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There are literally thousands of chemicals and substances that can be found associated with contaminated land. The key factor is use risk assessment to isolate those that are most likely to cause future problems.
Asbestos is very dangerous if present in the form of airborne particles as these can lodge in the lungs and give rise to cancer.
However if the asbestos is in the form of an asbestos tile (where it is in a matrix of concrete) then the risk is dramatically reduced as the asbestos is in effect “locked up”.
This effect can also occur in contaminated ground, where the geological regime is such that the pH (a measure of acidity) can effectively lock-up the normally mobile ons.
For example Heavy Metals, such as Cadium, tend to be very mobile at low pH – under acid conditions, but at high pH – under alkaline conditions (chalk, limestone etc) they do not pose a significant problem.
In general the following criteria are used to judge whether substances have the potential to cause problems with regard to contamination.
- Having a significant toxicity on humans
- Having a significant toxicity on the aquatic environment
- Having a significant toxicity on the ecosystem
- Having a significant effect on materials and structures used on sites
- Having a significant persistence in soil or a tendancy to bioaccumulate
- Being likely to occur in significant concentrations on many sites.
It appears that there are in the order of 100 substances that fall under this category as being significant with respect to contaminated land evaluation and remediation. Within the “hard-green” members of the European Community that have a history of heavy industrialisation (Holland and Germany in particular) the numbers are comparable.
However in view of the complications caused by differences in geology (on a regional scale), and in-site variations (on a local level), the current difficulty is to adequately define acceptable levels of risk, that can in turn be quantified in the form of a numerical guidelines as to an acceptable level of contamination.
Individual site variations can affect chemical and physical properties, and substances themselves can interact to increase or even reduce risk.
In general there are two approaches to classifying substances that can give rise to contamination, either by physical characteristics caused by past industrial usage (eg. gas works), or by chemical categorisation based on generic sub-groups (eg. heavy metals).