992.  The sampling site was chosen to reflect an area of loch bed which is believed to be relatively flat and likely to be devoid of any major in situ sediment disturbances, e.g. slumping.  The sediment core was sectioned immediately following retrieval, using a vertical piston extruder with 1.0 cm intervals accurately marked.  Extruded sections were carefully removed from the top of the core by a specifically machined copper slicer, and were placed in labelled zip-lock plastic bags.  The sectioning regime involved removal of 1.0 cm intervals from the uppermost 14 cm of the core (sections LN1 - LN14), and 2.0 cm intervals to a maximum depth of 54 cm (LN15 - LN34) thereafter.  The samples were deep frozen until required for further preparation.  Finally, the samples were transferred to evaporating dishes while still frozen, and were left to air-dry at ambient temperature and pressure before milling and homogenisation to a uniform fine powder. 

Dating
Average sediment accumulation rates, and a down-core chronology, have been determined from ¹³⁴Cs and ¹³⁷Cs caesium isotope data derived from gamma spectroscopy.  Approximately 5.0 to 15 g of air-dried material, from various sections of the core, were counted for a duration of at least one day on an E.G &

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G. Ortec system, employing a high purity germanium detector.  Counting replication and efficiency was checked on a regular basis with spiked material. 

Sample Extraction and Analysis
Between 2.0 and 10 g of air-dried sediment material in Whatman cellulose extraction thimbles, was soxhlet extracted with dichloromethane for 12 hours.  Copper turnings were incorporated during extraction to remove elemental sulphur.  Following extraction, the sample was split in a 2 : 1 ratio for the determination of PCBs and PAHs, respectively. 

PCB Purification and Analysis
Detailed information regarding the clean-up and analytical steps employed during the determination and quantification of PCBs in sediments can be found in Sanders et al. (1992).  In summary, matrix interferences are removed on a Florisil column, PCBs are eluted with hexane, concentrated to 0.5 ml, and analysed by high resolution capillary gas chromatography equipped with electron capture detection (HRGC-ECD).  Identification and quantification of PCBs was achieved by overlaying the chromatogram of a standard mix containing 51 individual congeners, and matching and naming peaks by their retention times.  This step was performed automatically using a VG Minichrom data processing package.  The 49 congeners present in the composite PCB standard were, in order of elution, Nos. 3, 10, 6, 8, 14, 30, 18, 15, 54, 28, 52, 104, 44, 37, 61/74, 66, 155, 101, 99, 119, 77/110, 82/151, 149, 118, 188, 153, 105, 138, 126, 187, 183, 128, 185, 202, 156, 204, 180, 169, 170, 198, 189, 208, 194/205, 206, 209.  Of the 49 congeners screened for, 30 have been quantified and are reported here.  The results are discussed with respect to the sum of these 30 congeners (sigmasPCB).

PAH Purification and Analysis
Details of the procedures involved in the clean-up and analysis of PAHs have been comprehensively described (Sanders, Jones, Hamilton-Taylor and Dorr, 1993).  Briefly, samples were cleaned-up on a column of Florisil, and all unsubstituted PAHs eluted with dichloromethane.  The eluent was reduced to 0.5 ml, and 2.0 to 5.0 µl was injected into a high performance liquid chromatography system (HPLC) interfaced to a fluorescence detector.  PAHs were identified and quantified by comparing the retention time of eluted peaks in samples to those in a composite standard.  In total, 12 PAHs were quantified and are reported in this paper; in order of elution, these were phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene/chrysene (co-elute), benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, dibenz[ah]anthracene, benzo[ghi]perylene and coronene.  Derived data is discussed in terms of sigmaPAH.

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Results and Discussion
Dating

Average sediment accumulation rates have been calculated, and dates applied to each section using the ¹³⁴Cs and ¹³⁷CS activity/depth relationships illustrated in Figure 3. (6K)  These plots show some basic chronological marker layers:  the surface of the core is assumed to date as 1992; corresponding ¹³⁴Cs and ¹³⁷Cs maximum activities, occuring at a depth of 2.5 cm, are representative of radio-isotope releases from the Chernobyl accident on 1st May 1986; a further sub-surface maximum of ¹³⁷Cs at 9.5 cm, albeit a squat, diffuse peak, is indicative of the most concentrated period of nuclear weapons testing, which took place between 1963 and 1964.  Although the Cs isotope method of chronological application is limited to post-1960 use, an average rate of sedimentation has been invoked between the section corresponding with 1963/64 and the bottom of the core.  To assist in this assumption, a distinct clay marker layer, ubiquitous to the entire loch bed, to differing magnitudes (Bennett, 1993), and occuring at a depth of 33 cm in this core, has been utilised.  This band is significant, and has been radiometrically dated at approximately the late 1860s/early 1870s (Bennett, 1993), and is believed to have resulted from grossly increased suspended particulate material loadings entering the system from the great flood of 1868 (Anon., 1868; Barron, 1985).  With the current absence of data for ²¹⁰Pb, the naturally occurring radio-isotope, the allocated chronology must be viewed with some ambiguity.  However, it is believed that the core has been sufficiently resolved, and that in-situ sedimentary processes (e.g. mixing) may be the dominant source of error while constructing time trends.

