Alone, the solvent is as toxic as emulsifier 1002, but blends X and Y, which have lower aromatic contents, are less toxic. Further experiments with BP 1002 indicated that the dilution rather than the amount is important in determining toxicity to plants. Dilution probably affects the penetration of the emulsifier. Van Overbeek and Blondeau (1954) observed that aqueous solutions do not penetrate stomata, whereas highly toxic hydrocarbons such as aromatics enter indiscriminately from the point of contact (Dallyn, 1953). The different golutions of BP 1002 which we used ranged between these extremes. Concentrations of emulsifier below 10 per cent probably had reduced penetrating ability. This will be further investigated by finding the penetration times of different dilutions for different species. Beach cleaning contractors at Milford Haven have occasionally applied emulsifier to oily areas by introducing it into water hoses to produce a jet of emulsifier solution of approximately 3 per cent. This is probably less damaging to salt marsh plants than the recommended practice of applying undiluted emulsifier followed by hosing with water. Future work As well as the replicate field experiments I have already mentioned, some of the greenhouse experiments involving growth stimulators, nutrients and emulsifiers will be repeated. We also hope to investigate rates of penetration of different oil fractions and emulsifier dilutions; effects of
plant kill and oil in the soil on soil oxygen and sulphide with particular reference to Spartina, and the physiological basis of the susceptibilities of different species to oil. Oil Pollution Research Unit, Orielton Field Centre, Pembroke, S. Wales.
Jennifer M. Baker
Armstrong, W. ( 1967 ) The use of polarography in the assay of oxygen diffusing from roots in anaerobic media, 'Physiologia Plantarum', 20 : 540-553. Dallyn, S. (1953), Herbicidal action of oils, 'Cornell Univ. Agr. Exp. Station Memoir', 316, Ithaca, N.Y. Field Studies Council Oil Pollution Research Unit (1969),'Annual Report 1968'. Goodman, P.J. (1959), The possible role of pathogenic fungi in die-back of Spartina townsendff agg., 'Trans. Brit. Mycol. Soc.', 42 : 409-415. Goodman, P.J. and Williams, W.T. (1961), Investigations into die-back in Spartina townsendff agg. III, 'J. Ecol.', 49 : 391-398. Lachman, W. H. (1944), The use of oil sprays as selective herbicides for carrots and parsnips, 'Proc. Amer. Soc. Hort. Sci.', 45 : 445-448. Van Overbeek, .1. and Blondeau, R. (1954), Mode of action of phytotoxic oils, 'Weeds', 3 : 55-65. Wardley Smith, J. (t968), Recommended methods for dealing with oil pollution, 'Ministry of Technology Warren Spring Laboratory Report', LR 79 (EIS) HMSO.
IVlarine Fish Farming The British aquaculture programme is largely concerned with the use of condenser cooling water discharged from coastal electricity generating plants. This represents an enormous volume of seawater with fluctuating temperature differentials up to 10 deg. C above ambient. The effects of temperature on growth are well known, and the aim is to use the warm water to maintain growth of potential farm species throughout the winter and so reduce the overall time from hatching to harvest. Three problems were faced initially in 1964: the effluent contains both deliberately added and waste chemicals; nuclear plants are permitted to release controlled amounts of radioactive waste; and at certain times and in abnormal operating conditions temperatures may be lethally high. During preliminary laboratory trials the effects were studied of elevated temperatures on the viability of plaice, Pleuronectes platessa, and sole, Solea solea, both of which are successfully reared in large numbers in hatcheries (Shelbourne, 1964, 1967). It was necessary to derive an indication of their growth and tolerance within the expected thermal range of the effluent and to establish feeding levels (Shelbourne and Nash, 1966). In 1966 site trials were carried out, one at a conventional coal-fired plant in Carmarthen Bay, South Wales, and the other at Hunterston, a nuclear plant in Scotland. These sites were chosen because they both use a system of injecting a continuous low concentration of chlorine into the intake culverts as opposed to intermittent high dosing which would have required elaborate by-pass arrangements. Controlled use of chemicals added to the cooling water is standard practice for reducing corrosion, marine fouling and condenser slimes. The residuals of these and other 28
