Document LJDRo1R253eQobvgD3REBvjBz

\ TltK BIOJOGICAE EFFECTS OP CHEMICAL SUBSTANCES llr M W Holdgntc, Central Unit on Environmental Pollution, Department of the Environment* Footnote. The views expressed in this oarer are those of the author and not nopeasarily those of the Department of the Environment. Pollution may bn defined as "the introduction by man into the environment , of Bubatances (or energy) liable to cause hazards to human health, harm to living resources or ecological systems, damage to amenity or interference with legitimate uses of the environment". This definition brings out the basic fact that in responding to pollution ' wn are concerned with actual or potential adverse effects - damage to our own physiology, to the living resources on which wo depend directly, or to the wider ecological systems of land and sea that ploy a vital part in the renewal of atmospheric oxygen, the elimination of many of our wastes, and the recycling of vital nutrients. In this oarer I am concerned with the effects of chemicals injected into the biosphere by man (whether injected directly or indirectly via the physical ' , environment), and the nature of our response to them. ! , Even the most apparently stable of living systems exhibits dynamic equilibrium. This is affected by physical and chemical variables at many levels. A pollutant in the environment may affect: (a) an ecosystem ' (b) a population of a single species (c) a single individual organism (d) nn organ or system within that organism (e) n biochemical or cellular subsystem or eevornl of these simultaneously HONS 040317 t : ; ' i I : ' ; ' ' m c. k '< 't u-n i <- /< nrruci-s ot- roKt.ui/ot'j Commonly, we consider pollution in terms of its effect upon whole individual organisms. It is evident that the responses of individuals nro in fact the integral of a complex web of subsidiary effects unon biochemical systems, leading to changes in cellular physiology and behaviour which in turn affect the functioning of whole organs. A pollutant may often have a demonstrable effect at biochemical or cellular level which, because of the homeostatic machinery of living creatures, may not be manifest at the level of the wholo individual at all. This does not mean that the individual is unaffected by the pollutant: indeed, it means that some of the biological capacity of that individual is being used up in the same' way that the discharge of a pollutant into a lake uses some of its dilution capscity even though it does not reach the threshold at which ecological Change ensues. Similarly, the responses of whole ecoloirical systems are the integral of many interdependent individual responses. It is quit's common for significant effects on individuals not to be manifested at all at the ecosystem level, where so many organisms of so many different species interact to produce a system that is in dynamic equilibrium and which displays considerable inertia. Those levels of effect are arranged hierarchically. The ecosystem level of response is the highest level and a "no response threshold" muy yet be maintained while there i3 a considerable pollution-induced mortality at the individual level, and even at the spccioo level should the species exterminated from the Ecosystem not bo of major importance in determining the characteristics of the whole. For example, it has been established that exposure of lichen species on the trunks of English oaks to mean annual sulphur dioxide concentrn- - 2- HONS 040318 tions of 40-180yug/ro?/ cnn be correlated with their progressive extermination - und, no doubt, that of the email insects that feed on them. This has no effect, so far ns we know, on the basic ecological stability of oak woods in the Midlands or South-East England, ^and, while it clearly leads to a decree of impoverishment compared with the natural situation, does not prevent the establish ment of v/oodland Motional Mature Reserves which supnort an otherwise rich and varied wildlife. Similarly, it would be perfectly possible to contemplate a pollutant effect which exterminated some species from a freshwater, or marine environment without affecting either the capacity of those waters to support a balanced and productive ecosystem or creating a system unacceptable to nan. -I In this situation pollutants can be considered to impose "stress" on the ecological system Just as other forms of human interference do. It seems probable that the very first effect is to increase the species diversity of the system, but thereafter rising levels of pollution are paralleled by reduction in diversity and also by a tendency to change from systems dominated by large, long-lived forms to those dominated by smaller species with shorter life cycles - as when woodland gives way to grasslands. In more technical language, the shift is toward systems in which the annual production is larger in proportion to the standing crop. This is not the place to go into details, but wo do now know a good deal about how ecological systems