Risk Evaluation in Regulatory Toxicology
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Risk evaluation is the step within the risk analysis process that links risk assessment (the final step of which is risk characterization) with risk management. This intermediary step is mostly not explicitly mentioned, or it is seen as a preliminary step in risk management. The goal of risk evaluation is to link exposure levels with corresponding risks and to identify sources of uncertainty in the scientific data used.
KeywordsRisk acceptance Risk assessment Risk evaluation Risk-management options Risk perception Socio-economic considerations
Based on the outcome(s) of the risk assessment, options for risk management need to be developed and evaluated for the decision-making process. Risk management covers all actions and decisions as to whether or not, and, if yes, how certain risks should be eliminated or reduced. Options and strategies developed for their possible implementation can be of regulatory, economic, informational, or technological nature. They need not to be mutually exclusive. In order to reach adequate and rational decisions, a risk must be seen in the context of other risks and evaluated considering various different factors.
Good risk management decisions should follow certain principles. Thus, the problem must be discussed within its health or ecological context and should consider the views of all those who would be affected by possible decisions. Such decisions must be based on a balanced scientific assessment and build on a full analysis of different regulatory and nonregulatory options for action. They must lead to a reduction or an elimination of the risk under consideration and be implementable in a rapid and efficient manner and with the support of all relevant stakeholders. Actions must, indeed, be proven to affect the risk to be minimized or eliminated. They should offer the possibility for being revised or changed if new information becomes available that would justify it.
Elements of Risk Evaluation
Context of the Risk Problem
A risk cannot be evaluated in an isolated manner. Often, a risk factor, for example, a chemical substance, has several sources that contribute to the overall exposure. In such cases the risk should be evaluated within the “multiple source context.” The risk evaluation must consider the contribution by each of these sources to the overall exposure in order to permit the development of effective risk management options that will, indeed, reduce the risk. The question here is mostly about the point of intervention that would achieve the most effective protection.
An exposure to the same risk factor could occur through different environmental media (e.g., air, water, drinking water). One example is lead. Human exposure is via air (inhalation; the main sources here are car exhaust emissions if lead-containing petrol is used, lead-containing paint, and various industrial processes), via drinking water (ingestion, e.g., in the case of lead water pipes), via food (ingestion, mainly through the use of lead-containing food cans), as well as via direct exposure through the use of lead-containing cosmetics (e.g., dermal exposure). A risk evaluation must therefore also consider exposure through all relevant environmental media (“multimedia context”).
The source of one risk factor might also release other substances that may pose an additional risk. Dioxins, for example, are encountered as food contaminants (e.g., in fish), often in combination with, inter alia, polychlorinated biphenyls, and methyl mercury. The three compounds have all neurotoxic effects among other toxic actions. The combined effects must be considered jointly. In such cases, individual compounds should not be evaluated independently from accompanying exposures (“multifactor context”).
Finally, a risk must be evaluated in comparison to other risks in the same group of population. This is important in order to set priorities for action and to initiate actions which are most urgently needed first (“multiple risk context”).
The decision as to whether or not a risk is acceptable requires a judgment in the context of social, political, and economic aspects. Of special importance to the risk evaluation is the way society judges the particular risk under consideration and to what extent certain exposures would be tolerated. Risk acceptance depends to a large extent on the perception of risk. Risks are not always seen by the public in scientific terms but often also based on qualitative perception. Thus, risks are accepted if they are common and known, if they are easy to control, if their mode of action is known, if the exposure is voluntary, if the effects are immediately seen and do not affect future generations, and if potential effects are reversible and/or are not of catastrophic nature. Trust in responsible institutions, lack of media interest, and clearly visible economic benefits also increase risk acceptance. In general, risks are more accepted if they are easy to see and their control appears to be easily accessible. Thus, the risk of a nuclear reactor accident is judged to be higher than that of a motorcycle accident or that of smoking. Aspects of risk acceptance must therefore be clearly delineated and fully considered in risk evaluation. Risk comparisons may help in providing an objective view in this context.