PCB Time Trends
The sigma PCB concentration/depth, and estimated flux/year profiles, derived from the analysis of the Loch Ness sediment core, are illustrated in Figures 4a and Figure 4b (5K) respectively.  PCB is defined as the sum of the 29 congeners, Nos.  82/151 (co-elute), 99, 101, 105, 77/110, 118, 119, 128, 138, 149, 153, 155, 156, 170, 180, 183, 185, 187, 188, 189, 194/205, 198, 202, 204, 206 and 208 - all congeners contain 5 chlorines.  U.K. PCB production data is also provided in Figure 5.  Fluctuations in PCB levels are apparent with time and depth (Figures 4a and Figure 4b, 5K graphs), inferring temporal changes in loadings entering the Ness system.  Traces of PCBs are evident throughout all the core sections extracted (down to a depth of 29 cm, approximately corresponding to the year 1890), with levels constituting approximately

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1.0 g kg^-1 (i.e. 1.0 part per billion).  However, PCB mixtures were not commercially produced until the 1930s, thus suggesting that levels found at the base of the core, pre-dating this period, may have resulted from: 

(1) Misallocation of ¹³⁴Cs and ¹³⁷Cs derived chronology, 

(2) In situ transport and diffusion down the core following compound deposition, 

(3) Contamination of deeper core sections during extrusion, due to smearing effects on the core tube wall,

 (4) Adsorption of PCBs from ambient air during air-drying of material, or

 (5) A combination of all these processes.

 Point (4) seems most likely to be responsible for this observation, since 90% to 95% of all atmospheric PCBs exist in the free gas-phase (Manchester-Neesvig and Andren, 1989).

Initial increases in loadings of PCBs are first observed around 1945, corresponding to a depth of 15 cm.  Thereafter, the sediments show a sharp escalation in sigmaPCB concentration and flux loadings, demonstrating a maximum input function between 12.5 and 7.5 cm, approximately 1954 and 1972.  Peak input was established at about 1958, 11.5 cm below the core surface.  Since the mid-1970s inputs of PCBs to Loch Ness and the Ness catchment system have shown a significant reduction.  Indeed, when compared against average concentrations and fluxes of PCBs sedimented out during the period of maximum input, the core data suggests an average decrease of 52% in sediment concentrations, which translates to a drop of around 37% in flux delivery, over the past 20 years.

The PCB input function determined from the Loch Ness core (Figures 4a and 4b) illustrates some anomalous characteristics with U.K. PCB production figures (see Figure 5,  6K). Production in the U.K. commenced in 1954, and peaked in the mid-1960s to late-1960s.  Approximately half of all PCBs produced in the U.K. were incorporated into 'closed' system transformer and capacitor usage.  Prior to this, small quantities had been imported, for promotional use only (Bletchly, 1983).  Higher than background levels of PCBs are, however, detected in the early-1940s, suggesting either that long-range transport and deposition of hydrophobic

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contaminants is significant within this rural region, and/or that temporal resolution within the core is insufficient to allow complete deconvolution of the contaminant input record.  Despite pre-1950 loadings, core inputs demonstrate good agreement with the pattern of PCB  production - United Kingdom PCB production peaked in the mid-1960s to mid-1970s (Figures 4a, 4b and 5).

Recent declines in environmental loadings of PCBs reflect national and international legislation and bans on usage and production, implemented in the 1970s.  Enhanced levels at or near the surface of the core may represent a recent increase in loadings, or inputs of 'fresh' material which have not yet undergone diagenetic processing (Sanders, 1993).  The latter phenomenon will be discussed in the following sections.  It is, however, expected that levels of PCBs entering the sediment of Loch Ness will continue to drop for the forseeable future.