respond to stress and this is vuluablc in predicting what new levels of pollution may do to patterns of vegetation and fauna. ' . -5- j^/ug/m^ is microgram per cubic metre MQN5 040319 At the populotion level , if one in concerned ninply to hove "no rnsnonso" in' terms of population size, enhanced mortality is acceptable so long as this is not on so great u scale that it leads to population decline. That is, it is permissible in those terms to substitute pollution for other forms of mortality that would otherwise remove the surplus of offspring produced in most populations of living creotureo. If the annual production of young seabirds, for example, is three times that required for recruitment into a stable breeding population and the norm is for the surplus two-thirds to die, in population terms it is immaterial whether this surplus is removed by competition for food, predation or chemical pollution, so long ns recruitment is sustained. The size of the population would be equally unaffected if the mortality among breeding adults wore increased by pollution, so lone QS enough young survived to maintain recruitment at the higher rate which would then become nncessory. Indeed it seems very probable that during the early 1960's the heron population in England was in just this position in relation to certain orgnnochlorine pesticides. We know that some adult herons were lothally poisoned and there is considerable evidence to suggest that sub-lethal residues affected egg-shell thickness and chick survival, resulting in a reduced output of young. Neither the adult mortality, nor the decrease in over-all breeding success, however, appear to hnvc reached a level where they affected more than the annual surplus present in the population and so the total heron population of England and Wales of 4,500 pairs remained unchanged. -4- MUMS 040320 /in'iin, h demand for "no response" al; the individual level permits organ, cellylnr, or biochemical changes, uo long ns mortality or a oerious retardation of growth or distortion of behaviour does not ensue. The influence of factor:ieo omitting fluoride on cuttle prating in their vicinity has been regulated on such a basis: a "no effect" standard at the physiological level has not been demanded, but the exposure han been restricted in such a way that unacceptable effects are avoided, linther similarly, some pasture grasses and crop plants in industrial areas of Britain may have their growth rates affoctcd by atmospheric pollution, including pollution by SOj, but this is regarded ns acceptable so long as yields are maintained above a certain threshold, determined by economics. Kven in man one sees this Bituatibn, alih'-ugh the threshold is usually set much morn stringently on heal' h grounds: eg, in ou!" acceptance of blood lead levols which affect, the activity of the enzyme delta-aminolaevul i nic acid dehydratase, so long as these are not nermitted to riso above around 56-hOyug/IOO ml of blood, which is commonly taken as the point beyond which we become socially concerned. Finally, if wc determine that we shall have a "no response" situation at the biochemical level, we are admitting of no detectable effect whatsoever and arc faced with .the most stringent of all demands for pollution control. Indeed, with an impossible situation, since some substances we release as pollutants are present naturally in our environment at levels which hove a biochemical effect. MONS 040321 In social terms, we tolerate different levels of effect according to the nature of the target and its immediacy to the human situation. For example, it is qommonly agreed that we should not accept significant effects at the organ level in man. V/e are indeed wary about the cumulative effects of lifelong cxnooure to substances which may only have minor demonstrable effects on human biochomictry, fearing that they may in some way progressively erode the body's homeostatic oiachincry and shorten life. Ue reflect significant effects nt the individual levoL - illneso or impaired growth - in cattle, nhenp, othor farm stock and domostic pets, '..'o reflect significant ecosystem effecta in marine Dnd freshwater ecosystems and in forestland wild vegetation, with their invertebrate and bacterial components. Sometimes, of course, the standard we net nt one level affects organisms for which we would otherwise only be seeking lesser decrees of protection: standards set for mercury in fish as human food for tut example, may lead to curbs on discharges of ohnot metal to the sea which from the point of view of protecting marine ecosystems would not be necessary. It does not follow that our Judgement in these matters is always wise (although I believe that it is defensible) but it does follow that we should be aware of the logic1 of our actions. t EXPOSURE AND EFFECT The effect on a target depends upon three groups of variables: (a) the nature of the pollutant, (b) the biological state of the target with which it is interacting, including the individual