Risk Characterization
Risk characterization is the final phase of the ERA and allows risk assessors to clarify the relationships between stressors, effects and ecological entities. Conclusions can be reached regarding the occurrence of exposure and the adversity of anticipated effects. Risk characterization combines the results of the exposure assessment and the effects assessment to evaluate the likelihood that adverse effects will occur as a result of exposure to the stressor and the magnitude of effects. Risk characterization involves three steps
1.Calculation of risk estimate
2.Uncertainty analysis
3.Interpretation of the ecological significance
Risk Estimate
Risk estimate can be calculated using a number of approaches and techniques. One technique is the quotient method, which is frequently used for single contaminants and exposure pathways with an individual receptor. This method can be used to identify the presence of a potential risk, but not its magnitude or probability. The quotient method involves dividing the expected environmental concentration (EEC), or exposure concentration, of the chemical by a benchmark effects concentration (BC) to obtain a value. The resulting value is known as a hazard quotient (HQ) or risk quotient and is shown below:
EECs can be measured directly or predicted from environmental fate models. Benchmarks are threshold contaminant concentrations in an environmental medium, such as surface water or fish tissue, that are considered 'safe', below which adverse effects are not expected. Site-specific benchmarks may be determined in the effects assessment, or generic environmental protection benchmarks may be established by government agencies and applied to all projects or activities with similar adverse impacts. Acceptable effect levels should be selected in consultation with environmental managers during the problem formulation in general, if the HQ is less than one, the site can be categorized as 'low risk' and there is no need to proceed further. If the HQ is greater than one, this indicates the presence of risk, and further analysis should be conducted.
Uncertainty Analysis
Analysis of uncertainty is a second key element of risk characterization. Uncertainty analysis identifies and quantifies uncertainty in problem formulation, exposure and effects assessment, and risk characterization and provides the environmental manager with an insight into the strengths and weaknesses of the ERA. Significant knowledge gaps can result in acceptable benchmark criteria being set so low that ecological components are not protected. Conversely, in the absence of adequate data, benchmarks can be set so conservatively high that the effluent treatment required is prohibitively expensive. The output of the uncertainty analysis is an evaluation of the impact of the uncertainties on the ERA and a description of the ways in which uncertainty could be reduced. Major sources of uncertainty are summarized in Table 2.
Ecological Significance
Interpreting the ecological significance of risk estimates relies heavily on professional judgement and provides an important link between the estimation of risk and the communication of assessment results. It should consider the effects, the spatial and temporal patterns of the effects, and the potential for recovery once a stressor is removed. Interpretation of ecological significance should include a discussion of the following questions:
• Which species are most likely to be at risk?
• What part of a year is risk likely to occur?
• Is the risk even over the entire area or are there 'hot spots' of high risk?
• How do the pollutants move from the release site to the receptors (e.g., surface water runoff, groundwater movement, food chain uptake from soil)?
• What is known about the ecology, biology, or behaviour of a species that appears to be at risk that may affect (i.e., mitigate or increase) this risk?
• Are some of the life stages of the organism at more risk than others?
• Should some of the species be of more concern because they create habitat or are a food source for a critical species of concern?
Risk Characterization
Risk characterization is the final phase of the ERA and allows risk assessors to clarify the relationships between stressors, effects and ecological entities. Conclusions can be reached regarding the occurrence of exposure and the adversity of anticipated effects. Risk characterization combines the results of the exposure assessment and the effects assessment to evaluate the likelihood that adverse effects will occur as a result of exposure to the stressor and the magnitude of effects. Risk characterization involves three steps
1.Calculation of risk estimate
2.Uncertainty analysis
3.Interpretation of the ecological significance
Risk Estimate
Risk estimate can be calculated using a number of approaches and techniques. One technique is the quotient method, which is frequently used for single contaminants and exposure pathways with an individual receptor. This method can be used to identify the presence of a potential risk, but not its magnitude or probability. The quotient method involves dividing the expected environmental concentration (EEC), or exposure concentration, of the chemical by a benchmark effects concentration (BC) to obtain a value. The resulting value is known as a hazard quotient (HQ) or risk quotient and is shown below:
EECs can be measured directly or predicted from environmental fate models. Benchmarks are threshold contaminant concentrations in an environmental medium, such as surface water or fish tissue, that are considered 'safe', below which adverse effects are not expected. Site-specific benchmarks may be determined in the effects assessment, or generic environmental protection benchmarks may be established by government agencies and applied to all projects or activities with similar adverse impacts. Acceptable effect levels should be selected in consultation with environmental managers during the problem formulation in general, if the HQ is less than one, the site can be categorized as 'low risk' and there is no need to proceed further. If the HQ is greater than one, this indicates the presence of risk, and further analysis should be conducted.
Uncertainty Analysis
Analysis of uncertainty is a second key element of risk characterization. Uncertainty analysis identifies and quantifies uncertainty in problem formulation, exposure and effects assessment, and risk characterization and provides the environmental manager with an insight into the strengths and weaknesses of the ERA. Significant knowledge gaps can result in acceptable benchmark criteria being set so low that ecological components are not protected. Conversely, in the absence of adequate data, benchmarks can be set so conservatively high that the effluent treatment required is prohibitively expensive. The output of the uncertainty analysis is an evaluation of the impact of the uncertainties on the ERA and a description of the ways in which uncertainty could be reduced. Major sources of uncertainty are summarized in Table 2.
Ecological Significance
Interpreting the ecological significance of risk estimates relies heavily on professional judgement and provides an important link between the estimation of risk and the communication of assessment results. It should consider the effects, the spatial and temporal patterns of the effects, and the potential for recovery once a stressor is removed. Interpretation of ecological significance should include a discussion of the following questions:
• Which species are most likely to be at risk?
• What part of a year is risk likely to occur?
• Is the risk even over the entire area or are there 'hot spots' of high risk?
• How do the pollutants move from the release site to the receptors (e.g., surface water runoff, groundwater movement, food chain uptake from soil)?
• What is known about the ecology, biology, or behaviour of a species that appears to be at risk that may affect (i.e., mitigate or increase) this risk?
• Are some of the life stages of the organism at more risk than others?
• Should some of the species be of more concern because they create habitat or are a food source for a critical species of concern?
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