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Marine pollution — Facts and fiction, the situation in Britain
Ocean Management, 5 (1979) 263--278 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
M a r i n e Pollution -- Facts and Fiction, t h e Situation in Britain
Herbert A. Cole
ABSTRACT The widely-held impression that serious biological damage has been done to the marine environment and its resources by pollutants is not soundly based. There is no evidence that any offshore stock of fish or shellfish has suffered a reduction in annual recruitment to the exploitable stock as the result of pollution. Production generally has been well maintained and where reduction in yield is evident, e.g. in herring around the British coasts, this is a consequence of over-fishing. Stocks of fish and shellfish inhabiting shallow coastal waters and particularly estuaries are subject to many human pressures, of which reduced water quality due to pullutants is one. The most damaging effects of pollution are reduction in available oxygen, increased turbidity due to suspended material and discolouration, and deposition of organic material on the bottom. Sewage and other organic effluents (such as food-processing wastes) with a high biological oxygen demand are the prime causes of these conditions. Potentially harmful metals and synthetic organic substances resistant to breakdown may accumulate in estuarine and coastal sediments, particularly muddy sands, silts and muds containing a high proportion of organic matter, and will continue to release potential pollutants long after shore discharges are controlled. Attention to marine pollution problems needs to be focussed on such estuarine and coastal sediments and the ways by which their polluting loads are built up and released. A better understanding of the effects of sewage discharge to the marine environment of the United Kingdom is needed and might bring about a modification of the present policy of sewage disposal. Increased research in this field is highly desirable.
INTRODUCTION The widely-held impression
that
the
productivity
of the
sea h a s b e e n
r e d u c e d b y p o l l u t a n t s is i n c o r r e c t . N o r is t h e r e a s e r i o u s t h r e a t t h a t t h i s w i l l o c c u r in t h e n e a r f u t u r e . T h e r e is n o e v i d e n c e f o r a b e l i e f t h a t s u b s t a n c e s at present
unrecognized
as
potentially
damaging
contaminants
are steadily
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building up in the sea and within a few years will reach catastrophic levels and will turn the oceans into deserts. In general, changes occur slowly in the sea and, although fisheries m a y appear to decline rather rapidly, as the herring fisheries around Britain have done, these major changes are principally the result of overfishing and are n o t due to natural fluctuations or pollution. It is generally agreed that no offshore stock of fish or shellfish shows evidence of reduction o f r e c r ui t m e nt to the exploitable stock as the result of pollution. In ot her words, there is no evidence o f significant reduction in the n u m b e r of y o u n g fish growing up to exploitable size year by year because of losses at the egg or larval stage, or diminished fecundity in the breeding stock, because of direct or insidious effects of oil, mercury, cadmium, chlorinated h y d r o c a r b o n s , radioactivity or any of the ot her pollutants known by name to journalists or broadcasters. Is there then no marine pollution problem? Is it just a not he r scare generated by sensation-hungy pressmen? The answer is, of course, n o - there are areas of concern, especially for resources in coastal waters and estuaries, and there are certain difficult public health and amenity problems. In considering these it is necessary to begin at the beginning with the definition o f marine pollution.
Dr. H.A. Cole is a graduate of the University of Wales. F r o m 1959 until he retired in 1974 he was Director of Fishery Research at the Fisheries L aborat ory, L ow est oft , England. He has written extensively on shellfish biology, fishery management and marine pollution.
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DEFINITIONS The internationally accepted definition of marine pollution is that used by the United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP) which reads: " I n t r o d u c t i o n by man of substances or energy to the marine environment resulting in such deleterious effects as harm to living resources or marine life, hazards to human health, hindrance to marine activities, including fishing, impairment of quality for use of seawater and reduction of amenities." As now stated, the definition reflects the confused English often used by multi-national committees and the words "or marine life" and "including fishing" are clearly superfluous while the value of the reference to seawater quality is dubious. However, the essential concept linking pollution with harm is sufficiently evident and the principal areas in which harmful effects may be experienced are clearly stated. At this point it may be useful to give established examples of each main category of harmful effect. In relation to living resources the deterioration of estuaries as the result of the discharge of sewage and other wastes, e.g. from food processing, slaughter houses, laundries and distilleries, which mop up the available oxygen and so prevent the passage of salmon, is well known, as, because of sewage contamination, is the banning of collecting and marketing of shellfish from such estuaries without purification. This is a human health risk (the second category of effects) but in many estuaries the environmental conditions are so poor that the shellfish themselves are no longer able to survive. Other well-known public health problems are the contamination by sewage of bathing beaches and the accumulation of mercury and cadmium in fish and shellfish in areas where wastes containing these metals have been discharged. Among conservation problems, the oiling of seabirds is so well-known as to need no elaboration here. On the amenity front we are all aware of the nuisance created by oil on beaches but examples of interference with other legitimate activities do n o t perhaps come readily to mind although they are, in fact, both numerous and varied. Sewage enrichment causes unwelcome growths of marine algae, particularly Ulva and Enteromorpha, which may be a nuisance on public beaches; silting of estuaries and approaches to ports may be accelerated if there is a heavy discharge of organic wastes or increased production due to nutrients derived from domestic wastes; waste plastic ropes and nets may become entangled in ships' propellers and plastic film may block the water intakes to their engines and, of course, the accumulation of such waste and other garbage, discharged by ships, is a persistent nuisance on many beaches.
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THE AREAS PRINCIPALLY AT RISK Man's capacity to alter the character of the open oceans or their productivity is quite limited. One must make an exception to this in respect of potentially toxic man-made chlorinated hydrocarbons which ar~ largely airborne and may be distributed worldwide, and this will be discussed further later in this paper. It is in shallow coastal water and particularly in estuaries (Royal Commission, 1972), inlets and semi-enclosed seas, e.g. the Baltic (ICES, 1977) and the Mediterranean (Osterberg and Keckes, 1977) that man's capacity to cause damage is most evident: it is in these areas that pollution prevention efforts should be concentrated. The estuarine environment is particularly subject to human pressure. Any estuary deep enough to admit ships inevitably attracts development while those which are shallow with low-lying shores are much in demand for recreational activities. Moreover, the rivers that discharge into estuaries are invariably regarded as the natural outlets for sewage and industrial wastes produced inland. The estuarine environment is naturally one where the animals and plants must be adaptable to a wide range of physical and chemical c h a n g e s - - t e m p e r a t u r e , salinity, current speed, suspended matter, e t c . - if they are to survive. The effects of the addition of sewage and industrial wastes are principally evident in loss of oxygen, additional suspended matter and reduction in light penetration. These are best regarded as a further addition to the environmental stresses to which the estuarine biota are normally subjected. However, depletion of oxygen and its immediate consequences on chemical balance must be regarded as a major new stress factor and, when combined with a heavy addition to the organic matter load, can be identified as the aspect of waste disposal likely to cause most harm. Although fish kills in rivers and estuaries as the result of the occasional inadvertent release of poisonous substances, such as cyanides, make the headlines because the damage is clearly evident, the gradual depressing effect of reduced oxygen levels and high suspended matter loads is much more serious and is the prime cause of the generally deplorable condition of estuaries in Britain. Nor can the situation be said to be improving much, although numerous plans have been discussed, because local and regional authorities generally tend to regard their sewage and waste disposal problems as solved if they can reach an estuary or the sea. Fortunately or unfortunately, depending on whether one is a waste disposer or concerned with conservation of natural resources, production of fish and shellfish from the estuaries of Britain does not represent a large part of the total catch. Its cash value at first sale is probably no more than 2% of the total value of all fish and shellfish landed and certainly less than 4%. It does, however, contain one species of great social importance, particularly in
