Risk Characterization General Aspects

In the risk characterization step, the health risk likely to occur in a given human population due to actual or predicted exposure to the particular chemical under evaluation is evaluated, and all the assumptions, uncertainties, and scientific judgments from the preceding three steps are considered. 

Toxicological Risk Assessments of Chemicals A Practical Guide 

Risk characterization is thus the step in the risk assessment process where the outcome of the exposure assessment (e.g., daily intake via food and drinking water, or via inhalation of airborne substances) and the hazard (effects) assessment (e.g., NOAEL and tolerable intake) are compared. If possible, an uncertainty analysis should be carried out, which produces an estimation of the risk. Several questions should be answered before comparison of hazard and exposure is made  

Exposure of the general population to chemicals present in the environment is an example of long-term exposure on a local or regional spatial scale. The general population is mainly exposed to environmental chemicals via oral exposure through food and drinking water and via inhalation from ambient and indoor air. The total body burden can, e.g., be expressed as a total oral intake (the outcome of the exposure assessment). This intake should be compared with a POD derived from preferably long-term studies or at least subchronic studies (outcome of the hazard (effects) assessment). 

The most frequently used POD for threshold effects (Section 4.2) is the NOAEL (Section 4.2.4). This NOAEL is generally obtained from studies in experimental animals. If reliable human data are available to derive the NOAEL, this value is preferable to the NOAEL from experimental animals. Where a NOAEL cannot be derived, a LOAEL, if available, can be used. An alternative POD to the NOAEL/LOAEL is the benchmark dose (BMD) (Section 4.2.5). The tolerable intake can also, in some cases, form the basis as the POD. In this chapter, the POD will be denoted as a derived no-effect level (DNEL) in order to provide a general term for the various types of PODs that can form the basis for the risk characterization. 

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Euras. 2006. Fact sheet 3 risk characterization, general aspects. MERAG program-building block, risk assessment, Annex 1, added versus total risk approach and its use in risk assessment and/or environmental quality setting. 

The process of risk characterization has been described and discussed extensively in the scientific literature. It is beyond the scope of this book to review aU these references. This chapter is limited to give a very short overview of some general aspects related to the risk characterization process, as well as of the currently used approaches in the WHO, the US-EPA, and the EU, and is thus not meant to be exhaustive. 

Part III deals with secondary reactions, their characterization, and techniques to avoid triggering them. Chapter 11 reviews the general aspects of secondary reactions, determination of the consequences of loss of control and the risk assessment. Chapter 12 is dedicated to the important category of self-accelerating reactions, their characteristics, and techniques allowing their control. The problem of heat confinement, in situations where heat transfer is reduced, is studied in Chapter 13. The different industrial situations where heat confinement may occur are reviewed and a systematic procedure for their assessment is presented together with techniques that may be used for the design of safe processes. 

Risk management is the part of the process where characterized risks are evaluated against options to reduce or avoid them. In general, aspects other than science (for instance cost, social responsibility, and (consumer) risk perception) are taken into account here. 

It is good to realize that the problem domains as defined above are generally characterized by a great complexity with regard to the composition of the samples. Moreover, very often the samples will contain not only dissolved material but also solid particles may be present with inherent risks of clogging of the analyzing equipment, etc. Dissolved gas may also cause problems, especially when the sample is heated and gas-bubble formation may occur. These problems may require special precautions to be taken in combination with pTAS such as filtration and degassing of the solutions. However, there are many more aspects to be considered which can be better discussed for the various domains separately. 

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