wastes are diluted significantly by the volume of the discharge and made harmless to living organisms (Markowski, 1958, 1960). Biologically, chlorine needs surveillance. Fortunately it combines with seawater in a complex form producing low residual levels. Although collectively called 'chlorine' these residuals include compounds and also derivatives of other halogens. Results of trials The results of the trials (my unpublished results) showed that both sole and plaice survived the low concentrations of 'chlorine' to which they were exposed (0.002-0.1 p.p.m.). This range is characteristic of effluent from a plant using a continuous injection system. The fish also benefited from daily feeding and attention and the higher temperature range. Most of them attained minimum marketable size (23-24cm) within 2 years, about 1 year before the most advanced individuals in natural conditions. Studies since then have been confined to Hunterston because Carmarthen is no longer a base-load plant. Following early difficulties in the management of small fish in large tanks built on the site (14.4 x 7.2 x 1.0 m deep), progress with husbandry, feeding techniques and stock density studies has been rapid. Experiments have shown that eggs of plaice and sole can be hatched in prepared effluent without harm, and that the high temperature (14 deg. C in April) and intensive larval feeding advances growth and development so that metamorphosis is complete by the fourth week. Young fish benefit from this accelerated start. From a population of several thousand The first part of this article was printed in the last issue of the 'Marine Pollution Bulletin' (1, No. 1 : 5, 1970).
plaice (selected and culled at intervals) more than 17 per cent reached marketable size 14 months after hatching. Survival in fattening tanks is high. Conditions in the tanks vary consistently according to weather, generating load and throughput of water. Oxygen concentrations in the effluent fluctuate above 100 per cent saturation but the oxygen consumption of fish densely crowded in tanks with abundant food is high. In adverse conditions of abnormally high temperature or 'chlorine' concentration, auxiliary systems of seawater and aeration are necessary. To indicate when this is necessary, detector systems are being developed.
Other organisms One of the chief concerns is the colonization of the enclosures by other marine organisms, particularly algae. The conditions within the condenser cooling water system do little to reduce the viability of many free swimming larvae or spores and while this demonstrates the suitability of the discharged water for rearing desirable species, it necessitates the controlling of undesirable species. True mixed farming of species occupying different niches can be anticipated. For example, algal browsers (ormers or abalones) and pelagic herbivorous fish (grey mullet) have been kept in the same tanks as bottom-living carnivorous flatfish. If this can be exploited commercially it will lead to economies in capital cost and space. Another possible way of reducing costs would be to re-use the water in further enclosures for less demanding species. Fish, shellfish and possibly commercially-needed algae may all prove possible to culture in tanks, ponds or lagoons adjoining a power plant. Moreover, as the warm waters produce conditions occurring naturally in other parts of the world, there is an opportunity to try and culture exotic foreign species which command a significantly high price. Two limiting factors at nearly all existing power plants are land availability and the problem of obtaining adequate water supply cheaply. Little will be accomplished at many of the plants. If, however, the concept of thermal aquaculture is immediately accepted, the many power plants necessary in the next 30 years can be sited and possibly designed with a view to exploiting this new technology. Thermal exposure The waste heat has always been considered a lost resource by engineers and the large volume of warm water returned to the environment by the big generating plants is cause for justifiable concern to ecologists. Some have termed the practice 'thermal pollution'. Aquaculture can be of practical use in that it would effect further cooling before final liberation to the environment. The use of a recognized industrial effluent in this way may seem to be an anomaly as I have stated (in the first part of this article published last month) that one of the basic requirements for aquaculture is a plentiful supply of unpolluted seawater. It is unfortunate that the word 'pollution' is now being applied to this water by some ecologists. It is neither foul nor unclean, merely warmer. Given time, new ecosystems would be established replacing those unable to tolerate the imposed conditions. A more accurate and less dramatic term would be 'thermal exposure'. It is important to appreciate the influence of climatic latitude and the availability of resources on exposure. In some situations there are species living near their limit of tolerance to temperature or oxygen. If the peak demand for electricity is in summer (when supplying cooling appliances) additional thermal exposure resulting from the requirement of extra generating capacity can be lethal to restricted or immobile species. Freshwater ecosystems are
