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Oil spill in Hong Kong
Marine Pollution Bulletin Gordon, D. C. Jr & Prouse, N. J. (1973). The effects of three oils on marine phytoplankton photosynthesis. Mar. Biol., 22, 329-333. Han, J. & Calvin, M. (1969). Hydrocarbon distribution of algae and bacteria, and microbiological activity in sediments. Proc. N.A.S., 64,436--444. Han, J., McCarthy, E. D., Van Hoeven, W., Calvin, M. & Bradley, W. H. (1968). Organic geochemical studies, II. A preliminary report on the distribution of aliphatic hydrocarbons in algae, in bacteria, and in a recent lake sediment. Proc. N.A.S., 59, 29-34. Hood, M. A., Bishop, W. S. Jr, Bishop, F. W., Meyers, S. P. & Whelan, T., III (1975). Microbial indicators of oil-rich salt marsh sediments. Appl. Microbiol., 30, 982-987. Lindall, N., Jr & Trent, L. (1975). Housing development canals in the coastal zone of the Gulf of Mexico: ecological consequences, regulations, and recommendations. Mar. Fish. Rev., paper 1163, 3700). Miget, R. J., Oppenheimer, C. H., Kator, H. I. & LaRock, P. L. (1969). Microbial degradation of normal paraffin hydrocarbons in crude oil. In Proc. A P I / F W P C A Joint Conf. on Prevention and Control o f OiI Spills. New York: American Petroleum Institute. Mulkins-Phillips, G. J. & Stewart, J. E. (1974). Distribution of hydrocarbon-utilizing bacteria in Northwestern Atlantic waters and coastal sediments. Can. J. Microbiol., 20, 955-962. Novelli, G. D. & ZoBell, C. E. (1944). Assimilation of petroleum
hydrocarbons by sulfate-reducing bacteria. J. BacterioL, 47, 447--448. Polich, W. M. Jr, Winters, K. & Van Baalen, C. (1974). The effects of a no. 2 fueloiland two crude oils on the growth and photosynthesis of microalgae. Mar. BioL, 28, 87-94. Rosenfeld, W. D. (1974). Anaerobic oxidation of hydrocarbons by sulfate reducing bacteria. J. BacterioL, 54, 664. Shelton, T. B. & Hunter, J. V. (1975). Anaerobic decomposition of oil in bottom sediments. JWPCF, 47, 2256--2270. Strickland, J. D. H. & Parsons, T. R. (1972). A practical Handbook of seawater analysis. FishRes. BdCan., Bulletin 167 (2nd edition), Ottawa. Walker, J. D. & Colwell, R. R. (1975). Extraction of petroleum hydrocarbons from oil-contaminated sediments. Bull. Env. Contamination ToxicoL, 13,245-247. ZoBell, C. E. (1946). Action of microorganisms of hydrocarbons. Bact. Rev., 10, 1-41. ZoBell, C. E. 0973). Microbial degradation of oil: present status, problems, and perspectives. In TheMicrobiaIDegradation of O i l Pollutants. pp. 3-16. D. G. Ahearn and S. P. Meyers (eds.), Center for Wetlands Resources, Louisiana State University, Baton Rouge, Publication No. LSU-SG-73-01. ZoBeil, C. E. & Prokop, J. F. (1966). Microbial oxidation of mineral oils in Barataria Bay bottom deposits. Zast AIg. MikrobioL, 6, 143-162.
Oil Spill in Hong Kong M O L L Y F. S P O O N E R
Marine Biological Association of the U.K., Citadel Hill, Plymouth, Devon, U.K.
Fish farming was seriously but only temporarily affected by a large spill of a very toxic product oil at Hong Kong. Field experiments were set up to follow tainting and depuration. Studies were made of hydrography, water quality, oil in sands, macro- and meio-fauna of shores, and some observations made of possible effects on plankton and open-water fisheries.
open shores in a few months. The other source of pollution from oil which had seeped into the foundation of the tank farm took 6 months to be removed largely by 8' ~. 15' [
A spill o f heavy marine diesel oil (specific gravity 0.89; about 40°70 aromatic content) occurred from the tank farm at Ap Lei Chau, owing to failure o f foundations, on the night o f 8 November 1973. The total loss was estimated as about 4000 tons. Evaporation must have been considerable, water temperature being 23-24°C. Slicks soon spread over East L a m m a Channel and were artificially dispersed there. In Picnic Bay, because of mariculture activities, mopping up with polyurethane foam sheets was tried and was effectively aided by onshore winds. Much oil was stranded on the shores of L a m m a Island--both on the open shores o f George Bay and in Picnic Bay where oil penetrated deep into the sands at the head of the Bay adjacent to the fish farms. In winter the predominant wind direction is from the northeast into the long narrow bay, thus hindering water exchange and the natural flushing of the sands. In summer south-west monsoon conditions improved water exchange and occasional very heavy rainstorms helped to flush some o f the oil out of the coarse sand. Even a year after the spill much oil was still present in deposits at the head o f the bay whereas it was greatly reduced on more 62
11409'
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Hang KongI Island
\ \ Ebb Floo~\u \ "~l
~
~
_ ~' "~~Aberdeen v ~ . ~ f ~r ~ - Horbou
14'
22"15' ~
14'
~
%
George Bay
°o
Ikrn L__--J
hares ~ 22°13'
13'
/ ~
~
P
i
c Bay n
i
c
Lamina Island I
H4°8'
~
4
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Fig. 1 Area affected by oil from the Hang Kong oil spill.