and temporal variation which is exhibited by individuals, organs and biochemical systems, (c) the concentration of the pollutant and the time of exposure (not usually, incidentally, capable of being summarised by a simple arithmetical multiplication. Short term exposures to very high concentrations need not always be the equivalent of exposures to half that concentration for twice the time or one-tenth the concentration for ten times as long. Ozone for example, can affect -6- HONS 04032Z eennitive plantu in hourly exposures to around 10-P0 pphn*: twice the time at half the level may have much los3 effect). In addition, it is important to know the site of nntry of the pollutant (eg skin, lung, put) nnd the site of action (nervous system, blood, kidney, liver etc). mu in Figure 1. It is evident that a whole series of physical nnd chemical properties and interactions influence this movement, and parameters such as diffusion coefficients, absorption properties in and from soil, solubility in water or other liquids, rctes of break down by ultraviolet radiation and reactivity with other components of air, water or soil can hove a major influence. This is well exemplified by the pathway of sulphur dioxide in air (Figure ?) washing'out in rain as dilute sulphuric acid and/or combination with amonia to form an ammonium sulphate haze ("Teosside mist") have an important influence on the actual nature of target exposure. Similarly, chlorofluoro hydrocarbon compounds emitted to the environment as aerosol propellants apparently persist for a long time under groundlevel conditions but are fairly rapidly degraded by ultraviolet radiation in the upper atmosphere: here physical mixing of layers of air will clearly bo an important determinant of persistence. In predicting the scale of a possible pollution problem, therefore, any model we develop must take full account of- the pathways, as well ns tho nature of the actual interaction of the pollutant and the target. It mur.t also cater for individual variations in susceptibility and -7- pphm pnrtn ner hundred million MQNS 040323 variations with time and circumstance. Sometimes these-variations can bo very largo. For cxomple, concontrationn of load in air in Britain may reach ?0-25yug/in^ in the centre of motorways by day and average 10-15yun/m7' over ?J\ hours. In ordinary busy streets, and around factories, ?A hour averages nre around In tho country levels are much lower - below 0.1yus/m^. Human exposure inevitably varies as neople move around. Human intake to the lungs likewise varies according to the volume of air we breathe in the day - and while the average for nn adult man is around 15 m^ this can be doubled by activity or halved by rest. Not all the lead particles passing tho nose or mouth reach, or stay in the lungs: various calculations (jive retentions of 10-6C?i of the potential intake. Only a proportion of the lead retained is absorbed - maybe 50/.' on average, but with much individual variation. If you sum the cumulative effect of all these variables, you can rt-adily see how there could be a thousandfold variation in human lead absorption from the air - and tho uncertainties in many figures cast doubts on tho usefulness of such a broad-brush calculation at all. Generally speaking, the effect of exposure to a pollutant is related to concentration, although the curve is unlikely to be linear. Moreover, the response to increasing concentration is frequently hierarchical in nature. That is, at the lowest concentrations t.lie-c is a biochemical effect. With increasing concentration thin becomes manifest in whole cell or whole organ changes, then in variations in individual behaviour. At higher concentrations still, individual mortality nay ensue while greater exposure leads on to whole population % or whole ecosystem changes. 8- HONS 040324 Vo hove partial documentation of many of these curves. Ort.on the information'-penulto from laboratory tests, under conditions remote from those in the field, of sinple pollutants npainst sinple tarpet species. Thiu may be rennonnblo enough for exposures to no]lutor.tr. with a specific action, like the effects of radiation on menotie systems pure--but how valid is it ns an indicator of wholepopulation or whole-organism responses to chemical factors? Often the ]aboratory toots estimate doses that kill 50?