Bioaccumulation of hydrocarbons derived from terrestrial and anthropogenic sources in the Asian clam, Potamocorbula amurensis, in San Francisco Bay estuary

Volume 24/Number

2/February

1992

Marine Pollution Bulletin, Volume 24, No. 2~ pp. 103-109, 1992.

Printed in Great Britain.

0025-326X/92 $5.00+0.00 © 1992 Pergamon Press plc

Bioaccumulation of Hydrocarbons Derived from Terrestrial and Anthropogenic Sources in the Asian Clam, Potamocorbula amurensis, in San Francisco Bay Estuary WILFRED E. PEREIRA, FRANCES D. HOSTETTLER and JOHN B. RAPP U.S. G.S., 345 Middlefield Road, Menlo Park, CA 95025, USA

water for agricultural, municipal, and industrial purposes has greatly reduced freshwater flow into the estuary (Nichols et al., 1986). Agricultural chemicals in run-off from the Central Valley of California are transported by the Sacramento and San Joaquin Rivers into San Francisco Bay (Nichols et al., 1986; Stephenson et al., 1986). Chlorinated pesticide and polychlorinated biphenyl (PCB) residues have been reported in clam tissues in the estuary (Stephenson et al., 1986). PCBs, polycyclic aromatic hydrocarbons (PAHs), and DDT have been determined in surficial sediments and biota in the San Francisco Bay System (Long et al., 1988). A chronic background contamination of hydrocarbons derived from petrogenic, pyrogenic, and urban sources is present in San Francisco Bay (Di Salvo et al., 1975; Hostettler et al., 1989). In addition, more than 30 municipal and 40 industrial waste treatment facilities and an additional 100 smaller industrial dischargers contribute point sources of contaminated wastes to San Francisco Bay Estuarine processes play an important role in the (Nichols et al., 1986). distributions and fate of contaminants. Anthropogenic Hydrophobic organic contaminants that enter compounds, derived from terrestrial and atmospheric estuaries are associated primarily with particles and sources, are subject to biogeochemical processes during colloids in the water column that flocculate and settle to their residence time in estuaries. These processes the sediment-water interface (Means et al., 1982). ultimately determine the distribution and fate of Sediment and particulate associated contaminants are contaminants in marine environments. thus available to biota and bioaccumulate in the lipid San Francisco Bay estuary is a large urbanized tissues of these organisms (Farrington et al., 1973, estuarine system located at the mouth of the Sacramento 1982a,b; Forster et al., 1987; Metcalf et al., 1990; and San Joaquin Rivers. The Bay drains a catchment Tatem, 1986; Roesijadi et al., 1978). Filter-feeding area of about 153 000 km 2 (Conomos et aL, 1985). The benthic invertebrates such as clams may therefore serve northern reach of the estuary is partially mixed, and as bioindicators and integrators of hydrophobic organic includes the Central Bay, San Pablo Bay, Suisun Bay, and contaminants. They can provide useful information the Delta. The South Bay, by contrast, is a tidally about the potential for biomagnification in the food oscillating lagoon with low fresh water inflows and long chain to higher trophic levels such as fish and other residence times (Wright et al., 1988). The discharge of wildlife species. the Sacramento-San Joaquin Delta into Suisun Bay The asian clam Potamocorbula amurensis was accounts for about 90% of the freshwater inflow to San introduced to San Francisco Bay in 1986 in ballast water Francisco Bay (Smith, 1987). However, diversion of from cargo ships. Since then, the population of this An assessment was made in Suisun Bay, California, of the distributions of hydrocarbons in estuarine bed and suspended sediments and in the recently introduced asian clam, Potamocorbula amurensis. Sediments and clams were contaminated with hydrocarbons derived from petrogenic and pyrogenic sources. Distributions of alkanes and of hopane and sterane biomarkers in sediments and clams were similar, indicating that petroleum hydrocarbons associated with sediments are bioavailable to Potamocorbula amurensis. Polycyclic aromatic hydrocarbons in the sediments and clams were derived mainly from combustion sources. Potamocorbula amurensis is therefore a useful bioindicator of hydrocarbon contamination, and may be used as a biomonitor of hydrocarbon pollution in San Francisco Bay.

