Quantitative risk analysis pathway

This chapter deals with flood risk analysis and assessment. The conceptual model source pathway receptor consequence for flood risk analysis is presented and its components are analyzed. The methodology to extract the predicted probability of coastal flooding from risk sources and pathways, as well as the expected damages from risk receptors axe introduced and examined. Reliability analysis of a coastal system is also briefly discussed. Quantitative methods to define acceptable flooding probabilities on the level of the protected area are presented. Tools such as cost-benefit analysis, utihty models, and the life quality index are introduced to define the tolerable risk of flooding. 

The chronic daily intake (CDI) estimated in the analysis of exposure, the second step of the risk assessment, is used to calculate the risks of both noncancer health effects and cancer. Risk calculations are also referred to as quantitative risk assessment, a term that is somewhat misleading because the word quantitative implies a high degree of accuracy, which is clearly not the case. In the first risk scenario described in Section 8.3, future residents drink arsenic-contaminated water from the aquifer beneath a former Superfund site. Their CDI by this pathway is estimated to be 0.0I6I mg/kg/day of arsenic. The oral reference dose (RfD) for arsenic is 3 x lO"" mg/kg/day, according to the EPA s Integrated Risk Information System (IRIS) (U.S. EPA 2009). The hazard index (HI) for noncancer health effects caused by this chemical of concern by this exposure pathway is calculated using Equation (8.3) ... 

The four steps of the risk-assessment process are hazard identification, analysis of exposure, analysis of effect, and risk characterization. In the hazard identification step, the risk assessor identifies chemicals of concern, environmental pathways of exposure, and populations and subpopulations at risk. The exposure analysis develops exposure scenarios and estimates the chronic daily intake of each chemical of concern. In the analysis of effect, the risk assessor combines the chronic daily intake calculated in the exposure analysis with toxicity data from animal studies (and/or human epidemiological studies, if available) to estimate the risk of toxic effects in exposed populations, whereby risks to public health are divided into two broad categories noncancer health effects and cancer. The final step of the risk-assessment process, risk characterization, is a narrative that marshals all the evidence of risk to public health, including quantitative risk assessments and qualitative evidence of risk. The risk assessor weighs all the evidence and uses professional judgment to draw conclusions about risks. 

Calculation of Exposure. A great advantage of Risk Assistant is that it allows users to consider a wide range of factors that will influence quantitative exposure estimates (e.g., specific exposure factors for different populations, pathways, and scenarios) with a minimum of effort. Thus, a user can rapidly produce alternative exposure evaluations, including best estimates, reasonable worst-case exposure estimates, and worst case exposure estimates. Moreover, the system provides the user with information on the degree of uncertainty contributed by various assumptions used in the analysis, which can guide the user s future data collection efforts so that they result in maximum reduction of uncertainty. 

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