Volume 8/Number 3/March 1977 pumping and tidal flushing. The importance o f wind direction and hydrography on rate of natural cleansing was clearly demonstrated. A study o f the hydrography o f the Picnic Bay area was rapidly undertaken by the Fisheries Research Division at the end o f N o v e m b e r 1973 and again in May 1974.
Water Quality The oil contents of the waters, particularly the toxic aromatic fractions, were determined by UV absorption and spectrofluorimetry f r o m several stations in the H o n g Kong area sampled at the end of N o v e m b e r and subsequently. In the waters around the Picnic Bay fish farm a marked i m p r o v e m e n t in water quality was reported f r o m a deduced oil content o f 45-60 ttg/l on 1 December 1973 to the level of 30 ug/l at the end o f March and 13 /tg/l in May 1974. Values o f 17-29 ttg/l were obtained near fish farms unaffected by the spill. At a clean water station, Kat 0, in the far north o f the New Territories 13-16 /tg/l was recorded. The level of 19-25 p g / l found in East L a m m a Channel in November 1973 was probably caused by the very heavy shipping traffic in H o n g Kong waters to which this spill made a chiefly t e m p o r a r y addition. It would have been impossible to have distinguished oil which sedimented down during this spill f r o m oil already probably present in bottom deposits.
Fisheries The 4 - 5 million inhabitants of H o n g Kong depend on the sea for a b o u t half their protein but this is derived from a wide area o f the South China Sea and fortunately no interference with the diverse general fisheries was reported. Fish cultured in cages suspended from rafts in the fish farms, especially those at the head of Picnic Bay (involving a b o u t 100 families) were, however, seriously affected. A slick had passed through the fish farms before a b o o m could be deployed. In Aberdeen, the main fishing harbour o f H o n g Kong, oil, dispersed because of the proximity of a power station, reached fish being cultured in scattered cages a m o n g the crowded junks. At both places the fish showed a b n o r m a l swimming behaviour, ignored food and were dying. Claims made for full compensation were paid at the current market value of the whole fish stocks plus an allowance per family for loss of earnings. The contents o f the fish farms had to be regarded as a total loss for the following reasons. (i) At Picnic Bay the mortality had reached 10070 of the total stock in under a month and the daily weights of dead fish were still mounting. (ii) Fish frequently showed some skin blemishes which would have made them unsaleable as selected live fish for the high-class trade and these blemishes would have been liable to fungal or bacterial infection leading to loss of condition or death. (iii) The fish were strongly tainted and eventual depuration of oil from any survivors was extremely problematical at the Picnic Bay site while oil was continuing to seep from the sands at the head of the bay. (iv) There would have been market resistance to fish from a c.mtaminated area. If the fish become tasteless only elaborate chemical
analyses could show whether or not there was any retention of heavier, tasteless and yet undesirable fractions of the oil. Serious consideration was given to the suggestion of moving the fish culture rafts to clean waters if a suitable sheltered locality could have been found. Not only were the fish farmers unwilling to move to a position far f r o m their homes, because the fish require constant attention, but the moving of so m a n y fish already in a p o o r state o f health would almost certainly have resulted in further heavy mortality. If left in the cages in Picnic Bay it was thought probable that at least 50070 would die, as indeed happened with those few contaminated fish which were retained there for experimental purposes. A small number of fish were carefully moved to clean water at Kat O but about 23070 died after arrival.