103

Marine Pollution Bulletin

bivalve mollusk has exploded and spread throughout northern San Francisco Bay (Carlton et aL, 1990; Nichols et al., 1990). It has been estimated that the effective pumping rates by this clam range from 1 to 5 I per clam per day; grazing by Potamocorbula amurensis may be responsible for the dramatic reduction in phytoplankton biomass in northern San Francisco Bay (Cole et al., 1989). In view of the ability of this clam to filter large quantities of water and associated particulates, a study was started to investigate distributions of hydrophobic organic contaminants in sediments and clam tissues in Suisun Bay. This study would provide a unique opportunity to study bioavailability of these compounds to a newly introduced species. This report describes a preliminary assessment of this distribution of hydrocarbons, derived from petrogenic and pyrogenic sources, in clams and sediments, and bioavailability of these compounds to Potamocorbula amurensis.

Materials and Methods Sample collection Samples were collected from eight sites in Suisun Bay. These sampling locations are shown in Fig. 1. Surficial bed sediments were collected from all eight sites using a Van Veen* grab sampler. A stainless steel pipe was used to collect an 8 cm surficial sample of sediment. Sediment samples were stored frozen until analysis. Suspended sediments were collected from sites 2 and 3 by pumping a large volume of water (100-200 1) through a continuous flow centrifuge (Westfalia). The centrifuge was operated at 9800 rpm (-10 000 g) at a flow rate of 2 1 min -1. The contents of the separation bowl were collected by slurrying the thin film of retained particles with water in the centrifuge bowl using a small teflon wash-bottle and teflon spatula. The slurry was rinsed into a 1000 ml wide-mouth glass jar and stored at 4°C. Clams were collected from sites 2, 3, 7, and 8 using a Van Veen grab sampler followed by screening. Clams were allowed to depurate for 48 hours in ambient water prior to storage in a freezer. It has been shown that a depuration period of 48 hours is long enough to remove any trace element signature indicative of undigested sediment (Brown et al., 1991).

(Forster et al., 1987). All extracts were analysed by gas chromatography-mass spectrometry (GC-MS).

Results and Discussion The organic carbon content of sediments and lipid content of Potamocorbula amurensis are shown in Table 1. Bed sediments from sites 4 (Honker Bay), 5 (Grizzly Bay), and 6, were fine grained and had a greater organic carbon content than the coarse grained sand sediments from the other sites, which lie within the shipping channel. The organic carbon content of the suspended sediment was much greater than the bed sediments. Sites 4, 5, and 6 may serve as entrapment areas for the fine grained sediments. Distributions of alkanes in bed sediments from Suisun Bay are shown in Fig. 2. In addition to n-alkanes from C~3 to C37 all chromatograms show varying degrees of an unresolved complex mixture (UCM) of compounds characteristic of a background contamination by weathered or biodegraded petroleum (Kennicutt et al., 122°30 '

122"

38*

37o45 '

5

0

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Fig. 1 Map of study area. TABLE 1 Organic carbon content of bed and suspended sediments, and lipid content of Potamocorbula amurensis from Suisun Bay. Site

Sample preparation and analysis Suspended and bed sediments were dewatered and air-dried. Samples were ground and uniformly mixed using a mortar and pestle. 2-4 g of dried suspended sediment or 10 g of bed sediment was extracted in a teflon-lined screw cap centrifuge tube with acetone and hexane by mechanical shaking followed by sonication. Sulphur was removed from the extracts using activated copper powder. Extracts were chromatographed on deactivated florisil, using hexane (alkane fraction) and hexane:diethylether, 1:1 (aromatic fraction) as eluants for the bed sediments, and hexane:diethylether, 1 : 1, for the suspended sediments. 2-4 g of clam tissue was analysed by following a previously published method *The use'of brand or product names in this article is for identification purposes only and does not constitute endorsement by the US Geological Survey.

104

10 Kilometers

Percent

Bed sediments

1 2 3 4 5 6 7 8

(4.1) (A) (B)

(433, Honker Bay) (416, Grizzly Bay) (408.1)

(c) (8.1)

0.19 0.09 0.09 1.78 1.48 1.17 0.40 0.70

Suspended sediments

2 (A) 3 03)

2.24 2.26

Potamocorbula amurensis

2 (A) 37 (C) (B) 8

0.48 0.59 0.57 0.32

(8.1) Sites in parentheses i'epresent sampling sites used by other researchers on the R.V. Polaris.

