These are the challenging questions underlying all risk assessment analyses of toxic chemical activity, questions such as high dose to low dose interpolation and species to species extrapolation. On screening, a sufficient number of samples taken from the site under investigation will need to be assayed in order to describe 'hot spots' for dioxin contamination. After establishing 'normal' background levels, a decision will need to be made as to what levels constitute significant excess, thus defining 'hot spots'. This type of screening allows not only the setting aside of suspected contamination areas which prove on the contrary to have much lower levels, as well as identification of areas needing more attention. Subsequent efforts and resources can then be focused on areas and samples most in need of attention and possible remediation.
Monitoring refers to the assay of samples before and after treatment or remediation.
In the case of fly ash, attempts are being made to destroy dioxin-like substances during the production process, thus the AhI method can be used to monitor the success of the control program. In the case of soil contaminated areas, there are new methods that are said to have the potential of degrading the dioxin-like substances already present. In both cases, the most important part of the method needing validation is to determine the reliability of getting the same answer on repeat assays of the same sample. Accuracy of measuring the concentration of individual or total congeners is much less important because of the extraordinary variation in the assessment of specific toxicities of individual congeners, especially at levels less than 15 parts per trillion. Whole cell systems are sometimes represented as the next best system when compared with whole body or in vivo systems.