Experiments on Tainting and Depuration The Fisheries Research Division set up rafts at both sites with cages to investigate changes in oil content of contaminated fish (checked for tainting by a tasting panel and by chemical analyses o f flesh and livers). Uncontaminated fish were introduced to Picnic Bay cages both in December and in April and similarly tested, to indicate the time at which fish farming could safely be restarted at Picnic Bay. By adding to the very limited data on tainting and depuration rates then available, it was hoped that results would be useful to mariculture generally. T w o o f the three species c o m m o n l y cultured in H o n g Kong and used in these experiments, namely the bream Mylio berda and Rhabdosagus sarba, did not retain or take up taint in the flesh so much as did the more expensive red spotter grouper (Epinephahis akaara). As was to be expected deputation was more rapid in clean water, but it was a surprise and a relief to find that despite the proximity of heavily oil polluted sands, only some fish showed a trace of taint after 4 months, and 8 months later when a second experiment was ended the bream were pronounced to be very good eating. A trace of taint in a surviving, originally contaminated grouper would probably have passed undetected or be accepted by the public, who are apparently accustomed to such flavours in some of the groupers caught in H o n g Kong waters. Fish farmers restarted active culturing in the late spring and in less than a year even with weathered oil still present in nearby sands there were more fish farmers establishing themselves in Picnic Bay than ever before. It would appear that the fish were able to cope metabolically with the levels of oil in the water recorded at Picnic Bay and at another fish farm, although they had been overwhelmed by the very high levels of oil including aromatics present in the waters soon after the spill. Two bream were exposed in an experimental tank at H o n g Kong University for two days to marine diesel at about l m g / l in Picnic Bay water. Extracts of liver tested by UV absorption and fluorescence seemed to indicate the presence o f marine diesel at 1 4 0 p g / g compared wttll 80/.tg/g in a control bream in Picnic Bay water alone (the oil content of which water was 30/tg/l). Four sample, of fish which had been taken from Picnic Bay in Decemb,.r and March were frozen and transported to the T o r r y Research Station, Aberdeen, Scotland to be analysed by 63
Marine Pollution Bulletin
a standard technique, comparing the n-alkane patterns in the C~5-C33 range. Extracts o f the muscle flesh failed to show any similarity with the pattern-from this marine diesel oil. There is no doubt that similar fish had been tainted and moderate or slight taint was reported in parallel samples. It is possible however that depuration from the flesh to a level too low for chemical detection could have already taken place and it should be noted that the 'diesel oil flavour' can be caused by dimethyl sulphide, detectable by some people at extreme dilution, and possibly contaminating the fish initially along with the hydrocarbons. While the chemical aspects o f these and other tainting tests were somewhat inconclusive, the tests for flavour, to which the public would respond, have given a reasonable and quite reassuring picture of the ability of the fish to depurate, providing the environmental level of oil is not too high. Polluted bream from Picnic Bay sampled in December 1973 and analysed in Scotland revealed no polynuclear aromatic hydrocarbon ( P N A H ) contamination attributable to the spilt oil, but both these fish and some pomfret caught in open sea o f f Hong Kong had a trace of another unknown P N A H at a concentration too low to be considered a health risk.
Plankton Plankton was examined soon after the spill to determine the proportion o f living and dead organisms. A kill attributed to the oil had occurred but the quality o f the surface water was rapidly improving about 3 weeks after the spill. The mixing o f water masses had probably carried in new plankton from unaffected areas and surface waters would have been losing toxicity by evaporation. A phytoplankton bloom followed a calm spell in December, suggesting that no appreciable harm to basic productivity had occurred. A few dead fish fry were seen in November, but when proper sampling startedin February, 1974 many species of fish fry were collected; nothing can be stated about relative abundance because o f lack o f previous information. Though the life span o f commercial fish is short (1-3 yr) the diversity of species in this area is such that little harm to catches would be expected from a localized kill over a short period. There seemed, however, to have been a shortage of sparid (bream) fry at the head of Picnic Bay early in 1974, but whether this was due to spawning fish having avoided a heavily contaminated area or to mortality of eggs and very young larvae is not known. After some initial difficulties the fish farmers were able to restock with sparids which are the mainstay o f mariculture in Hong Kong.
Other Fish and Invertebrates The effects of the oil spill on the natural populations of fish and invertebrates of the sublittoral zone and shores have been investigated by the Fisheries Research Division helped by volunteer divers. Severe mortalities of bivalves, gastropods, sipunculids, crabs, etc. occurred on the more heavily polluted shores, but virtually no commercially valuable species were affected. The small fishes washed up at first were those species, such as damsel fish which 64
have a strongly territorial behaviour; a few weeks later dead bottom-dwellers such as porcupine fish and several mid-water species were stranded. Divers reported some affected and dead fish in the silty waters just within Picnic Bay on 2 December but they also saw some normally active fish there. The fauna of a coral reef at 7-10 m off Lamina Island was apparently unharmed. Monitoring of shore fauna has been used to follow recovery stages. A proliferation of algae in winter was attributable largely to normal seasonal sequence in these latitudes. Recolonization by fauna in the less affected areas was already apparent in the summer of 1974 but the return was very slow at the head of Picnic Bay, probably largely because of the severe anaerobic conditions which developed in these sands (Stirling, in press). The meiofauna (minute organisms living interstitially in the deposit) were studied, it is thought for the first time in detail after an oil spill (Wormold, 1976). A total kill of this group in the oily deposits was observed immediately after the spill. Anaerobic conditions, if not the presence of the oil as well, have hindered their return. Nematodes appeared first on the lower part of the shore, followed by harpacticid copeopods, but large fluctuations in numbers occurred for several months indicating an ecological disturbance. Unfortunately it was not possible to organize any bacteriological studies.