Volume24/Number 2/February 1992 suspended sediments and lipid tissues of Potamocorbula

1987). The n-alkanes in sediments from all sites, except sites 2 and 3, show a pronounced odd/even predominance in the n-alkane range C23-C33 , characteristic of higher plant waxes from terrigenous sources (Eglinton and Hamilton, 1967; Caldicott & Eglinton, 1973). The n-alkanes in sediments from sites 2 and 3 show, in addition to the terrigenous input, a suite maximizing at C23 with no odd/even predominance, indicative of a petrogenic input characteristic of petroleum. Sites 2 and 3 are at the same location, but ~ere sampled on two consecutive days at maximum flood tide and the beginning of flood tide, respectively. Several other classes of compounds, including the acyclic isoprenoid hydrocarbons pristane and phytane, tricyclic and pentacyclic triterpanes, steranes, and polycyclic aromatic hydrocarbons were identified in bed and

amurensis.

Mass chromatograms of alkanes (m/z 71), tricyclic and pentacyclic triterpanes (m/z 191), and steranes (trdz 217) in sediments and clam tissues at site 3 are shown in Fig. 3. A well characterized crude oil not necessarily related to Bay contamination but containing typical hydrocarbon distributions is also included for comparison in Fig. 3. Tricyclic terpanes (C2o-C29), and pentacyclic triterpanes or hopanes (C27-C33), all with the 170c(H),21l](H)- configuration which is characteristic of a geochemically mature source such as petroleum, were present in bed and suspended sediments and clams. R and S epimers of diasteranes (1]0~D27 and ~0cD29) with the 1313(H),17~(H)- configuration and steranes (0c~C29) with the 5~(H),14~(H),170c(H)-

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Fig. 2 Gas chromatogramsof alkanesin bed sedimentsfromSuisunBay. 105

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Volume 2 4 / N u m b e r 2/February 1992 TABLE 2 Geochemical correlation parameters in sediments and Potamocorbula amurensis. Steranes (m/z 217) o~ototC2 S___~_ S+R

MP

DMP

P

P

0.60 0.52 0.68 0.67 0.55 0.61 0.44 0.66

0.52 0.36 0.40 0.44 0.42 0.35 0.21 0.30

0.71 0.42 0.62 0.45 0.61 0.46 0.53 0.78

0.71 2.90 1.50 0.59 0.52 0.38 0.72 0.81

1.1 1.1

0.56 0.57

0.41 0.41

1.0 0.39

1.4 0.95

1.0 1.1 1.3 1.1

0.57 0.65 0.62 0.62

0.46 0.36 0.37 0.34

-0.10 0.08 --

0.88 0.41 0.41 0.64

Pristane Phytane

Tm Ts

Bed sediments: 1 2 3 4 5 6 7 8

0.8 1.1 0.8 1.4 1.0 0.8 0.8 1.2

1.0 1.6 1.0 1.4 1.2 1.2 1.8 1.5

Suspended sediments: 2 3

0.9 0.9

Clams: 2 3 7 8

0.4 0.4 0.4 0.3

Site

Hopanes (m/z 191) C3~xl3 S.._~ S+R

configuration, were identified in sediments and clams. Similar distribution patterns of these compounds in sediments and clam tissues indicate that hydrocarbons associated with sediments are bioavailable to Potamocorbula amurensis. Pentacyclic triterpanes of the hopane series have been reported in oysters from the coast of Kuwait, and mussels from bays and coastal areas of California (Anderlini et al., 1981). Steranes are not found in living organisms that have not been exposed to petroleum hydrocarbons, but represent products that have been formed by reduction of sterols from biological systems originally incorporated into the sedimentary record (Philp, 1985). Both hopanes and steranes evolve from biogenic molecules whose carbon skeleton has remained intact through processes of diagenesis and thermal maturation. As such, they serve as molecuar biomarkers that are useful for correlation of oils with each other, and with their proposed source rocks, and for the assessment of thermal maturity (Mackenzie, 1984). Various geochemical correlation parameters, including ratios of molecular biomarkers and other hydrocarbons were examined, in an attempt to better understand sources of hydrocarbons and processes that control their bioavailability to P o t a m o c o r b u l a amurensis. This data is shown in Table 2. Pristane/ phytane ratios ranged from 0.8 to 1.4 in bed and suspended sediments, and from 0.3 to 0.4 in clam tissues. Pristane is formed via oxidation and decarboxylation of the phytyl side chain of chlorophyll (Maxwell et al., 1972; Ikan et al., 1975), and phytane is formed via dehydration and reduction (Ikan et al. 1975). Pristane/phytane ratios have been proposed as measures of the redox potential of sediments (Didyk et al., 1978). The lower pristane/phytane ratios in clam tissues suggest that the phytyl side chain of chlorophyll probably is degraded to phytane under anaerobic conditions in the digestive system of P o t a m o c o r b u l a amurensis. Phytane is present in crude oils and is not found in most biota that have not been exposed to petroleum hydrocarbons (Anderlmi et al., 1981).

