Next, I want to illustrate some of the complexity associated with preventive environmental management using a particular system case study. This case study starts out by considering a specific pollution problem, related to a single toxic substance. But when we address this problem using the preventive paradigm, we are led rapidly into considering a complex system of material interactions. This example serves therefore to illustrate the peculiar demands which preventive environmental management places on the management of the industrial economy.
The starting point for the analysis is this: how do we reduce environmental pollution from the heavy metal mercury? Mercury (which has the chemical symbol Hg) has already been mentioned in connection with a tragic pollution incident in Japan. Acute mercury poisoning (sometimes designated Minamata disease after the Japanese incident) leads to stomach pains, delirium, coma and death. Low-level mercury poisoning includes a number of effects related to the nervous system. The expression 'mad as a hatter' refers to mercury poisoning amongst hatters who used mercury in the preparation of felt.
In fact, mercury is one of a group of metals5 which are toxic, persistent and liable to accumulate through the food chain. These properties—toxicity, persistence and liability to bioaccumulate—are all the characteristics (see Chapter 3) which combine to produce the maximum potential for hazard.
Where does mercury come from? There are some natural flows of mercury. For instance, it is naturally present in very small quantities in certain kinds of soils and rocks, and is released through natural processes of weathering. But the main source of mercury that flows through the environment is the economy. There is a number of different sources. Some of them are 'accidental' ones. For instance, mercury is present in very small quantities in coal. When coal is burnt, the metal is released and either gets emitted to the atmosphere or ends up in the combustion ash.
At the same time mercury has proved itself to be a very useful material in the industrial economy. It has been employed for a variety of specific purposes: aside from its former use in felt-making, it has also been used traditionally in dental amalgams; it is used in the chemical industry; it is also used in industrial switches, in thermometers and in batteries.
Each of these different uses carries with it different patterns of release of mercury into the environment. For instance, during the lifetime of a dental patient the mercury used in dental amalgams is bound up chemically and considered relatively safe. But some mercury poisoning episodes have resulted amongst dental technicians. There is also increasing concern about the release of mercury from fillings during cremation.
The biggest single use of mercury in many industrial countries has been in the electrolysis of brine (Figure 23) to produce the chemicals chlorine (Cl) and sodium hydroxide (NaOH). Early 'management' of the mercury wastes generated by the chloralkali industry relied on a dilute-and-disperse philosophy. Concern over the accumulation of these wastes in the environment and their return to the human food chain led to the adoption of end-of-pipe removal technologies. The sulphide purification process, for example, precipitates mercury out of industrial effluent as
Figure 23 Mercury flows through the chloralkali process mercury sulphide. The limitations of end-of-pipe processes have already been mentioned. In the case of mercury, a further issue was that the efficiency of the purification process was limited. And there were concerns that remaining levels of discharge into the environment were still too high.
A more preventive solution to the problem of mercury contamination from the chloralkali industry emerged with the recent development of membrane technology. This new technology replaced the need for mercury cells altogether. From the point of view of mercury, this technology therefore represents a completely clean (i.e. mercury-free) alternative. Of course there are still environmental impacts from the new technology. For instance, its energy requirements generate environmental impact. But the development of membrane cells for the chloralkali industry could certainly be described as an important, innovative technological breakthrough.
Most new chloralkali plants now use membrane technology. On the other hand, there is a capital cost associated with implementing a new technology. And in some countries this presents a very significant barrier to environmental improvement. In the UK, ICI has plans to replace its chloralkali capacity entirely with membrane technology. The same is true in Sweden, where it is now law that all mercury cells must be replaced by the year 2010. But a number of older mercury cell plants are still in operation, some of them with no environmental controls operating at all. At one particular facility in the former Czechoslovakia which I visited during the preparatory work for this book, liquid mercury was sitting in pools on the plant floor, and mercury-contaminated sludges and effluent were regularly dumped into an unprotected local landfill site which was believed to be leaking into local ground-water supplies. There was no real prospect of investment in new technologies at the plant.
