Exposure assessments site-specific characterizations

A risk assessment is defined as a qualitative and quantitative process conducted by EPA to characterize the nature and magnitude of risks to public health from exposure to hazardous substances, pollutants, or contaminants released from specific sites. Risk assessments include the following components hazard identification, dose-response assessment, exposure assessment, and risk characterization. Statistical and biological models are used in quantitative risk... 

Although the Hazard Identification and Dose-Response Assessment of an agent are generic, the risks that the agent poses are specific to a particular location and set of circumstances in which exposure to the agent occurs. In order to assess site-specific risks of an agent, the assessor must perform a specific Exposure Evaluation for the site, and combine it with information on the Hazards posed by the agent to yield a Risk Characterization for the site. 

Population Characterization. An important part of any exposure assessment is the development of a detailed and up-to-date human demographic data base for the area being studied. These data can provide the basis for estimates of subpopulations associated with different exposure pathways. In national exposure assessments it is common to use an average population density for the total U.S. or to simply distinguish between rural and urban densitites. In a geographic exposure assessment in which site-specific data on pollutant releases, environmental fate and ambient levels are measured or estimated, it is important to have equally detailed population data. Population breakdowns by age, sex, housing and... 

The extrapolation methods related to differences in media and matrices are mainly governed by sorption processes. Therefore, uncertainty analysis should try to address toxicant properties related to sorption (KD, A"ow, Ka, etc.) and matrix-specific characterization of sorption sites (qualitative and quantitative). Some of the computerized models for exposure and effects assessment explicitly include options for treating key variables as probability distributions (e.g., AQUATOX). 

The first phase of the framework is problem formulation. Problem formulation includes a preliminary characterization of exposure and effects, as well as examination of scientific data and data needs, policy and regulatory issues, and site-specific factors to define the feasibility, scope, and objectives for the ecological risk assessment. The level of detail and the information that will be needed to complete the assessment also are determined. This systematic planning phase is proposed because ecological risk assessments often address the... 

EPA risk assessment practice, (and the Risk Assistant software) reflects this distinction between generic and site-specific information in the prediction of the risks associated with an agent at a specific site. The results of authoritative Hazard Identifications and Dose-Response Assessments are not expected to be re-evaluated by the risk assessors evaluating specific sites these assessors are expected to concentrate on site-specific Exposure Evaluation and Risk Characterization. 

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. 

Part 2 and its chapters presented the topic of human lead exposure in global and categorical terms, addressing the technical areas of lead intakes, uptakes (absorption), toxicokinetics, integration of toxicokinetics into in vivo disposition in a manner allowing quantitative assessments of lead exposure, etc. In contrast to these broadly descriptive aspects of human Pb exposme, the applied health discipline of quantitative risk assessment requires prescriptive approaches for site-specific, case-specific, and environmental scenario-specific lead exposure characterizations. Data from such specific exposure characterizations are combined with available data for lead dose—response relationships to arrive at some quantitative risk characterization indexed as some endpoint for human health risk. 

ATSDR health assessments are based on environmental characterization information, community health concerns, and health outcome data. Because of the nature of these databases, health assessments use quantitative as well as qualitative data, focusing on medical public health and toxicological perspectives associated with exposure to a site. The health assessment specifically addresses community health concerns (e.g., sensitive populations, possible disease outcomes) and evaluates relevant, community-specific health outcome data. Combined with environmental data, information obtained from those two data sources are used to determine the public health implications of the site guiding the initiation of follow-up health activities when indicated. 

This section presents three case examples of site-based lead exposure characterizations for subsequent risk assessment purposes. The case studies are based on research where environmental media-specific levels of Pb were determined as part of the epidemiological and statistical designs. For purposes of this section, such two-part case studies are desirable for, first, quantifying baseline exposure characterizations and eventual baseline human health risk characterizations and, second, for identification of which... 

---