> of the exposed orpanisns (LDf>0) in 24, 48 or 72 hours or over n longer noriod of days. Often, the dose concentrations used in such toots are relatively high - sometimes this is necessary to demonstrate a response in a convenient time. The tost species used are often selected for convenience in the laboratory and basic (and sometimes sweeping) assumptions are made about tho similarity of response other organisms may be expected to show. But what of the situation in nature, when we are dealing with mobile populations, forrninp part of a much more complex system , and able to move away from areas of high pollution. There can be no confidence in their extrapolation to the r.oal world. Often, too, ecologically significant effects can be sub-lethal and will not show up at all in I.DrpO tests. For instance, seaweed growth rater, can bo related to degrees of marine pollution ^Fipu-no 4) /flurro'-'O,--V}--J, with conse quences for herbivorous marine animals; and fish physiology con be adversely affected by DDT levels below the directly lethal dose, mnkinc fish more likely to succumb to cold or to be unsuccessful on miprntion y4fef',wc 0)" ( Anderson, *10-- A pood example of a complex and imperfect framework of knowlcdpo is provided by sulphur dioxide in air - one of the commonest nnd most- MONS 040325 studied of atmospheric contaminants. Ar, Figure if, inolies, quite a lot is known about tho exposures at which various kinds of plant firnt show injury and then serious damage. Likewise, tho onset of symptoms in tho most sensitive people (bronchitics) 3.3 predictable. But in both ennes allowance must be made for a very wide range of individual variation (in man there i3 probably a thousandfold range in sensitivity in an average population);furthermore, there i3 a Great deal of variation in response according to the duration of the . exposure, and at least in man, the levels of smoko accompanying the f>0p exposure are critical. Thus, the "threshold" level for SOp, averaged over SA hours, is SOO^ug/m^ when accompanied by 250/ug/m^ smoke ^rgurc 7) (In'wther;---------^ whereas laboratory studies have failed to find significant impairment of human respiratory function by OOp alone at concentrations below 2500/ug/m^ for comparable periods. In this case we do have- enouGh knowledge of dcoc/rosponoc rclati.cr.rhipc to conclude that in order to protect vulnerable people we should seek to keep daily average sulphur dioxide levels in air below 500yug/ra^ and smoko below PJO^ug/m^ and these figures have been adopted us short-term objectives by a WHO-Working Party. If we consider that the manifest sensitivity of lichens indicates potential biochemical disturbance which, while we cannot prove its parallel existence in man, ought in common prudence to be avoided, we would need to take on annual moan of around hOyug/mJ as our environmental quality goal - and SVfi that peaks never greatly exceeded this figure. Although we have little information on other species, this would almost certainly also prevent any crop losses and protect most forms of life while it would not eliminate the lcortcficial action of air-borne OOp in correcting sulphur deficiency in some soils. The recently published national - 10 - HONS 040326 for a very few days in the year, whereas in London and in the midland nnd northern towns it is frequently exceeded, hut in many rural areas it io not''surprising that the British Lichenological Society has recorded considerable impoverishment of the lichen florn in the whole central midland zone The question is whether this is paralleled by any significant agricultural losses (one report placed these at A0 million ;"r annum in England, but with an enormous possible margin of.prior) and sufficiently serious to justify the major expenditure that would be required to reverse it (especially in the current energy situation). Only rarely do we hove even this degree of detailed information about enjiomnm-offeet relationships. More commonly all that we h-vo is a broad, descriptive correlation between nollution levels, generally . . ft* assessed, and biological response: an^oxnmplo for fresh water, jo H-ven There is clearly a need for more research to determine rigorous "criteria" on which our social judgement of the need for more-(or less) intensive effort to combat pollutiQn must depend. Such work needs to take into account the biochemical means by which the whole-organism responses are mediated. We need a better understanding of individual variations in response, and how variables such an ago, nutritional state or reproductive condition of the individual interact with environmental chemical factors in determining them. Till! 1KTK!(ACTION OF J'OLI.UTAi'TJ AND OT!!ER FACTORS This lends to another important generalisation: pollutants rarely operate in isolation. I would like to give a case history that _ is - HONS 040327 underlines thio rather well end illustrates the true complexity of the kind of `situation that confronts us. Botwoon .iurur.tnnd November 1969 about 17,000 seabirds died in theIrish Sen. They were almost nil of one species (Brin snlre. the Guillemot); they wore almost all adults, nnd nearly ell of them came ashore after September'poles in an emaciated, condition. Investigation /[----y showed, however, that the pales were not the primary cause, for while the peak in the number of strandinps coincided with the storms, some birds had bopun to leave the water in a distressed condition before the pales bepnn and While pales of equal severity had affected tho whole western seaboard of Britain,the mortality was concentrated in the Irish Oea north of a line from Holyhead to Dublin and south of a lino