Chapter 3: Principles and Concepts in Risk Assessment
hazard
object with the potential for creating undesireable or adverse consequences
exposure
situation of vulnerability to hazards
risk
probability or likelihood of an adverse effect due to some hazardous situation
Nature of chemical hazard, exposure, and risk
Hazard identification and accounting (problem characterization and hazard identification, hazard accounting) –> Vulnerability analysis (problem conceptualization, exposure assessement) –> Consequence/Impact Assessment (quantification of consequences, risk assessment and risk management)
risk assessment
–systematic process for arriving at estimates of all significant risk factors that are associated with an entire range of exposure scenarios in connection with some hazard
–data collection and evaluation –> exposure assessment –> toxicity assessment –> risk characterization –> risk management
General categories of risk assessment
–hazard assessment
–exposure assessment
–consequence assessment
–risk estimation
Nature of risk assessments
–retrospective or predictive
uncertainty
–lack of confidence in the estimate of a variable’s magnitude or probability of occurrence
–scientific judgement becomes important in problem solving under these conditions
–decision analysis provides the means of representing the uncertainties in a manner that allows informed decisions
–risk assessments are a major component of public/environmental health management and decision making (uncertainty MUST be well documented)
–characterizing uncertainty can be accomplished using sensitivity analysis and/or probability analysis techniques
sensitivity analysis
–requires data on the range and probability function of each exposure factor within the scenario
–determination of how rapidly the output changes with respect to variations in the input data
–provides a range of likely estimates
–recommended that this become an integral part of a risk assessment
qualitative estimates of risk
–use terms like “weight of evidence” or “strength of evidence”
quantitative estimates of risk
–use pure numeric parameters or a combination of alpha-numeric parameters
Conservatism
–common practive in risk assessment is to over-estimate risk
–also called “worst-case scenario” or “plausible upper bound”
–can be a source of error (is the final result still plausible?)
–can lead to poor decision making
–new research focuses on making estimates more realistic
individual risk
–frequency at which a given individual could potentially sustain a given level of adverse consequences from a hazard
group risk
–provides an estimate of the extent of harm to society as a whole
risk perception
–spatial and temporal dimensions
–public risk perception is very different from scientifically developed risk estimates
–“outrage factor” can dramatically influence risk perception
–involuntary vs. voluntary
–influenced by sources of information, style of presentation, personal background, education levels
de manifestis risk
–a risk so great that it must not be allowed to occur
de minimis risk
–a risk so insignificant that it is not addressed regardless of the insignificance of the cost
–essentially a threshold concept (threshold of “concern” below which there would be indifference to change in the level of risk)
–typically these risks are below 1 in 1 million
–compares favorably with risk levels from some normal human activities (smoking, driving a car, using birth control pills, getting an X-ray)
risk acceptability and risk tolerance
–risk levels between de manifestis and de minimis are typically a balancing act of costs, feasibility of mitigation actions, and socioeconomics
Purpose and attributes
–paradigm for risk assessment can be predictive or retrospective
–aims at answering the following questions:
1. What could potentially go wrong?
2. Who could be affected?
3. What are the chances for this to happen?
4. What are the anticipated consequences if this does indeed happen?
–Objective of a risk assessment is to help develop risk management decisions (systematic, more comprehensive, more accountable), determine need for and degree of mitigation required for chemical exposures, effective tool for evaluating the effectiveness of remedies at contaminated sites
Attributes
MAJOR ATTRIBUTES
–identification and ranking of all existing in and anticipated potential hazards
–explicit consideration of all current and possible future exposure scenarios
–qualification and/or quantification of risks associated with the full range of hazard situations, system responses, and exposure scenarios
–identification of all significant contributors to the critical pathways, exposure scenarios, and/or total risks
–determination of cost effective risk reduction policies via the evaluation of risk-based remedial action alternatives and/or the adoption of effiecient risk management and risk prevention programs
–identification and analysis of all significant sources of uncertainties
Risk management
–risk management process utiliizes prior generated risk assessment information (making a decision on how to protect public health)
–risk assessment focuses on evaluating the likelihood of adverse effects
–risk management focuses on the selection of a course of action in response to an identified risk (social, legal, political, or economic factors also contribute)
Risk assessment as a diagnostic tool
–risk assessment is often considered an integral part of the diagnostic assessment of chemical exposure problems
–procedures typically include identification of the sources, determination of chemical exposure routes, identification of populations potentially at risk, and determination of receptor response to chemical exposures
baseline risk assessment
–identify the primary threats associated with a situation and provides valuable input to the development and evaluation of alternative risk management and mitigative options
–generally used to document the magnitude of risk at a given locale as well as the primary causes of risk, help determine whether any response action is necessary for the problem, prioritize the need for remedial action, provide a basis for quantifying remedial action objectives, develop and modify remedial action goals, and support and justify “no further action” decisions
comparative risk assessment
–have become an important part of risk analysis
–directed at developing risk rankings and priorities (puts various kinds of hazards on an ordered scale from small to large)
–two principal forms of comparative risk assessment (specific risk comparisons, programmatic comparative risk assessment)
public health risk assessments
–all forms should consider the following issues:
1. level of hazardous substance present
2. likelihood that people might be exposed
3. exposure pathways and routes via which people might be exposed
4. nature of harm the substances might cause to people
5. potential health impacts on populations working and/or living near the source
6. other dangers that could potentially exacerbate the likely effects of the chemical exposure problem
–primary sources of information are environmental data, health data, and community concerns
–exposure investigation includes biomedical testing, environmental testing, and exposure-dose reconstruction analysis
biomonitoring
–utilization of exposure biomarkers
–important in the evaluation of the impacts of human exposure to a variety of chemicals
–residue analysis (parent compounds and metabolites)
–endpoints that represent interactions between xenobiotic and endogenous components (enzyme inhibition, protein adducts, receptor complexes, antibody-antigen complexes, and mutation)
physiologically-based pharmakokinetic modeling (PBPK modeling)
–pharmakokinetics describes the time course disposition of a xenobiotic, its transformed products, and its interactive products within the body
–each tissue group is described mathematically and expresses the rate of change of the chemical concern in each compartment (species-specific physiological parameters)
–use physiologic and thermodynamic parameters (organ volumes, blood flows, and metabolic rate constants are determined to become part of the model)
–physiologic models allow public health risk analysts to quantitatively account for differences in pharmakokinetics that occur between different species, dose levels, and exposure scenarios
Key issues with risk assessment implementation strategey
1. What chemicals pose the greatest threat?
2. What are the concentrations of the chemicals of concern in the exposure media?
3. Which exposure routes are the most important?
4. Which population groups, if any, face significant risk as a result of possible exposures?
5. What is the range of risks to the affected populations?
6. What are the public health implications for any identifiable corrective action and/or risk management alternatives?
risk assessmenta as a holistic tool
–as a holistic approach to environmental and public health management, risk assessment integrates all relevant environmental and health issues and concerns surrounding a specific problem situation in order to arrive at risk management decisions that are said to belong to all stakeholders
–A holistic approach should generally incorporate information that helps to answer these pertinent questions:
1. Why is the project being undertaken?
2. Can the results and conclusions on the project be used?
3. What specific processes and methodologies will be utilized?
4. What are the uncertainties and limitations surrounding the study?
5. Does a contingency plan exist for resolving newly identified issues?
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