ABSTRACT
It is necessary to determine which chemicals are present and in what amounts. This process may involve soil sampling, air monitoring, and tests on water and foliage. The nature of the chemicals must be considered. Some chemicals such as polychlorinated biphenyls (PCB) are persistent - this quality which makes them so useful to industry makes them extremely toxic (they are not broken down so they accumulate). The difficulty is isolating the toxins, as many chemicals may be present. In the case of airborne emissions, chemicals may combine with backround pollution to give higher concentrations.