During diagenesis and thermal maturation, hopane and sterane biomarkers undergo isomerization at specific chiral centres on the carbon skeleton. As this isomerization approaches equilibrium with increasing maturity, two possible configurations with different thermodynamic stabilities are formed, giving rise to different amounts of the R and S epimers. Internal ratios of sterane and terpane epimers are used as indicators of the maturation of oils with increasing time and temperature. The equilibrium ratios of the 17e(H),211~(H)-C31 hopane S/(S+R) and the 50~(H),14~(H),17~(H)-C29 sterane S/(S+R) in a mature oil are 0.6 and 0.5 respectively. The ratios of these maturity indicators (Mackenzie, 1984) in the clams lie within the range of the ratios of these compounds in the bed and suspended sediments. In addition, the ratio in the clams of 170t(H)22,29,30-trisnorhopane (Tm) to 18~(H)-22,29,30-trisnorneohopane (Ts), which is used as a source and/or maturation parameter of crude oils (Seifert & Moldowan, 1978), falls within the range of the ratios of Tm/Ts in the bed and suspended sediments. These data indicate that the molecular biomarkers in the clams were derived from sediments contaminated with geochemically mature petroleum residues. In addition to the biomarkers, ratios of the polycyclic aromatic hydrocarbon methyl phenanthrene 0VIP) and dimethylphenanthrene (DMP) to phenanthrene (P) were examined to determine if these compounds were derived from combustion or petrogenic sources. Ratios of MP/P (Prahl and Carpenter, 1983) are reported to be in the range of 0.5 to 1.0 for sediments dominated by combustion PAHs and from 2-6 for sediments dominated by petroleum hydrocarbons. Ratios of DMP/P in petroleum contaminated sediments are relatively greater (Killops & Howell, 1988). Ratios of MP/P and DMP/P in Table 3 indicate that these compounds in this study area are derived mainly from combustion sources. However, sediments from sites 2 and 3 also have a petrogenic contribution. Priority pollutant (Keith et al., 1979) PAl-Is in sediments and clams were quantified. Concentrations of 107

Marine Pollution Bulletin TABLE 3

Concentrations of polycyclic aromatic hydrocarbons in bed sediments, suspended sediments, and Potamocorbula amurensis (ng g ~dry wt).

PAH 3 Naphthalene Acenaphthylene Acenaphthene 9 H-fluorene Phenanthrene Anthracene Fluoranthene Pyrene Benz[a]anthracene Chrysene Benzo[b]fluoranthene Benzo[k]fluoranthene Benzo[a]pyrene Indeno[ 1,2,3-cd]pyrene Dibenz[a.h]anthracene Benzo[g.h.i]perylene Total PAHs

Suspended sediments Site

Bed sediments Site

0.3 nd nd 1.2 1.5 0.3 2.8 4.5 1.8 2.1 2.1 1.0 2.8 1.5 1.2 0.3 23

1).3 nd nd nd 1.0 nd 2.1 2.8 1.8 1.7 0.5 0.2 1.5 1.6 nd 1.0 15

0.2 0.8 nd 2.1 4.4 0.5 5.0 5.5 nd nd nd nd nd 1.7 nd 1.3 22

4

5

6

7

3.7 0.8 1.5 1.0 3.6 2.2 1.4 0.8 1.7 0.6 0.7 1.1 6.8 3.0 3.2 3.3 83 26 32 8.1 26 6.6 5.6 1.1 113 38 48 5.8 194 52 46 6.5 58 23 29 2.4 92 31 106 1.8 14 32 34 0.9 5.7 34 31 0.3 39 34 31 1.7 15 18 15 1.7 2.9 4.2 1.5 nd 17 21 17 1.1 675 326 403 38

