Contaminated Land and Bioremediation
Contaminated land is another example of a widely appreciated, yet often poorly understood, environmental problem, in much the same way as discussed for pollution in the last. That this should be the case is, of course, unsurprising, since the two things are intimately linked, the one being, in essence, simply the manifestation of the other. The importance of land remediation in cleaning up the residual effects of previous human activities on a site lies in two spheres. Firstly, throughout the world, environmental legislation is becoming increasingly strin-gent and the tightening up of the entire regulatory framework has led to both a real drive for compliance and a much greater awareness of liability issues within industry. Secondly, as the pressure grows to redevelop old, unused or derelict so-called ‘brown-field’ sites, rather than develop previously untouched ‘green-field’, the need to remove any legacy of previous occupation is clear. A number of tech-nologies are available to achieve such a clean-up, of which bioremediation, in its many individual forms, is only one. Though it will, of course, provide the main focus of this discussion, it is important to realise that the arguments presented elsewhere in this book regarding the high degree of specificity which governs technology selection within biotechnological applications also appliesbetween alternative solutions. In this way, for some instances of contamination, expressly nonbiological methods of remediation may be indicated as the best practicable environmental option (BPEO). It is impossible to disassociate contextual factors from wider issues entirely. Accordingly, and to establish the relevancy of the wider setting, alternative remediation techniques will be referred to a little later.
The idea of ‘contaminated land’ is something which is readily understood, yet, like pollution, somewhat more difficult to define absolutely. Implicit is the pres-ence of substances which, when present in sufficient quantity or concentration, are likely to cause harm to the environment or human health. Many kinds of sites may give rise to possible contamination concerns, such as asbestos works, chemical works, garages and service stations, gas works, incinerators, iron and steel works, metal fabrication shops, paper mills, tanneries, textile plants, timber treatment plants, railway yards and waste disposal sites. This list is not, of course, exhaustive and it has been estimated that in the UK alone something in the region of 360 000 hectares (900 000 acres) of land may be affected by contamination in one form or another (BioWise 2001). Much of this will, of course, be in prime urban locations, and therefore has the potential to command a high market price, once cleaned up.
Since the whole question of contaminated land increasingly forms the basis of law and various professional codes of practice, there is an obvious need for a more codified, legal definition. The version offered in Section 57 of the UK Environment Act 1995 is a typical example:
any land which appears. . . . .to be in a condition that. . . . .significant harm is being caused or there is a significant possibility of significant harm. . . . (or). . . . .pollution of controlled waters.
In this, harm is expressly defined as to human health, environment, property . As was mentioned earlier, land remediation continues to grow in importance because of pressures on industry and developers. The motive force is, then, a largely commercial one and, consequently, this imposes its own set of conditions and constraints. Much of environmental biotechnology centres on the ‘unwanted’ aspects of human activity and the clean-up of contaminated land is no exception to this general trend. As such, it is motivated by necessity and remedies are normally sought only when and where there is unacceptable risk to human health, the environment and occasionally to other vulnerable targets. In broad terms it is possible to view the driving forces on remediation as characterised by a need to limit present or future liability, increase a site’s value, ease the way for a sale or transfer, comply with legislative, licensing or planning requirements, or to bolster corporate image or public relations. Generally, one or more of these have to be present before remediation happens.
Having established the need for treatment, the actual remedies to be employed will be based on a realistic set of priorities and will be related to the risk posed. This, of course, will require adequate investigation and risk assessment to deter-mine. It is also important to remember in this context that, since the move to remediate is essentially commercial, only land for which remediation is either necessary or worthwhile will tend to be treated and then to a level which either makes it suitable for its intended use or brings it to a condition which no longer poses an unacceptable risk.
It should be apparent, then, from the preceding discussion that the economics of remediation and the effective use of resources are key factors in the whole contaminated land issue. Hence, in purely economic terms, remediation will only take place when one or more of the driving forces becomes sufficiently com-pelling to make it unavoidable. It will also tend towards the minimum acceptable standard necessary to achieve the required clean-up. This is not an example of industrial self-interest at its worst, but rather the exercise of responsible manage-ment, since resources for remediation are typically limited and so their effective use is of great importance. To ‘over’ remediate any one given site could seriously compromise a company’s ability to channel sufficient funds to deal with others. The goal of treating land is to make it suitable for a particular purpose or so that it no longer poses unacceptable risk and, once the relevant aim has been achieved, further treatment is typically not a good use of these resources. Gen-erally it would be judged better to devote them to cleaning up other sites, which maximises the potential reuse of former industrial land thereby protecting urban open spaces and the countryside from development pressure. In the long term, the sustainable use of land largely depends on making sure that it is maintained at a level which enables its continued best use for its current or intended pur-pose. In this respect, discussions of absolute quality become less relevant than a consideration of minimum acceptable standards.
The choice of method and the determination of the final remediation standard will always be chiefly governed by site-specific factors including intended use, local conditions and sensitivities, potential risk and available timeframe. For this reason, it is appropriate to take a brief overview of the available technologies at this point, to set the backdrop for the discussions of the specifically biotechno-logical methods to come.
The currently available processes for soil remediation can be divided into five generalised categories:
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