Oil in Sand The manual removal of some heavily oiled surface sand had slightly reduced the quantity of oil held at the head o f Picnic Bay, but owing to fairly rapid penetration into the coarse sand, much oil had to be left as a potential chronic source which might affect the fish farms. Percentage oil content decreased noticeably at first, but then the loss became very slow. The higher oil contents, 2-3 °70, were then found at greater depths in the deposit and farther down the beach slope. Gradually the sand at and below mid-tide level became cleaner. The surface sands o f the upper shore were improved for amenity use by the innovation of regular burning of rubbish--at the time of the spill the amount of rubbish on that shore was the worst ever seen. The outer beaches were clean enough for amenity use from soon after the spill, while those at the head o f the bay were used during the summer despite the presence of oily sand below the surface. The development of black layers in the sand, indicating that biodegradation had started, were first noted 15 days after the stranding of oil. Owing to relatively calm conditions or onshore winds oil was only slowly flushed from the beach and estuary. With the onset of warmer weather (April onwards) there was very strong development of anaerobic conditions which prevented chemical degradation and greatly hindered biodegradation. Black sands reached the surface and there was a strong smell of hydrogen sulphide. (The particular marine diesel oil spilt was rich in sulphur compounds.) With change in wind direction and improved flushing, conditions were considerably improving by the end of the summer, 9 months after the spill. GLC analyses showed that the oil before it stranded had already lost lighter fractions and changes during weathering of interstitial oil were followed both
Volume 8 / N u m b e r 3 / M a r c h 1977
quantitatively and qualitatively. A heavy rainfall in April 1974 carried away much oil and silt, but subsequently the rainfall was much below normal until October when a typhoon also markedly disturbed the sand at the head o f the bay. Oil flushed out was probably rapidly removed from the bay. Some oil remained at least until 1975 and small amounts are still present, but the generally slow rate of flushing of weathered oil does not seem to have affected the success of the fish farms. Owing to m a n y minor oil slicks from shipping, organisms capable of degrading oil are undoubtedly frequent in the area. Nutrient levels are probably influenced by the abundant sewage discharged into H o n g Kong waters. Some estimates of nutrients in Picnic Bay and in interstitial waters were attempted, suggesting that nutrients would be quite adequate to facilitate biodegradation. Oxygen shortage in the beach restricted biodegradation in situ, decomposition of the oil probably took place chiefly after it had been flushed out. The importance of various other processes, physical and chemical, involved in the ultimate disappearance and degradation of the oil have been discussed. No serious widespread or lasting effects could be attributed specifically to this spill in an already polluted area.
Although the effects were initially catastrophic to fish farming near the spill the rate of recovery has been surprisingly rapid once the high levels of oil in the water disappeared and the cages were restocked.
For the H o n g Kong Government Fisheries Research Division Dr W. L. Chan, Mr R. Chivers, Mr R. C h u n g and Mr Luk and Dr H. Stirling have reported on various aspects mentioned above. Dr D. K. O. C h a n and Dr M. Lie of Hong Kong University analysed oil content of water samples and sands, including changes during weathering. A n n W o r m o l d then at the Chinese University st udied the meiofauna. Dr H. T o k u d a from Tokyo, acting as consultant to the H o n g Kong Government, reported on the toxicity of the oil to diatoms and made G L C analyses o f oil in sands. The percentage oil in sand samples was determined at the Shell Laboratory. Analyses o f oil in fish were carried out at the laboratory of the Hong Kong Government Chemist and at the Torry Research Station, Scotland. The author acted as a biological consultant for Shell Oil Co. to w h o m she is indebted for the opportunity to study such an important spill of toxic oil; she was assisted by Mr H. Richards.
Chung, R. T. (in press). Studies of the effect of the A p Lei C h a u oil spill on food intake, growth, survival and flavour of reared marine fish.
Hong Kong Fish. Bull., 5. Stifling, H. (1976). (ln press). Wormold, A. P. (1976). Effects of a spill of marine diesel oil on the m e i o f a u n a of a sandy beach at Picnic Bay, Hong Kong. Environ. Pollut., ! !, 117-130.