8 0.7 nd 0.1 1.8 6.5 0.7 3.7 3.5 1.8 2.6 1.4 0.5 2.4 1.0 1.2 0.1 28

2 11 6.5 3.9 9.0 40 13 65 97 44 56 34 37 33 20 4.9 24 498

3 18 11 8.8 18 142 21 244 216 59 151 54 34 48 nd nd 34 1059

Potamocorbula amurensis Site 2 16 5 4 9 79 33 166 224 48 70 108 87 53 48 nd 52 1002

3

7

8

7 nd nd 6 58 30 143 192 51 87 68 55 54 59 nd 81 891

13 nd nd nd 38 13 77 119 37 60 101 77 60 33 15 46 688

19 4 nd 19 83 nd 51 115 30 33 60 46 35 nd nd nd 496

n d = n o t detected.

these compounds are shown in Table 3. Suspended sediments had higher concentrations than bed sediments of PAHs. Bed sediments from sites in the main channel (1, 2, 3, 7, and 8) which had low organic carbon contents, also had low levels of PAHs, while bed sediments from sites 4, 5, and 6 with higher organic carbon content, had relatively higher levels of PAHs, thereby indicating the importance of organic carbon in sorption of non-ionic compounds to sediments (Chiou et aL, 1985). Sites 4, 5, and 6 probably serve as entrapment areas for suspended sediments and associated PAHs. Significant concentrations of PAHs were found in Potarnocorbula amurensis, indicating that the natural lipid pool of these organisms serve as a sink for PAHs and other hydrocarbons derived from petrogenic and pyrogenic sources. Conclusions The results of this study clearly demonstrate that sediments and the asian clam Potamocorbula amurensis are contaminated with a chronic background of hydrocarbons which are present in Suisun Bay. Distribution of biomarkers provide a useful basis for the assessment of bioavailability of hydrocarbons to Potamocorbula amurensis. These compounds are strongly retained in lipid tissues of these organisms and probably are only slowly depurated. Potamocorbula amurensis is a food source for other species such as diving-ducks and sturgeon. Therefore, these compounds have the potential for biomagnification in the food chain. Because of its recent advent in the estuary. Potamocorbula amurensis may serve as a biomonitor of future changes in contamination by hydrocarbons in San Francisco Bay. The authors wish to thank the crew of the RV Polaris for assistance with sampling. Special thanks to Jan Thompson, Cindy Brown, and Francis Parchaso of the USGS for help with collection of Potamocorbula aml~rensis.

Anderlini, V. C., AI-Harmi, L., DeLappe, B. W., Risebrough, R. W., Walker. W., Simoneit, B. R. T. & Newton, A. S. (1981). Distributions