Socio-economic analysis is a well-established method of weighing up the pros and cons of an action for society as a whole and need to contain a description of the risks as well as information on the health and environmental benefits, the associated costs, and other socio-economic impacts. In asocio-economic analysis, one needs to analyze and document whether the socio-economic benefits of continued use of the substance outweigh the risks of continued use for human health and the environment.
An economic valuation provides important information for risk management. Economic considerations should therefore form an integral part of risk evaluation, including potential benefits which would be brought about through an improved health and environmental protection. In particular, two aspects should be looked at. The cost-benefit analysis considers economic and/or social gains emanating from a risk-producing process in comparison to its costs, which should also include those costs related to eventual damages to human health and environmental integrity. The cost-effectiveness analysis, in contrast, evaluates rather the “efficiency of a certain intervention” (e.g., a regulatory measure or a technological evaluation) in controlling a certain risk. Here, the expected economic and/or social benefit due to a certain proposed measure is quantified and compared to the cost caused by such a measure. In both processes, the quantification of positive and negative effects on human health and the environment in economic/monetary terms is a major problem.
Risk management decisions are political in nature. Therefore, options developed in risk evaluation need to reflect social and political considerations. Among the questions to be addressed, the issue of other risks that occur concomitantly and need also to be managed figures prominently. In this context, different risks are evaluated in a comparative manner, and a rational weighting is performed. Often, it is necessary to assess which risks should be given priority in reaching risk management decisions and which can be addressed at a later stage, since it is difficult, if not impossible, to address all risk factors at the same time. This process of comparing risks and weighing risk management options is defined as “risk balancing.”
Sometimes, an action taken to control a given risk factor may lead to the appearance of new risks to health and/or the environment. Replacement of a chemical in a technological process with another, for example, can produce new risks. A practical example would be to abandon the disinfection of drinking water to avoid the risk due to chlorination by-products: the expected reduction of the health risks due to chlorinated organic compounds in drinking water would be linked to a significant increase in the risk of waterborne infectious diseases. Considerations of this kind fall under the term “risk-risk tradeoffs.” The main question to be addressed here is: “which risks do we take if we control another through certain measures?”
Another aspect of sociopolitical and ethical nature is that of “environmental equity.” In this context, considerations are made as to whether or not the population group(s) that benefits from a certain activity is the same as those who carry the risk. The aim is to avoid situations where a group carries all (or the larger part) of risk, without profiting from the risk-producing process, and that all benefits come to another group that carries no or a substantively lower part of the risk.
Uncertainty and Variability: Scientific and Economic Aspects
Since risk evaluation is an intermediary step linking risk characterization with risk management, uncertainty and variability issues that emerged and were discussed in risk characterization must also be fully considered when developing options to minimize or eliminate risks. Problems that could be of relevance at this step could target scientific or economic aspects. Examples of scientific issues include the relevance of toxicological studies under real-life conditions (risk prediction), the possibility to detect and consider differences in susceptibility among exposed populations, as well as the identification of highly exposed groups. In addition, questions concerning realistic exposure scenarios and on interactions between different risk factors may be of relevance. Economic problems include the difficulty of quantifying health and environmental aspects from an economic point of view. Other issues target the inconsistency of economic analyses and the uncertainties connected with it, as well as the inadequacy of methods to validate the advantages of potential risk management actions for human health and the environment.
Aspects described in this chapter are within the context of evaluating a given risk in the context of other risks and with consideration given to risk acceptance, as well as political and economic factors. Such considerations constitute a judgment of the characterized risk in connection with the development of control options as a prerequisite for managing the risk. Risk evaluation, thus, has a bridging function between the pure science and the political decision-making process. Even though this step is not explicitly included as a separate process in the usual risk assessment and risk management paradigms, risk evaluation is an important basis for decisions. Modern approaches to risk analysis, such as the one proposed by the US National Research Council in 2009, promote a more integrated approach to risk assessment and management, during which questions related to risk evaluation are addressed from start (problem formulation) to end (risk management), ensuring stakeholder involvement and risk communication throughout.
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