Health risk assessment exposure characterizations

Human health risk assessment has often been dominated by the use of default assumptions and worst case analyses, based on the use of upper bounds on the dose from exposure instead of distributional characterizations of that dose. There are severe limitations associated with the use of default assumptions and upper bounds instead of distributions when detailed exposure and/or dose-response data are available. The US National Academy of Sciences, the USEPA, and many others have recognized the need for new risk assessment methodology (NRC, 1983, 1993, 1994 USEPA, 1992 CRARM, 1997). This need has promoted the development of new quantitative risk assessment methods that use probabilistic techniques, especially Monte Carlo simulation and distributional characterizations of dose-response, exposure, and risk. For these reasons, this paper uses a probabilistic approach. An indication of some of these new methods and the type of results they produce are given below. 

Risk assessment is an empirically based process that estimates the risk of adverse health effects from exposure of an individual or population to a chemical, physical, or biological agent or property. The health risk assessment process involves the following steps hazard identification, effects assessment (dose-response assessment), exposure assessment, and risk characterization (Van Leeuwen and Vermeire 2007). 

The exposure assessment characterizes the pathways, magnitude, frequency, and duration of human exposures from various sources. Chapter 5 provides an overview of these components and addresses the principles of exposure assessment in children. General principles of exposure assessment have been reviewed in a number of publications (USEPA, 1992a, 2005a IPCS, 1999a, 2000 Needham et al., 2005). This chapter will focus on the considerations that are important when applying the exposure data to a children s health risk assessment (see Box 2). 

Health risk assessment is defined as tlie process or procedure used to estimate tlie likelihood that humans or ecological systems will be adversely affected by a chemical or physical agent under a specific set of conditions. Tlie health risk evaluation process consists of four steps hazard identification, dose-response assessment or liazard assessment, exposure assessment, and risk characterization. 

Human health risk assessments with chemicals and other agents (biological, physical) typically follow a paradigm that involves four steps - hazard identification, dose-response assessment, exposure assessment, and risk characterization. The process was recommended by the US National Research Council in the 1980s, and is usually applied to a single agent and exposures associated with one or more routes (oral, dermal, inhalation). This has been more recently referred to as aggregate exposure and risk assessment. 

Being able to predict the human health risk from exposure to airborne chemicals can be complex, requiring reliable analysis of human exposure. While the basic principles of risk assessment are applicable to various conditions of exposure, characterizing how an individual s health status can significantly influence the threshold for effects can be a most challenging component of the risk assessment process. One needs to consider the overall scientific weight-of-evidence to predict whether or not an individual may be uniquely susceptible to certain... 

Risk assessment is a process where the magnitude of a specific risk is characterized so that decision-makers can conclude whether the potential hazard is sufficiently great that it needs to be managed or regulated, reduced or removed. The National Research Council (NRC, 1983) of the National Academy of Sciences (NAS) first described the process of human health risk assessment, with an update in 1994 and 1996, as a four-component paradigm (i.e., hazard identification, dose-response assessment, exposure assessment, and risk characterization), with risk communication as a fifth area of study. The first four components are described briefly below. 

Some reviewers of earlier drafts of this interim framework proposed that the term "exposure" — which, as used in human health risk assessment, generally refers to chemical stressors — not be used for the nonchemical stressors that can affect a variety of ecological components. Other terms, including "characterization of stress," have been suggested. At this time, EPA prefers exposure, partly because characterization of stress does not convey the important concept of the co-occurrence and interaction of the stressor with an ecological component as well as exposure does. 

The four major steps in a health risk assessment are hazard identification, dose-response assessment, exposure assessment, and risk characterization. 

As discussed in the previous problem set, the four major steps in a health risk assessment are hazard identification, dose-response assessment, exposure assessment, and risk characterization. A health risk assessment initially involves the identification of human health effects attributed to exposure to a chemical, usually on a continuous basis. A dose-response assessment determines how different levels of exposure to a hazard or pollutant affect the likelihood or severity of the health effects. An exposure assessment determines the extent of human exposure. These are combined to provide a risk characterization value. 

Health risk assessment has 4 major components hazard identiHcation dose-response assessment exposure assessment and, risk characterization. 

Health risk assessments for sites contaminated with chemical warfare agents require a comparison of the potential levels of exposure with a characterization of the toxic potency of each chemical. For noncancer health effects, toxic potency is expressed in terms of Reference Doses (RfD). 

CHPPM (2000) Depleted uranium - Human exposure assessment and health risk characterization in support of the environmental exposure. Report Depleted Uranium in the Gulf (II) Health risk assessment consultation No. 26-MF-7555-99D. OSAGWI, Washington, DC... 

Risk characterization Comparison of exposure levels to acceptable levels to determine whether potential risk is tolerable. Iri a human health risk assessment (using the terminology common in the European Union), the estimated exposure level is compared to the lowest DNEL/DMEL value for that exposure pattern to determine the RCR in an ecological risk assessment, the PEC is compared to the PNEC. 

Risk assessment in human populations is broadly defined within the vocabulary of the National Academy of Science/National Research Council (NAS/ NRC) (1983) monograph on the topic as [quantitative] characterization of the potential adverse health effects from quantified exposures of humans to environmental hazards. In keeping with the NRC report s use of the term, both qualitative and quantitative risk assessments are considered when dealing with lead contamination and adverse effects in this text, although the most useful information emerged when empirical determination or modeling estimations produced a numerical outcome. Part 4 (Chapters 20—24) of this monograph presents the topic of human health risk assessment in detail. 

Part 4 continues with lead-specific discussions of the four components of a human health risk assessment as structurally articulated in 1983 by the NAS/NRC (1983) Chapter 21, human health hazard characterization for lead and diverse human populations Chapter 22, dose—toxic response relationships for lead in humans Chapter 23, illustrative uses of case- or setting-specific lead exposure characterizations and. Chapter 24, the last part of health risk assessment, the overall final and most quantitative step in actualizing (in a relative sense) the estimates of risk outcomes. 

This chapter s characterization of lead as a neurotoxic hazard does not include detailed dose—response relationships with various levels of biomarkers such as PbB linked to various neurotoxic outcomes. The topics of dose/ exposure metrics and defining full-spectrum dose—response relationships are presented in the next part, the section dealing with the elements of human health risk assessment for environmental lead. Here, for ease of discussion, only a broad yardstick is provided for toxic lead exposures. Specifically, general PbB ranges associated with the various categories of lead neurotoxicity, especially in children, are noted. 

The second element of health risk assessment for lead is the identification of dose—response relationships for the various adverse health effects noted in the previous chapter. Dose—response relationships, like health hazard characterizations, are general in nature and independent of site-specific lead exposure scenarios. 

As in a human health risk assessment, an ecological risk assessment concludes with a narrative characterization of risk (Figure 9.1). The evidence marshaled in the exposure and effect analyses provides the basis for estimating the risk to the ecological value identified in the management goal. The risk estimate includes quantitative... 

There are two components to the analysis phase characterization of exposure and characterization of effects. Overall, this phase is similar to the exposure and toxicity assessment components of a human health risk assessment. The primary differences relate to the variety of ways in which exposure and toxicity can be measured in an ecological risk assessment. 

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