PAH Time Trends

PAHs have been present within the natural environment since the advent of fire, and as such have been determined and quantified throughout the entire length of the core.  Figures 6a and 6b (5K) give concentration/depth, and flux/year relationships, for the sum of 12 unsubstituted PAHs to a depth of 54 cm, representing a historical record spanning from the present day back to the beginning of the 1800s.

Similar to the PCB profile, major changes in the sedimentary loadings of PAHs are obvious during the 180-year time period encapsulated (Figures 6a and 6b, 5K graphs).  SigmaPAH concentrations found at the base of the core constitute sub-part per million levels.  It is likely that these loadings are indicative of pre-Industrial Revolution baseline levels (53 to 37 cm depth).  A marked increase in inputs is apparent at a depth of 35 cm in the core, presumably a direct response to the increased consumption of coal and wood, linked with the expansion of mechanisation and productivity, generated during the Industrial Revolution.  Concentrations and fluxes of PAHs incorporated into bottom sediment rapidly multiplied to some nine times above background levels in the space of less than 50 years.  Greatest inputs occur about 1922 (6.4 mg per kg^-1), prior to a 25% reduction seen over the following 15-year period.  This sudden drop may reflect the decrease in heavy industrial manufacturing processes and general socio-economic hardship endured during the Great Depression.

After demonstrating a further sub-surface maximum in the mid-1940s (15 cm), sedimentary inputs begin to show significant reductions in levels incorporated into

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bottom sediment.  Declines are especially evident from the late-1950s and prevail until the early 1980s, where inputs are slightly higher than background, representing an 84% reduction from maximum inputs.  Despite evidence suggesting a marked improvement in air quality over the past 30 to 40 years, the uppermost 3.0 cm of the core show a net increase in PAH flux to the loch bed.  The reasons for this are unclear, but may be related to recent point source release(s), or supply of 'fresh' unprocessed material. 

The primary source of PAHs to the environment is the combustion of coal.  It is likely, however, that the impact of this source has diminished significantly since the introduction of new 'cleaner' residential heating methods (e.g. gas-fired and electrical central heating), and improved combustion efficiencies in power generating plants.  Figure 7 (10K) illustrates the pattern of coal consumption from the mid-1800s to the present day for the United Kingdom, and compares the relative importance of domestic and electrical generation uses throughout this period.  The patterns of consumption and usage correspond well with the sedimentary record of PAHs found in the Loch Ness core (Figures 6a and 6b).

Worth noting is the rapid growth in coal consumption from 1860, which escalates to an initial maximum spanning 1900 to 1920, approximately.  Following the onset of the Great Depression, the burning of coal shows a significant drop, before becoming re-established in the early 1930s.  The sedimentary response to these fluctuations tends to be non-synchronous, and date slightly later than the date when the events actually took place.  It is likely that this effect is a combination of biotic mixing of the bottom sediment, and a source-transport-deposition time lag.

Despite sediment loadings illustrating a peak input at around 1945, and subsequent reductions thereafter, coal consumption actually showed an increase to a maximum in the early 1950s, and maintained a high turnover until the late 1960s.  Coincidentally, the trend of usage changed markedly at this point in time.  Until the mid-1940s to early 1950s the dominant uses of coal were associated with many small point sources employing inefficient combustion processes, e.g. residential heating and industrial on-site electricity generating.  The introduction of the Clean Air Act in 1956 proved to be successful in restricting the effect of small point source pollution emissions.  In addition, the implementation of this legislation served to increase the number of central electricity generating plants, which utilised relatively efficient high-temperature combustion techniques.  These measures, in combination with a gradual decline in heavy industry, have resulted in an overall reduction in PAH emissions.

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PCB and PAH Contamination in the Sediments of Loch Ness 

In the absence of reliable data regarding past environmental loadings of contaminants, it is often advantageous to employ retrospective assessment techniques in order to build a picture of temporal pollution trends.  In this capacity the use of dated lacustrine sediment cores has proved valuable (Hites et al., 1977; Wickstrom and Tolonen, 1987; Eisenreich et al., 1989; Sanders et al., 1992 and 1993).

