Partial order theory in the assessment of environmental chemicals: formal aspects of a precautionary pre-selection procedure

Man-made chemicals have been shown over recent decades to exhibit unwanted effects on a global scale. The possible occurrence of such global effects have turned out to be difficult to model with traditional assessment procedures. Alternative, non-traditional procedures have been proposed in recent years as a response to this challenge. The present thesis proposes to develop such an alternative assessment procedure, namely one that is based on the concept of exposure (the physical occurrence of a substance in the environment), rather than being based exclusively on known effects (which are inherently difficult to predict). This approach meets a restricted definition of the precautionary principle. Exposure of a chemical is presently modeled with two scenarios, while ensuring that the assessment procedure herein developed can allow for additional scenarios to be taken into consideration at a later stage. The validity of non-traditional assessments that aim at assessing chemical substances beyond known adverse effects is often doubted both inside and outside of the scientific community. In order to respond to these reservations the present thesis establishes a formal setting. As this details each step in the definition of the procedure, this permits a more systematic discussion. It also facilitates the study of the procedure for formal contradictions and helps to contain the use of political input. This setting also allows to develop tools which can be used to decide if the procedure is adequately defined, and consequently to isolate the critical areas in the definition of the procedure if such should emerge. The formal setting is found to be very similar to what is encountered in classical problems of decision making (i.e. in decision theory), such as election problems. Importantly, the present work shows that well-understood results from these related areas can be used due to this kinship. Such results are used in the thesis, and a number of illuminative insights are gained from their application: a number of derivations are made based on these results, which include the fact that the formal setting presently chosen requires the assessment procedure to be calibrated with the help of a reference. The calibration is conducted with the use of information on existing regulatory status of chemicals. In order for the calibration to be performed, a number of mostly technical assumptions are made. It is shown that the assessment procedure is not adequately defined by the formal setting and the (technical) assumptions, if only existing regulatory status is taken as a reference. This demonstrates the importance of the formal setting: the discussion of the procedure within this setting permits to show that the procedure is not suitable (i.e. not adequately defined), a result which would else be difficult to arrive at. The formal frame of the assessment and certain assumptions therein made must be revisited as a consequence of this result. This clearly weakens the procedure from a formal point of view. The necessary adjustments, however, do not appear to be far-fetched and it appears that the definition of an assessment procedure that is based on the concept of exposure (and hence embodies the precautionary principle) can be arrived at by choosing an appropriate formal setting and by using existing regulatory status of reference chemicals for the calibration of the assessment. The results for calibration are critically dependent on stability, and hence cannot be used in a carefree manner: a sensitivity and robustness analysis fortunately shows no major problem with respect to stability. Despite the fact that a suitable procedure can be described, a number of critical areas are isolated, which should draw more attention. These areas concern the technical definition of the threat scenarios, as well as the number of classes that the assessment procedure is required to produce (e.g. ”innocuous”, ”alarming” etc.). In order to demonstrate the resulting assessment procedure, a set of test chemicals is assessed with the procedure in the last part of the present work. It turns out that on one hand a number of brominated and chlorinated chemicals exhibit large environmental threat, whereas on the other hand a number of chemicals that are discussed for global regulation (such as silicones and carbamates) are innocuous with respect to global threat (under consideration of the two scenarios herein used). From a more methodological point of view, the present thesis proposes a novel, simple graphical tool to test the consistency of a procedure with respect to the requirements made to it, and introduces special types of partially ordered sets (weak orders and interval orders) to the assessment of environmental chemicals.