Exposure Factors, Sources

In order to determine the exposure of a population, it is necessary to have data about the activities that can lead to an exposure. These data are called exposure factors. They are generally drawn from the scientific literature or governmental statistics. Eor example, exposure factors may be information about amount of various foodstuffs eaten, breathing rates, or time spent for various activities, e.g., showering or car-driving. The main U.S. and EU sources of exposure factors will be described in the following text, and examples of human exposure factors are addressed in more detail in Section 7.3. 

The US-EPA Exposure Factors Handbook (US-EPA 1997), first published in 1989, provides a summary of the available data on consumption of drinking water consumption of fmits, vegetables, beef, dairy products, and fish soil ingestion inhalation rates skin surface area soil adherence lifetime activity patterns body weight consumer product use and the reference residence (data that are available on residence characteristics that affect exposure in an indoor environment). 

The US-EPA Child Specific Exposure Factors Handbook (US-EPA 2006), first published in 2002, consolidates all children s exposure factors data into one document. The document provides a summary of the available and up-to-date statistical data on various factors assessing children s exposures. These factors include drinking water consumption soil ingestion inhalation rates dermal factors including skin area and soil adherence factors consumption of fruits, vegetables, fish, meats, dairy products, homegrown foods, and breast milk activity patterns body weight consumer products and life expectancy. 

The US-EPA Consolidated Human Activity Database (CHAD) (US-EPA 2007b) contains data obtained from preexisting human activity studies that were collected at city, state, and national levels. CHAD is intended to be an input file for exposure/intake dose modeling and/or statistical analysis. CHAD is a master database providing access to other human activity databases using a consistent format. This facilitates access and retrieval of activity/and questionnaire information from those databases that US-EPA currently has access to and uses in its various regulatory analyses undertaken by program offices. 

In 2002, the European Exposure Factors (ExpoFacts) database started as a 2-year project funded by CEFIC-LRI (European Chemical Industry Council, Long Range Research Initiative) to create a European database of factors affecting exposure to environmental contaminants. The aim was to create a public access data source, similar to the US-EPA Exposure Factors Handbook (US-EPA 1997), which has been widely used by European researchers, but with European data. Since 2006, the project is hosted by the European Commission s Joint Research Centre (JRC 2007). 

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AIHC (1994). Exposure Factors Source Book, American Industrial Health Council, Washington, DC, USA. 

Source Layton (1993, as cited in US-EPA 1997) modified from US-EPA, Exposure Factors ... 

Source Modified from US-EPA, Exposure Factors Handbook, National Center for Environmental Assessment, Washington, DC, 1997. Available at http //www.epa.gov/ncea/efh... 

Source From Hopkins and Ellis (1980, as cited in ECETOC 2001) modified from ECETOC, Exposure Factors. Sourcebook for European Populations, with Focus on UK Data, Technical Report No. 79, 2001. Available at http //ecb.jrc.it/tgdoc/... 

Sections that indicate the extent of past and present human exposure, the sources of exposure, the people most likely to be exposed and the factors that contribute to the exposure are included at the beginning of each monograph. 

What are the key sources of uncertainty in the exposure assessment This question can also be posed as Which exposure factors contribute the most to the overall uncertainty in the inventory This insight can be used, in turn, to target resources to reduce the largest and most important uncertainties. There are various ways to answer this question, including various forms of sensitivity analysis. For example, in the context of a probabilistic uncertainty simulation for an overall exposure assessment, various statistical methods can be used to determine which input distributions are responsible for contributing the most to the variance of the output. 

Quantified values for human exposure factors are best determined on a case-by-case basis, with site-specific and source-specific circumstances driving choices about appropriate values for intake rates, exposure duration and frequency, body weight, averaging time and other related variables affecting calculation of the ADD. Each exposure assessment is unique and the assessor must construct a scenario and tailor related human exposure factors to fit the conditions at hand. 

Referenced Calculations. Exposure assessment involves numerous calculations, covering both cross-media transfers of chemicals and the derivation of exposures from concentrations and scenario-specific parameters. In general terms, such calculations can be viewed as the limiting case (in simplicity) of either theoretical or empirical models. All calculations in Risk Assistant for deriving exposures from concentrations in an appropriate medium (e.g. inhalation exposures from air concentrations) are obtained from the Exposure Factors Handbook (4). Equations for evaluating cross-media transfer for particular exposure scenarios (e.g. volatilization from domestic water to household air) are obtained from literature sources. For such equations, the original reference is provided for the user. 

Applicable target risk limits (TR) for health protection can be matched to levels specified by the environmental regulatory authority. Toxicological parameters for each contaminant can be determined from published references, such as the U S. EPA Integrated Risk Information System (IRIS). Exposure rates correspond to the chronic rate of contact or intake of the affected exposure medium (air, water, soil) by the receptor under anticipated land use conditions. As a conservative measure, these rates can be estimated based on standard exposure factors published by the regulatory authority or other source (e.g., American Industrial Health Council) for the anticipated land use at the site (e.g., residential, commercial, etc.). 

Various primary sources for estimating the exposure parameters associated with daily intake quantities of (lead-containing) media were used and are noted. A child exposure-specific source of parameter selection for media of interest was the U.S. EPA Child-Specific Exposure Factors Handbook (2008). 

Another factor in oxidative degradation is ultraviolet radiation, of which sunlight is a rich source. The oxidation of parylene appears to be enhanced by ultraviolet radiation. 02one may play a mechanistic role in the ambient temperature exposure of parylenes to ultraviolet radiation in the presence of oxygen. For the best physical endurance, exposure of the parylenes to ultraviolet light must be minimised. 

Options. Traditional control options for overexposure are material substitution, process change, containment, enclosure, isolation, source reduction, ventilation, provide personal protection, change work practices, and improve housekeeping. A simple way of looking at selection of control options is to find the cheapest option that results in the desired amount of exposure reduction. It is not actually that simple, however, because the various options differ in ways other than cost and degree of control. Some of the other factors to consider in selection of control options are operabiUty, rehabiUty, and acceptabihty. 

Ha2ard is the likelihood that the known toxicity of a material will be exhibited under specific conditions of use. It follows that the toxicity of a material, ie, its potential to produce injury, is but one of many considerations to be taken into account in assessment procedures with respect to defining ha2ard. The following are equally important factors that need to be considered physicochemical properties of the material use pattern of the material and characteristics of the environment where the material is handled source of exposure, normal and accidental control measures used to regulate exposure the duration, magnitude, and frequency of exposure route of exposure and physical nature of exposure conditions, eg, gas, aerosol, or Hquid population exposed and variabiUty in exposure conditions and experience with exposed human populations. 

Injury to plants and vegetation is caused by a variety of factors, of which air pollution is only one. Drought, too much water, heat and cold, hail, insects, animals, disease, and poor soil conditions are some of the other causes of plant injury and possible plant damage (3). Estimates suggest that less than 5% of total crop losses are related to air pollution. Air pollution has a much greater impact on some geographic areas and crops than others. Crop failure can be caused by fumigation from a local air pollution source or by more widespread and more frequent exposure to adverse levels of pollution. 

A difficulty that should not be overlooked is that airborne particulates are rarely homogeneous. They vary greatly in size and shape, and their chemical composition is determined by factors specific to the source and location of the emissions. The combined effects and interactions of various substances mixed with particulates have not yet been established (except for sulfur dioxide), but they are believed to be significant, especially where long-term exposure occurs. Measurement techniques and their reliability may vary across regions and countries, and so may other factors, such as diet, lifestyle, and physical fitness, that influence the human health effects of exposure to particulates. 

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