from llonepal to the Hull of Kintyre /pipure-ffi. Histolopical examination showed that many of the birds had lesions in the kidney and Diver and chanpcc in the heart end perice.rd.ium which paralleled experimental effects obtained by exposinp birds to larpc concentrations of polychlorinated biphenyls (PCBs). Chemical analysis subsequently showed hiph levels of PCBs in liver and kidney, and to a lessor extent in brain f.Table-'4^. It would bo temptinp, therefore, to frame the hypothesis that these birds died of PCB,,poisoning.. This, too, would he an oversimplification, since healthy birds shot off the west coast of Scotland contained whole-body loads of PCBs comparable with those in tho victims of the disaster /^efcKhr"t'j. The difference was thut in the healthy birds tho PCBs were distributed in tho body fat and the levels in liver and kidney were low. The conclusion of tho. study was that wo were dealinp with a multi variate situation. Tho moot plausible hypothesis was that noraothinp. 12 - MUNS 040328 poonibly climatic change, caused a reduction in the available food supply of these birds in midoummer at a time when their reserves were fairly low after the breeding season and they were about to go into the moult, which imposes a further stress. The oceanographers were unable to detect any change in marine life, but nincc those birds feed only'in the very top layer of the water, a long clear spell vii th bright sun might have led their food organisms to descend slightly deeper than normal, thereby shutting off the food supply but not crcetin changes detectable with the marine biologist's tow net. Be that as it may, the initiating cause of the mortality was .very possibly an interruption of feeding. This would, of course, have led to the mobilisation of body fat, which would have brought the PCBs stored there into the blood stream and on their way to liver and kidneys. This in turn might well have had minor behavioural effects at the whole-organism level. It might have made the birds a little less efficient at feeding, thus exacerbating the situation, and more prone to exhaustion by storm, especinlly since their food reserves were already low; any further stress could only lead to the increasing flushing of rCBs into the. blood. There would then be the recipe for o localised disaster in the area where the initial imbalance between food-intake and food requirement had occurred, and the whole disaster would be attributable not directly to PCB poisoning, but to the impact of thi3 pollutant within the system, tipning the scale between survival and death when the environment imposed external r.tress. I believe that this is likely to bo a model commonly valid in the pollution area and that many pollutants must be looked on as operating in this way, changing the probabilities between health and disease in a situation depending on a groat .complex of variables. - 15 - MONS 0403^9 rtiK nncracTicw w twewm In predicting whpt will happen under a variety of circumstsncen, it in clonr t'<nt wo must take account of the consitivity of orpanions to various levels of exposure 1;o both individual significant pollu tants and combinations of pollutants, be must also endeavour to predict the levels of exposure at these target organisms, nnd these in turn depend on the pathways of the pollutants and the factors determining their rate of input to and removal from the environment. It is well known that all chemical substances vary in these respects. It is self-evident that the pollutants likely to attain significant concentrations in regions remote from their sources of emission arc those released in large quantities, readily soluble in water or easily dispersed in air, having a rapid rate of diffusion nnd having a low rate of chemical or biological transformation into innocuous products or a low rate of settlement of sedimentation from air or water in ^which they are suspended and perhaps ultimately exhibiting the phenomenon of concentration via food chains. Those of high persistence, but less ready dispersal, on the other hand, are clearly type-cast to create "hot snots" about points'of emission. In both cases, if wo know about their inherent toxicity and the way by which that toxicily takC3 effect, we hove the recipe for predicting the likely seriousness of a pollutant substance. It would bo useful wore wo able to go further than this, and predict from the molecular structure of a substance what its behaviour in the environment was likely to be, Sometimes this can be done to a degree, on with the probability of biodegradation of certain detergents 14 MUNS 040330 '/ changes alter tho behaviour of molecules to a surprising decree. For tho forosocnblo future wo can expect to have to roly as tho chonir.nl industry now does on laboratory and field testing prior to the introduction of new substances or new formulations, '.."hat we can ensure however is that the mass of available information is more offeetdvoly retrieved, and this i.3 the aim of the information