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Scotland, the Atlantic salmon. Although some additional salmon could no d o u b t be produced by cleaning up rivers which formerly supported it and which still have satisfactory conditions for spawning in the upper reaches, as has been shown previously (Cole, 1974), examination of the statistics of landings from existing salmon rivers reveals no evidence of the effects of pollution during the post-war period of industrial re-development and population increase. By the expenditure of vast sums, including the provision of fish passes in the freshwater reaches, no d o u b t British Members of Parliament could be enabled to fish for salmon from the terrace of the Houses of Parliament but where would the survivors go to spawn? But to return to the question of the value of estuarine production in Britain. This is also important for certain classes of molluscan shellfish, especially mussels, cockles and oysters, but these fisheries have been allowed to decline very greatly due to the pressure of development. They have succumbed to the argument that their cash value is less than that of the industrial, housing or recreational activities with which t h e y have been largely replaced in m a n y estuaries. It may be regarded as a failure of national planning and, although often stated, the argument that certain estuaries are uniquely suited environmentally to the production of shellfish and should be reserved, and fully developed, for that purpose, has rarely prevailed. There are one or two tiny examples of successful conservation that could be quoted from the United Kingdom, such as the Helford River in Cornwall and the N e ~ l o w n River in the Isle of Wight, but these must be set against a very long list of grounds productive at the end of the last century (Bulstrode 1896) where there are either no full-time fishermen at all or only the remnants of a dying industry. In 1976 Nephrops (scampi) and scalops and queens together represented nearly 60% by value of the UK shellfish landings. In that year oysters, mussels and cockles -- the estuarine species - represented only about 6% by value compared with approximately 40% 60 years ago. Although estuaries are crucially important to only a few species of fish (salmon, sea trout, eels, smelts and flounders) which together represent only about 1% of the total landings, sheltered shallow coastal bays and inlets are in a different category. They are the nursery grounds of several very important sea fish, e.g. plaice, sole, turbot, herring, etc. which together figure largely in the British catch. Any drastic alteration of these shallow coastal nursery areas by pollutants could reduce survival of young fish and so affect recruitment. The expression "drastic alteration" is used deliberately because the natural losses of young fish during their early stages are very high indeed and small reductions due to pollution would certainly be insignificant. Most fish are highly fecund and this excessive production of eggs and
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larvae is the mechanism whereby high natural losses due to predation in the planktonic stage and adverse environmental factors, such as out-of-phase production of food organisms, can be absorbed without damaging effects on recruitment. Nevertheless it is important to understand that natural recruitment in species that have been studied shows great variation from year to year (by two orders of magnitude or more in some species).
SEWAG E There are certain aspects of sewage
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high cost of such offshore pipelines (often involving pumping of effluent) creates pressure to reduce treatment and to discharge comminuted crude sewage. Moreover, as t r e a t m e n t is reduced, it becomes possible to accept toxic industrial wastes which it would not be feasible to take at the sewage works if full treatment were given. These toxic wastes, although diluted, are therefore discharged to the sea through the pipline virtually untreated. Unfortunately, although there has been a determined effort to maintain the water quality of rivers and streams and their biological conditions ("fish life"), and some improvement has been claimed here and there, it has remained official policy in the United Kingdom to permit, and even encourage, the discharge of sewage to estuaries and to the sea after no more treatment than screening and comminution. Although this " t r e a t m e n t " has the effects of making sewage less recognizable, and of aiding dispersion and breakdown, it does not reduce its polluting capacity. Although some open coast beaches may become less contaminated because of this policy, estuaries are rarely regarded as bathing areas and, although important for sailing, this is not a sport which is deemed to require seawater of a high sanita.ry quality. A rather low water quality is therefore acceptable on amenity grounds. The general necessity, in inland areas, of taking industrial wastes into the public sewage system, and the demand for high emission standards for effluents to protect fish life in rivers, lead inevitably to a situation where sewage plant sludges from industrial areas contain substantial amounts of metals and organic s u b s t a n c e s - especially synthetic compounds such as chlorinated h y d r o c a r b o n s - - w h i c h are resistant to breakdown. These contaminated sludges are increasingly being dumped at sea where the persistent materials largely accumulate in sediments and are only very slowly dispersed. Because sea dumping is an expensive operation compared with land disposal, dumping grounds tend to be rather near the land and certainly within fishing depth. Some sites used historically have proved to be very suitable for dispersion, e.g. the outer Thames, but others have proved rather hazardous, e.g., New York Bight. If dumping of sewage sludge at sea is to be extended then the choice of sites needs to be made only after expert assessment of the anticipated water movements, including those at the sea bottom, and of the likely effects on fish and shellfish (see Kullenberg, 1975).
OIL Oil pollution is an emotive subject in Britain because of the continued presence of tar balls and oiled seabirds on m a n y south- and east-coast recreational beaches. However, from the point of view of fisheries, one has
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to say that oil is a serious problem only to those engaged in the cultivation of molluscan shellfish, owing to oily flavours and fouling. To those engaged in offshore fishing, the presence of an oil industry in British waters has often meant an additional source of income from the use of obsolescent fishing vessels for various purposes connected with the oil industry and, one suspects, a source of compensation for damage to fishing gear by drums, wires and other obstacles on the seabed without the necessity for absolute proof of the origin of the obstacles. Undoubtedly, ships servicing oil rigs and production platforms dump rubbish at sea but so do ships of other kinds, including fishing vessels. Because oil and gas rigs and platforms must be located where the resources are found, and it is necessary to prescribe safety zones around such structures in which fishing is prohibited, some loss of fishing opportunity must be sustained. Similarly with pipelines which, although initially buried, may later be exposed. However, since adequate conservation is the prime requirement to maintain the productivity of fish stocks in the present highly competitive situation, any device which incidentally protects some part of the stock from exploitation (and gives other benefits) should surely be welcomed. Tainting by oil, or by any of the range of strong-smelling organic substances, such as phenols, which produce " o f f " fiavours, is occasionally experienced in fish and more often in shellfish taken close inshore. It is known, however, that these taints can be caused naturally by heavy feeding on certain species, e.g. of planktonic organisms. Such taints may cause serious short-term disruption of marketing which may lead to financial loss. When present in molluscan shellfish they may persist for several months due, it is believed, in the case of oil, to limited capacity to metabolise certain hydrocarbons (GESAMP, 1977). Obviously, heavy oil spills, such as that from the Amoco Cadiz, can blanket large areas of shore, and mollusc cultivators may suffer severe losses where stocks are concentrated. Nevertheless, it is remarkable how little damage of this kind has been done by the major oil spills which have occurred throughout the world. In the example of the Torrey Canyon spill there were no significant losses of this kind, indeed no significant effects on fisheries of any kind. Stocks of certain seabirds, particularly auks, in British waters, are becoming depleted by oil pollution (Bourne, 1976). Because most of these birds produce only one egg, their power of recovery is limited and this, coupled with human disturbance of their breeding haunts, seems likely to result in extinction of the remaining colonies of a few species on the south and southwest coasts of the British Isles. However, the species affected are extremely a b u n d a n t further north, particularly in northwest Scotland, the Scottish Islands and along the Atlantic coast of Ireland. Attempts to reduce losses off
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southern Britain or to rehabilitate oiled birds seem unlikely to add significantly to the survival of the stock and the effort involved would, perhaps, be better diverted to serious research on methods of increasing survival, e.g. by control of predators, particularly rats, at major breeding sites in areas well away from the main oil tanker routes. Bird watching is an important pastime, and hence has an economic value, and the northwest of Britain is no longer to be regarded as out of reach of the main centres of population. Although estimates of the relative importance of different sources of oil in the sea differ widely (GESAMP, 1977), the major cause of oiled seabirds is undoubtedly spillage from ships. Operational discharges are already fully covered by the regulations made by the Intergovernmental Maritime Consultative Organisation (IMCO) on the basis of the various international conventions dealing with the prevention of oil polution. Unfortunately, not all countries operating oil tankers have ratified these conventions and enforcem e n t of their provisions is very difficult. The need is not, however, for more regulation since most spills arise from human frailty or neglect rather than from inadequacy of the regulations. Even attempts at closer regulation of ship traffic in crowded shipping lanes, e.g. in the English Channel, are unlikely to produce much effect unless the men engaged accept greater responsibility for their actions and the possible environmental consequences. It can, however, be claimed that the tightening up of regulations that has occurred over the last 10 years or so has had a beneficial effect, since oil pollution has remained at about the same level, although the a m o u n t of oil moved around the oceans has substantially increased. Further improvement will only come very slowly as appreciation of the importance of environmental quality grows as the result of education and publicity. This seems an appropriate m o m e n t to say that such education and publicity (particularly the latter) must n o t take the form of propagating 'scares' associated with such emotive subjects as cancer. In the longer term these tactics (over-statem e n t to attract attention ) are u n d o u b t e d l y counterproductive--they may sell newspapers but they do not remedy pollution.
