Chapter 4: Principal Elements of a Public Health Risk Assess
Characterization of chemical exposure problems
–Risk = exposure(dose) * potency
–exposure is characterized by contacting of the human body or organ and the chemical-containing media at a specified time interval
–At the time of exposure, the dose is defined as the amount of chemical that is absorbed or deposited (not necessarily the same as the amount you are exposed to)
–process used to establish presence or absence of chemical hazards, to delineate the nature and degree of hazards, and to determine the possible threats posed by nature
Data used when characterizing exposures data
–models and default assumptions
–information from direct exposures and/or indirect exposures (preferable)
Factors affecting exposure characterization
–General types of data and information needed for investigation of potential hazards:
1. identities of the chemicals of concern
2. concentrations contacted by potential receptors of interest
3. receptor characteristics
4. characteristics of the physical and environmental setting
5. receptor response upon contact (not always known)
–Additional parameters that should be investigated:
1. exposure duration and frequency
2. target receptor attributes
3. exposure media and routes
4. potential exposure receptor
hazard identification
–identificationn of chemical exposure sources
–compilation of the lists of all chemical stressors present at the locale and potential impacts to target receptors
–identification and selection of the specific chemicals of potential concern (based on hazardous properties)
–compilation of summary statistics for the key constituents selected for further evaluation
exposure assessment
–estimate of the actual and/or potential receptor exposures to chemicals present in the human environment (frequency, duration, nature, size of exposed population, past/present/future exposures)
toxicity assessment
–describing the quantitative relationship between the amount of exposure to a substance and the extent of toxic injury or disease
–compiling toxicological profiles for the chemicals of potential concern
–non-carcinogens (RfD)
–Carcinogens (SF)
risk characterization
–process of estimating the probable instance of adverse impacts to potential receptors under a set of exposure conditions
–summarizes and integrates the toxicity and exposure assessments
–elaboration of uncertainties
–to the extent possible, should include distribution of risk among the target populations
determining exposure-related health effects
–conclusions based on human data (preferable), animal studies (must extrapolate across species), and modeling data
–use best available data (IRIS, ATSDR, RTECS, Toxicology textbooks, scientific journals)
Evaluating factors that influence adverse health outcomes
–other medical and toxicological factors include toxicokinetics, cumulative effects of toxicants, reversible vs. irreversible, allergic reactions, previously diseased organ or tissue
health implications for sensitive sub-populations
–age of receptor (very young or very old)
–gender of receptor (pregnant women and lead)
–biochemical and/or genetic susceptibility (some ethnic groups are more sensitive to alveolar destruction and pulmonary emphysema)
–socioeconomic factors (indicator of susceptibilities to specific pollutants)
Health implications of corrective actions and interventions
–previous, current, and planned intervention strategies can play a very important role in drawing conclusions about exposure-related health concerns
Human health risk assessment in practice
–chemical hazard identification
1. what chemicals are present in the environment of interest?
2. are those chemicals likely to have an adverse effect on the potential human receptor?
–toxicity assessment
1. what is the relationship between the exposure/dose to the chemical and the response?
2. what harmful effects can be caused by the target chemicals and at what concentration?
–exposure asssessment
1. what individuals, sub-populations, or population groups may be exposed to the chemicals of potential concern?
2. how much exposure is likely to result from various activites of the potential receptor?
–risk characterization
1. what is the estimated incidence of adverse effect to the individuals or population groups?
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