referral system beirjr developed for the United Nations, with the active participation of tho UK Chemical Information Service /renchuy,-- Tho construction of meaningful numerical models of environmental pollution is'extremely difficult. Not only is one confronted with the almost endless variation in biological response, but the curves relating omissions to concentrations in the environment at a particular point and time are influenced by a very larRe number of factors, ''a have at the present time some relatively crude models for the behaviour of pollutants in water, particularly rivers, which have tho merit of beinR relatively confined.and subject to predictable patterns of flow. Such models are bcinR attempted for the sea, but are prone to Great difficulty, while for air they have succeeded only at the most superficial level. Clearly, we need nony more studies of pathways and effects, and those are the two key areas for research upon which must depend our social response in terms of Juii^inG the relntive seriousness of a pollution problem and therefore the priority we must civo to its control. For we must remind ourselves that we live in n world in which chemical factors are, and always have been, important in ocolory and phyniolopy. Many of the pollutants to which wo are exposed arc natural substances whose concentrations and distributions, rnthor than - 15 - HONS 040331 eliminate thoeo substances; .indeed many of them rire csnenti.nl at low concentrations to our well-being. Wo could not expect to take their concentrations bhok to pre-industrial levels even if we knew what these were. What we can do in neck to predict the points at which their concentrations become socially unacceptable and to work out the most efficient means, in economic and technological terms, of restrict ing those levels below that threshold. Jlnd none pollutants, eg 1'CJJs, are entirely unknown in nature. Here also we must apply the principle of restricting their concentrations to the threshold of social unacceptibility. On the basis of this knowledge, too, we can make a more sensible decision about the parameters we need to monitor in the environment and the frequency of the sumpling we require in space and time, 'uite evidently, that monitoring must allow us to assess os accurately and precisely as possible the cleg-roe of exposure of various targets. It would bo logical to son the network of measurements most closely grouped about targets in which wo are not prone-red to see any significant changes at individual level, while a looser network of monitoring might be acceptable where we are concerned only to prevent changes at the ecosystem -level. Moreover, if we are prepared to accept changes at all levels 3hort of tho ecosystem lovel, biological monitoring becomes evidently acceptable. If wo monitor tho performance of indicator species, we are tacitly accepting that we are prepared to see their numbers or their performance impaired but because the ecosystem level is unlikely to show change until such impairment at individual level has occurred on a substantial scale, the biological monitoring programme yet gives us something of a safety factor and time span in which to effect corrections should that be needed. On the other hand, biological monitoring may be less acceptable where we - 16- MONS 040332 nrc seeking to prevent damage at the individual level unless wo can find an organism which in an order of magnitude more susceptible than tho tarr.ots we qre chiefly concornod to nrotnet and disnlnying a similar sensitivity to the whole interacting mutrix of factors. Alternatively, we can monitor at the biochemical level (for example following lend levels in human blood or orgonochlorine levels in wild life) so n3 to pain early warning of effects at tho organ or individual level. Whatever conclusion we roach, the design of a competent monitoring nystcra must be greatly influenced by our knowledge of the exposure-effect relationship between pollutunts and the targets with which we are particularly concerned. TRENDS IN FOIXUTICN AND SOCIAL REOIONSE Pollution has become a subject of increasing national and international concern in the last two decades. But it is fair to point nut that the majority of tho incidents which have served to focus this concern have been due to localised concentrations of particular pollutants in pollution "hot spots" (eg smoke and sulphur dioxide in the London "smogs" of tho 1950ai mercury and cadmium in water receiving effluent from certain Japanese factories, and raised blood lead levels near a number of factories using lead). It is also fair to add that while tho number of incidents causing concern has mounted, the actual damage due to pollution has declined: London "pea-soupers" and acute pollution near ' industries almost certainly harmed more people fifty years ago. |i|Mr There in no evidenco of damage to human health or ecological stability on a global scale, due to a globally-distributed pollutant (except perhaps for the statistical