CHLORINATED HYDROCARBONS There is much misunderstanding of the status of DDT, dieldrin, etc., as marine pollutants. Although their use as insecticides has u n d o u b t e d l y caused severe depletion of certain birds of prey, notably the peregrine, the only marine fishery problems created, have, with one exception, arisen from heavy discharges of residues to rivers from plants making the pesticide or from industrial use, e.g. in the moth-proofing of carpets. The exception is the banning of the sale for human consumption of codliver oil derived from
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Baltic fish in certain riparian countries in that area following heavy use of DDT. Yet, as is generally known, DDT or its breakdown products have been found t h r o u g h o u t the oceans of the world in biological material wherever t h e y have been looked for with the highly sensitive instrumentation now available to the analytical chemist. This worldwide spread has occurred for three main reasons: (a) heavy losses to the atmosphere during spraying; (b) persistence (half-life in the sea is thought to lie between 10 and 20 years); and (c) passage through food chains with possibly some biomagnification in top predators such as birds of prey and seals. No adverse effects in human beings due to consumption of seafood contaminated by DDT or its breakdown products have been demonstrated. In several species of seabirds, however, egg shell thinning and loss o f reproductive capability have been demonstrated. In seals, particularly in the Baltic, changes in reproductive organs leading to loss of fertility, possibly sufficient to produce an effect at population level, have been shown to occur in animals containing high levels of DDT and PCBs, but the latest studies seem to implicate PCBs as the principal causative factor (Jensen, 1977). PCBs were used in industry with substantial losses to the environment for about 20 years before adverse effects were suspected (Jensen, 1972). They have now been shown to be distributed worldwide and there is some field evidence of adverse effects in the marine environment, particularly on reproductive performance. Their continued use in situations where loss may occur to the environment has been generally condemned and restrictions have been introduced in many c o u n t r i e s - in the UK on a voluntary basis. Unfortunately PCBs seem to be even more persistent than DDT and other chlorinated hydrocarbon pesticides and whereas levels of DDT and its metabolites have fallen in recent years in marine biota in European seas, levels of PCBs have remained virtually unchanged (OECD analyses).
PERSISTENCE OF POTENTIAL POLLUTANTS IN SEDIMENTS Sediments, particularly those containing a high proportion of fine material (silt and clay fractions) and a substantial content of organic material, are the main resting place of most of the potentially harmful substances discharged to the sea. Coarse and fine sands and gravels are much less effective in holding potential pollutants. The substances readily held by adsorptive sediments of the character described include mercury, lead, ruthenium, zirconium/ niobium, caesium and plutonium; many chlorinated hydrocarbon pesticide residues and PCBs; and aromatic hydrocarbons derived from oil. This list contains most of the substances causing concern because their presence in seafood could create a human health risk.
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Where fine sediments and organic matter come to rest on the sea b o t t o m is, of course, governed by the location of sources (e.g., rivers and major sewage and industrial waste discharge points), current speed and direction, tidal movements, wind, and underlying bottom topography. No general statement can be made about the distribution of soft deposits around the coasts of the United Kingdom. However, it will be obvious that they occur extensively inside and just outside the mouths of estuaries, in sheltered inlets and bays and in deeper channels and holes below the effects of wave action. They are scarce close inshore on open rocky coasts exposed to wind and tide. As a broad generalisation, soft bottoms (fine sand, silt and mud) are more productive and hence support greater quantities of fish and shellfish than b o t t o m s of coarse sand, gravel, stones or rock. By definition, they are subject to less disturbance by water movement and this reduces the rate of removal of adsorbed material into the overlying water mass. Because soft bottoms generally contain a richer benthic fauna than coarse grounds, they are favoured by bottom-feeding fish. These factors tend to provide a situatioa in which transfer of adsorbed substances from the bottom and benthic fauna to fish is facilitated and it is not surprising to find, for example, that a flatfish such as the flounder (Platichthys flesus) which lives and feeds over soft bottoms and spends much of its time in estuaries, yields high values for mercury (MAFF, 1971, 1973). It cm~ easily be appreciated that the policy of discharging comminuted sewage with included industrial wastes to estuaries and coastal waters, combined with increased dumping of sewage sludges, must lead to a continuing build-up of these "blacklist" substances in coastal sediments. Although they are all subject to gradual dispersion into deeper water, this process is very slow in the case of metals such as mercury and lead, which are converted to virtually insoluble sulphides in the deeper layers of sediments, and complex organic substances such as the synthetic halogenated hydrocarbons for which natural breakdown processes through the action of microorganisms are virtually absent. Thus even if their potential for harm is recognised and the discharges reduced or stopped, a reserve of these persistent pollutants u n f o r t u n a t e l y will remain for many years in the sediments, which will continue to contaminate the overlying water, benthic organisms and the fish and other animals that feed on them. In the case of mercury, which is slowly converted from inorganic to methylated form in the sediments, the potentiality for causing serious contamination to seafood may be only slowly reduced over a period of years. Lead requires special attention because much of that reaching the sea is derived from the use in m o t o r cars of petrol containing lead anti-knock additives. Perhaps in 50 years, due to the running down of oil reserves, the use of petrol may diminish but no d o u b t by then alternative fuels will have been
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developed and may still require the addition of anti-knock compounds. However, for the immediate future (i.e., 10--20 years), a steady increase in the use of petrol-driven cars seems inevitable. This continued addition of lead, to .the air, even on the present scale, and its transfer to coastal sediments must be viewed with concern because already levels in seafood, especially molluscs, are high enough to attract official attention (MAFF, 1972, 1975). Although attention is at the m o m e n t rightly focussed on drinking water in softwater areas with lead pipes in the household supply systems (Beattie et al., 1972; Dept. of Environment, 1974, 1977), further research seems likely to increase rather than diminish concern about possible effects of lead on mental performance in young children. In such a context the fact that seafood may be a major source of lead in the diet might adversely effect sales. Some further t h o u g h t needs to be given not only to lead levels in air in urban environments but to the ultimate fate of much of this airborne lead and its distribution on the sea b o t t o m . The dynamics of the exchange between air, seawater, sediments and biota need to be further elucidated. The general adoption of improved methods of sample collection, treatment and analysis is essential.