particularly vulnerable and the use of cooling towers should be an integral part of inland plants, although the towers are not the complete answer. On the coast the resource availability is considerably greater and subsequent dilution more effective and rapid. Dangers to marine life are considerably less. It is therefore justifiable to construct power plants on the coast in preference to inland waters and to take advantage of the thermal effect by well planned aquaculture systems. It is also important to understand the requirements of the farms themselves regarding water temperature. Excessive thermal exposure will still be a danger to some species at spawning time or in the hatcheries. With adequate auxiliary systems it can be controlled. In the artificial environment for fattening, the use of waste heat will be a distinct advantage. The capacity and design of a farm at a coastal generating plant will be based on available volume of water during peak winter demand, when the priority is temperature maintenance. It is not expected that all the effluent will be available or even desirable; a considerable part will always be required by a nuclear plant to dilute and carry off radioactive waste. The fulfilment of this function will have to be considered in relation to the withdrawal point of water for the sea farm and the proximity of the outlet to the farm. Although the volume discharged is considerable, in a large mixed farm it will have to he used efficiently. It may be sufficient merely to overwinter some species in their first year when juveniles have little demand on space and water. The stock could then be transferred to ambient seawater facilities. Future coastal farms may be supplied with such established juveniles -- a parallel to existing industries for fingerling trout and day-old chicks. Raceway farming There is also the possibility of raceway farming. This practice makes the most of limited space and demands high water throughput. The capacity for production is considerable and no auxiliary pumping power will be required if the site topography is favourable. To illustrate these proposals more specifically, the nuclear complex at Hunterston will be discharging nearly 40 million gallons of water every hour. This volume is equivalent to one complete change per day of water in ponds 6 feet deep covering an area of one square mile. Alternatively, based on raceway culture of freshwater fish, it has been estimated that annual production could be at least 50 pounds/gallon/rain (Gaucher, 1968). In these terms, using only 10 per cent of the Hunterston flow in raceways, production would be possible in excess of 1,500 tons per annum. Total landings of Dover sole in England and Wales in 1968 amounted to 1,737 tons. Other countries have not been slow to follow the initiative of the White Fish Authority. In America, private and state utilities are cooperating in research programmes and a commercial operation for oyster cultivation has been started at a fossil fuel plant on the east coast. The Russians are using both inland and coastal sites to rear a variety of species and the Japanese are adapting their own techniques. The principle is sound and the product acceptable. Farmed fish have been well received by taste panels and by members of the public. Samples of fish from the Hunterston site are examined frequently by representatives of the Ministry of Agriculture, Fisheries and Food for the presence of artificial radionuclides of a character liberated by the Hunterston plant. No differences have been recorded between them and accompanying background samples of wild fish. Planning for coordinated production of power and protein means the designation of suitable areas. These must 29
then be protected from pollution and this requires the delimitation of zones by coastal hydrographers within which certain standards will have to be met by industry, agriculture and local authorities. Commercial investment in marine farming will be confined in the first place to the fast growing crustaceans (tropical shrimps and prawns), profitable molluscs (oysters, clams, ormers and mussels) and some desirable fish. The most practical areas of operation will unquestionably be where the waters are naturally clean and warm. By enlightened and skilful planning, countries of colder latitudes could manipulate parts of their environment to create similar conditions or lessen apparent disadvantages. Later, research will be diverted to examine possibilities with species not immediately attractive commercially but which may, after all, become the domesticated marine species of the future. White l:ish Authority, Marine Fish Cultivation Unit, Hunterston, W. Kilbride, Ayrshire, Scotland.
