Risk Characterization Currently Used Approaches

This section gives a short overview of the currently used risk characterization approaches in the WHO, the US-EPA, and the EU. 

The WHO and its bodies, e.g., IPCS, JECEA, and JMPR, are primarily involved in standard settings rather than risk characterization in its strict meaning, i.e., comparing the outcome of the hazard (effects) assessment and the outcome of the exposure assessment. 

Examples of standard settings developed by the WHO include air quality guidelines (Section 9.2.1.1) and drinking water guidelines (Section 9.2.1.2), and (in collaboration with the FAO) maximum residue limits (MRLs) for pesticides and veterinary drugs and maximum levels for food additives (Section 9.2.1.3). 

In 1995, the US-EPA updated and issued the current Agency-wide Risk Characterization Policy (US-EPA 1995). The Policy called for all risk assessments performed at US-EPA to include a risk characterization to ensure that the risk assessment process is transparent. It also emphasized that risk assessments should be clear, reasonable, and consistent with other risk assessments of similar scope prepared by programs across the Agency. 

The US-EPA s Risk Characterization Handbook (US-EPA 2000) was developed to implement the Risk Characterization Policy. This Handbook provides a single, centralized body of risk characterization implementation guidance for the US-EPA s risk assessors and risk managers to help make the risk characterization process Transparent and the risk characterization products. Clear, Consistent, and Reasonable (TCCR). TCCR became the underlying principle for a good risk characterization. The Handbook has two parts. 

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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. 

Some aspects of degree of concern currently can be considered in a quantitative evaluation. For example, EPA considers human and animal data in the process of calculating the RfD, and these data are used as the critical effect when they indicate that developmental effects are the most sensitive endpoints. When a complete database is not available, a database UF is recommended to account for inadequate or missing data. The dose-response nature of the data is considered to an extent in the RfD process, especially when the BMD approach is used to model data and to estimate a low level of response however, there is no approach for including concerns about the slope of the dose-response curve. Because concerns about the slope of the dose-response curve are related to some extent to human exposure estimates, this issue must be considered in risk characterization. (If the MOE is small and the slope of the dose-response curve is very steep, there could be residual uncertainties that must be dealt with to account for the concern that even a small increase in exposure could result in a marked increase in response.) On the other hand, a very shallow slope could be a concern even with a large MOE, because definition of the true biological threshold will be more difficult and an additional factor might be needed to ensure that the RfD is below that threshold. 

The approach to exposure assessment is not as internationally harmonized as hazard assessment. A synopsis of current activities regarding exposure assessment for industrial chemicals in a number of OECD Member countries has been published (OECD 2006). The executive summary of this document states that while there is a significant level of sharing of approaches used for hazard characterization for risk assessment, this is not the case for exposure characterization. Although broad consistency in the overall approaches used by different countries in conducting exposure assessment exists, there is variation in policy-related factors, including the regulatory context for assessment and the way that information is applied, as well as in the types of approaches and tools used. 

The National Research Council (NRC) published a report, Science and Judgment in Risk Assessment, that critiqued the current approaches to characterizing human cancer risks from exposure to chemicals. One issue raised in the report relates to the use of default options for assessing of cancer risks. These general guidelines can be used for risk assessment when specific information about a chemical is absent. Research on 1,3-butadiene indicates that two default options may no longer be tenable Humans are as sensitive as the most sensitive animal species and the rate of metabolism is a function of body surface area rather than inherent species differences in metabolic capacity. 

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