RADIOACTIVITY Public debate concerning radioactive waste disposal is concerned mostly with the admittedly severe problem of safe disposal of high-level material, especially that derived from fuel reprocessing. In a small, heavily populated country such as the United Kingdom, although rock formations could be located in which high-level wastes could be safely contained underground, it seems highly unlikely that public consent will be obtained for their use. For this reason, burial within suitable rock formations under the sea, preferably under international control, may well be adopted. A scheme for such a burial facility is described and illustrated in the 6th Report of the Royal Commission on Environmental Pollution (1976), and is recommended for study as a "reasonable o p t i o n " . At present, low-level liquid waste and low- and medium-level solid wastes are disposed of at sea, the former by discharge from pipelines and the latter by dumping in very deep water well beyond the edge of the Continental Shelf. There is no evidence that radioactive waste disposal by the United Kingdom by either method has created any public health hazard or has had any discernible effect on organic production. British disposal practice is based firmly upon the interpretation by the Medical Research Council of the recommendations of the International Council on Radiological Protection (ICRP) and the results of disposals to the marine environment have been
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regularly described and published (see Mitchell, 1977, and earlier papers from the Fisheries Radiobiological Laboratory, Lowestoft). According to the definition of pollution generally adopted internationally (see above), radioactive waste disposal in the seas around Britain has created no pollution; certainly no harm has been done to living resources and human health has been fully safeguarded.
DISCUSSION AND CONCLUSIONS Sewage disposal u n d o u b t e d l y constitutes the main source of marine pollution problems. It is a worldwide problem which is bound to increase in importance in all countries whether developed and industrialised or undeveloped and mainly engaged in primary production. The scale of the problem is inevitably controlled by population size and distribution and gross national product per unit of population. As "prosperity" increases the problem becomes more severe. Problems associated with sewage disposal to the sea have received much less attention from research and far less publicity than those due to metals and pesticides, which are much easier to control. Oil is, like sewage disposal, indispensible in a civilised society but, apal~ from accidents due to human frailty, does not seem to be capable of causing lasting damage to the marine environment leading to a loss of production. It is likely to continue as a severe and costly amenity problem and losses of seabirds cannot be avoided. Radioactivity is a natural characteristic of the marine environment and the production of nuclear energy for peaceful purposes does not seem likely to create a significant hazard to human health or living resources in a marine context. It is assumed that means of safely disposing of high-level radioactive wastes will be internationally adopted, of which burial within the sea bed seems to be a possible choice for the United Kingdom. Significantly damaging effects of pollution are likely to be confined to coastal waters and, particularly, estuaries, especially where soft b o t t o m sediments adsorb and retain substantial amounts of potentially harmful metals and persistent organic substances. More attention should be given to the condition of these sediments, to the mechanisms by which pollutants accumulate and are released and to the exchange between water, sediments and biota. The results should be applied in a review of present U.K. sewage disposal policy which tends to maintain conditions in rivers at the expense of estuaries and the sea. In respect of contaminants such as mercury and cadmium, which are objectionable because t h e y may accumulate in coastal seafood to levels which are unacceptable on public health grounds, there is no practicable
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alternative to removal from wastes at t he factory, or in special waste treatmerit centres on land. Discharge to sewers must be avoided since o r t h o d o x t r e a t m e n t merely transfers the bulk o f the metals to the sludges which can be neither disposed of satisfactorily on land, nor d u m p e d at sea. Wastes containing organic substances which are both highly persistent and potentially toxic, such as PCBs, can be dest royed by incineration and this has successfully been done on ships at sea, where air cont am i nat i on problems associated with land-based incinerators can be avoided. If substances of unique industrial importance, such as mercury, are considered to be sufficiently objectionable to require special measures to control their loss to the environment, then a licensing system may have to be introduced. It is interesting, however, to not e that a recent report from the National Swedish E nvi r onm ent Protection Board, while maintaining the chlor-alkali industry as the main source o f " i n t e n t i o n a l " air-borne release of mercury, lists dentistry as the principal source of " i n t e n t i o n a l " water-borne mer cu r y ( A n o n y m o u s , 1978). " U n i n t e n t i o n a l " sources of release are listed b u t their comparative i m por t ance is not stated. The flux of lead to coastal waters, its distribution, residence time in sedimerits and accumulation in seafood needs to be more closely studied. Although there are substantial discharges by rivers of lead released from metalliferous rocks, particularly disused mines, it is the continued increase in m o t o r traffic using leaded petrols that causes most concern since a substantial p r o p o r t i o n of the lead discharged from m o t o r exhausts reaches the sea. The processes of transfer from air to sea, seawater to sediments and seawater/sediments to biota have been little studied and are w o r t h y of closer atten tio n . The possible p r o d u c t i o n of organo-lead c o m p o u n d s in the marine en v ir o n m e nt needs to be considered. Because, locally, habitat modification and disturbance due to developmen t and human pressure may be even more damaging than reduction in water quality due to the discharge o f sewage and industrial wastes, it may be desirable to designate certain estuaries, inlets, bays and even stretches of open coast as 'areas of special importance to fisheries' because of their high productivity, unique environmental conditions, use as spawning grounds or migration paths, and to give these special p r o t e c t i o n by means of planning restrictions. The need to p r o t e c t highly productive agricultural land has already been generally conceded but, as has oft en been stated, the yield of protein-rich food from well-managed shellfish beds may equal or exceed that from good-quality farm land.
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ACKNOWL EDG EM ENT T h i s p a p e r is b a s e d u p o n a l e c t u r e g i v e n a t t h e S e p t e m b e r , 1 9 7 8 , m e e t i n g of Section D ( Z o o l o g y ) of the British Association for the A d v a n c e m e n t of Science.
REFERENCES Anonymous, 1978. Sources of mercury pollution in Sweden. Ambio, 7(3): 113. Beattie, A.D., Moore, M.R., Miller, A.R. and Goldberg, A., 1972. Environmental lead pollution in an urban soft-water area. Brit. Med. J., 27.5.72, pp. 491--3. Bourne, W.R.P., 1976. Seabirds and pollution. In: R. Johnston (Editor), Marine Pollution. Academic Press, London, pp. 403--592. Bulstrode, H.T., 1896. In: Reports and Papers on the Cultivation and Storage of Oysters and Certain other Molluscs, 24th Ann. Rep., Local Government Board, H.M. Stationery Office, London, pp. 1--108. Cole, H.A., 1974. Marine pollution and the United Kingdom fisheries. In: F.R. Harden Jones (Editor), Sea Fisheries Research. Elek Science, London, pp. 277--303. Cole, H.A., and Holden, M.J., 1973. History of the North Sea Fisheries, 1950--1969. In: E.D. Goldberg (Editor), North Sea Science, MIT Press, Cambridge, Mass., pp. 337-360. Dept. of the Environment, 1974. Lead in the environment and its significance to man. Pollution Pap., 2, 47 pp. (H.M. Stationery Office, London). Dept. of the Environment, 1977. Lead in drinking water: a survey of Great Britain 1975-76. Pollution Pap. 12, 47 pp. (H.M. Stationery Office, London.) GESAMP, 1976. Review of harmful substances. Reports and Studies, 2, United Nations, New York, 79 pp. Hetherington, J.A., Jefferies, D.F., Mitchell, N.T., Pentreath R.J. and Woodhead, D.S., 1976. Environmental and public health consequences of the controlled disposal of transuranic elements to the marine environment. Proc. Syrup. I.A.E.A., San Francisco, 17--21 Nov. 1975, pp. 139--154. (International Atomic Energy Agency, Vienna.) International Council for the Exploration of the Sea. 1977. Studies of the pollution of the Baltic Sea. Co-op. Res. Rep., 63, 97 pp. Goldberg, E.D., 1976. The Health of the Oceans. UNESCO, Paris, 172 pp. Jensen, S., 1972. The PCB story. Ambio, 1: 123:131. Jensen, S., 1977. Effects of PCB and DDT on mink (Mustela vision) during the reproductive season. Ambio, 6: 239. Korringa, P., 1973. The edge of the North Sea as nursery ground and shellfish area. In: E.D. Goldberg (Editor), North Sea Science. pp. 361--382. MIT Press, Cambridge, Mass. Kullenberg, G.E.B., 1975. Ocean dumping sites. Ocean Manage., 2(3): 189--209. MAFF, 1971, Survey of Mercury in Food. H.M. Stationery Office, London, 33 pp. MAFF, 1972, Survey of Lead in Food. H.M. Stationery Office, London, 31 pp. MAFF, 1973, Survey of Cadmium in Food. H.M. Stationery Office, London, 31 pp. MAFF, 1973, Survey of Mercury in Food: A Supplementary Report. H.M. Stationery Office, London 23 pp. MAFF, 1975, Survey of Lead in Food: First Supplementary Report. H.M. Stationery Office, London, 34 pp. GESAMP, 1977. Impact of oil on the marine environment. Reports and Studies, No. 6. FAO, Rome, 250 pp. Mitchell, N.T. 1977. Radioactivity in surface and coastal waters of the British Isles, 1976,
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Part 1. The Irish Sea and its environs. Tech. Rep. Fish. Radiobiol. Lab., MAFF Direct. Fish. Res. (FRL 13), 15 pp. Osterberg, C. and Keckes, S., 1977. The state of pollution of the Mediterranean Sea. Ambio, 6(6): 321--328. Royal Commision on Environmental Pollution, 1972. Third Report: Pollution in Some British estuaries and Coastal Waters. H.M. Stationery Office, London, 127 pp. Royal Commission on Environmental Pollution. 1976. Sixth Report: Nuclear Power and the Environment. H.M. Stationery Office, London, 237 pp.
