Components of an Exposure Assessment

The exposure assessment can be described by the following four steps. 

In tliis step, the assessor cluiractcrizes Uie exposure setUng wiUi respect to Uie general physical characteristics of Uie site and Uie cliaracterizations of the 

Sources of tliis information include site descriptions mid data from the preliminary assessment (PA), site inspection (SI), and remedial investigation (RI) reports. Other sources include local soil sur eys, wetland maps, aerial photographs, and reports by the National Oceanograpliic and Atmospheric Association (NOAA) and tlie U.S. Geological Sur ey (USGS). One cmi also consult with appropriate tecluiical e.xperts (e.g., hydrogeologists, air modelers) as needed to cluuacterize tlie site. 

transported (e.g., convected downstream in water or onto suspended sediment or tlwough the atmosphere) 

chemically transformed (e.g., photolysis, hydrolysis, oxidation, reduction, etc.)  

In tills step, the assessor cluuacterizes tlie exposure setting witli respect to tlie general physical characteristics of tlie site and tlie cliaracterizations of the 

In tliis step, tlie exposure assessor identifies tliose patliways by ihich the previously identified populations may be exposed. Each exposure pathway describes a unique niechanisni by which a population may be exposed to the chemical at or originating from tlie site. E. posure patliways are identified based on consideration of the sources, releases, types, and location of chemicals at the site, the likely environmental fate (including persistence, partitioning, tnuisport, and intermedia transfer) of tliese chemicals, and the location and acti ities of the potentially exposed populations. Exposure points (points of potential contact with the chemical) and routes of e.xposure (e.g., ingestion, iiilialation) are identified for each exposure patliway. 

In this step, the assessor characterizes die e.xposure setting widi respect to die general physical clianicteristics of die site and die characterizations of the 

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It is important to note that it is not always necessary for all data for, and thus all components of, an exposure assessment to be of uniform quality, as defined by the four hallmarks. Often the magnitude and uncertainty of predicted exposure may be strongly determined by a small number of assessment inputs and be relatively insensitive to others. If it is concluded that the quality of an assessment needs to be improved, it is usually efficient to target efforts towards the data inputs that contribute most to the uncertainty of the output (presuming that uncertainty in this input can be reduced). However, a high level of transparency in discussion of key inputs is always desirable, such that an accurate assessment of uncertainty associated with each input can be made. 

This process measures the intensity, frequency, and duration of exposure to an agent. More precisely, it evaluates the potential exposure to each chemical of concern by the potential receptor populations or indicator species that are biotic components of any ecosystems in the site which may be affected. Two important components of an exposure assessment are (a) an exposure pathway analysis, and (b) the estimation of exposure point concentrations. To evaluate potential exposures, one requires concentrations of the chemicals of concern in the exposure media (e.g., surface water or sediments). 

There are many parameters and factors that are components of an exposure assessment. Where there is lack of adequate information on any of these parameters and factors, default assumptions are used. However, some of these parameters and factors (e.g., body weight, exposure frequency, and duration) can be represented by a range of values. If these uncertainties are not reduced, a highly conservative risk may result. 

Risk assessment An empirically based paradigm that estimates the risk of adverse effects) from exposure of an individual or population to a chemical, physical or biological agent. It includes the components of hazard identification, assessment of dose-response relationships, exposure assessment and risk characterization. 

Exposure of an organism to a surfactant in surface water will depend on the amount of material used, disposal practice, removal rate during sewage treatment, dilution in the receiving stream, and sorption on particles or aquatic dissolved organic carbon. The exposure component of an environmental hazard assessment utilizes information from the fate studies described in the previous section, mathematical modeling to predict environmental concentrations, and environmental monitoring to verify model predictions. 

Identifying dose-response relationships is an important component of any risk assessment. This process establishes the exposure levels that produce effects, as well as those that produce no effects. As noted in Box 2, it is important to characterize what data were used, what model was employed to develop the dose-response curve(s), and whether chemical-specific information is available to support the observed dose-response relationship. While the risk assessment paradigm shown in Figure 21 separates hazard... 