Colin E. Nash
Impact of Industry on Plants and Animals The meeting of the Lirmean Society in London on 15 January was devoted to a discussion of man's impact on the environment but was concerned with two matters that have not received much attention recently: the reclamation of land that has suffered from industrial activities, and matters relating to the hot water effluent at power stations. Mr R.-S. A. Beauchamp of the Central Electricity Generating Board introduced the latter topic. With the increasing size of generating stations, the difficulty of finding adequate cooling water from lakes and rivers, and the high cost of building cooling towers, power stations are increasingly sited on the coast where seawater can be used for cooling. The chief problem is fouling of culverts and the narrow cooling pipes by (principally) Mytilus. Once established, mussels can withstand exposure to heavily chlorinated water (20 p.p.m.) simply by closing their shells. Their growth rate is reduced but previous attempts to control fouling by periodically increasing the chlorine concentration was ineffective and in some cases caused fish deaths. Current practice is to treat cooling water with small quantities of chlorine (0.5 p.p.m.), which inhibits settlement of the fouling organisms in new or cleaned installations. The chlorinated hot water effluent is harmless to young fish and is used at Hunterston to ~upply the fish rearing tanks in a fish farming experiment. Mr P. D. V. Savage (CEGB, Southampton) discussed the effects of warm water and sudden heating on phytoplankton. Growth, measured by uptake of 14C, is not appreciably reduced by a temperature increase maintained for a time comparable to those experienced in power station condenser systems, although a 20 deg. C, increase above ambient temperature maintained for about 20 rain results in a decrease of approximately 25 per cent in the subsequent growth rate. Net phytoplankton productivity is actually increased near hot water outfalls but the effect is very local. Hot water effluents from power stations'evidently have a negligible effect on the marine environment in British waters. This may not be true in the tropics where ambient 30
Gaucher, T . A . (1968), Potential for aquaculture, 'Connecticut Res. Comm., Contract RSA-66-8'. Markowski, S. (1958), The cooling water of power stations a new factor in the environment of marine and freshwater invertebrates, 'J. Anita. Ecol.', 28 : 243, Markowski, S. (1960), Observations on the response of some benthonic organisms to power station cooling water, 'J. Anim. Ecol.', 29 : 349. Shelbourne, J. E (1964), The artificial propagation of marine fish, 'Adv. Mar. Biol.'~ 2, 1. Shelbourne, J . E . (1967), A technique for massproducing young sole (Solea solea) in hatcheries, 'ICES Fisheries Improvement Committee CM 1967/ E : 9' (mimeo). Shelbourne, J, F., and Nash, C.E. (1966), Sea fish culture in Britain, 'Proco Nutr. Soc.', 25, 133.
temperatures are closer to the thermal death point of marine organisms Department of Zoology, The University, Newcastle upon Tyne NE 1 7RU.
R. B. Clark
Prevention and Control of 0il Spillage A 3 day conference on prevention and control of oil spillage was sponsored by the American Petroleum Industry and the Federal Water Pollution Control Administration (FWPCA) in New York on 15-17 December 1969. Twelve hundred people registered - approximately three times as many as expected when the technical sessions and exhibitions were scheduled earlier in 1969 following the Santa Barbara offshore blow-out. Summing up the thirty-eight technical reports presented, Curtis G. Cortelyou, coordinator of air and water conservation, Mobil Oil Corporation, said that the most important lesson learned is that 'we still have a long way to g o . . . The unknowns still outweigh the knowns'. Officials of the FWPCA told the conference that while spectacular oil spills such as that at Santa Barbara catch the headlines, oil spill incidents are approaching 10,000 a year. Approximately two-thirds of these occur in port or harbour areas and most result from regular transfer operations. Ernest Cotton, air and water conservation adviser, Gulf Oil Corporation, told the conference that to police and clean up spills 'which do occur in spite of our efforts at prevention', the petroleum industry has already organized twenty-three cooperatives that are fully operational in US harbour areas. A further twenty-seven are being developed. In spite of millions of dollars spent on new cleanup techniques, chemical dispersants and development of boom variations, straw is generally accepted by the experts as the most practical and effective method for cleaning up spills along shorelines. Collecting the straw afterwards, however, presents a major problem. Summing up the conference, H. A. Bernard, chief, agri-