prediction of increased radiation damage HONS 0 4 0 3 3 3 ntnosphere). The most-quoted examples of global trends in pollution, the gradual >j noreaso in the proportion of carbon dioxide in the atmosphere, the trace quantities of DPT and other pesticides to be found in oceans and wildlife throughout the world, and the possible chanson in atmospheric turbidity due to the .injection of fine duet into the'fair, are all no more than changos in pollutant level without as yot proven consequences for living "targets". Nonetheless, it does not follow that increased omissions of pollutants will not hove unwelcome effects, both through the creation of more and more unacceptable local "hot spots" and through tho elevation of tho general level, of contamination of ocean and atmosphere to tho noj.nt at which undesirable climatic or ecological changes ensue. Granted that the latter process, in particular, is likely to build up slowly and require an equally long tine and grant effort to reverse, it is clearly important to improve cur scientific knowledge of pollutants and their effects and our predictive capability, as well as our technical capacity to control pollution. In tho past, we have allov/od pollution domngc to develop, and had to cure it when wo no longer found it acceptablej in tho future we need to forestall such dnmngo, and this requires better understanding than we now have. , TIlKinrl IN rOlIUTAKT EMISSION . It in a historical fact that some pollutants have been omitted in ntoudily rising quantities, in parallel with mounting human populations and increasing industrialisation. The generation of nan's body v sics and food residues, end the body wastes of his livestock, inevitably rise in direct proportion to population. Energy generation through the 10 - MGNS 040334 burning of fossil fuel releases carbon dioxide,. carbon monoxide, oxides of nitrogen and of sulphur,' water-vapour^ hydrocarbon.'! and n variety of particulates. Total emissions of all these 1 :vn risen otondily over past docadoa or even centuries, although non still adds lono of many of them to the environment than is contributed by natural processes. There is a similsr tcndcnc^ for the vastly wider range of pollutants generated by industry likewise to rise in direct relation to industrial growth, unless anti-pollution measures arc taken, or unless inherently 'cleaner' processes are developed. m> m ...... ............. ... --ipinr nm^iniitrinrrirurnin minn i - persistent iw VmmlAlKjtfrtbknown /ilinr. This in because of recognition of the need for abatement and the development of increasingly efficient pollution control technology. The pollutants still on a rising trend are generally those not known to be harmful at present or projected levels and hence not yet justifying control. Hecognition of the need for control, eg on omissions of hydrocarbons, carbon monoxide and lead from cars, lend from industry or sulphur oxides from low level chimneys, has nlready begun to affect tho trends in the products of fossil fuel combustion, until recently looked on as harmless. However, abrupt changes in the cost of various fuels will necessarily have a modifying effect on control policies adopted in future for various forms of energy generation. For we live in a situation where marginal benefits and marginal control costs have to be balanced, and the balance can shift cither way. - 19 - MQNS 040335 FACTORS TMFIAIENCII'C FUTURE TRE1SDU In crude tonn3 $he concentrntion of a pollutant in the onvirnntiient in the result of emission and removal. In practical torn.-,, tho important detornininc factor io nan's deliberate control over emissions This is in turn governed by the coota and benefits of the activities t. lending to the Generation of the pollution and the actual or predicted coot to tho community of tho damage it dons. Research, leading to a deeper understanding of these matters io likely to bo a poworful determinant of tho actual future trends in emission, concentration and effects of sny substance. It is impossible to catalogue all mn^or pollutants and predict their future levels. Rut we can reliably forecast a continuing decline in damaging industrial emissions such as acicic and alkaline vapours, particulates and heavy metals, am) in persistent organohalogons such as 3'CBs and DDTo, for which substitutes cither exist or ore being nought. Wc can predict a slowing down in the upward curve of omission of pollutants from motor vehicles since most developed countries nre adopting standards that will halt, or even reverse, this trend within their borders. Substitution of nuclear for fossil energy sources will also load to a not decline in gaseous and particulate emissions, although imposing a demand for continuing stringent controls on radioactive discharges. Recent international agreements seem to lead to a progressive reduction in the dunping or discharge of orgunohnlogen oils, heavy metals and known carcinogens to the sea and rivers, and tho levels of these substances in the ocean