Dissolved and Particulate Trace Metals in the Rhine Estuary and the Southern Bight J. C. D U I N K E R and R. F. N O L T I N G Netherlands Institute f o r Sea Research, P. 0. Box 59, Texei, Netherlands
Dissolved and particulate trace metals have been measured in the Southern Bight and the Rhine estuary in order to study the relative importance of precipitation and sedimentation processes as compared to mobilization processes in the estuary, and their impact on trace metal levels in the Southern Bight. To understand what effect trace metals derived from river systems may have on the levels in the marine environment, it is important to distinguish between particulate and dissolved species. It has been suggested that the Rhine estuary acts as a sink for a considerable fraction (20-60°70) of river-borne particulate matter and a number of its associated trace metals such as iron, copper and zinc (Duinker & Nolting, 1976). River-borne material that is not trapped in the estuary can escape to the marine environment; the transport of suspended particles is quite different from that of dissolved species. Up to 50070 of the suspended matter in the coastal area may enter the Dutch Wadden Sea where it is accumulated against the gradient and may be trapped in b o t t o m sediments as has been explained by P o s t m a (1961), van
Straaten & Kuenen (1957,1958) and Verwey (1966). Species that are and remain dissolved in seawater are likely to be able to escape to the open sea according to hydrographical conditions of the area (van Bennekom etal., 1975). Two models describing the behaviour o f trace metals in the Rhine estuary are available in the literature. Mobilization of a considerable number of trace metals from suspended matter in the estuarine region was suggested by de G r o o t (1975) on the basis of b o t t o m sediment data. Duinker & Nolting (1976) on the basis of analyses of metal concentrations in suspended matter (Cu, Zn, Fe, Mn) and in solution (Zn, Fe, Mn) during three consecutive cruises in the area in a u t u m n 1973, found no indication for a net mobilization. On the contrary, iron was found to be removed from the dissolved state, as well as manganese. Dissolved zinc was found to behave as in a conservative way during estuarine mixing. In the present study we shall describe the results of a cruise in the Southern Bight (Fig. l) in February 1975 with the aim to investigate these aspects more fully. Fresh 65
hydrocarbons by sulfate-reducing bacteria. J. BacterioL, 47, 447--448. Polich, W. M. Jr, Winters, K. & Van Baalen, C. (1974). The effects of a no. 2 fueloiland two crude oils on the growth and photosynthesis of microalgae. Mar. BioL, 28, 87-94. Rosenfeld, W. D. (1974). Anaerobic oxidation of hydrocarbons by sulfate reducing bacteria. J. BacterioL, 54, 664. Shelton, T. B. & Hunter, J. V. (1975). Anaerobic decomposition of oil in bottom sediments. JWPCF, 47, 2256--2270. Strickland, J. D. H. & Parsons, T. R. (1972). A practical Handbook of seawater analysis. FishRes. BdCan., Bulletin 167 (2nd edition), Ottawa. Walker, J. D. & Colwell, R. R. (1975). Extraction of petroleum hydrocarbons from oil-contaminated sediments. Bull. Env. Contamination ToxicoL, 13,245-247. ZoBell, C. E. (1946). Action of microorganisms of hydrocarbons. Bact. Rev., 10, 1-41. ZoBell, C. E. 0973). Microbial degradation of oil: present status, problems, and perspectives. In TheMicrobiaIDegradation of O i l Pollutants. pp. 3-16. D. G. Ahearn and S. P. Meyers (eds.), Center for Wetlands Resources, Louisiana State University, Baton Rouge, Publication No. LSU-SG-73-01. ZoBeil, C. E. & Prokop, J. F. (1966). Microbial oxidation of mineral oils in Barataria Bay bottom deposits. Zast AIg. MikrobioL, 6, 143-162.
Oil Spill in Hong Kong M O L L Y F. S P O O N E R
Marine Biological Association of the U.K., Citadel Hill, Plymouth, Devon, U.K.
Fish farming was seriously but only temporarily affected by a large spill of a very toxic product oil at Hong Kong. Field experiments were set up to follow tainting and depuration. Studies were made of hydrography, water quality, oil in sands, macro- and meio-fauna of shores, and some observations made of possible effects on plankton and open-water fisheries.
open shores in a few months. The other source of pollution from oil which had seeped into the foundation of the tank farm took 6 months to be removed largely by 8' ~. 15' [
A spill o f heavy marine diesel oil (specific gravity 0.89; about 40°70 aromatic content) occurred from the tank farm at Ap Lei Chau, owing to failure o f foundations, on the night o f 8 November 1973. The total loss was estimated as about 4000 tons. Evaporation must have been considerable, water temperature being 23-24°C. Slicks soon spread over East L a m m a Channel and were artificially dispersed there. In Picnic Bay, because of mariculture activities, mopping up with polyurethane foam sheets was tried and was effectively aided by onshore winds. Much oil was stranded on the shores of L a m m a Island--both on the open shores o f George Bay and in Picnic Bay where oil penetrated deep into the sands at the head of the Bay adjacent to the fish farms. In winter the predominant wind direction is from the northeast into the long narrow bay, thus hindering water exchange and the natural flushing of the sands. In summer south-west monsoon conditions improved water exchange and occasional very heavy rainstorms helped to flush some o f the oil out of the coarse sand. Even a year after the spill much oil was still present in deposits at the head o f the bay whereas it was greatly reduced on more 62
11409'
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Hang KongI Island
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14'
~
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George Bay
°o
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13'
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Fig. 1 Area affected by oil from the Hang Kong oil spill.
Volume 8/Number 3/March 1977 pumping and tidal flushing. The importance o f wind direction and hydrography on rate of natural cleansing was clearly demonstrated. A study o f the hydrography o f the Picnic Bay area was rapidly undertaken by the Fisheries Research Division at the end o f N o v e m b e r 1973 and again in May 1974.