As a first step in the risk assessment of chemicals, it is essential to have an insight into the magnitude and duration of exposure. Following the toxicological principle that dose determines the effect, one may assume that no exposure means no risk. In the case of chemical mixtures, a proper assessment of exposure assists in adequately interpreting the interacting effects of chemicals. So, exposure assessment is an essential component of any risk assessment study of mixtures, since it can be used to reduce uncertainty and provide data. 

Exposure assessment The component of an ecological risk assessment that estimates the exposure resulting from a release or occurrence in a medium of a chemical, physical, or biological agent. It includes estimation of transport, fate, and uptake. 

The exposure from each of the routes of exposure (drinking water ingestion, dietary consumption and herbicide handling by workers) is described by an equation in the atrazine and simazine assessment. Some of the components of these equations have values that are variable (e.g. from individual to individual, from one year to the next, from one serving of a specific food to another serving, and from one handling of a herbicide to another handling). These variable components of the exposure equations are described by probability distributions that reflect the relative frequency of the different values for the variable. 

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... 

Research is needed to explore the impacts of nanomaterials and nanomaterial production on the environment and public health. One framework for assessing these impacts is that of comparative risk assessment. Applied to an assessment of the production, use, and disposal of nanomaterials, a risk assessment typically considers both the potential for exposure to a given material and (once exposed) potential impacts such as toxicity or mutagenicity. The need to elucidate both of these components of risk in assessing the consequences of nanomaterials on the environment and public health is essential. 

Perhaps the easiest definition of ecological risk assessment is the probability of an effect occurring to an ecological system. Note that the word "probability" is key here. Important components of a risk assessment are the estimations of hazard and exposure due to a stressor. 

A particularly important component of the risk assessment concerns the assumptions and data used to develop an estimate of human exposure - the human dose. Elements of the dosimetry problem were described in Chapter 2 and we do not intend to go into them in more detail here. Certain additional aspects of this issue should be brought out, however, because they critically affect the meaning that is to be attached to the risk estimates produced under the regulatory principles. 

While risk assessment in the context of protecting public health has been performed for many years, it is the 1983 U.S. National Academy of Sciences Report (Committee on the Institutional Means for Assessment of Risks to Public Health Commission on Life Sciences National Research Council 1983) that has served as the tenet for practicing risk assessors (see Chapter 1). Risk assessment was defined as the characterization of the potential adverse health effects of human exposures to environmental hazards. The predictive aspect of risk assessment was set by the use of the word potential. A fundamental expectation of the risk assessment process was that it should attempt to accm-ately predict adverse effects before there is evidence of disease in the population. Thus, risk assessment goes beyond the mere description of epidemiological and clinical case-control studies. In that report, the committee defined logical components of a risk assessment which still serve as guiding principles today. They were and are (a) hazard assessment or the qualitative determination that a stressor poses a hazard as evidence by causal evidence of an ill effect,... 

The migration and fate of contaminants in each transport pathway can be simulated using MEPAS components. The transport pathways are systematically integrated with an exposure assessment component that considers the type, time, and duration of exposure and the location and size of the population exposed. These various pathways and their interactions as considered by MEPAS are discussed in Droppo et al. (5). 

Thus, the distinction between the hazard (an inherent toxic property of a chemical that may or may not be manifested, depending on exposure potential) and risk (the consequences of being exposed to a hazardous chemical at a particular exposure level) is critical (Purchase, 2000). Each component of a risk assessment—hazard identification, dose-response evaluation, and exposure assessment—is essential for evaluating the potential risks associated with the use of a substance such as a nanomaterial. The components of a risk assessment are universal in their application for assessing the hazards and risks of chemicals or products for a variety of industries or environmental exposures, regardless of the types of chemicals of interest (such as solvents, fibers, particulates and nanomaterials). 

There were actirally three different components to the study a cross-sectional component an historical cohort component and a prospective component. Central to each of these studies was an exposure assessment. [ This expostrre assessment categorized the study subjects into related exposure groups and assigned them a relative ranking (i. e., high exposure, low exposure, etc.). 

This is the component of a risk assessment where risks are estimated by combining exposure and toxicity information for the chemicals at a site. There is an important distinction between cancer and non-cancer chemicals in this step. These two types of effects are separately discussed below. 

The component of an ecological risk assessment in which exposure is evaluated. This is parallel to the exposure assessment component of a human health risk assessment. 

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