and marine life should soon begin to fall. M0NS 040336 Nevertheless, pollutants continue to bo an inevitable accompaniment of man's increasingly technological society, and wc shall always have v'vt \V-. f'o of in 1;hr rnvi vonm^ni;, i V. i ***' legitimate to u30 tho environment for this purpono, so long ns we Oo not ovor-tnx its finite capacity to disperse and degrade antes. With increasingly stringent demands for tho testin'' of now substnneas for environmental effects before they are used or discharged, and increasingly precise analytical, toxicological reecarch methods at our disposal, tho probability in that pollutant levels will loss and le.no frequently bn allowed to mount to tho point nt which damage begins. THE TREED IN THE COUT OF POLLUTION CONTROL This essentially optimistic projection is grounded on history, for in Britain and moot other developed countries, pollution has become a diminishing problem as our awareness, scientific understanding and technological capabilities have grown. But there is a price to pay for continued optimism. There is a tendency for tho energy cost of pollution abatement cr prevention to rise disproportionately as popula tions grow and the otandard of living and technological development increase. This is because: (a) the capacity of the environment to disperne and degrade pollutants is finite, and any increment of pollution over and above that capable of natural degradation demands treatment prior to release, (h) tho larger that increment, the purer tho effluent may have to ho, volume for volume, if the qualify of the environment is to ho sustained,' HONS,, 040337 (c) tho costs of'removing pollution from an effluent tend to mount exponentially os one moves towards greater purity, (d) the development of substitute or now products becomes more and morn' costly as tho connunity demands increasingly strini.' ia tests of their safety, (e) the environmental quality which people demand tends also V to rise in parallel with tho standard of living, and this provides a "positive feed-back" increasing the costs listed above, (f) or we become more and more dependent on technology to purify emissions and protect the environment, so the consequences of break-down become leas acceptable and more thorough "fail-safe" mechanisms are needed, often a.t substantial cost (c.f. the standards required for nuclear as against convential power stations). As economic and technological growth proceeds, an increasing proportion of CNF thus tends to be demanded for environmental protection. If this is to be prevented, increasing effort needs to be devoted to the development of better, safer and more efficient technolonies, Riving higher quality controls at less- cost. This is one of the needs of society to which chemistry has shown itself responsive, and must continue to respond. _ HONS 040338 Onntionn for fiimirc3 Figure 1. V The pathways of pollutants from source to the point of effect. Figure 2. The pathway of sulphur dioxide in air (from Kellogg, V W Cudlc, H.D., Allen, E li, Lazarus, A L and Kartell, E A, Science (February "1972), Vol. 175, No 4022). Figure 3. Thresholds of sulphur dioxide effect on some plants and people. MONS 040339 Sources Chemical Xrarsfcreation <n Air cr i'ater Dispersion Tia Air or Sater_____ PICOS 1 V Surface or Iirget-------------(jeiweahility varies according to nature of substance and surface) Dispersion sithin Target (effected by solubility. reactivity etc.) Biochedcel - Interaction MONS 0 4 0 3 4 0 Checic&l Transformation in Soil------------ i------------ fathray in Sediua Entry to Target Pathway to Target 9' HOLIKKfil AND RF.MD: xso, Particles in Lower Stratosphere Grow by Coa<juUt:on and Settle Out or Mix Downward 11 to 2 Yrs. Residence Time) '.V.ml Mrr.-.n Sea Salt XSO, t 130 SO.. XSO; i ?17 ,50- iMo U o- Carried to Occam Ijv Rivers Rjm Over llie Lam! w\\W so.. XSO, pka Plant Uptake and Dry Deposition so. XSO. H.S(SO ) I A' 45 I * Volcanoes ^ H,S. SO . XSO * TOTAL % * 2G8 / c' li/ri/ wA ' *>! utmusplnru sulphur < i>/'npuntn(\. Cnits me HT //m\ <u/< ulalcrf tt\ sulphate per rear . y K.7- t / ., ) K- y i' 7. | y/ u.itcr. \eeetati^n or structure': in^tliex max be trans formed in the air into oilier sul>4aiice' which. in soiyr* e.i'e'. in.iync more ohnoxioir mlian the oriental oneX / 'concern are those emitted in Ia ree^qTuTrrrncvr-es pec ia 11 as a result of iWf combustion. The eliiel' of tlte->e ar carbon dioxide/carbon monoxide. hxdrocarhoiis. oxide HONS 040341 ;00.0.00 n 10.000 ' V. I 100 10 PEOPLE TtOLERABLE OV HEALTHY I ADULTS AT WORK PLANTS t \ . > ' . C- -4000 SMOKE many increaseo death! C--2506 THRESHOLD OF SOi action alone - - HARMFUL TO SENSITIVE PEOPLE HARMFUL TO MOST PLANTS C - - 400 MOST LICHENS C ELIMINATED C- -170 . SOME CROP PLANTS DAMAGED OR CHECKED 500 V SMOKE P BRONCHITIS AFFECTED 300 '' C + 85. . ! SOME CONIFCRS AFFECTED C-l-30 SENSITIVE LICHENS AFFECTED NOT ENOUGH FOR MAXIMUM ' CROP GROWTH IN SOME AREAS S O , -CONCENTRATION P g /n r - L 0 C5 NATURAL BACKGROUND HONS 040342