Water Quality The oil contents of the waters, particularly the toxic aromatic fractions, were determined by UV absorption and spectrofluorimetry f r o m several stations in the H o n g Kong area sampled at the end of N o v e m b e r and subsequently. In the waters around the Picnic Bay fish farm a marked i m p r o v e m e n t in water quality was reported f r o m a deduced oil content o f 45-60 ttg/l on 1 December 1973 to the level of 30 ug/l at the end o f March and 13 /tg/l in May 1974. Values o f 17-29 ttg/l were obtained near fish farms unaffected by the spill. At a clean water station, Kat 0, in the far north o f the New Territories 13-16 /tg/l was recorded. The level of 19-25 p g / l found in East L a m m a Channel in November 1973 was probably caused by the very heavy shipping traffic in H o n g Kong waters to which this spill made a chiefly t e m p o r a r y addition. It would have been impossible to have distinguished oil which sedimented down during this spill f r o m oil already probably present in bottom deposits.
Fisheries The 4 - 5 million inhabitants of H o n g Kong depend on the sea for a b o u t half their protein but this is derived from a wide area o f the South China Sea and fortunately no interference with the diverse general fisheries was reported. Fish cultured in cages suspended from rafts in the fish farms, especially those at the head of Picnic Bay (involving a b o u t 100 families) were, however, seriously affected. A slick had passed through the fish farms before a b o o m could be deployed. In Aberdeen, the main fishing harbour o f H o n g Kong, oil, dispersed because of the proximity of a power station, reached fish being cultured in scattered cages a m o n g the crowded junks. At both places the fish showed a b n o r m a l swimming behaviour, ignored food and were dying. Claims made for full compensation were paid at the current market value of the whole fish stocks plus an allowance per family for loss of earnings. The contents o f the fish farms had to be regarded as a total loss for the following reasons. (i) At Picnic Bay the mortality had reached 10070 of the total stock in under a month and the daily weights of dead fish were still mounting. (ii) Fish frequently showed some skin blemishes which would have made them unsaleable as selected live fish for the high-class trade and these blemishes would have been liable to fungal or bacterial infection leading to loss of condition or death. (iii) The fish were strongly tainted and eventual depuration of oil from any survivors was extremely problematical at the Picnic Bay site while oil was continuing to seep from the sands at the head of the bay. (iv) There would have been market resistance to fish from a c.mtaminated area. If the fish become tasteless only elaborate chemical
analyses could show whether or not there was any retention of heavier, tasteless and yet undesirable fractions of the oil. Serious consideration was given to the suggestion of moving the fish culture rafts to clean waters if a suitable sheltered locality could have been found. Not only were the fish farmers unwilling to move to a position far f r o m their homes, because the fish require constant attention, but the moving of so m a n y fish already in a p o o r state o f health would almost certainly have resulted in further heavy mortality. If left in the cages in Picnic Bay it was thought probable that at least 50070 would die, as indeed happened with those few contaminated fish which were retained there for experimental purposes. A small number of fish were carefully moved to clean water at Kat O but about 23070 died after arrival.
Experiments on Tainting and Depuration The Fisheries Research Division set up rafts at both sites with cages to investigate changes in oil content of contaminated fish (checked for tainting by a tasting panel and by chemical analyses o f flesh and livers). Uncontaminated fish were introduced to Picnic Bay cages both in December and in April and similarly tested, to indicate the time at which fish farming could safely be restarted at Picnic Bay. By adding to the very limited data on tainting and depuration rates then available, it was hoped that results would be useful to mariculture generally. T w o o f the three species c o m m o n l y cultured in H o n g Kong and used in these experiments, namely the bream Mylio berda and Rhabdosagus sarba, did not retain or take up taint in the flesh so much as did the more expensive red spotter grouper (Epinephahis akaara). As was to be expected deputation was more rapid in clean water, but it was a surprise and a relief to find that despite the proximity of heavily oil polluted sands, only some fish showed a trace of taint after 4 months, and 8 months later when a second experiment was ended the bream were pronounced to be very good eating. A trace of taint in a surviving, originally contaminated grouper would probably have passed undetected or be accepted by the public, who are apparently accustomed to such flavours in some of the groupers caught in H o n g Kong waters. Fish farmers restarted active culturing in the late spring and in less than a year even with weathered oil still present in nearby sands there were more fish farmers establishing themselves in Picnic Bay than ever before. It would appear that the fish were able to cope metabolically with the levels of oil in the water recorded at Picnic Bay and at another fish farm, although they had been overwhelmed by the very high levels of oil including aromatics present in the waters soon after the spill. Two bream were exposed in an experimental tank at H o n g Kong University for two days to marine diesel at about l m g / l in Picnic Bay water. Extracts of liver tested by UV absorption and fluorescence seemed to indicate the presence o f marine diesel at 1 4 0 p g / g compared wttll 80/.tg/g in a control bream in Picnic Bay water alone (the oil content of which water was 30/tg/l). Four sample, of fish which had been taken from Picnic Bay in Decemb,.r and March were frozen and transported to the T o r r y Research Station, Aberdeen, Scotland to be analysed by 63
Marine Pollution Bulletin
a standard technique, comparing the n-alkane patterns in the C~5-C33 range. Extracts o f the muscle flesh failed to show any similarity with the pattern-from this marine diesel oil. There is no doubt that similar fish had been tainted and moderate or slight taint was reported in parallel samples. It is possible however that depuration from the flesh to a level too low for chemical detection could have already taken place and it should be noted that the 'diesel oil flavour' can be caused by dimethyl sulphide, detectable by some people at extreme dilution, and possibly contaminating the fish initially along with the hydrocarbons. While the chemical aspects o f these and other tainting tests were somewhat inconclusive, the tests for flavour, to which the public would respond, have given a reasonable and quite reassuring picture of the ability of the fish to depurate, providing the environmental level of oil is not too high. Polluted bream from Picnic Bay sampled in December 1973 and analysed in Scotland revealed no polynuclear aromatic hydrocarbon ( P N A H ) contamination attributable to the spilt oil, but both these fish and some pomfret caught in open sea o f f Hong Kong had a trace of another unknown P N A H at a concentration too low to be considered a health risk.
