Exposure factors

Schwellenwert, m. threshold value, threshold Photog.) exposure factor. 

The heat transfer to the liquid from an engulfment fire has been estimated at around lOOkW/m, and the above formula equates this to the vapor produced from this input as latent heat. The exponential is an area exposure factor, which recognizes that large vessels are less likely to be completely exposed to flames. 

The author assumed that the Born radii of atoms can be estimated from the solvent exposure factors for sampling spheres around the atoms. Two spheres were used in a five-parameter equahon to calculate the Born radii. The parameters of the equahon were eshmated using numerical calculahons from X-ray protein structures for dihydrofolate reductase. In addition to AGol the author also considered the AGJ term accounting for cavity formahon and dispersion of the solute-solvent interactions as ... 

USEPA] US Environmental Protection Agency. 1993b. Wildlife exposure factors handbook, Vol. 1. United States Environmental Protection Agency, Method EPA 600-R-93- 187a. 

The magnitude of exposure in a geographic area is a function not only of the amount of pollutant to which a "typical" individual is exposed but also of the size of the population exposed. This is especially important in the calculation of risk for an area or subpopulation. The resulting quantity is a population exposure factor which is the product of the individual pollutant intake level per unit time (average or maximum) multiplied by the population size exposed. 

EPA. 1989c. Exposure factors handbook. Washington, DC U.S. Environmental Protection Agency, Office of Health and Environmental Assessment. EPA/600/8-89/043. 

Pollutant Exposure and Chemical Composition of Plants Let us consider the influence of various exposure factors on the chemical composition of plant species in the arctic islands. It seems the most influential factor is the distance from the ocean shore. For example, in arctic willow growing a few meters from the tide line, the content of Zn, Cu, Pb, and Ni was higher than that of the same plant... 

Exposure factor a factor that mitigates the potential effects of an incident... 

FIGURE 7.1 Inhalation - correlation between exposure concentration and internal dose. (Modified from US-EPA, Exposure Factors Handbook, National Center for Environmental Assessment, Washington DC, 1997.) Available at http //www.epa.gov/ncea/efh/... 

The European Commission s Joint Research Centre (on behalf of DG S ANCO) has started a project known as European Information System on Risks from Chemicals Released from Consumer Products/Articles (EIS-ChemRisks) (EU 2004), which is designed as a network to collect exposure data, exposure factors, exposure models, and health-related data. The overall objective is to develop tools and reference data to enable harmonized exposure assessment procedures in the EU. A toolbox has been designed to collect exposure information from four reference systems to systematically support exposure assessors in the EU ... 

EU-ExpoFactors (European Reference System for Exposure Factors)... 

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. 

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). 

When the project was started in 2002, European exposure factor data were scattered within numerous national and international institutions. ExpoFacts has created no new data, but instead compiled the existing data into one Internet database, where it can be easily found, screened, and downloaded from. Data were collected from the EU countries, candidate countries to EU, and EFTA countries. As a result, the ExpoFacts database contains data from 30 European countries. In addition to the population time use patterns and exposure route information, e.g., dietary statistics, the database contains socio-demographic and physiologic information to enable database use as a tool for population-wide exposure modeling and risk assessment. 

In the following sections, human exposure factors for ambient air (Section 7.3.1), soil (Section 7.3.2), and drinking water (Section 7.3.3) will be described. These media are used as examples, which serve to illustrate the differences in exposure factors provided by various exposure factor documents. Such differences can have a great impact on the risk characterization (Chapter 8) as well as on the development of regulatory standards and health-based guidance values (Chapter 9), and it is therefore important that the most relevant and reliable values are used for the particular situation. 

In the Exposure Factors Handbook, US-EPA (1997) has identified five key studies and five other studies on VRs. The results of these studies, which are all from the United States, show the following general tendencies ... 

The recommended VRs in the Exposure Factors Handbook (US-EPA 1997) are summarized in Table 7.3 the VR for each age group was calculated as the average of the VRs for the various activity levels, see Table 7.2. 

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

ECETOC (2001) has collected exposure data in the Exposure Factors Sourcebook for European Populations. For VRs, the Sourcebook presents the values, which are recommended by the US-EPA in the Exposure Factors Handbook (US-EPA 1997), see Table 7.3. ECETOC states that these values are probably representative of Europeans as well. 

In the Exposure Factors Handbook, US-EPA (1997) has identified seven key studies which employ methods based on measurements of tracer elements, and nine other studies on soil intake among children. The individual key studies used between three and eight different tracer elements. Not all the tracer elements turned out to be useful for estimation of the daily soil intake aluminum, silicon, and yttrium appeared to be the most reliable. The results of the studies are summarized in Table 7.4. 

In the Exposure Factors Handbook, US-EPA (1997) has identified three studies where the daily soil intake for adults has been estimated. In one of these studies, an annual average soil intake of 60.5 mg/day was estimated based on assumptions regarding the amount of soil and dust on the hands, so-called mouthing behavior , and indoor and outdoor activities. In the second study, a daily soil intake of 50 mg/day was estimated based on measurements of urinary arsenic, mouthing behavior , and information about behavior patterns. In the third study, a daily soil intake of 30-100 mg/day was estimated based on tracer element measurements. The latter study was evaluated by the US-EPA as the most reliable one. 

Table 7.6 summarizes soil ingestion recommendations in the Exposure Factors Handbook (US-EPA 1997). 

In the Exposure Factors Handbook, US-EPA (1997) has identified three key studies and nine other studies on drinking water intake. The results of these studies, which apart from one are aU from the United States, showed a good agreement across studies for the estimate of the mean and 90th percentile. The results also showed an increase in drinking water intake with age, with level of physical activity, and with ambient temperature, and US-EPA notes that based on body weight, children consume more water than adults, and old people consume more than middle-aged people. Table 7.7 presents the results of one central study (Ershow and Cantor 1989 - cited in US-EPA 1997). Table 7.8 summarizes the results of the three key studies and Table 7.9 the results of the nine other studies. 

Daily Intake of Drinking Water. Results from Other (Nonkey) Studies Cited in the Exposure Factors Handbook... 

---