108

of hydrocarbons in the oyster, Pinctada margarit!fem, along the coast of Kuwait. Mar. Pollut. Bull. 12, 57-62. Brown, C. & Luoma, S. (1991). Unpublished results. Caldicott, A. B. & Eglinton, G. (1973). Surface waxes. In Phytochemistry 111, Inorganic Elements and Special Groups of Chemicals (L. P. Miller, ed.), pp. 162-194. Van Nostrand Reinhold, New York. Carlton, J. T., Thompson, J. K., Schemel, L. E. & Nichols, E H. 11991)), Remarkable invasion of San Francisco Bay (California, USA) by the asian clam Potamocorbula amurensis. Introduction and dispersal. Mar. Ecol. Progr. Ser. 66, 81-94. Chiou, C. T., Shoup, "12 D. & Porter, P. E. (1985). Mechanistic roles of soil humus and minerals in the sorption of nonionic organic compounds from aqueous and organic solutions. Org. Geochem. 8, 9-14. Cole, B. E., Thompson, J. T. & Cloern, J. E. 11991). Measurement of filtration rates by infaunal bivalves in a recirculating flume. Mar. Biol. (In press). Conomos, T. J., Smith, R. E. & Gartner, J. W. (1985). Environmental setting of San Francisco Bay. Hydrobiologia 129, 1-12. Didyk, B., Simoneit, B. R. T., Brassell, S. C. & Eglinton, G. (1978). Organic geochemical indicators of paleoenvironmental conditions of sedimentation. Nature 272,216-222. DiSalvo, L. H., Guard, H. E. & Hunter, L. (1975). Tissue hydrocarbon burden of mussels as potential monitor of environmental hydrocarbon insult. Environ. Sci Technol. 9,247 251. Eglinton, G. & Hamilton, J. R. (1967). Leaf epicuticular waxes. Science 156, 1322-1335. Farrington, J. W. & Quinn, J. G. (1973). Petroleum hydroocarbons in Narraganset Bay I. Survey of hydrocarbons in sediments and clams. Estuar. Coast. Mar. Sci. 1, 71-79. Farrington, J. W., Davis, A. C., Frew, N. M. & Rabin, K, S. 11982), No, 2 Fuel Oil compounds in Mytilus edulis; retention and release after an oil spill. MarBull. 66, 15-26. Farrington, J. W., Tripp, B. W., Teal, J. M., Mille, G., Tjessem, K., Davis, A. C., Livramento. J. B., Hayward. N. A. & Frew, N. M. (1982). Biogeochemistry of aromatic hydrocarbons in the benthos of microcosms. Toxicol. and Environ. Chem. 5,331-346. Forster, G. D., Baksi, S. M. & Means, J. C. (1987). Bioaccumulation of trace organic contaminants from sediments by Baltic clams (Macoma Balthica) and soft shell clams (Mya Arenaria), Environ. Ibxicol. Chem. 6,969-976. Hostettler, F. D., Rapp, J. B., Kvenvolden, K. A. & Luoma, S. L. (1989). Organic markers as source discriminants and sediment transport indicators in South San Francisco Bay, California. Geochim. Cosrnochim. Acta 54, 1563-1576. Ikan, R., Baedecker, M. J. & Kaplan, I. R. (1975). Thermal alteration experiments on organic matter in recent marine sediments--ll. Isoprenoids. Geochim. Cosmochim. Acta 39, 187-194. Keith, L. H. & Telliard, W. A, (1979). Priority pollutants I--a perspective view. Environ. Sci. TechnoL 13,416-423. Kennicut, M. C., II, Sericano, J. L., Wade, T. L., Alcazar, E & Brooks, J. M. (1987). High molecular weight hydrocarbons in Gulf of Mexico continental slope sediments. Deep-Sea Res. 34,403-424.

Volume 24/Number 2/February 1992 Killops, S. D. & Howell, V. J. (1988). Sources and distribution of hydrocarbons in Bridgewater Bay (Severn Estuary, U.K.) intertidal surface sediments. Estuar Coast. Shelf Sci. 27,237-261. Long, E., MacDonald, D., Baker Malta, M., Van Ness, K., Buchman, M. & Harris, H. (1988). Status and trends in concentrations of contaminants and measures of biological stress in San Francisco Bay. National Oceanic and Atmospheric Administration, NOAA Technical Memorandum NOS OMA 41. Seattle, Washington. Mackenzie, A. S. (1984). Application of biological markers in Petroleum Geochemistry. In Advances in Petroleum Geochemistry. Vol. 1 (J. Brooks & D. Welte, eds), pp. 115-214. Academic Press, London. Maxwell, J. R., Cox, R. E., Ackman, R. G. & Hooper, S. N. (1972). The diagenesis and maturation of phytol. The stereochemistry of 2,6,10,14-tetramethylpentadecane from an ancient sediment. In Advances in Organic" Chemist~ 1971 (H. R. Von Gaertner & H. Wehner, eds), pp. 277-291. Pergamon Press, Oxford. Means, J. C. & Wijayaratne, R. D. (1982). Role of natural colloids in the transport of hydrophobic pollutants. Science 215,968-970. Metcalf, J. L. & Charlton, M. N. (1990). Freshwater mussels at biomonitors for organic industrial contaminants and pesticides in the St. Lawrence River. Sci. ~n. Environ. 97/98,595-615. Nichols, F. H., Cloern, J. E., Luoma, S. N. & Peterson, D. H. 11986). The modification of an estuary. Science 231,525-648. Nichols, F. H., Thompson, J. K. & Schemel, L. E. (1990). Remarkable invasion of San Francisco Bay (California, USA) by the asian clam Potamocorbulu amurensis. 11. Displacement of a former community. Mar. EcoL Progr. Ser. 66, 95 101. Philp, R. P. (1985). Fossil fuel biomarkers, applications and spectra. In