Plankton Plankton was examined soon after the spill to determine the proportion o f living and dead organisms. A kill attributed to the oil had occurred but the quality o f the surface water was rapidly improving about 3 weeks after the spill. The mixing o f water masses had probably carried in new plankton from unaffected areas and surface waters would have been losing toxicity by evaporation. A phytoplankton bloom followed a calm spell in December, suggesting that no appreciable harm to basic productivity had occurred. A few dead fish fry were seen in November, but when proper sampling startedin February, 1974 many species of fish fry were collected; nothing can be stated about relative abundance because o f lack o f previous information. Though the life span o f commercial fish is short (1-3 yr) the diversity of species in this area is such that little harm to catches would be expected from a localized kill over a short period. There seemed, however, to have been a shortage of sparid (bream) fry at the head of Picnic Bay early in 1974, but whether this was due to spawning fish having avoided a heavily contaminated area or to mortality of eggs and very young larvae is not known. After some initial difficulties the fish farmers were able to restock with sparids which are the mainstay o f mariculture in Hong Kong.
Other Fish and Invertebrates The effects of the oil spill on the natural populations of fish and invertebrates of the sublittoral zone and shores have been investigated by the Fisheries Research Division helped by volunteer divers. Severe mortalities of bivalves, gastropods, sipunculids, crabs, etc. occurred on the more heavily polluted shores, but virtually no commercially valuable species were affected. The small fishes washed up at first were those species, such as damsel fish which 64
have a strongly territorial behaviour; a few weeks later dead bottom-dwellers such as porcupine fish and several mid-water species were stranded. Divers reported some affected and dead fish in the silty waters just within Picnic Bay on 2 December but they also saw some normally active fish there. The fauna of a coral reef at 7-10 m off Lamina Island was apparently unharmed. Monitoring of shore fauna has been used to follow recovery stages. A proliferation of algae in winter was attributable largely to normal seasonal sequence in these latitudes. Recolonization by fauna in the less affected areas was already apparent in the summer of 1974 but the return was very slow at the head of Picnic Bay, probably largely because of the severe anaerobic conditions which developed in these sands (Stirling, in press). The meiofauna (minute organisms living interstitially in the deposit) were studied, it is thought for the first time in detail after an oil spill (Wormold, 1976). A total kill of this group in the oily deposits was observed immediately after the spill. Anaerobic conditions, if not the presence of the oil as well, have hindered their return. Nematodes appeared first on the lower part of the shore, followed by harpacticid copeopods, but large fluctuations in numbers occurred for several months indicating an ecological disturbance. Unfortunately it was not possible to organize any bacteriological studies.