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M a r i n e Pollution -- Facts and Fiction, t h e Situation in Britain
Herbert A. Cole
ABSTRACT The widely-held impression that serious biological damage has been done to the marine environment and its resources by pollutants is not soundly based. There is no evidence that any offshore stock of fish or shellfish has suffered a reduction in annual recruitment to the exploitable stock as the result of pollution. Production generally has been well maintained and where reduction in yield is evident, e.g. in herring around the British coasts, this is a consequence of over-fishing. Stocks of fish and shellfish inhabiting shallow coastal waters and particularly estuaries are subject to many human pressures, of which reduced water quality due to pullutants is one. The most damaging effects of pollution are reduction in available oxygen, increased turbidity due to suspended material and discolouration, and deposition of organic material on the bottom. Sewage and other organic effluents (such as food-processing wastes) with a high biological oxygen demand are the prime causes of these conditions. Potentially harmful metals and synthetic organic substances resistant to breakdown may accumulate in estuarine and coastal sediments, particularly muddy sands, silts and muds containing a high proportion of organic matter, and will continue to release potential pollutants long after shore discharges are controlled. Attention to marine pollution problems needs to be focussed on such estuarine and coastal sediments and the ways by which their polluting loads are built up and released. A better understanding of the effects of sewage discharge to the marine environment of the United Kingdom is needed and might bring about a modification of the present policy of sewage disposal. Increased research in this field is highly desirable.
INTRODUCTION The widely-held impression
that
the
productivity
of the
sea h a s b e e n
r e d u c e d b y p o l l u t a n t s is i n c o r r e c t . N o r is t h e r e a s e r i o u s t h r e a t t h a t t h i s w i l l o c c u r in t h e n e a r f u t u r e . T h e r e is n o e v i d e n c e f o r a b e l i e f t h a t s u b s t a n c e s at present
unrecognized
as
potentially
damaging
contaminants
are steadily
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building up in the sea and within a few years will reach catastrophic levels and will turn the oceans into deserts. In general, changes occur slowly in the sea and, although fisheries m a y appear to decline rather rapidly, as the herring fisheries around Britain have done, these major changes are principally the result of overfishing and are n o t due to natural fluctuations or pollution. It is generally agreed that no offshore stock of fish or shellfish shows evidence of reduction o f r e c r ui t m e nt to the exploitable stock as the result of pollution. In ot her words, there is no evidence o f significant reduction in the n u m b e r of y o u n g fish growing up to exploitable size year by year because of losses at the egg or larval stage, or diminished fecundity in the breeding stock, because of direct or insidious effects of oil, mercury, cadmium, chlorinated h y d r o c a r b o n s , radioactivity or any of the ot her pollutants known by name to journalists or broadcasters. Is there then no marine pollution problem? Is it just a not he r scare generated by sensation-hungy pressmen? The answer is, of course, n o - there are areas of concern, especially for resources in coastal waters and estuaries, and there are certain difficult public health and amenity problems. In considering these it is necessary to begin at the beginning with the definition o f marine pollution.
Dr. H.A. Cole is a graduate of the University of Wales. F r o m 1959 until he retired in 1974 he was Director of Fishery Research at the Fisheries L aborat ory, L ow est oft , England. He has written extensively on shellfish biology, fishery management and marine pollution.
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DEFINITIONS The internationally accepted definition of marine pollution is that used by the United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution (GESAMP) which reads: " I n t r o d u c t i o n by man of substances or energy to the marine environment resulting in such deleterious effects as harm to living resources or marine life, hazards to human health, hindrance to marine activities, including fishing, impairment of quality for use of seawater and reduction of amenities." As now stated, the definition reflects the confused English often used by multi-national committees and the words "or marine life" and "including fishing" are clearly superfluous while the value of the reference to seawater quality is dubious. However, the essential concept linking pollution with harm is sufficiently evident and the principal areas in which harmful effects may be experienced are clearly stated. At this point it may be useful to give established examples of each main category of harmful effect. In relation to living resources the deterioration of estuaries as the result of the discharge of sewage and other wastes, e.g. from food processing, slaughter houses, laundries and distilleries, which mop up the available oxygen and so prevent the passage of salmon, is well known, as, because of sewage contamination, is the banning of collecting and marketing of shellfish from such estuaries without purification. This is a human health risk (the second category of effects) but in many estuaries the environmental conditions are so poor that the shellfish themselves are no longer able to survive. Other well-known public health problems are the contamination by sewage of bathing beaches and the accumulation of mercury and cadmium in fish and shellfish in areas where wastes containing these metals have been discharged. Among conservation problems, the oiling of seabirds is so well-known as to need no elaboration here. On the amenity front we are all aware of the nuisance created by oil on beaches but examples of interference with other legitimate activities do n o t perhaps come readily to mind although they are, in fact, both numerous and varied. Sewage enrichment causes unwelcome growths of marine algae, particularly Ulva and Enteromorpha, which may be a nuisance on public beaches; silting of estuaries and approaches to ports may be accelerated if there is a heavy discharge of organic wastes or increased production due to nutrients derived from domestic wastes; waste plastic ropes and nets may become entangled in ships' propellers and plastic film may block the water intakes to their engines and, of course, the accumulation of such waste and other garbage, discharged by ships, is a persistent nuisance on many beaches.
