is run. The most troublesome detergents include substances like sodium tetrapropylene benzene sulphonate (TBS); it has a molecule with many branches in its carbon chain (Fig. 5) and this is associated with its resistance to bacteria. Other substances which act as anti-foaming agents, including kerosene, have been added to effluents to prevent foaming; unfortunately they do not remove the detergent, only mask its presence, and may actually aggravate the pollution. Recently entirely new chemicals, as efficient in washing clothes, but much more easily broken down by bacteria, have been introduced. These have straight carbon chains and include Dobane JN sulphonate, and finally sodium alkane sulphonate (SAS) which is at least 99 per cent broken down as it passes through the sewage works. The breakdown products are, as far as is known, non-poisonous. Already some countries, including Western Germany, have made the sale of the so-called “hard” detergents, i.e. those with branched-chain molecules which are so stable, illegal, and some progress with their replacement by the “soft,” straight-chain substances has been made in Britain. It therefore seems possible that in a few years this form of pollution may have disappeared. However, there are many useful lessons to be learned from this subject. Detergent pollution might not have been noticed but for the appearance of “swans.” Other cases of pollution may go undetected when new substances are used, for instance in industry, so constant monitoring of effluents and the rivers into which they run is obviously necessary.
Other very stable substances are found polluting water, but with more serious results than those resulting from the presence of the relatively non-poisonous detergents. The most serious effects have resulted from the presence of the chlorinated hydrocarbon insecticides, which are both persistent and poisonous to most forms of life, but particularly to fish and aquatic insects. This subject is discussed in detail below (see here), when consideration is given to the whole question of environmental pollution by pesticides.
Many rivers to-day are altered by industry, particularly by electric power stations, by having the temperature of the water raised. Where this warming accompanies organic pollution, the effects are greatly increased, as the oxygen level is lowered while the rate of metabolism of the bacteria and other forms of life is increased. In some cases different animals and plants, more adapted to warm conditions, have colonised regions where heated effluents are discharged. This heating of rivers and lakes is something which is likely to increase with growing industrialisation, and it needs to be watched from many points of view, including that of the preservation of wild life.
Rivers may also be cooled, if heat pumps are introduced to warm our cities. These installations remove the heat energy from the water, and pilot plants have reduced the temperature by two or three degrees. This will probably slow down many biological processes, but it is unlikely to have a very great effect on the composition of the flora and fauna.
It is difficult to foresee just what will happen to the lakes, streams and rivers of Britain in the future. So long as sewage and industrial effluents are discharged into our rivers, these will cease to have their “natural” fauna and flora, even if the more unpleasant symptoms of pollution are no longer tolerated. If no effluent were to be discharged, under present conditions, many of our river beds would be dry for most of the year. The policy of drawing water supplies from the lowest reaches of the rivers instead of from the cleaner streams above the towns is one which appeals to the conservationist more than it did to most water engineers in the past, though changes in policy now bring these different organisations closer together. Certain river authorities now wish to use their upland reservoirs for storage only, discharging them into the rivers which act as channels to bring the water to the lowland towns. This means that the catchment areas can be used for recreation and agriculture, as pollution is less important when the water, abstracted further down, must be purified anyhow.
Fig. 5 Chemical structure of “hard” and “soft” detergents.
A: TBS (hard)
B: Dobane PT (hard)
C: Dobane JN sulphonate (soft)
D: Sodium alkane sulphonate (soft)
If sea-water can be economically desalinated, the pressure on our fresh-water supplies will be eased, and further improvement of their purity will be possible. It may be difficult fully to restore conditions in lakes which have become polluted, and every effort should be made to prevent the discharge of even the “cleanest” effluent into such places. So far comparatively few species of animals or plants have been totally exterminated from fresh water in Britain, and streams which have been cleaned up have usually been recolonised with the appropriate forms. This may not happen in the future unless every effort is made to render our fresh waters not only safe but also pure.
CHAPTER FOUR RADIATION
Since the first atomic bombs were dropped on Japan in 1945, we have been aware of the dangers of “atomic radiation.” Radiation, in sufficient quantities, is clearly dangerous to human and to other forms of life. Man has polluted the earth by releasing radiation and radio-active materials as the result of testing nuclear weapons, by accidental discharges from nuclear power stations, by the waste products from these power stations, by the use of radio-active substances in industry, in research and in medicine and by the use of X-rays in clinical diagnosis and in the treatment of disease. My task here is to assess the danger to man, animals and plants from the pollution that has so far occurred, and to discuss possible future risks from this source.
This is not the place for a detailed discussion of the nature of radiation, but some account is necessary for readers with little background knowledge of the subject. Atomic radiations, which are physically of several different kinds, some consisting of electromagnetic waves and some of bits of atoms moving at high speeds, all have similar chemical and biological effects. These radiations are invisible, and they penetrate living tissues to a greater or lesser extent; some are stopped in the first fraction of an inch of skin, others go deep into the body. All the radiations we are considering here are called “ionising radiations”; this means that they have the property of knocking out electrons from the atoms in the substances they pass through, and producing “ionised atoms” which have great chemical activity. When this occurs in a living cell, the usual effect is for the cell to be damaged. A large dose of radiation, producing many active ions, can cause the cell to die almost immediately. A very small dose may have no noticeable effect, though even the most minute amount of radiation causes some change in some part of the cell.
Ionising radiations arise from various sources. Before man made his contribution natural background radiation existed, and is still the most important source in most areas of the world, and it has the greatest effect on its human and other inhabitants. Three-quarters of the background radiation affecting man comes from outside his body; a third of this fraction is due to cosmic rays reaching the earth from outer space, and two-thirds is due to the local radioactivity of many of the rocks. Cosmic ray radiation is partially absorbed by the atmosphere, and is therefore much greater at the top of mountains; at higher altitudes it may increase enormously, and could be a serious hazard to astronauts. Even high-flying birds will receive more cosmic rays than those which remain near the ground. The radio-activity of rocks varies in different parts of the world. Near uranium deposits it may be high, but the differences between different parts of Britain are probably under 50 per cent.
The rest of the natural radiation affecting man comes from radio-active substances within his body. The most important of these is potassium. Potassium is an essential constituent of all living tissues. A tiny fraction, about one part in ten thousand, of this naturally occurring potassium is radio-active,