Figure 8 (11K) compares the present Loch Ness data to historical PCB and PAH trends determined from various other sediment cores in Great Britain and North America, with emphasis on key time-points and significant changes in environmental burdens.  Of the four cores, Loch Ness shows the latest onset in increases of PCB contamination (15 to 20 years later than the other examples), while demonstrating a slightly earlier response to the onset of the Industrial Revolution than the Esthwaite Water core (from PAH data, Figure 8).  Unfortunately the Lake Ontario cores analysed were not sufficiently deep to resolve pre-industrial baseline levels.  The period of maximum PCB and PAH input also differs from core to core.  PCB maxima vary from 1958 (Loch Ness) to 1970 (Lake Ontario, G-32).  It is  more pertinent, however, to consider the time-span duration of highest PCB input, and draw comparisons by this means. 

Employing this approach identifies a 20-year window, during which time PCB maxima occured in all cores.  PAH maxima also illustrate a slight diversity in temporal correlation between cores.  There are two maxima in the Loch Ness core, corresponding to 1922 and 1945.  In Esthwaite Water and the two Lake Ontario cores, highest inputs are seen at 1952, 1949 and 1948, respectively.  The onset in reductions in PAH inputs to Loch Ness do, however, correspond well with that observed in both Lake Ontario cores.  Finally, declines in environmental loadings of PCBs and PAHs are corroborated by all examples.  Current fluxes of PCBs, relative to maximum inputs, to Loch Ness, Esthwaite Water, Lake Ontario E-30 and G-32 are 50%, 40%, 70% and 60% respectively.  Despite recent near surface increases in PAHs in Loch Ness, levels here have fallen 80% from maximum inputs.  Reductions in Esthwaite Water and both Lake Onatrio cores are 60%, 70% and 70%.  Although much improvement in sediment quality is evident, which presumably is transposable to other environmental compartments, present-day loadings still remain many times greater than background contamination levels. 

The amount of PCB and PAH contamination found in the Loch Ness core tends to reflect the relatively rural location of Loch Ness and its remoteness from large residential and industrial conurbations.  Maximum PCB fluxes to Esthwaite Water, Lake Ontario E-30 and G-32 are 5.0, 46 and 42 times greater than inputs to Loch Ness (Sanders et al., 1992; Sanders, 1993).  Lake Ontario, however, is an example of a polluted watershed, whereas Esthwaite Water,

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is a shallow semi-rural lake which receives limited quantities of treated sewage.  Fluxes of PAHs are also considerably lower to Loch Ness sediment than the other examples cited.  Esthwaite Water, Lake Ontario E-30 and G-32 sediment cores received 15, 4.0 and 3.0 times greater fluxes of PAH, respectively, during maximum input (Sanders et al., 1993; Sanders, 1993).  It should be noted, however, that some inter-core differences exist in the number of PCB congeners and PAH compounds quantified in the various studies.

 Possible Disturbances to the Sediment Record
Physical processes continually at work within sediments can lead to a gradual alteration, and possible disturbance, of the accumulating stratigraphy.  Such mechanisms eventually result in partial loss of temporal resolution within the core, or in the case of  very slowly accumulating sediments, complete destruction of the historical record.  As such, contaminant profiles in all sediment  cores are distorted to varying degrees.

Physical mixing of bottom sediment can be particularly detrimental when carrying out historical monitoring.  Resuspension of surface sediment via water turbulence and fetch are highly unlikely to create any disturbance at the 210 m depth from where the core was obtained.  Reworking of bottom sediment by benthos and burrowing organisms (e.g. oligochaete worms) is, however, likely to be of significance.  Sub-surface burrowing by 'conveyer-belt' feeders will result in the movement of particulate matter, and hence will mix those substances bound to the solid phase.  The population of benthos, and rate of sedimentation, will regulate the specific impact of bioturbation, and thus govern the potential degree of historical record disruption.  Molecular diffusion of chemicals through the aqueous phase will supplement the mixing effect.  This process is primarily dependent upon the aqueous solubility of the chemical, and may also be influenced by the levels of dissolved organic carbon in the sediment pore water.

  It is also important to consider the fate of a compound following deposition to a water surface, and the potential losses incurred during its passage through the water column and after incorporation into the sediment profile.  For example, biotic and abiotic degradation may serve to deplete certain susceptible compounds, and enhance levels of the more recalcitrant components.  It is therefore important to acknowledge that historical sediment records do not quantifiably reflect inputs to a water body, but rather provide an overall qualitative time-trend assessment of

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the remaining resistant component.  Sediment trap studies, for example, have suggested that typically <10% of the PCB fraction entering the water column becomes incorporated into the bottom sediment (Sanders, 1993).  A large proportion of the remainder is returned to the atmosphere following outgassing across the water/air surface.