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THE AREAS PRINCIPALLY AT RISK Man's capacity to alter the character of the open oceans or their productivity is quite limited. One must make an exception to this in respect of potentially toxic man-made chlorinated hydrocarbons which ar~ largely airborne and may be distributed worldwide, and this will be discussed further later in this paper. It is in shallow coastal water and particularly in estuaries (Royal Commission, 1972), inlets and semi-enclosed seas, e.g. the Baltic (ICES, 1977) and the Mediterranean (Osterberg and Keckes, 1977) that man's capacity to cause damage is most evident: it is in these areas that pollution prevention efforts should be concentrated. The estuarine environment is particularly subject to human pressure. Any estuary deep enough to admit ships inevitably attracts development while those which are shallow with low-lying shores are much in demand for recreational activities. Moreover, the rivers that discharge into estuaries are invariably regarded as the natural outlets for sewage and industrial wastes produced inland. The estuarine environment is naturally one where the animals and plants must be adaptable to a wide range of physical and chemical c h a n g e s - - t e m p e r a t u r e , salinity, current speed, suspended matter, e t c . - if they are to survive. The effects of the addition of sewage and industrial wastes are principally evident in loss of oxygen, additional suspended matter and reduction in light penetration. These are best regarded as a further addition to the environmental stresses to which the estuarine biota are normally subjected. However, depletion of oxygen and its immediate consequences on chemical balance must be regarded as a major new stress factor and, when combined with a heavy addition to the organic matter load, can be identified as the aspect of waste disposal likely to cause most harm. Although fish kills in rivers and estuaries as the result of the occasional inadvertent release of poisonous substances, such as cyanides, make the headlines because the damage is clearly evident, the gradual depressing effect of reduced oxygen levels and high suspended matter loads is much more serious and is the prime cause of the generally deplorable condition of estuaries in Britain. Nor can the situation be said to be improving much, although numerous plans have been discussed, because local and regional authorities generally tend to regard their sewage and waste disposal problems as solved if they can reach an estuary or the sea. Fortunately or unfortunately, depending on whether one is a waste disposer or concerned with conservation of natural resources, production of fish and shellfish from the estuaries of Britain does not represent a large part of the total catch. Its cash value at first sale is probably no more than 2% of the total value of all fish and shellfish landed and certainly less than 4%. It does, however, contain one species of great social importance, particularly in
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Scotland, the Atlantic salmon. Although some additional salmon could no d o u b t be produced by cleaning up rivers which formerly supported it and which still have satisfactory conditions for spawning in the upper reaches, as has been shown previously (Cole, 1974), examination of the statistics of landings from existing salmon rivers reveals no evidence of the effects of pollution during the post-war period of industrial re-development and population increase. By the expenditure of vast sums, including the provision of fish passes in the freshwater reaches, no d o u b t British Members of Parliament could be enabled to fish for salmon from the terrace of the Houses of Parliament but where would the survivors go to spawn? But to return to the question of the value of estuarine production in Britain. This is also important for certain classes of molluscan shellfish, especially mussels, cockles and oysters, but these fisheries have been allowed to decline very greatly due to the pressure of development. They have succumbed to the argument that their cash value is less than that of the industrial, housing or recreational activities with which t h e y have been largely replaced in m a n y estuaries. It may be regarded as a failure of national planning and, although often stated, the argument that certain estuaries are uniquely suited environmentally to the production of shellfish and should be reserved, and fully developed, for that purpose, has rarely prevailed. There are one or two tiny examples of successful conservation that could be quoted from the United Kingdom, such as the Helford River in Cornwall and the N e ~ l o w n River in the Isle of Wight, but these must be set against a very long list of grounds productive at the end of the last century (Bulstrode 1896) where there are either no full-time fishermen at all or only the remnants of a dying industry. In 1976 Nephrops (scampi) and scalops and queens together represented nearly 60% by value of the UK shellfish landings. In that year oysters, mussels and cockles -- the estuarine species - represented only about 6% by value compared with approximately 40% 60 years ago. Although estuaries are crucially important to only a few species of fish (salmon, sea trout, eels, smelts and flounders) which together represent only about 1% of the total landings, sheltered shallow coastal bays and inlets are in a different category. They are the nursery grounds of several very important sea fish, e.g. plaice, sole, turbot, herring, etc. which together figure largely in the British catch. Any drastic alteration of these shallow coastal nursery areas by pollutants could reduce survival of young fish and so affect recruitment. The expression "drastic alteration" is used deliberately because the natural losses of young fish during their early stages are very high indeed and small reductions due to pollution would certainly be insignificant. Most fish are highly fecund and this excessive production of eggs and
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larvae is the mechanism whereby high natural losses due to predation in the planktonic stage and adverse environmental factors, such as out-of-phase production of food organisms, can be absorbed without damaging effects on recruitment. Nevertheless it is important to understand that natural recruitment in species that have been studied shows great variation from year to year (by two orders of magnitude or more in some species).
SEWAG E There are certain aspects of sewage
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high cost of such offshore pipelines (often involving pumping of effluent) creates pressure to reduce treatment and to discharge comminuted crude sewage. Moreover, as t r e a t m e n t is reduced, it becomes possible to accept toxic industrial wastes which it would not be feasible to take at the sewage works if full treatment were given. These toxic wastes, although diluted, are therefore discharged to the sea through the pipline virtually untreated. Unfortunately, although there has been a determined effort to maintain the water quality of rivers and streams and their biological conditions ("fish life"), and some improvement has been claimed here and there, it has remained official policy in the United Kingdom to permit, and even encourage, the discharge of sewage to estuaries and to the sea after no more treatment than screening and comminution. Although this " t r e a t m e n t " has the effects of making sewage less recognizable, and of aiding dispersion and breakdown, it does not reduce its polluting capacity. Although some open coast beaches may become less contaminated because of this policy, estuaries are rarely regarded as bathing areas and, although important for sailing, this is not a sport which is deemed to require seawater of a high sanita.ry quality. A rather low water quality is therefore acceptable on amenity grounds. The general necessity, in inland areas, of taking industrial wastes into the public sewage system, and the demand for high emission standards for effluents to protect fish life in rivers, lead inevitably to a situation where sewage plant sludges from industrial areas contain substantial amounts of metals and organic s u b s t a n c e s - especially synthetic compounds such as chlorinated h y d r o c a r b o n s - - w h i c h are resistant to breakdown. These contaminated sludges are increasingly being dumped at sea where the persistent materials largely accumulate in sediments and are only very slowly dispersed. Because sea dumping is an expensive operation compared with land disposal, dumping grounds tend to be rather near the land and certainly within fishing depth. Some sites used historically have proved to be very suitable for dispersion, e.g. the outer Thames, but others have proved rather hazardous, e.g., New York Bight. If dumping of sewage sludge at sea is to be extended then the choice of sites needs to be made only after expert assessment of the anticipated water movements, including those at the sea bottom, and of the likely effects on fish and shellfish (see Kullenberg, 1975).