Even when capital resources are more plentiful than they are at the moment in Central and Eastern Europe, a wise investor would certainly want to question whether reinvestment in process technology was justified. Amongst the factors that he or she would need to assess in answering this question is (see Box 8) the value of the product or service provided by that process technology. From a preventive perspective, we would also emphasise the need to look upstream and address the source of environmental problems. And the root of the problem lies beyond the technological process. It is to be found in the demand for particular goods and services.
What are the goods and services provided by the chloralkali industry? In this case, there are of course two products: chlorine and sodium hydroxide, each of which supplies a number of different services. Let us just focus for the moment on chlorine.
Chlorine is itself the subject of environmental concerns. A large number of chlorinated products have environmental implications. Chlorinated organic compounds, for instance, are virtually absent from natural material cycles. Many of them are highly toxic to humans, but because of their organic nature are easily assimilated by biological organisms. Some of them metabolise or degrade in the environment in inherently unpredictable ways, and the degradation products are themselves dangerous.
Particular examples of chlorinated organic compounds which have caused environmental concern are: CFCs, used in refrigerators and aerosols and responsible for the destruction of the ozone layer; PCP (penta-chlorinated phenol), used as a preservative in the leather-tanning process but banned in industrial countries because of high levels of contamination in footwear; PCBs (poly-chlorinated biphenyls) used in capacitors and other electrical devices but highly toxic to wildlife, and
implicated in soil and water pollution; insecticides like aldrin and DDT which are now banned in industrial countries because of their toxic properties but still widely used in developing countries; and dioxins, which tend to be formed, for instance, during bleaching processes and when chlorinated organic compounds are incinerated.
In fact, there seem to be so many health and environmental problems associated with chlorine and chlorinated substances that some people have argued for the production of chlorine to be phased out altogether (Plate 4).6 The implications of such a strategy would be quite profound because chlorine is used so widely in the industrial economy. One thing is clear, however: if we are to phase out chlorine use, it makes no sense at all to spend large amounts of money replacing chlorine production capacity. As the economist Herman Daly puts it: 'To do more efficiently that which should not be done in the first place is no cause for rejoicing.' The problem of mercury contamination from the chloralkali industry could be solved more easily by not producing chlorine.
Would it be feasible to phase out chlorine use? What would the implications be for the industrial economy? As you might guess from earlier discussions in this book, it is not so much chlorine itself that we want anyway. Rather we use chlorine and chlorinated products to provide certain kinds of goods and services. In fact, chlorine is such a ubiquitous material in the industrial economy that it is hard to overemphasise the implications of a chlorine ban. As Figure 24 shows, chlorine is widely used as an industrial feedstock in a variety of different sectors. For instance, it is used in the disinfection and sanitation of water supplies, as a bleaching agent in the paper and pulp industry and in domestic products, in the manufacture of plastics, polymers, vinyls, solvents and resins, and in the formulation of a variety of other chemical compounds which have already been mentioned: refrigerants and propellants, insulators, preservatives, and pesticides.
Clearly, some of these uses are more important than others in terms of the service which they provide to society. Phasing out chlorine in one use may not be so drastic in terms of lost service as phasing out chlorine in another use. Alternatives might be found for some uses but not for others. We could only really assess the overall system impacts of a chlorine phase-out by a rather careful analysis on a sector-by-sector basis. Such a level of detail is beyond the scope of this book. But the point is that by looking upstream for solutions to a particular contamination problem we have been led into a complex network of interrelated material flows driven by a variety of different needs and the demand for a number of different services.
As it happens, the problem of reducing emissions of chlorinated organic solvents has been close to the centre of attention in the early pollution prevention initiatives. Because these substances offer both occupational hazards during use and environmental hazards through dispersion and disposal, considerable effort has been put into developing appropriate substitutes for a variety of applications. Substitutes have been developed in the printing industry, for paints and dyes, in the electronics industry and in the chemicals industries.
But organic solvents are only one of the uses to which chlorine is put in the industrial society. Let us look at one of the most important services which chlorine provides—the purification of water supplies. We could not conceive of a chlorine ban without identifying some other suitable means of providing for the decontamination of drinking water. Are there alternatives to chlorine as a water purifier? Can we substitute chlorine-based purification with another process?