 Sources of PCBs and PAHs to Loch Ness

The catchment area of Loch Ness is vast, covering an approximate area of 1,775 km² (Maitland, 1981).  The Foyers system drains the east side of the loch, while the significantly larger Moriston, Caledonian (Oich and Garry) and Enrick catchments drain from the west.  Establishing specific contaminant source functions is therefore particularly complex, and is not attempted in this paper.  It is, however, pertinent to suggest potential modes of contaminant supply to the loch and its catchment, and broadly to discuss their potential impact on the region.

Potentially significant point sources of PCBs are likely to be small in number, and at worst would be restricted to leakages from dispersed transformer units.  PAHs are likely to be delivered to the catchment from many small point sources, e.g. residential burning of coal and wood.  The significance of these emissions in such a sparsely populated area is difficult to predict.  Heather and stubble burning would also add to environmental burdens of PAHs.  Just how widespread these methods are practised within the catchment is not known.  Emissions from motor vehicles traversing lochside routes, and motor boats passing through the loch itself, are examples of mobile sources which may play an important role in the supply of PAHs.  Seasonal increases in tourist traffic are likely to have a significant bearing on the importance of this source.

 
Atmospheric deposition may be of great consequence as a source of pollution to this relatively rural and non-industrialised region.  PCBs and PAHs in the gaseous phase or particulate-bound solid phase may be transported hundreds or even thousands of miles in the upper atmosphere from areas of high level contamination, and then be deposited onto areas of low contamination.  Atmospherically derived sources to the Central Highland region may originate from industrial and urban conurbations elsewhere in Britain through northerly wind directions.  In addition, prevailing westerly winds may deliver pollutant packages from North America, and occasional east winds will transport contaminated aerosols from the industrial heartlands of Central Europe.  Particle-rainout has been reported to be the dominant deposition process (Ballschmitter, 1991), and will be of particular significance in this area of relatively high rainfall.  Dry-

 

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deposition (gravity) is less significant, but is nevertheless an important atmospheric contaminant removal mechanism.  Particle-bound contaminants will be washed into streams and rivers, eventually find their way downstream, and so ultimately enter the loch.  Flood events will be particularly important in delivering large masses of suspended particulate material to terminal water bodies, and may result in a subsequent increase in pollutant fluxes.

General Comments
This short paper has attempted to interpret concentration/depth data, derived from a dated lacustrine sediment core, for both PCBs and PAHs - two groups of compounds whose environmental presence, persistence, and potential toxicological effects are currently being viewed with concern.  The historical record preserved within the core has been discussed in general terms, and in relation to production, usage and source functions.  The advantages, disadvantages and realisticity of employing retrospective assessment techniques have been discussed.  Despite some slight ambiguity in the present data, the Loch Ness core corroborates the findings of other sediment studies, both national and international.  It also helps to form a broader picture of PCB and PAH loadings in the U.K. environment, both historical and spatial.

 Acknowledgements
The authors would like to express their thanks to the following for assistance during the course of this work:  the Natural Environment Research Council for funding, under grant number GT4/89/AAPS/28; Dr. Mike Kelly, University of Lancaster, for determing Cs activities; Mr. John Minshull, skipper of the RV Ecos; and Mr. Mungo Sanders for helpful advice.

References

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Ballschmitter, K. and Zell, M.  (1980).  Analysis of polychlorinated biphenyls (PCBs) by glass capillary gas chromatography.  Fresenius' Zeitschrift für Analytische Chemie, 302: 20-31.

Barron, H.  (1985). The  County of Inverness.  Third Statistical Account of Scotland, Vol. 16.  Edinburgh:  Scottish Academic Press.

Bennett, S.  (1993).  Patterns and Processes of Sedimentation in Loch Ness.  B.Sc. Dissertation, University of Staffordshire.

 

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Jones, K.C., Grimmer, G. Jacob, J. and Johnston, A.E.  (1989).  Changes in the polynuclear aromatic hydrocarbon (PAH) content of wheat grain and pasture grassland over the last century from one site in the U.K.  Science of the Total Environment,  78: 117-130.

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Received May 1993

Dr. Gordon Sanders,

Institute of Environmental and Biological Sciences,

University of Lancaster, LANCASTER, Lancashire LA1 4YQ.

Dr. Kevin C. Jones,

Institute of Environmental and Biological Sciences,

University of Lancaster, LANCASTER, Lancashire LA1 4YQ.

Mr. Adrian J. Shine,

Loch Ness and Morar Project,

Loch Ness Centre, DRUMNADROCHIT, Inverness-shire IV3 6TU.