OIL Oil pollution is an emotive subject in Britain because of the continued presence of tar balls and oiled seabirds on m a n y south- and east-coast recreational beaches. However, from the point of view of fisheries, one has
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to say that oil is a serious problem only to those engaged in the cultivation of molluscan shellfish, owing to oily flavours and fouling. To those engaged in offshore fishing, the presence of an oil industry in British waters has often meant an additional source of income from the use of obsolescent fishing vessels for various purposes connected with the oil industry and, one suspects, a source of compensation for damage to fishing gear by drums, wires and other obstacles on the seabed without the necessity for absolute proof of the origin of the obstacles. Undoubtedly, ships servicing oil rigs and production platforms dump rubbish at sea but so do ships of other kinds, including fishing vessels. Because oil and gas rigs and platforms must be located where the resources are found, and it is necessary to prescribe safety zones around such structures in which fishing is prohibited, some loss of fishing opportunity must be sustained. Similarly with pipelines which, although initially buried, may later be exposed. However, since adequate conservation is the prime requirement to maintain the productivity of fish stocks in the present highly competitive situation, any device which incidentally protects some part of the stock from exploitation (and gives other benefits) should surely be welcomed. Tainting by oil, or by any of the range of strong-smelling organic substances, such as phenols, which produce " o f f " fiavours, is occasionally experienced in fish and more often in shellfish taken close inshore. It is known, however, that these taints can be caused naturally by heavy feeding on certain species, e.g. of planktonic organisms. Such taints may cause serious short-term disruption of marketing which may lead to financial loss. When present in molluscan shellfish they may persist for several months due, it is believed, in the case of oil, to limited capacity to metabolise certain hydrocarbons (GESAMP, 1977). Obviously, heavy oil spills, such as that from the Amoco Cadiz, can blanket large areas of shore, and mollusc cultivators may suffer severe losses where stocks are concentrated. Nevertheless, it is remarkable how little damage of this kind has been done by the major oil spills which have occurred throughout the world. In the example of the Torrey Canyon spill there were no significant losses of this kind, indeed no significant effects on fisheries of any kind. Stocks of certain seabirds, particularly auks, in British waters, are becoming depleted by oil pollution (Bourne, 1976). Because most of these birds produce only one egg, their power of recovery is limited and this, coupled with human disturbance of their breeding haunts, seems likely to result in extinction of the remaining colonies of a few species on the south and southwest coasts of the British Isles. However, the species affected are extremely a b u n d a n t further north, particularly in northwest Scotland, the Scottish Islands and along the Atlantic coast of Ireland. Attempts to reduce losses off
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southern Britain or to rehabilitate oiled birds seem unlikely to add significantly to the survival of the stock and the effort involved would, perhaps, be better diverted to serious research on methods of increasing survival, e.g. by control of predators, particularly rats, at major breeding sites in areas well away from the main oil tanker routes. Bird watching is an important pastime, and hence has an economic value, and the northwest of Britain is no longer to be regarded as out of reach of the main centres of population. Although estimates of the relative importance of different sources of oil in the sea differ widely (GESAMP, 1977), the major cause of oiled seabirds is undoubtedly spillage from ships. Operational discharges are already fully covered by the regulations made by the Intergovernmental Maritime Consultative Organisation (IMCO) on the basis of the various international conventions dealing with the prevention of oil polution. Unfortunately, not all countries operating oil tankers have ratified these conventions and enforcem e n t of their provisions is very difficult. The need is not, however, for more regulation since most spills arise from human frailty or neglect rather than from inadequacy of the regulations. Even attempts at closer regulation of ship traffic in crowded shipping lanes, e.g. in the English Channel, are unlikely to produce much effect unless the men engaged accept greater responsibility for their actions and the possible environmental consequences. It can, however, be claimed that the tightening up of regulations that has occurred over the last 10 years or so has had a beneficial effect, since oil pollution has remained at about the same level, although the a m o u n t of oil moved around the oceans has substantially increased. Further improvement will only come very slowly as appreciation of the importance of environmental quality grows as the result of education and publicity. This seems an appropriate m o m e n t to say that such education and publicity (particularly the latter) must n o t take the form of propagating 'scares' associated with such emotive subjects as cancer. In the longer term these tactics (over-statem e n t to attract attention ) are u n d o u b t e d l y counterproductive--they may sell newspapers but they do not remedy pollution.
CHLORINATED HYDROCARBONS There is much misunderstanding of the status of DDT, dieldrin, etc., as marine pollutants. Although their use as insecticides has u n d o u b t e d l y caused severe depletion of certain birds of prey, notably the peregrine, the only marine fishery problems created, have, with one exception, arisen from heavy discharges of residues to rivers from plants making the pesticide or from industrial use, e.g. in the moth-proofing of carpets. The exception is the banning of the sale for human consumption of codliver oil derived from
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Baltic fish in certain riparian countries in that area following heavy use of DDT. Yet, as is generally known, DDT or its breakdown products have been found t h r o u g h o u t the oceans of the world in biological material wherever t h e y have been looked for with the highly sensitive instrumentation now available to the analytical chemist. This worldwide spread has occurred for three main reasons: (a) heavy losses to the atmosphere during spraying; (b) persistence (half-life in the sea is thought to lie between 10 and 20 years); and (c) passage through food chains with possibly some biomagnification in top predators such as birds of prey and seals. No adverse effects in human beings due to consumption of seafood contaminated by DDT or its breakdown products have been demonstrated. In several species of seabirds, however, egg shell thinning and loss o f reproductive capability have been demonstrated. In seals, particularly in the Baltic, changes in reproductive organs leading to loss of fertility, possibly sufficient to produce an effect at population level, have been shown to occur in animals containing high levels of DDT and PCBs, but the latest studies seem to implicate PCBs as the principal causative factor (Jensen, 1977). PCBs were used in industry with substantial losses to the environment for about 20 years before adverse effects were suspected (Jensen, 1972). They have now been shown to be distributed worldwide and there is some field evidence of adverse effects in the marine environment, particularly on reproductive performance. Their continued use in situations where loss may occur to the environment has been generally condemned and restrictions have been introduced in many c o u n t r i e s - in the UK on a voluntary basis. Unfortunately PCBs seem to be even more persistent than DDT and other chlorinated hydrocarbon pesticides and whereas levels of DDT and its metabolites have fallen in recent years in marine biota in European seas, levels of PCBs have remained virtually unchanged (OECD analyses).
PERSISTENCE OF POTENTIAL POLLUTANTS IN SEDIMENTS Sediments, particularly those containing a high proportion of fine material (silt and clay fractions) and a substantial content of organic material, are the main resting place of most of the potentially harmful substances discharged to the sea. Coarse and fine sands and gravels are much less effective in holding potential pollutants. The substances readily held by adsorptive sediments of the character described include mercury, lead, ruthenium, zirconium/ niobium, caesium and plutonium; many chlorinated hydrocarbon pesticide residues and PCBs; and aromatic hydrocarbons derived from oil. This list contains most of the substances causing concern because their presence in seafood could create a human health risk.
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Where fine sediments and organic matter come to rest on the sea b o t t o m is, of course, governed by the location of sources (e.g., rivers and major sewage and industrial waste discharge points), current speed and direction, tidal movements, wind, and underlying bottom topography. No general statement can be made about the distribution of soft deposits around the coasts of the United Kingdom. However, it will be obvious that they occur extensively inside and just outside the mouths of estuaries, in sheltered inlets and bays and in deeper channels and holes below the effects of wave action. They are scarce close inshore on open rocky coasts exposed to wind and tide. As a broad generalisation, soft bottoms (fine sand, silt and mud) are more productive and hence support greater quantities of fish and shellfish than b o t t o m s of coarse sand, gravel, stones or rock. By definition, they are subject to less disturbance by water movement and this reduces the rate of removal of adsorbed material into the overlying water mass. Because soft bottoms generally contain a richer benthic fauna than coarse grounds, they are favoured by bottom-feeding fish. These factors tend to provide a situatioa in which transfer of adsorbed substances from the bottom and benthic fauna to fish is facilitated and it is not surprising to find, for example, that a flatfish such as the flounder (Platichthys flesus) which lives and feeds over soft bottoms and spends much of its time in estuaries, yields high values for mercury (MAFF, 1971, 1973). It cm~ easily be appreciated that the policy of discharging comminuted sewage with included industrial wastes to estuaries and coastal waters, combined with increased dumping of sewage sludges, must lead to a continuing build-up of these "blacklist" substances in coastal sediments. Although they are all subject to gradual dispersion into deeper water, this process is very slow in the case of metals such as mercury and lead, which are converted to virtually insoluble sulphides in the deeper layers of sediments, and complex organic substances such as the synthetic halogenated hydrocarbons for which natural breakdown processes through the action of microorganisms are virtually absent. Thus even if their potential for harm is recognised and the discharges reduced or stopped, a reserve of these persistent pollutants u n f o r t u n a t e l y will remain for many years in the sediments, which will continue to contaminate the overlying water, benthic organisms and the fish and other animals that feed on them. In the case of mercury, which is slowly converted from inorganic to methylated form in the sediments, the potentiality for causing serious contamination to seafood may be only slowly reduced over a period of years. Lead requires special attention because much of that reaching the sea is derived from the use in m o t o r cars of petrol containing lead anti-knock additives. Perhaps in 50 years, due to the running down of oil reserves, the use of petrol may diminish but no d o u b t by then alternative fuels will have been
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developed and may still require the addition of anti-knock compounds. However, for the immediate future (i.e., 10--20 years), a steady increase in the use of petrol-driven cars seems inevitable. This continued addition of lead, to .the air, even on the present scale, and its transfer to coastal sediments must be viewed with concern because already levels in seafood, especially molluscs, are high enough to attract official attention (MAFF, 1972, 1975). Although attention is at the m o m e n t rightly focussed on drinking water in softwater areas with lead pipes in the household supply systems (Beattie et al., 1972; Dept. of Environment, 1974, 1977), further research seems likely to increase rather than diminish concern about possible effects of lead on mental performance in young children. In such a context the fact that seafood may be a major source of lead in the diet might adversely effect sales. Some further t h o u g h t needs to be given not only to lead levels in air in urban environments but to the ultimate fate of much of this airborne lead and its distribution on the sea b o t t o m . The dynamics of the exchange between air, seawater, sediments and biota need to be further elucidated. The general adoption of improved methods of sample collection, treatment and analysis is essential.