In fact, there are other options—the most commonly used alternatives are based on oxygen chemistry rather than chlorine chemistry, and substances such as hydrogen peroxide and sodium percarbonate have been used successfully as bleaches and disinfectants in a number of applications. A different technological route uses ultraviolet light to disinfect and decontaminate water. Before we go into a detailed examination of technological alternatives, however, let us ask another question, a question that takes us even further upstream in the matrix: why do we need water purification services? Could we reduce the need for water decontamination by reducing the contamination of water supplies?
This is a complex question because water contamination is a complex issue. Water supplies become contaminated with many different kinds of substances. Pathogens,7 nutrients, micro-organic chemicals and heavy metals are just a few of the materials which raise health concerns in drinking water. As a water purifier, chlorine is effective mainly in reducing pathogenic contamination—that is, contamination with microorganisms and bacteria. It is of course extremely important that we do reduce this kind of contamination because these are the kinds of organisms that carry communicable diseases such as cholera. So we might assume that water purification is an irreducible need in this context. But two factors obscure a straightforward conclusion.
First, one of the main sources of this kind of contamination in our water supplies is the practice of using water as a sewerage medium. Raw sewage is a major source of pathogenic contamination. Second, levels of pathogenic activity in water are inversely related to oxygen levels in the water. As oxygen levels fall, pathogenic activity is likely to increase. The addition of oxidants (such as chlorine) into the water is what kills off pathogenic activity. But oxygen levels in rivers, lakes, and ground-waters are dependent on a number of factors. As I pointed out in Chapter 1, excess nutrients can lead to growth in the bacterial and protozoan populations and the subsequent depletion of oxygen. In addition, a number of chemical effluents can have the effect of reducing the levels of available oxygen in the receiving water.
From this perspective we can see that some at least of the need for water purification services (such as might be provided by chlorine) is the result of environmental impacts from other economic activities. If there were less contamination of water supplies from anthropogenic sources, the oxygen levels in the water would be higher, and the natural resistance to pathogenic contamination increased.
If we were to seek preventive alternatives to the use of chlorine for water purification, a number of opportunities present themselves. First, of course, we could reduce our reliance on water as a carrying medium for our sewage. The development of low-water sewerage systems would help. These options are really specific examples of improved efficiency— in this case efficiency in the use of water resources. Quite generally, improvements in water efficiency would reduce the demand we make on water supplies, reduce the contamination that inevitably comes from use, increase the time available for natural purification processes to operate, and increase the available supply from which we could choose clean water. In addition, of course, it is clear that by reducing pollution at the source, both in industry and in the households, we would reduce the burden on our water supplies, reduce the need for chlorination, reduce the need for chlorine production, and reduce the environmental impacts of chlorine production—amongst them, possibly, mercury contamination.
Finally, it would be remiss of me to leave this system analysis without commenting briefly on the second co-product of the chloralkali industry: sodium hydroxide. Caustic soda (as it has been known since before the industrial revolution) has a variety of important industrial uses including the manufacture of soaps, artificial fibres, dyes and paper. Phasing out chloralkali production would obviously raise the question of providing an alternative source of caustic soda with which to supply these uses.
In fact, the chloralkali industry is a relatively recent source of caustic soda in the industrial economy (see Chapter 2). Although the electrolytic process was known in the eighteenth century, it was only after 1890 that sodium hydroxide was actually produced in this way for industrial consumption. Instead, caustic soda was usually produced by treating soda ash (sodium carbonate) with lime (calcium hydroxide). It was not until the 1940s that output from the electrolytic process began to exceed the output from the earlier process. Certainly, therefore, there are possibilities for producing caustic soda which do not involve chlorine as a co-product. A more detailed analysis would need to investigate the resource implications of these alternative processes.8 But, once again, the more important avenue for exploration, from a preventive viewpoint, is the service output from caustic soda production. This further level of complexity is beyond the scope of this example.
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