Edited

Methods in Geochemistry and Geophysics. Vol. 23. Elsevier, New York. Prahl, F. G. & Carpenter, R. (1983). Polycyclic aromatic hydrocarbons (PAH)-phase associations in Washington coastal sediment. Geochim. Cosmochim. Acta 47, 1013-1023. Roesijadi, G., Anderson, J. W. & Blaylock, J. W. (1978). Uptake of hydrocarbons from marine sediments contaminated with Prudhoe Bay crude oil: influence of feeding type of test species and availability of polycyclic aromatic hydrocarbons. J. Fish. Res. Board. Can. 35, 608-614. Siefert, W. K. & Moldowan, J. M. (1978). Applications of steranes, terpanes and monoaromatics to the maturation, migration and source of crude oils. Geochim. Cosmochim. Acta 42, 77-95. Smith, L. H. (1987). A review of circulation and mixing studies of San Francisco Bay, California. US Geological Survey Circular 1015, 138. Stephenson, M., Smith, D., lchikawa, G., Goetzl, J. & Martin, M. (19861. State Mussel Watch Program: Preliminary Data Report, 1985-1986. Report from California Department of Fish and Game to California State Water Resources Control Board, July, 1986. Tatem, H. E. (1986). Bioaccumulation of polychlorinated biphenyls and metals from contaminated sediments by freshwater prawns, Machrobmchium rosenbergii, and clams, Corbicula fluminea. Arch. Environ. Contam. Toxicol. 15, 171-183. Wright, D. A. & Phillips, D. J. H. (1988). Chesapeake and San Francisco Bays, a study in contrasts and parallels. Mar. Polh~t. Bull, 19, 454458.

by D. J. H. Phillips

The objective of BASELINE is to publish short communications for the concentration and distribution of elements and compounds in the marine environment. Only those papers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to 'Baseline--A Record of Contamination Levels' (Mar. Pollut. Bull. 13,217-218). Marinel'ollutionBulletin, Volume24, No. 2, pp. 1119 114.1992. Printedin GreatBritain.

0025 326X/92$5.00+0.00 © "1992PergamonPresspie

Baseline Levels o f Hydrocarbons in Seawater of the Southern Ocean Natural variability and regional patterns G. C. CRIPPS British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK

The Antarctic marine ecosystem is almost uncontaminated by anthropogenic hydrocarbons (Platt & Mackie, 1980; Clarke & Law, 1981; Reinhardt & Van Vleet, 1986; Cripps, 1990). In order to use the Southern Ocean both as a barometer for global changes, and in local pollution monitoring, clearly defined baselines are

needed. Only when the range of natural variability is quantified can these threshold values be estimated. There are various environmental and biological factors which can influence the distribution and abundance of natural hydrocarbons in marine ecosystems. For instance, in the case of global monitoring, it is necessary to identify systematic regional variations which are attributable to differences between water masses. The sampling stations in this study were divided into three categories: 1. Uncontaminated Antarctic sites (locations C-K, Fig. 1). 2. North of the Antarctic Convergence (A and B). 3. Potentially contamined inshore sites (L and M). Category 1. was used to estimate the baseline values for the Southern Ocean. By combining the categories the ability to differentiate polluted waters and those north of the Antarctic Convergence from uncontaminated sites was investigated. Seawater was sampled in the open ocean, and inshore at Factory Cove, Signy Island, South Orkney Islands, and Cumberland and Stromness Bays, South Georgia, in the Austral summer 1987-88. The cruise track traversed the major oceanographic features of the region, including the Weddell-Scotia Confluence, the Antarctic Convergence, and the area to the west of the Bransfield Strait where water from the Bellingshausen Sea mixes with that from the Weddell Sea (Fig. 1) (Patterson & Sievers, 1980; Heywood, 1985). Water masses were identified from their temperature and salinity. The samples were taken at various depths with General Oceanics 2.25 1 PVC Niskin bottles on a 109