Oil in Sand The manual removal of some heavily oiled surface sand had slightly reduced the quantity of oil held at the head o f Picnic Bay, but owing to fairly rapid penetration into the coarse sand, much oil had to be left as a potential chronic source which might affect the fish farms. Percentage oil content decreased noticeably at first, but then the loss became very slow. The higher oil contents, 2-3 °70, were then found at greater depths in the deposit and farther down the beach slope. Gradually the sand at and below mid-tide level became cleaner. The surface sands o f the upper shore were improved for amenity use by the innovation of regular burning of rubbish--at the time of the spill the amount of rubbish on that shore was the worst ever seen. The outer beaches were clean enough for amenity use from soon after the spill, while those at the head o f the bay were used during the summer despite the presence of oily sand below the surface. The development of black layers in the sand, indicating that biodegradation had started, were first noted 15 days after the stranding of oil. Owing to relatively calm conditions or onshore winds oil was only slowly flushed from the beach and estuary. With the onset of warmer weather (April onwards) there was very strong development of anaerobic conditions which prevented chemical degradation and greatly hindered biodegradation. Black sands reached the surface and there was a strong smell of hydrogen sulphide. (The particular marine diesel oil spilt was rich in sulphur compounds.) With change in wind direction and improved flushing, conditions were considerably improving by the end of the summer, 9 months after the spill. GLC analyses showed that the oil before it stranded had already lost lighter fractions and changes during weathering of interstitial oil were followed both
Volume 8 / N u m b e r 3 / M a r c h 1977
quantitatively and qualitatively. A heavy rainfall in April 1974 carried away much oil and silt, but subsequently the rainfall was much below normal until October when a typhoon also markedly disturbed the sand at the head o f the bay. Oil flushed out was probably rapidly removed from the bay. Some oil remained at least until 1975 and small amounts are still present, but the generally slow rate of flushing of weathered oil does not seem to have affected the success of the fish farms. Owing to m a n y minor oil slicks from shipping, organisms capable of degrading oil are undoubtedly frequent in the area. Nutrient levels are probably influenced by the abundant sewage discharged into H o n g Kong waters. Some estimates of nutrients in Picnic Bay and in interstitial waters were attempted, suggesting that nutrients would be quite adequate to facilitate biodegradation. Oxygen shortage in the beach restricted biodegradation in situ, decomposition of the oil probably took place chiefly after it had been flushed out. The importance of various other processes, physical and chemical, involved in the ultimate disappearance and degradation of the oil have been discussed. No serious widespread or lasting effects could be attributed specifically to this spill in an already polluted area.
Although the effects were initially catastrophic to fish farming near the spill the rate of recovery has been surprisingly rapid once the high levels of oil in the water disappeared and the cages were restocked.
For the H o n g Kong Government Fisheries Research Division Dr W. L. Chan, Mr R. Chivers, Mr R. C h u n g and Mr Luk and Dr H. Stirling have reported on various aspects mentioned above. Dr D. K. O. C h a n and Dr M. Lie of Hong Kong University analysed oil content of water samples and sands, including changes during weathering. A n n W o r m o l d then at the Chinese University st udied the meiofauna. Dr H. T o k u d a from Tokyo, acting as consultant to the H o n g Kong Government, reported on the toxicity of the oil to diatoms and made G L C analyses o f oil in sands. The percentage oil in sand samples was determined at the Shell Laboratory. Analyses o f oil in fish were carried out at the laboratory of the Hong Kong Government Chemist and at the Torry Research Station, Scotland. The author acted as a biological consultant for Shell Oil Co. to w h o m she is indebted for the opportunity to study such an important spill of toxic oil; she was assisted by Mr H. Richards.
Chung, R. T. (in press). Studies of the effect of the A p Lei C h a u oil spill on food intake, growth, survival and flavour of reared marine fish.
Hong Kong Fish. Bull., 5. Stifling, H. (1976). (ln press). Wormold, A. P. (1976). Effects of a spill of marine diesel oil on the m e i o f a u n a of a sandy beach at Picnic Bay, Hong Kong. Environ. Pollut., ! !, 117-130.
Dissolved and Particulate Trace Metals in the Rhine Estuary and the Southern Bight J. C. D U I N K E R and R. F. N O L T I N G Netherlands Institute f o r Sea Research, P. 0. Box 59, Texei, Netherlands
Dissolved and particulate trace metals have been measured in the Southern Bight and the Rhine estuary in order to study the relative importance of precipitation and sedimentation processes as compared to mobilization processes in the estuary, and their impact on trace metal levels in the Southern Bight. To understand what effect trace metals derived from river systems may have on the levels in the marine environment, it is important to distinguish between particulate and dissolved species. It has been suggested that the Rhine estuary acts as a sink for a considerable fraction (20-60°70) of river-borne particulate matter and a number of its associated trace metals such as iron, copper and zinc (Duinker & Nolting, 1976). River-borne material that is not trapped in the estuary can escape to the marine environment; the transport of suspended particles is quite different from that of dissolved species. Up to 50070 of the suspended matter in the coastal area may enter the Dutch Wadden Sea where it is accumulated against the gradient and may be trapped in b o t t o m sediments as has been explained by P o s t m a (1961), van
Straaten & Kuenen (1957,1958) and Verwey (1966). Species that are and remain dissolved in seawater are likely to be able to escape to the open sea according to hydrographical conditions of the area (van Bennekom etal., 1975). Two models describing the behaviour o f trace metals in the Rhine estuary are available in the literature. Mobilization of a considerable number of trace metals from suspended matter in the estuarine region was suggested by de G r o o t (1975) on the basis of b o t t o m sediment data. Duinker & Nolting (1976) on the basis of analyses of metal concentrations in suspended matter (Cu, Zn, Fe, Mn) and in solution (Zn, Fe, Mn) during three consecutive cruises in the area in a u t u m n 1973, found no indication for a net mobilization. On the contrary, iron was found to be removed from the dissolved state, as well as manganese. Dissolved zinc was found to behave as in a conservative way during estuarine mixing. In the present study we shall describe the results of a cruise in the Southern Bight (Fig. l) in February 1975 with the aim to investigate these aspects more fully. Fresh 65