Chapter 5: Chemical Hazard Determination
Chemical Hazard Identification: Sources
Includes:
–a review of the major sources of chemical hazards that could potentially contribute to a given chemical exposure and possible risk situation (background info on uses, chemicals used in process, potential sources, etc)
–qualitative information at this poing
–can include quantitative methods (modeling or decision analyses to determine chemmical fate and behavior attributes following exposure)
Data collection and evaluation considerations
–typical work plan (sampling and analysis plan, quality assurance/quality control plan)
–goal is to maintain sample integrity and encompass adequate quality assurance and control
–expensive and time consuming (budget accordingly)
–proper handling and accuracy of procedures are required to help minimize uncertainties
–together with receptor information, this data is used to decide on chemicals of concern (COC)
sample collection protocols
–must be followed and documented to validate sample analysis
–most chemical sampling and analysis procedures offer numerous opportunities for sample contamination (variety of sources)
–include QC samples (controls)
–detailed procedures with documentation
–sensitivity of analytical procedures
non-detected and quantitation limits
–below instrument detection limits or quantitation limits
–referred to as non-detects or censored data
–IMPORTANT:
1. this does not mean the chemical is not present, only that the chemical concentration was below the detectable or quantifiable limits of the instrument for a particular analytical method
2. can only be reported as less than <0.00#
exposure point concentration
–consists of appropriate statistical evaluation of the exposure sampling data
–statistical procedures used for the evaluation of such data can significantly affect the conclusions of a given exposure characterization and risk assessment (in relation to proper averaging techniques, especially)
non-parametric methods
–distribution-free method (not dependent on the assumption that the data follow any particular statistical distribution)
–reduces the number of underlying assumptions
–typically employed
parametric methods
–several assumptions must be met to use these methods
–preferable method
–more powerful
lognormal statistical distribution vs gaussian (normal) distributionn
–use of lognormal distribution requires a log transformation to expect data to be normally distributed
–goodnes-of-fit formal statistical tests of the hypothesis that a specific set of sampled observations is an independent sample from the assumed distribution (chi-square test, shapiro-wilks’ test)
statistical evaluation of non-detect values
–use a fraction of the sample quantitation limit (SQL)
–the best estimate of ND values for lognormally distributed data sets is SQL/sq. root of 2
geometric mean
–has been extensively used as an averaging parameter
–advantage: minimizes the effects of outliers
–disadvantage: discounting these values when they may represent true variations in concentration for one part of the affected area over another
Estimating chemical exposure point concentrations from limited data
–in the absence of adequate or appropriate field sampling data, can use mathematical algorithms and/or models
–serves a variety of purposues:
1. to gain a better understanding of the fate and behavior of chemicals in human living and work environments
2. to determine temporal and spatial distribution of chemical exposure concentrations at potential receptor locations
3. to predict future consequences of exposure under various chemical contacting or loading conditions, exposure scenarios, or risk management decisions
–using models or algorithms effectively depends heavily on the selection of the models most suitable
–dependent upon types of COC, nature of impacted and threatened media that are being evaluated in the specific investigation, and type of corrective actions contemplated
simple example models
–screening level estimation of chemical volatilization into shower air
–estimation of household air contamination resulting from volatilization from domestic water supply
–contaminant bioconcentration in meat and dairy products
–estimation of contaminant concentrations in fish tissues and products
determination of the level of chemical hazard
(process/approach used to estimate a potential receptor’s EPC)
–determining the distribution of the chemical exposure/sampling data and fitting the appropriate model
–developing the basic statistics for the exposure/sampling data to include calculation of the relevant statistical parameters such as the upper 95% confidence limit
–calculation of the EPC (usually defined as the minimum of either the UCL or the maximum exposure/sampling data value. conceptually represented as EPC = min [UCL 95 or max-value]
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