RADIOACTIVITY Public debate concerning radioactive waste disposal is concerned mostly with the admittedly severe problem of safe disposal of high-level material, especially that derived from fuel reprocessing. In a small, heavily populated country such as the United Kingdom, although rock formations could be located in which high-level wastes could be safely contained underground, it seems highly unlikely that public consent will be obtained for their use. For this reason, burial within suitable rock formations under the sea, preferably under international control, may well be adopted. A scheme for such a burial facility is described and illustrated in the 6th Report of the Royal Commission on Environmental Pollution (1976), and is recommended for study as a "reasonable o p t i o n " . At present, low-level liquid waste and low- and medium-level solid wastes are disposed of at sea, the former by discharge from pipelines and the latter by dumping in very deep water well beyond the edge of the Continental Shelf. There is no evidence that radioactive waste disposal by the United Kingdom by either method has created any public health hazard or has had any discernible effect on organic production. British disposal practice is based firmly upon the interpretation by the Medical Research Council of the recommendations of the International Council on Radiological Protection (ICRP) and the results of disposals to the marine environment have been
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regularly described and published (see Mitchell, 1977, and earlier papers from the Fisheries Radiobiological Laboratory, Lowestoft). According to the definition of pollution generally adopted internationally (see above), radioactive waste disposal in the seas around Britain has created no pollution; certainly no harm has been done to living resources and human health has been fully safeguarded.
DISCUSSION AND CONCLUSIONS Sewage disposal u n d o u b t e d l y constitutes the main source of marine pollution problems. It is a worldwide problem which is bound to increase in importance in all countries whether developed and industrialised or undeveloped and mainly engaged in primary production. The scale of the problem is inevitably controlled by population size and distribution and gross national product per unit of population. As "prosperity" increases the problem becomes more severe. Problems associated with sewage disposal to the sea have received much less attention from research and far less publicity than those due to metals and pesticides, which are much easier to control. Oil is, like sewage disposal, indispensible in a civilised society but, apal~ from accidents due to human frailty, does not seem to be capable of causing lasting damage to the marine environment leading to a loss of production. It is likely to continue as a severe and costly amenity problem and losses of seabirds cannot be avoided. Radioactivity is a natural characteristic of the marine environment and the production of nuclear energy for peaceful purposes does not seem likely to create a significant hazard to human health or living resources in a marine context. It is assumed that means of safely disposing of high-level radioactive wastes will be internationally adopted, of which burial within the sea bed seems to be a possible choice for the United Kingdom. Significantly damaging effects of pollution are likely to be confined to coastal waters and, particularly, estuaries, especially where soft b o t t o m sediments adsorb and retain substantial amounts of potentially harmful metals and persistent organic substances. More attention should be given to the condition of these sediments, to the mechanisms by which pollutants accumulate and are released and to the exchange between water, sediments and biota. The results should be applied in a review of present U.K. sewage disposal policy which tends to maintain conditions in rivers at the expense of estuaries and the sea. In respect of contaminants such as mercury and cadmium, which are objectionable because t h e y may accumulate in coastal seafood to levels which are unacceptable on public health grounds, there is no practicable
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alternative to removal from wastes at t he factory, or in special waste treatmerit centres on land. Discharge to sewers must be avoided since o r t h o d o x t r e a t m e n t merely transfers the bulk o f the metals to the sludges which can be neither disposed of satisfactorily on land, nor d u m p e d at sea. Wastes containing organic substances which are both highly persistent and potentially toxic, such as PCBs, can be dest royed by incineration and this has successfully been done on ships at sea, where air cont am i nat i on problems associated with land-based incinerators can be avoided. If substances of unique industrial importance, such as mercury, are considered to be sufficiently objectionable to require special measures to control their loss to the environment, then a licensing system may have to be introduced. It is interesting, however, to not e that a recent report from the National Swedish E nvi r onm ent Protection Board, while maintaining the chlor-alkali industry as the main source o f " i n t e n t i o n a l " air-borne release of mercury, lists dentistry as the principal source of " i n t e n t i o n a l " water-borne mer cu r y ( A n o n y m o u s , 1978). " U n i n t e n t i o n a l " sources of release are listed b u t their comparative i m por t ance is not stated. The flux of lead to coastal waters, its distribution, residence time in sedimerits and accumulation in seafood needs to be more closely studied. Although there are substantial discharges by rivers of lead released from metalliferous rocks, particularly disused mines, it is the continued increase in m o t o r traffic using leaded petrols that causes most concern since a substantial p r o p o r t i o n of the lead discharged from m o t o r exhausts reaches the sea. The processes of transfer from air to sea, seawater to sediments and seawater/sediments to biota have been little studied and are w o r t h y of closer atten tio n . The possible p r o d u c t i o n of organo-lead c o m p o u n d s in the marine en v ir o n m e nt needs to be considered. Because, locally, habitat modification and disturbance due to developmen t and human pressure may be even more damaging than reduction in water quality due to the discharge o f sewage and industrial wastes, it may be desirable to designate certain estuaries, inlets, bays and even stretches of open coast as 'areas of special importance to fisheries' because of their high productivity, unique environmental conditions, use as spawning grounds or migration paths, and to give these special p r o t e c t i o n by means of planning restrictions. The need to p r o t e c t highly productive agricultural land has already been generally conceded but, as has oft en been stated, the yield of protein-rich food from well-managed shellfish beds may equal or exceed that from good-quality farm land.
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ACKNOWL EDG EM ENT T h i s p a p e r is b a s e d u p o n a l e c t u r e g i v e n a t t h e S e p t e m b e r , 1 9 7 8 , m e e t i n g of Section D ( Z o o l o g y ) of the British Association for the A d v a n c e m e n t of Science.
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Part 1. The Irish Sea and its environs. Tech. Rep. Fish. Radiobiol. Lab., MAFF Direct. Fish. Res. (FRL 13), 15 pp. Osterberg, C. and Keckes, S., 1977. The state of pollution of the Mediterranean Sea. Ambio, 6(6): 321--328. Royal Commision on Environmental Pollution, 1972. Third Report: Pollution in Some British estuaries and Coastal Waters. H.M. Stationery Office, London, 127 pp. Royal Commission on Environmental Pollution. 1976. Sixth Report: Nuclear Power and the Environment. H.M. Stationery Office, London, 237 pp.
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