Term
Fundamental issues and considerations |
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Definition
*risk characterization is the integration of toxicity and exposure assessment **can only be as good as its parts *should fully, openly, and clearly characterize risks and disclose analysis, uncertainties, and assumptions **document sources for processes and protocols |
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Term
Non-standard pollution groups |
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Definition
*care must be taken to ensure that assumptions about population parameters in the dose-response analysis are consistent with the population parameters used in the exposure analysis |
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Term
Adjustment for chemical absorption |
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Definition
*may be necessary to ensure that the exposure estimate and the toxicity value being compared during the risk characterization are both expressed as absorbed or administered doses **adjustments are made for vehicles of exposure, administered to absorbed dose for RfD and SFs |
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Term
Aggregate effects of chemical mixtures |
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Definition
*when combining multi-chemical risk estimates for multiple chemical sources, it should be noted that **if two sources do not affect the same individual or subpopulation, the sources' individual risk should not be combined **in mixture assessment (within the context for interactions): ***carcinogenic effects--segregated by weight-of-evidence category ***non-cancer effects--grouped by similar toxic endpoint/mode of action |
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Term
Fundamental considerations in health assessment of carcinogens |
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Definition
*qualitative issues: **weight-of-evidence--from case studies, epidemiological studies, long-term animal studies, long-term bioassays, short-term tests, and SARs **mechanistic inference--multistage process that is characterized by a non-threshold assumption ***may not be true for each step, only for the process as a whole **exposure route specificity--some chemicals may not pose a carcinogenic effect via ingestion, but may pose a carcinogenic risk via inhalation **role of epidemiological data--can give more weight to a well-designed epi study rather than a well-designed animal study, remembering that the potential for association remains especially relevant for animal data **sensitive and susceptible populations--independently address the associated health concerns **structure activity relationships (SARs)--can be crucial in estimating toxicity factors for those chemicals that have little or no data available **chemical interactions--we assume an additive effect, but we have to make a qualitative statement about the certainty of this with regard to mode of action *quantitative issues **dose scaling--from animal to human and when using epi studies ***individual sensitivities **pharmakokinetics/pharmacodynamics--delivered dose rather than the exposure dose is important ***using exposure dose is conservative in most cases **mechanistic considerations--extrapolations from high to low doses must consider which mathematical model to use ***most conservative model is best if there are equally plausible models **individual vs. population risk--if possible experimental models, molecular biology, and epidemiology should be used to make the best estimate of risk |
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Term
Carcinogenic risk effects |
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Definition
*calculated using one of two models, then take the sum for all carcinogens in the assessment **linear low dose: CR = CDI * SF ***based on linearized multistage model assuming multiple stages for cancer ***good for low intake levels **one-hit model: CR = 1 - exp(-CDI*SF) ***assumes single stage for cancer and that one molecular or radiation interaction induces malignant change ***good for high intake levels **if risk is greater than 1 in 1 million, this is considered unacceptable |
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Term
Non-carcinogenic risk effects |
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Definition
*hazard quotient **HQ = E/RfD **for each chemical *hazard index **HI = ΣHQi **summation of the HQ for each chemical in the assessment *if the hazard index is greater than 1, this indicates unacceptable risk |
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Term
Population excess cancer burden |
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Definition
*to assess the population cancer burden associated with a chemical exposure problem: **one can estimate the number of cancer cases due to an exposure source within a given community (cancer burden) Bgi = Σ (Rgi * Pg) ***Bgi = excess cancer burden for a group ***Rgi = excess lifetime cancer risk for a group ***Pg = number of persons in exposed population group |
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Term
Uncertainty and variablity |
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Definition
*variability--arises from true heterogeneity in characteristics such as **dose-response differences **differences within a population **differences in exposure factors **differences in exposure levels *uncertainty--arises from lack of knowledge about factors |
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Term
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Definition
*spatial--across locations **can be regional or local (i.e. fish intake) *temporal--across time *inter-receptor--amongst individual receptors **human characteristics and behaviors |
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Term
Types and nature of uncertainty |
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Definition
*parameter values **incomplete or biased data *parameter modeling **model inadequacy or representation of situation *degree of completeness **representativeness of evaluation scenarios |
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Term
Sources of uncertainty in human health assessment |
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Definition
*health effects **toxicity data *measuring or calculating exposure point concentrations *calculating exposure dose |
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Term
Commonly encountered limitations |
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Definition
*toxicity extrapolations *adjustments in dose-response evaluation *toxicity of mixtures *models *background exposures *representativeness of sampling plan |
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Term
Uncertainty and variability analysis |
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Definition
*uncertainty/sensitivity analysis **involves identifying parameters that will make the most contribution to uncertainty **estimating the most appropriate value using distributions and non-point estimates **provides full spectrum of information |
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Term
Qualitative analysis of uncertainties |
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Definition
*determination of the general quality and reasonableness of the risk management data, parameters, and results *most important for screening and preliminary assessments *can contain errors, incomplete analysis, limitations, bad assumptions |
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Term
Quantitative analysis of uncertainties |
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Definition
*Monte Carlo simulations **assign a probability distribution to input variables **estimate risk using an iterative process to calculate risk by changing the input variables in the risk equation **produces a risk distribution instead of a point estimate |
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Term
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Definition
*measures relative response of output variables caused by variations of the input variables and parameters *purpose is to identify the influential input variables and to develop bonds on the model output *more resources can be directed to reduce the uncertainty in the most sensitive parameter |
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