these problems have become more serious in recent years. The need for more research in these subjects is obvious, if irreparable damage to wild life, and to man, is to be avoided. Equally important, we must make sure that the results of such research are quickly and efficiently applied.
CHAPTER TWO AIR POLLUTION
Perhaps the most obvious way in which man has contaminated his environment is by polluting the air with smoke and with the waste products from industry. Everyone has seen the pall of smoke hanging over a city. He knows that many plants and animals are not found in the middle of a city. It is, however, difficult to find exactly how this pollution has affected wild life, notwithstanding much intensive study of the subject. Although some lichens and other plants seem to be particularly susceptible to the effects of atmospheric pollution, and their distribution may be correlated with it, nevertheless the position is far from simple. This is perhaps not surprising, as we seldom have a constant amount of any noxious substance in the air at any place over any long period of time. The smoke emitted from a domestic fire or from a factory is in bursts followed by periods of comparative inactivity; in some towns factories are only allowed to give out black smoke for five minutes in an hour. The weather has a profound effect; calm clear periods, particularly when temperature conditions prevent upward circulation, allow the pollution to concentrate, while strong winds ventilate the area though they carry the substances in detectable amounts to distant parts of the country.
As soon as man discovered fire, he made smoke and so polluted the atmosphere. The effects were local and slight until about the thirteenth century, when coal fires in cities were found to produce winter fog and punitive laws were introduced, apparently with little permanent effect. As cities were small, and little coal was burned, probably no great damage was done except perhaps to men themselves living in unventilated houses. When cities grew, smoke became, and still is, a major problem.
Industrial development in the nineteenth century was accompanied by new types of pollution. Hydrochloric acid gas from alkali works caused a public outcry, with resulting legislation. Attempts have since been made to restrict all the emissions from factories to a “safe” level. This happened none too soon. Much of the gross pollution accompanying the dereliction in areas like the lower Swansea Valley was airborne from factories in the area.
The results of atmospheric pollution differ in an interesting way from those of insecticides which are discussed in later chapters. Man himself has been the major victim of polluted air; insecticides have had serious effects on wild life, but man has seldom been injured by the direct effect of these substances. The ecological significance of this difference is discussed in later chapters.
Every urban housewife is only too well aware of the reality of atmospheric pollution. Curtains and furnishings remain clean for months or years in the country; in the towns they are grimy in a matter of days. Students of pathology who have only seen inside the corpses of city-dwellers are amazed, and think they have found some new disease, when they see for the first time the healthy red lungs of a farm worker who has never lived in or near a town. Walkers on the moors of the Peak District know that their clothes will be blackened if they sit on the heather, and most flocks of sheep there, except immediately after shearing, seem to consist only of black sheep. The Peak District sheep on moors surrounded by industrial towns contrast with the much whiter animals found in the remoter highlands of Scotland, and this colour difference has been suggested as a rough and ready means of estimating pollution.
Air pollution in Britain to-day is mainly due to burning coal and oil. Local effects from many chemical processes, and petrol and from diesel engines also make their contribution. Perhaps the most serious chemical problem is due to fluorine, mainly from brick works, and this is specially mentioned below. Legislation and regulations have reduced the amount of many pollutions to such an extent that wild life is usually not seriously harmed, except in particular danger areas, but the amounts of dust, smoke and sulphur dioxide produced from fuel are so enormous and so unaesthetic that they cannot be ignored.
Britain consumes annually about 200,000,000 tons of coal and 25,000,000 tons of fuel oil. The output of noxious products is estimated at 1,000,000 tons of dust, 2,000,000 tons of smoke and over 5,000,000 tons of sulphur dioxide. Coal produces relatively more smoke and dust, and oil more sulphur dioxide. This pollution is obviously very unevenly spread over the country. The Ministry of Technology, formerly the Department of Scientific and Industrial Research, compiles reports from some 2,111 recording instruments spread all over Britain. These show that in heavily industrialised areas over 1,000 tons of grit and dust must fall on each square mile in a year; this corresponds to about two pounds on each square yard. In cities generally the figure is in the region of a quarter of a pound, and in rural districts it may be less than a tenth of an ounce. Sulphur dioxide, being a gas, is dispersed more readily, and the rural concentration is probably about a tenth of the urban or industrial figure, though under unfavourable conditions much higher values may be obtained adjacent to some factories. The housewife knows that polished silver or copper tarnishes more quickly in the town than in the country; this is correlated with the SO2 in the air.
The effects of industrial pollution on man have been studied intensively, but with somewhat confusing results. It is believed that the four-day “smog” in December, 1952, killed some 4,000 Londoners. Exactly how smog, which is looked on as a brand of fog containing more contaminants and smaller and more penetrating particles, kills is not understood. It may act as a general irritant which acts as the “last straw” in the weak and those with respiratory trouble. It has been suggested that the excess of free sulphuric acid is the lethal factor, but total amounts are small (only 0·05 parts per million as a maximum) and this view is not generally accepted. There is no doubt that smog is a killer, and it kills other animals than man if they are exposed (many cattle died at the 1957 Smithfield Show), but fortunately it does not often spread outside our largest cities. Mist, which consists of relatively clean water particles, is of course widespread. Fog, which is essentially mist containing amounts of smoke, penetrates some distance from industrial areas, but seems to have comparatively little acute effect on man or animals.
Acute effects on man and animals of smog, and possibly of fog, can be shown to occur even if they cannot be fully explained. Chronic effects of the usual urban levels of pollution no doubt occur, but are not so easily demonstrated. Lung cancer is higher in cities than in the country, but we do not know the precise cause. Respiratory diseases are similarly commonest in industrial areas. Although we ourselves filter the air we breathe and reject much of the dirt, city dwellers’ lungs are impregnated with dirt particles, and it is difficult to feel sure that this is not harmful. For these reasons considerable efforts are being made to reduce atmospheric pollution. “Smoke-free” zones have been scheduled in most cities, and some progress is being slowly achieved to reduce the smoke and dust. Fogs and smogs are less serious than they were, though the amount of sulphur dioxide in the air is less easily controlled and tends to increase even in smoke-free zones.
Farmers near to cities suffer from the effects of smoke and grime. It has been estimated that pollution, by damaging pastures in particular, costs the East Lancashire farmers over two and a half million pounds a year. Horticulturalists find that smoke reduces light intensity indoors and out, and obscures the glass of greenhouses, covering them with deposits which are difficult and costly to remove.
Smoke, by reducing light intensity, will obviously retard plant growth, and may encourage some species at the expense of others, though there seems remarkably little evidence of this happening except in industrial areas. Many city gardens do indeed suffer from the lack of light, but this is not due to pollution so much as to shading from buildings, and, more particularly, from trees. The luxuriant growth on bomb sites was a revelation to many. Here shading from buildings and trees was reduced to a minimum. Often one finds that spring
